Moyenne Mobile Prévision Modèle Désavantages

The Zettabyte Era Tendances et analyses Cisco Enhanced PDF Ce document fait partie de l'index de réseau visuel (VNI) Cisco reg, une initiative permanente pour suivre et prévoir l'impact des applications de réseau visuel. Le document présente quelques-unes des principales conclusions de la prévision du trafic IP mondial de Ciscos et explore les implications de la croissance du trafic IP pour les fournisseurs de services. Pour un aperçu plus détaillé des prévisions et de la méthodologie qui la sous-tend, visitez le site Cisco VNI: Forecast and Methodology, 20152020. Le trafic IP global annuel dépassera le seuil zettabyte (ZB 1000 exabytes EB) d'ici la fin de 2016 et atteindra 2,3 ZB par an d'ici 2020. À la fin de 2016, le trafic IP mondial atteindra 1,1 ZB par an, soit 88,7 EB par mois, et d'ici 2020, le trafic IP mondial atteindra 2,3 ZB par an, soit 194 EB par mois. Le trafic IP mondial augmentera de près de trois fois au cours des 5 prochaines années. Dans l'ensemble, le trafic IP croîtra à un taux de croissance annuel composé de 22% entre 2015 et 2020. Le trafic IP mensuel atteindra 25 Go par habitant d'ici 2020, en hausse par rapport à 10 Go par habitant en 2015. Le trafic Internet Croissance plus rapide que la moyenne du trafic Internet. Le trafic Internet a augmenté de 51% en 2015, comparativement à une croissance de 29% du trafic moyen. Le trafic Internet à haut débit augmentera de 4,6 entre 2015 et 2020, et le trafic Internet moyen augmentera de 2,0. Le trafic des smartphones dépassera le trafic PC d'ici 2020. En 2015, les PC représentaient 53% du trafic IP total, mais en 2020, les PC ne représenteront que 29% du trafic. Les téléphones intelligents représenteront 30% du trafic IP total en 2020, contre 8% en 2015. Le trafic généré par PC augmentera à un TCAC de 8% et les téléviseurs, tablettes, smartphones et modules machine à machine (M2M) Auront des taux de croissance du trafic de 17 pour cent, 39 pour cent, 58 pour cent et 44 pour cent, respectivement. Le trafic des périphériques sans fil et mobiles représentera les deux tiers du trafic IP total d'ici 2020. En 2020, les périphériques câblés représenteront 34% du trafic IP, et le Wi-Fi et les périphériques mobiles représenteront 66% du trafic IP. En 2015, les appareils filaires représentaient la majorité du trafic IP, soit 52%. Les réseaux de distribution de contenu (CDN) porteront près des deux tiers du trafic Internet d'ici 2020. Soixante-quatre pour cent de tout le trafic Internet traversera CDN d'ici 2020 à l'échelle mondiale, contre 45 pour cent en 2015. Le nombre de périphériques connectés aux réseaux IP sera plus de trois fois la population mondiale d'ici 2020. Il y aura 3,4 appareils en réseau par habitant d'ici 2020, contre 2,2 périphériques en réseau par habitant en 2015. Il y aura 26,3 milliards de périphériques en réseau en 2020, contre 16,3 milliards en 2015. Les vitesses à large bande devraient presque doubler d'ici 2020. En 2020, les vitesses globales du haut débit fixe atteindront 47,7 Mbit / s, contre 24,7 Mbit / s en 2015. Faits saillants sur la vidéo et le jeu sur Internet Global Il faudrait plus de 5 millions d'années pour regarder la quantité de vidéo qui traversera les réseaux IP mondiaux en 2020. Chaque seconde, un million de minutes de contenu vidéo traversera le réseau d'ici 2020. Globalement, le trafic vidéo IP représentera 82% de l'ensemble du trafic IP (entreprises et consommateurs) d'ici 2020, contre 70% en 2015. Le trafic vidéo IP à l'échelle mondiale sera multiplié par trois de 2015 à 2020, soit un TCAC de 26%. Le trafic vidéo sur Internet sera multiplié par quatre entre 2015 et 2020, soit un TCAC de 31%. Le trafic vidéo sur Internet a presque doublé en 2015. De 272 pétaoctets par mois à la fin de 2014 à 516 pétaoctets par mois en 2015. Le trafic de vidéosurveillance sur Internet sera multiplié par dix entre 2015 et 2020. Globalement, 3,9 pour cent de tout le trafic vidéo Internet sera dû à la vidéosurveillance en 2020, 1,5 pour cent en 2015. Le trafic de réalité virtuelle quadruplé en 2015. De 4,2 petabytes (PB) par mois en 2014 à 17,9 PB par mois en 2015. Globalement, le trafic de réalité virtuelle augmentera de 61 fois entre 2015 et 2020, un TCAC de 127 pour cent. La vidéo sur Internet à la télévision a augmenté de 50 pour cent en 2015. Ce trafic continuera de croître à un rythme rapide, augmentant de 3,6 fois d'ici 2020. La vidéo sur Internet à la télévision sera de 26 pour cent du trafic vidéo Internet fixe en 2020. Le trafic vidéo sur demande (VoD) . Le trafic VoD en 2020 équivaut à 7,2 milliards de DVD par mois. Le trafic de jeux sur Internet croîtra sept fois de 2015 à 2020. Un TCAC de 46 p. Globalement, le trafic de jeux sur Internet représentera 4% du trafic Internet consommateur en 2020, contre 2% en 2015. Global Mobile Highlights Globalement, le trafic de données mobiles augmentera de huit fois entre 2015 et 2020. Le trafic de données mobiles croîtra à un TCAC de 53% entre 2015 et 2020, atteignant 30,6 exaoctets par mois d'ici 2020. Le trafic mondial de données mobiles augmentera presque trois fois plus vite que le trafic IP fixe de 2015 à 2020. Le trafic IP fixe augmentera à un TCAC de 19% entre 2015 et 2020, alors que le trafic mobile croîtra à un TCAC de 53%. Le trafic de données mobiles à l'échelle mondiale représentait 5% du trafic IP total en 2015 et représenterait 16% du trafic IP total d'ici 2020. Le trafic IP croît le plus rapidement au Moyen-Orient et en Afrique, suivi de l'Asie-Pacifique. Le trafic au Moyen-Orient et en Afrique croîtra à un TCAC de 41 pour cent entre 2015 et 2020. Sommaire des taux de croissance régionaux: Le trafic IP en Amérique du Nord atteindra 59,1 EB par mois d'ici 2020, avec un TCAC de 19 pour cent. Le trafic IP en Europe de l'Ouest atteindra 28,0 EB par mois d'ici 2020, pour atteindre un CAGR de 20%. Le trafic IP en Asie-Pacifique atteindra 67,8 EB par mois d'ici 2020, pour atteindre un CAGR de 22%. Le trafic IP en Amérique latine atteindra 11,6 EB par mois d'ici 2020, pour atteindre un CAGR de 21%. Le trafic IP en Europe centrale et orientale atteindra 17,0 EB par mois d'ici 2020, pour atteindre un CAGR de 27%. Le trafic IP au Moyen-Orient et en Afrique atteindra 10,9 EB par mois d'ici 2020, pour atteindre un CAGR de 41%. Remarque: Plusieurs outils interactifs sont disponibles pour vous permettre de créer des aperçus personnalisés et des graphiques de prévisions par région, par pays, par application et par segment d'utilisateur final (voir l'outil Cisco VNI Forecast Highlights et Cisco VNI Forecast Widget). Faits saillants des affaires mondiales Le trafic IP des entreprises croîtra à un TCAC de 18% entre 2015 et 2020. L'adoption accrue de communications vidéo avancées dans le segment des entreprises entraînera un accroissement du trafic IP des entreprises d'un facteur 2 entre 2015 et 2020. Le trafic Internet des entreprises croîtra à un rythme plus rapide que celui de l'IP WAN. Le trafic WAN IP croîtra à un TCAC de 6%, comparativement à un TCAC de 21% pour les services Internet fixes et de 47% pour le trafic Internet des entreprises mobiles. Le trafic IP des entreprises croîtra le plus rapidement au Moyen-Orient et en Afrique. Le trafic IP des entreprises au Moyen-Orient et en Afrique croîtra à un TCAC de 21 pour cent, un rythme plus rapide que la moyenne mondiale de 18 pour cent. En volume, l'Asie-Pacifique aura la plus grande quantité de trafic IP des entreprises en 2019, à 11,4 EB par mois. L'Amérique du Nord sera deuxième, avec 9,1 EB par mois. La prévision actuelle de l'indice de réseau visuel Cisco (VNI) prévoit que le trafic IP global sera presque triplé entre 2015 et 2020. L'annexe A présente un résumé détaillé. On prévoit que le trafic IP global atteindra 194 EB par mois d'ici 2020, contre 72,5 EB par mois en 2015, soit un TCAC de 22% (figure 1). Cette croissance ne représente qu'une légère diminution par rapport au taux de croissance projeté de l'an dernier pour 2014 à 2019, soit 23%. Il semble que la croissance mondiale du trafic IP se stabilise dans la fourchette de 2025%. Figure 1. Prévisions VNI de Cisco 194 EB par mois de trafic IP d'ici 2020 Source: Prévision du trafic IP mondial Cisco VNI, 20152020 Pour plus de détails sur la méthodologie de prévision Ciscos, consultez le document Cisco VNI: Prévisions et méthodologie, 20152020. Pour comprendre l'ampleur Des volumes de trafic IP, il aide à regarder les chiffres en termes plus familiers: d'ici 2020, le gigabyte (GB) équivalent de tous les films jamais fait traversera l'Internet mondial toutes les 2 minutes. Globalement, le trafic IP atteindra 511 terabits par seconde (Tbps) en 2020, l'équivalent de 142 millions de personnes diffusant simultanément de la vidéo haute définition (HD) en ligne, toute la journée, tous les jours. Le trafic IP mondial en 2020 équivaut à 504 milliards de DVD par an, 42 milliards de DVD par mois, soit 58 millions de DVD par heure. Le trafic Internet total a connu une croissance spectaculaire au cours des deux dernières décennies. Il y a plus de 20 ans, en 1992, les réseaux Internet mondiaux transportaient environ 100 Go de trafic par jour. Dix ans plus tard, en 2002, le trafic Internet global s'élevait à 100 gigaoctets par seconde (GBps). En 2015, le trafic Internet mondial a atteint plus de 20 000 GBps. Le tableau 1 donne un aperçu des repères historiques pour le trafic Internet total. Source: Cisco VNI, 2016 La croissance du trafic IP et Internet par habitant a suivi une courbe de croissance similaire au cours de la dernière décennie. Globalement, le trafic IP mensuel atteindra 25 GB par habitant d'ici 2020, contre 10 GB par habitant en 2015, et le trafic Internet atteindra 21 GB par habitant d'ici 2020, contre 7 GB par habitant en 2015. Il n'y a pas longtemps, en 2008 , Le trafic Internet par habitant était de 1 Go par mois. En 2000, le trafic Internet par habitant était de 10 mégaoctets (Mo) par mois. Les sections qui suivent explorent les tendances qui contribuent à la croissance continue du trafic IP mondial. La figure 2 montre que globalement, les appareils et les connexions (CAGR à 10%) connaissent une croissance plus rapide que la population (1,1% du TCAC) et les internautes (6,5% du TCAC). Cette tendance accélère l'augmentation du nombre moyen d'appareils et de connexions par ménage et par utilisateur Internet. Chaque année, divers nouveaux dispositifs sous des formes différentes et dotés de capacités et d'intelligence accrues sont introduits et adoptés sur le marché. Un nombre croissant d'applications M2M, comme les compteurs intelligents, la vidéosurveillance, la surveillance des soins de santé, le transport et le suivi des colis ou des actifs, contribuent de façon importante à la croissance des appareils et des connexions. D'ici 2020, les connexions M2M seront 46% du total des périphériques et des connexions. Figure 2. Chiffres de croissance des appareils mondiaux et des connexions (n) se réfèrent à 2015, part de l'appareil 2020. Source: Prévisions de trafic IP Cisco VNI Global, 20152020 Les connexions M2M seront la catégorie de croissance la plus rapide, augmentant de près de 2,5 fois au cours de la période de prévision, à 20% CAGR, à 12,2 milliards de connexions d'ici 2020. (En augmentant d'un facteur de 1,8). Les téléviseurs connectés (qui comprennent les téléviseurs à écran plat, les décodeurs, les adaptateurs multimédia numériques DMA, les lecteurs de disques Blu-ray et les consoles de jeux) devraient connaître une croissance proche de celle de 12%, à 3,1 milliards d'ici 2020. Les PC continueront (Baisse de près de 2%) au cours de la période de prévision. Cependant, il y aura plus de PC que de comprimés d'ici la fin de 2020 (1,35 milliards de PC contre 785 millions de comprimés). D'ici 2020, la part des consommateurs dans le total des appareils, y compris les appareils fixes et mobiles, sera de 74 pour cent, les entreprises prétendant les 26 pour cent restants. La part des consommateurs augmentera à un rythme légèrement plus lent, à 9,5% du TCAC par rapport au segment d'affaires, qui croîtra à 12% du TCAC. Pour plus de détails sur la croissance des périphériques et des connexions dans les secteurs résidentiel, mobile grand public et d'entreprise, consultez l'outil Cisco VNI Service Adoption Forecast Highlights. Globalement, le nombre moyen d'appareils et de connexions par habitant passera de 2 en 2015 à 3,2 en 2020 (tableau 2). Parmi les pays qui auront la plus haute moyenne de périphériques par habitant et de connexions d'ici 2020, on trouve les États-Unis (12,3), la Corée du Sud (12,2) et le Japon (11,9). Le mélange changeant d'appareils et de connexions et la croissance de la propriété multidisque affectent le trafic et peuvent être vus dans la contribution changeante de l'appareil au trafic IP total. À la fin de 2015, 47% du trafic IP et 37% du trafic Internet grand public proviennent de périphériques non PC. En 2020, 71% du trafic IP et 71% du trafic Internet grand public proviendront de périphériques non PC (Figure 3). Figure 3. Trafic IP mondial par périphériques Les chiffres (n) renvoient à 2015, part de l'appareil 2020. Comme dans le cas des réseaux mobiles, les dispositifs vidéo peuvent avoir un effet multiplicateur sur le trafic. Un téléviseur HD Internet-enabled qui tire 45 minutes de contenu par jour à partir d'Internet générerait autant de trafic Internet qu'un ménage entier aujourd'hui. Avec la croissance de l'affichage vidéo sur les smartphones et les tablettes, le trafic provenant de ces périphériques augmente en pourcentage du trafic Internet total. Les tablettes représenteront 15% du trafic mondial global d'Internet d'ici 2020, contre 9% en 2015. Les smartphones représenteront 37% du trafic mondial global d'ici 2020, contre 11% en 2015 (figure 4). Figure 4. Trafic global d'Internet par type de périphérique Les chiffres (n) se réfèrent à 2015, part de l'appareil 2020. Source: Prévisions de trafic IP Cisco VNI Global, 20152020 L'impact vidéo des périphériques sur le trafic est plus prononcé en raison de l'introduction de la diffusion vidéo ultra-haute définition (UHD) ou 4K. Cette technologie a un tel impact parce que le débit binaire pour la vidéo 4K à environ 18 Mbps est plus du double du débit vidéo HD et neuf fois plus que le débit binaire vidéo standard (SD). Nous estimons qu'en 2020, 40% des téléviseurs à écran plat installés seront en UHD, contre 8% en 2015 (figure 5). Figure 5. Augmentation de la définition de la vidéo: D'ici 2020, plus de 40 pour cent des téléviseurs à écran plat connectés seront 4K Source: Cisco VNI Global IP Traffic Forecast, 20152020 UHD (ou 4K) VoD IP représentera 21 pour cent du trafic global VoD En 2020 (figure 6). Figure 6. Trafic vidéo mondial 4K Les chiffres (n) se réfèrent aux parts de trafic 2015, 2020. Le passage d'un environnement IPv4 à un environnement IPv6 fait d'excellents progrès, avec des augmentations des capacités des périphériques IPv6, de l'activation du contenu et des opérateurs implémentant IPv6 dans les environnements IPv6. Leurs réseaux. Ces évolutions sont d'autant plus importantes que l'Asie, l'Europe, l'Amérique du Nord et l'Amérique latine ont déjà épuisé leurs attributions IPv4 et que l'Afrique devrait épuiser son allocation d'ici à 2018. Le tableau 3 montre les dates d'épuisement prévues en mai 2016, Registres Internet (RIR). Tableau 3. Dates d'épuisement des adresses IPv4 Registres Internet régionaux En s'appuyant sur l'analyse des périphériques compatibles IPv6 de VNI, les prévisions prévoient que, à l'échelle mondiale, il y aura près de 13 milliards d'IPv6capables d'appareils fixes et mobiles d'ici 2020, contre près de 4 milliards en 2015. 27 pour cent. En termes de pourcentages, 48 ​​pour cent de tous les appareils en réseau fixes et mobiles seront équipés d'IPv6 d'ici 2020, contre 23 pour cent en 2015 (figure 7). Cette estimation est basée sur la capacité du périphérique et de la connexion réseau à prendre en charge IPv6 et n'est pas une projection de connexions IPv6 actives. La capacité IPv6 du périphérique mobile est évaluée en fonction du support OS d'IPv6 et des estimations des types d'infrastructure de réseau mobile auxquels le périphérique peut se connecter (3,5 génération 3.5G ou plus tard). La capacité IPv6 à périphérique fixe est évaluée en fonction du support de périphérique de IPv6 et une estimation de la capacité des équipements résidentiels locaux des clients (CPE) ou des routeurs professionnels à prendre en charge IPv6, en fonction du segment d'utilisateur final du périphérique. Globalement, 90% des smartphones et des tablettes seront équipés d'IPv6 d'ici à 2020, contre 60% en 2015. Globalement, il y aura une augmentation du nombre de smartphones et de tablettes compatibles IPv6 en 2015. 5,8 milliards de smartphones et tablettes compatibles IPv6 d'ici 2020, contre 2,1 milliards en 2015. D'ici 2020, 30% des connexions M2M seront équipées d'IPv6, atteignant 3,7 milliards, soit un TCAC de 67%. Selon l'Organisation mondiale de lancement IPv6 en mai 2016, les opérateurs de réseaux fixes et mobiles dans le monde entier déploient IPv6 et commencent à signaler une génération de trafic IPv6 notable. Romanias RCS amp RDS a déclaré près de 12 pour cent, Frances Free Telecom a déclaré 22 pour cent, KDDI rapporté près de 28 pour cent, Comcast a déclaré 45 pour cent, ATampT a déclaré 59 pour cent, et Verizon Wireless a déclaré 69 pour cent de déploiement. Selon Google, en mai 2016, le pourcentage d'utilisateurs qui accèdent à Google via IPv6 est d'environ 11 pour cent. Parmi ces développements de l'industrie, la prévision VNI s'efforce d'estimer le potentiel de trafic réseau IPv6 qui pourrait être généré si un pourcentage d'appareils compatibles IPv6 devient activement connecté à un réseau IPv6 compte tenu de la moyenne mondiale estimée du trafic mensuel par type d'appareil . En ce qui concerne 2020, si 60% des appareils compatibles IPv6 sont activement connectés à un réseau IPv6, les prévisions estiment que globalement le trafic IPv6 s'élèverait à 55 EB par mois, soit 34% du trafic Internet total (Figure 8). Cette estimation initiale du trafic IPv6 potentiel est basée sur les hypothèses selon lesquelles la capacité des périphériques IPv6, l'activation du contenu IPv6 et le déploiement du réseau IPv6 se maintiendront à un rythme soutenu Avec les tendances actuelles, et peut même s'accélérer pendant la période de prévision. Compte tenu de l'interdépendance de ces variables, les hypothèses de prévision pourraient faire l'objet de raffinements à mesure que notre analyse se poursuit. Les fournisseurs de contenu cherchent également à accroître l'activation IPv6 de leurs sites et services. Selon les laboratoires Cisco IPv6. D'ici 2020, le contenu disponible sur IPv6 sera d'environ 35%. Cependant, il peut y avoir des variations en fonction de la popularité des sites Web entre les régions et les pays. En outre, les initiatives spécifiques des pays et les déploiements de fournisseurs de contenu ont eu une incidence positive sur l'accessibilité du contenu IPv6 local. Dans l'ensemble, la probabilité qu'une partie importante du trafic Internet soit générée sur les réseaux IPv6 offre aux opérateurs de réseaux, aux fournisseurs de contenu et aux utilisateurs finaux la possibilité d'acquérir les avantages d'évolutivité et de performance d'IPv6 et d'activer Internet de tout. Tendance 3: les applications M2M dans de nombreuses industries Accélèrent la croissance IoE Le phénomène IoE (Internet of Everything), où les gens, les processus, les données et les choses se connectent à Internet et entre eux, affiche une croissance tangible. Globalement, les connexions M2M augmenteront de près de 2,5 fois, passant de 4,9 milliards en 2015 à 12,2 milliards d'ici 2020 (figure 9). Il y aura 1,6 M2M connexions pour chaque membre de la population mondiale d'ici 2020. Figure 9. Global M2M Connection Source de croissance: Cisco VNI Global IP Traffic Forecast, 20152020 Les applications domestiques connectées, telles que la domotique, la sécurité domestique et la vidéo surveillance, Des biens et des applications de suivi, représentera 47%, soit près de la moitié, des connexions M2M totales d'ici 2020, ce qui montre l'omniprésence du M2M dans nos vies (figure 10). Les soins de santé connexes, avec des applications telles que les moniteurs de santé, les distributeurs de médicaments, la connectivité des premiers intervenants et la télémédecine, seront le segment de l'industrie qui connaît la croissance la plus rapide, avec un TCAC de 49%. Les applications liées à la voiture auront la deuxième croissance la plus rapide, à 37 pour cent CAGR. Les puces pour animaux de compagnie et le bétail, les moniteurs de santé numériques et de nombreux autres services M2M de prochaine génération font la promotion de cette croissance. Figure 10. Croissance globale de la connexion M2M par secteur d'activité Autres activités comprennent l'agriculture, la construction et les services d'urgence. Source: Prévisions de trafic IP Cisco VNI Global, 20152020 Bien que le nombre de connexions soit multiplié par trois, le trafic IP M2M mondial croîtra six fois au cours de cette même période, passant d'un EB par mois en 2015 (1,4% du trafic IP mondial) à 6,3 EB par 2020 (3,2% du trafic IP mondial se réfèrent à la figure 11). La quantité de trafic croît plus vite que le nombre de connexions en raison de l'augmentation du déploiement d'applications vidéo sur les connexions M2M et de l'utilisation accrue d'applications telles que la télémédecine et les systèmes de navigation intelligents qui nécessitent une plus grande bande passante et une latence plus faible. Graphique 11. Croissance mondiale du trafic M2M: exabytes par mois Source: Prévisions du trafic IP mondial Cisco VNI, 20152020 Tendance 4: Tendances de l'adoption des services: résidentiel, mobile grand public et services aux entreprises Services résidentiels mondiaux: la vidéo continue de croître entre 2014 et 2015, La croissance la plus importante s'est produite sur le côté Internet dans les jeux en ligne, avec une croissance de 15% par rapport à l'année dernière (YoY). Le réseautage social a été le service Internet résidentiel le plus largement adopté, avec une croissance annuelle de 8,5%, passant de 1,3 milliard d'utilisateurs en 2014 à 1,4 milliard d'utilisateurs en 2015. D'ici 2020, la télévision numérique et le réseautage social seront les deux services avec les taux de pénétration les plus élevés , Avec 87 pour cent et 76 pour cent, respectivement. La croissance la plus rapide proviendra des services de télévision à retardement, comme les enregistreurs vidéo personnels (PVR) et les enregistreurs vidéo numériques (DVR), à 7% de la CAGR. Le jeu en ligne (5,3% du TCAC) sera le service Internet résidentiel qui connaîtra la croissance la plus rapide. La croissance des jeux en ligne est accélérée principalement par des améliorations technologiques dans les ordinateurs tels que les graphiques, la détection de mouvement, la reconnaissance des gestes, etc. (Figure 12). Figure 12. Note d'adoption et de croissance des services résidentiels mondiaux. D'ici 2020, la population résidentielle mondiale résidentielle fixe sera de 2,4 milliards le nombre de foyers TV mondiale sera de 1,8 milliard. Source: Cisco VNI Service Adoption Forecast, 20152020 Global Consumer Mobile Services Entre 2014 et 2015, tous les services mobiles grand public à l'exception d'un ont augmenté de plus de 10% par rapport à la même période de l'année précédente. La croissance la plus élevée a été enregistrée dans les services de localisation axés sur les consommateurs (LBS), avec une croissance de 38% par rapport à l'année précédente, passant de 585 millions d'utilisateurs en 2014 à 807 millions en 2015. , Suivi de la vidéo mobile (35%). Des régions comme l'Amérique latine (croissance de 62% en glissement annuel) et le Moyen-Orient et l'Afrique (croissance de 52% en glissement annuel) ont connu la croissance la plus rapide du marché des services mobiles mobile. La banque mobile et le commerce ont également connu la plus forte croissance en Amérique latine, avec une croissance de 49% en glissement annuel. La croissance de la vidéo mobile a été menée par le Moyen-Orient et l'Afrique, avec une croissance de 43% en glissement annuel. De 2015 à 2020, six des huit services mobiles grand public augmenteront à plus de 14% du TCAC, trois croîtront à plus de 20% du TCAC et l'un diminuera. La croissance la plus rapide aura été enregistrée chez les consommateurs LBS (3,9%), suivie du commerce mobile (22,7%). Le Moyen-Orient et l'Afrique, l'Europe centrale et orientale, l'Amérique latine et l'Asie-Pacifique connaissent des taux de croissance particulièrement élevés dans les services de commerce mobile, qui ont toujours été mal desservis (ou non atteints) par les institutions financières traditionnelles (Figure 13 ). Figure 13. Note sur l'adoption et la croissance des services mobiles grand public. D'ici 2020, la population mondiale de consommateurs mobile sera de 5 milliards. Source: Prévisions d'adoption des services Cisco VNI, 20152020 Global Business Services Entre 2014 et 2015, la croissance la plus élevée a été en affaires LBS, avec une augmentation de 32%, passant de 92 millions d'utilisateurs en 2014 à 121 millions en 2015. Dans la vidéoconférence sur ordinateur (25 pour cent se réfèrent à la figure 14). Business LBS comprend les services utilisés par les abonnés d'entreprise dans lesquels l'abonnement est généralement payé par l'employeur. Ces services incluent l'automatisation de la force de vente et de la force de campagne, la gestion de flottes, etc. Nous constatons que la vidéoconférence personnelle ou de bureau remplit de plus en plus la conférence en salle car la vidéo devient plus simple et plus intégrée aux offres de services de communications unifiées. De 2015 à 2020, le service d'entreprise qui connaît la croissance la plus rapide devrait être une vidéoconférence personnelle ou personnelle. La croissance de la vidéoconférence personnelle, en particulier la télécommunication unifiée basée sur les communications, s'est récemment accélérée en raison de la qualité supérieure et de la baisse du prix des nouveaux services et produits. Il est également causé par la disponibilité des offres de vidéoconférence de bureau, qui peut être autonome ou intégré. De plus, la croissance des clients mobiles favorisera la croissance de la vidéoconférence. À l'inverse, l'utilisation de la conférence Web sans vidéo montrera un déclin de 4% du TCAC au cours de la période de prévision (Figure 14). Figure 14. Note sur l'adoption et la croissance des services aux entreprises mondiales. D'ici 2020, la population mondiale d'Internet d'affaires sera de 2,2 milliards le nombre d'utilisateurs d'entreprises seront 577 millions. Source: Cisco VNI Service Adoption Forecast, 20152020 Pour plus de détails sur tous les aspects de l'étude d'adoption des services, utilisez l'outil Cisco VNI Service Adoption Highlights. Tendance 5: Applications Croissance du trafic La somme de toutes les formes de vidéos IP, incluant la vidéo sur Internet, la VoD IP, les fichiers vidéo échangés par le partage de fichiers, les jeux vidéo et la vidéoconférence, continuera d'être comprise entre 80 et 90 Pourcentage du trafic IP total. Globalement, le trafic vidéo IP représentera 82% du trafic d'ici 2020 (figure 15). Figure 15. Trafic mondial de la PI par catégorie d'application Les chiffres (n) se rapportent à 2015, parts de la circulation 2020. Source: Cisco VNI Global IP Prévision du trafic, 20152020 Les implications de la croissance vidéo sont difficiles à exagérer. Avec la croissance vidéo, le trafic Internet évolue d'un flux relativement régulier de trafic (caractéristique du trafic P2P peer-to-peer) à un trafic plus dynamique. Au cours de la dernière année, les fournisseurs de services ont observé une augmentation marquée du trafic lié aux téléchargements de jeux. Les consoles plus récentes telles que la Xbox One et la PlayStation 4 disposent d'une mémoire de stockage suffisante pour permettre aux joueurs de télécharger de nouveaux jeux plutôt que de les acheter sur disque. Ces jeux graphiquement intenses sont de gros fichiers et les téléchargements de jeux représentent déjà 2% du trafic Internet fixe des consommateurs et atteindront 4% du trafic Internet fixe des consommateurs d'ici 2020. En outre, ces téléchargements ont tendance à se produire pendant les périodes d'utilisation maximale. Jusqu'à 10 pour cent du trafic des heures occupées. Impact de la vidéo sur la symétrie du trafic À l'exception des appels vidéo et vidéo de courte durée, la plupart des formes de vidéo sur Internet ne disposent pas d'un grand composant en amont. En conséquence, le trafic ne devient pas plus symétrique, une situation que beaucoup attendaient lorsque le contenu généré par les utilisateurs est devenu populaire. L'émergence d'abonnés en tant que producteurs de contenu est un phénomène social, économique et culturel extrêmement important, mais les abonnés consomment encore beaucoup plus de vidéo qu'ils ne produisent. Le trafic en amont a légèrement diminué en pourcentage depuis plusieurs années. Il semble probable que le trafic Internet résidentiel restera asymétrique pour les prochaines années. Cependant, de nombreux scénarios pourraient se traduire par une augmentation de la symétrie, par exemple: les fournisseurs de contenu et les distributeurs pourraient adopter le P2P comme mécanisme de distribution. Il y a longtemps que le P2P est un système de diffusion de contenu peu coûteux, mais la plupart des fournisseurs de contenu et des distributeurs ont opté pour la distribution directe, à l'exception des applications telles que PPStream et PPLive en Chine. Offrent des flux vidéo en direct par le biais du P2P et ont connu un grand succès. Si les fournisseurs de contenu d'autres régions suivent leur exemple, le trafic pourrait rapidement devenir très symétrique. Les communications vidéo haut de gamme pourraient accélérer, nécessitant une bande passante symétrique. PC-à-PC appel vidéo gagne du terrain, et le marché des appels vidéo mobile naissant semble avoir la promesse. Si les appels vidéo haut de gamme deviennent populaires, le trafic pourrait se déplacer vers une plus grande symétrie. En règle générale, si les fournisseurs de services fournissent une large bande passante en amont, les applications qui utilisent la capacité en amont commenceront à apparaître. Tendance 6: Analyse de coupe de cordon Dans le contexte de la prévision de VNI, Cord-coupe se réfère à la tendance dans laquelle la télévision traditionnelle et la télévision par abonnement est de plus en plus supplantée par d'autres moyens de visionnement vidéo, comme la vidéo en ligne et mobile, qui sont disponibles Aux téléspectateurs via des connexions Internet fixes et mobiles. On constate une tendance dans laquelle la croissance du service de télévision numérique qui désigne la télévision à travers toutes les plateformes numériques (câble, IPTV, satellite, etc.) croît beaucoup plus lentement par rapport à la vidéo mobile (figure 16). Cette tendance est plus prononcée dans des régions comme l'Amérique du Nord et l'Europe occidentale, où la pénétration de la télévision numérique est déjà élevée. La vidéo en ligne, que nous avons constatée était de plus en plus rapide jusqu'à l'année dernière, est maintenant presque à égalité avec la télévision numérique. En outre, dans les régions émergentes, les taux de croissance de la vidéo mobile sont encore plus élevés, car ces régions ignorent la connectivité fixe. Un autre facteur qui soutient cette tendance est que le total des marchés adressables pour ces services, les utilisateurs d'Internet résidentiels, les utilisateurs de mobiles grand public et le total des foyers de téléviseurs ( Pour les ménages de télévision numérique) présentent des profils de croissance significativement différents (figure 17). On s'attend à ce que les utilisateurs résidentiels d'Internet augmentent à un CAGR de presque 3,2 pour cent, et les consommateurs mobiles utilisateurs à 2,8 pour cent, alors que dans le même temps, le nombre de foyers TV s'effondre, avec un maigre 1,8 pour cent prévus CAGR. Figure 17. Croissance des utilisateurs résidentiels d'Internet dans le monde par rapport à la croissance dans les ménages télévisuels mondiaux Source: Prévisions du trafic IP mondial Cisco VNI, 20152020 En outre, si l'on considère les dispositifs Internet tels que les adaptateurs de médias numériques (DMA) 9 pour cent de tous les décodeurs connectés à Internet (STB), y compris les STB de fournisseurs de services, les consoles de jeux et les téléviseurs Internet connectés directement à l'horizon 2020, ils représenteront 32% du trafic Internet STB mondial. Cette tendance démontre à nouveau que les STB gérés par les fournisseurs de services pour l'accès Internet en général et pour la vidéo sont de moins en moins dépendants (figure 18). Figure 18. Croissance des adaptateurs de médias numériques globaux Les DMA incluent des périphériques tels que Roku, Apple TV, Chromecast, etc. Source: Prévisions de trafic IP mondiales Cisco VNI, 20152020 Du point de vue de la circulation, nous nous attendons à ce qu'un ménage qui est encore linéaire La télévision générera beaucoup moins de trafic qu'un ménage qui a coupé le cordon et s'appuie sur la vidéo sur Internet (Figure 19). Un ménage coupant la corde va générer 102 Go par mois en 2016, comparativement à 49 Go par mois pour un ménage moyen. Cette différence se produit parce que la télévision linéaire génère beaucoup moins de trafic (un flux de vidéo partagé à travers de nombreux ménages de télévision linéaire) que la vidéo sur Internet, qui est unicast pour chaque périphérique vidéo sur Internet. Figure 19. Global Cord Cutting Generates Double the Traffic Source: Cisco VNI Global IP Traffic Forecast, 20152020 Trend 7: Security Analysis Users expect their online experience to be always available and always secureand for their personal and business assets to be safe. Annual security reports for 2016 from industry giants in the security space highlight the need for increased focus on cybercrimes, data breaches and espionage, and mitigation strategies (Figure 20). Figure 20. SecurityIndustry Top of Mind The last several years have been easily the most eventful period from a security threat perspective, with many serious data breaches that have been discussed widely in the media. There were a total of 780 breaches with a total of nearly 178 million records stolen in 2015. The number of records stolen per data breach averaged 228 thousand in 2015, according to 2015 data breach statistics from IDT911. The average cost paid for each sensitive lost or stolen record increased 6 percent from 2015 to 2016, according to a joint study by IBM and Ponemon Institute. More secure Internet servers leads to a large footprint of security and authentication, better serving end users with secure transactions and communication. The percentage of secure Internet servers that conduct encrypted transactions over the Internet using Secure Sockets Layer (SSL) compared to the total number of web-facing servers depicts the nature of the secure footprint. Western Europe led with the number of secure Internet servers per 1 million people with 50 percent, followed by Central and Eastern Europe with 29 percent, North America with 27 percent, and Asia Pacific with around 23 percent. The average number of breaches was highest in Asia Pacific organizations and lowest in U. K. and U. S. enterprises in 2015, according to a recent study published by McAfee. Sixty percent of data stolen was through web protocols, file transfer and tunneling protocols, or email. Two-thirds of breaches involved traditional corporate networks, and cloud break-ins accounted for the remaining one-third, according to McAfee and LemonFish (Figure 21). Figure 21. How Is Data being Breached Source: McAfee, Lemonfish, Cisco VNI 2016 Frequency of distributed denial-of-service (DDoS) attacks has increased more than 2.5 times over the last 3 years, according to Arbor Networks. DDoS attacks are increasing at roughly the same rate as traffic. Peak DDoS attack size (Gbps) is increasing in a linear trajectory, with peak attacks reaching 300, 400, and 500 Gbps respectively, in 2013, 2014, and 2015, at about 10 to 15 percent per year. DDoS attacks can represent up to 10 percent of a countrys total Internet traffic while they are occurring. The average size of DDoS attacks is increasing steadily and approaching 1 Gbps, enough to take most organizations completely off line. In 2015 the top motivation behind DDoS attacks was criminals demonstrating attack capabilities, with gaming and criminal extortion attempts in second and third place, respectively. DDoS attacks account for more than 5 percent of all monthly gaming-related traffic and more than 30 percent of gaming traffic while they are occurring. The events from 2015 and the first quarter of 2016 once again demonstrated that the attackers are increasing their computing resources to perform DDoS attacks. Amplification attackers, who have tools for carrying out a DDoS attack, exploit vulnerabilities in the network and compute resources. With the growth of the IoE and spread of vulnerable devices and traditional PCs, the abundance of configuration drawbacks with applications can be targeted. Security vendors continue to ensure these attacks are financially unviable for the cybercriminals. Globally the number of DDoS attacks grew 25 percent in 2015 and will increase 2.6-fold to 17 million by 2020 (Figure 22). Figure 22. Global DDoS Attacks Forecast, 2015-2020 Figures (n) refer to 2015, 2020 traffic shares. Source: Cisco VNI Global IP Traffic Forecast, 2015-2020 Trend 8: Impact of Accelerating Speeds on Traffic Growth Broadband speed is a crucial enabler of IP traffic. Broadband-speed improvements result in increased consumption and use of high-bandwidth content and applications. The global average broadband speed continues to grow and will nearly double from 2015 to 2020, from 24.7 Mbps to 47.7 Mbps. Table 4 shows the projected broadband speeds from 2015 to 2020. Several factors influence the fixed broadband-speed forecast, including the deployment and adoption of fiber to the home (FTTH), high-speed DSL, and cable broadband adoption, as well as overall broadband penetration. Among the countries covered by this study, Japan, South Korea, and Sweden lead within the VNI countries in terms of broadband speed largely because of their wide deployment of FTTH. Table 4. Fixed Broadband Speeds (in Mbps), 20152020 Source: Cisco VNI, 2016 Consider how long it takes to download an HD movie at these speeds: at 10 Mbps, it takes 20 minutes at 25 Mbps, it takes 9 minutes but at 100 Mbps, it takes only 2 minutes. High-bandwidth speeds will be essential to support consumer cloud storage, making the download of large multimedia files as fast as a transfer from a hard drive. Table 5 shows the percentage of broadband connections that will be faster than 10 Mbps, 25 Mbps, and 100 Mbps by region. Table 5. Broadband Speed Greater Than 10 Mbps, 20152020 Greater Than 10 Mbps Greater Than 25 Mbps Greater Than 100 Mbps Central and Eastern Europe Middle East and Africa Source: Cisco VNI, 2016 There is a strong correlation between experienced speeds and number of video minutes viewed per viewer (Figure 23). As speeds increase in each country covered in the study, the number of video minutes per viewer also increases. Figure 23. Increase in Experienced Speeds (Mbps) Increases Internet Video Viewership (Minutes)2016 Source: Cisco VNI Global IP Traffic Forecast, 20152020 Globally, the average mobile network connection speed in 2015 was 2.0 Mbps. The average speed will more than double and will be 6.5 Mbps by 2020. Smartphone speeds, generally third-generation (3G) and later, are currently nearly three times higher than the overall average. Smartphone speeds will nearly double by 2020, reaching 12.5 Mbps. Anecdotal evidence supports the idea that overall use increases when speed increases, although there is often a delay between the increase in speed and the increased use, which can range from a few months to several years. The reverse can also be true with the burstiness associated with the adoption of tablets and smartphones, where there is a delay in experiencing the speeds that the devices can support. The Cisco VNI Forecast relates application bit rates to the average speeds in each country. Many of the trends in the resulting traffic forecast can be seen in the speed forecast, such as the high growth rates for developing countries and regions relative to more developed areas (Table 6). Table 6. Projected Average Mobile Network Connection Speeds (in Mbps) by Region and Country Source: Cisco VNI Mobile, 2016 Current and historical speeds are based on data from Ooklas Speedtest. Forward projections for mobile data speeds are based on third-party forecasts for the relative proportions of 2G, 3G, 3.5G, and 4G among mobile connections through 2020. A crucial factor promoting the increase in mobile speeds over the forecast period is the increasing proportion of fourth-generation (4G) mobile connections. The impact of 4G connections on traffic is significant, because 4G connections, which include mobile WiMAX and Long-Term Evolution (LTE), generate a disproportionate amount of mobile data traffic. Wi-Fi Speeds from Mobile Devices Globally, Wi-Fi connection speeds originated from dual-mode mobile devices will nearly double by 2020. The average Wi-Fi network connection speed (10.6 Mbps in 2015) will exceed 18.5 Mbps in 2020. North America will experience the highest Wi-Fi speeds, 29 Mbps, by 2020 (Table 7). Wi-Fi speeds inherently depend on the quality of the broadband connection to the premises. The speed also depends on the Wi-Fi standard in the CPE device. The latest standard, IEEE 802.11ac, is considered a true wired complement and can enable higher-definition video streaming and services that require higher data rates. Also an important factor in the use of Wi-Fi technology is the number and availability of hotspots. Table 7. Projected Average Wi-Fi Network Connection Speeds (in Mbps) by Region and Country Source: Cisco VNI, 2016 Trend 9: Mobility (Wi-Fi) Continues to Gain Momentum Globally, there will be nearly 433 million public Wi-Fi hotspots by 2020, up from 64 million hotspots in 2015, a sevenfold increase. By 2020, China will lead in total number of hotspots, followed by the United States and France. Western Europe had 45 percent of the worlds Wi-Fi hotspots share in 2015. By 2020, public Wi-Fi along with community hotspots are accounted for as well. Community hotspots or homespots are just emerging as a potentially significant element of the public Wi-Fi landscape. In this model, subscribers allow part of the capacity of their residential gateway to be open to casual use. The homespot may be provided by a broadband or other provider directly or through a partner. Asia Pacific will lead in adoption of homespots. By 2020, China will lead in total number of homespots, followed by France and Japan. Adoption of homespots has been led by Western Europe and then North America in 2015, but Asia Pacific will lead by 2020. Critical enablers of Hotspot 2.0 adoption are higher-speed Wi-Fi gateways and the adoption of the IEEE 802.11ac and 802.11n standards. Globally, the prevalence of IEEE 802.11ac, the latest Wi-Fi standard, will gain momentum from 2015 through 2020. In 2015, 59.5 percent of all home Wi-Fi routers shipped globally were 802.11ac-enabled. By 2020, 96.6 percent of all home Wi-Fi routers will be equipped with 802.11ac. IEEE 802.11n, which was ratified in 2007, provides a range of speeds that allow users to view medium-resolution video streaming because of the higher throughput. The latest standard, IEEE 802.11ac, with very high theoretical speeds, is considered a true wired complement and can enable higher-definition video streaming and services with use cases that require higher data rates (Figure 24). Figure 24. Future of Wi-Fi as Wired Complement The rapid growth of mobile data traffic has been widely recognized and reported. The trend toward mobility carries over into the realm of fixed networks as well, in that an increasing portion of traffic will originate from portable or mobile devices. Figure 25 shows the growth in Wi-Fi and mobile traffic in relation to traffic from wired devices. By 2020, wired networks will account for 34 percent of IP traffic, and Wi-Fi and mobile networks will account for 66 percent of IP traffic. In 2015, wired networks accounted for the majority of IP traffic, at 52 percent Wi-Fi accounted for 43 percent and mobile or cellular networks accounted for 5 percent of total global IP traffic. Figure 25. Global IP Traffic, Wired and Wireless Wireless traffic includes Wi-Fi and mobile. Source: Cisco VNI Global IP Traffic Forecast, 20152020 Narrowing the focus to Internet traffic and excluding managed IP traffic yields a more pronounced trend. By 2020, wired devices will account for 22 percent of Internet traffic, and Wi-Fi and mobile devices will account for 78 percent of Internet traffic (Figure 26). In 2015, wired devices accounted for less than half of Internet traffic, at 38 percent. Figure 26. Global Internet Traffic, Wired and Wireless Source: Cisco VNI Global IP Traffic Forecast, 20152020 Trend 10: Traffic-Pattern Analysis (Peak Compared to Average and CDN Uptake) Although average Internet traffic has settled into a steady growth pattern, busy-hour traffic (or traffic in the busiest 60minute period of the day) continues to grow more rapidly. Service providers plan network capacity according to peak rates rather than average rates. In 2015, busy-hour Internet traffic grew 51 percent, and average traffic grew at 29 percent. Between 2015 and 2020, global busy-hour Internet use will grow at a CAGR of 36 percent, compared with 25 percent for average Internet traffic (Figure 27). Video is the underlying reason for accelerated busy-hour traffic growth. Unlike other forms of traffic, which are spread evenly throughout the day (such as web browsing and file sharing), video tends to have a prime time. Because of video consumption patterns, the Internet now has a much busier busy hour. Because video has a higher peak-to-average ratio than data or file sharing, and because video is gaining traffic share, peak Internet traffic will grow faster than average traffic. The growing gap between peak and average traffic is amplified further by the changing composition of Internet video. Real-time video such as live video, ambient video, and video calling has a peak-to-average ratio that is higher than on-demand video. Figure 27. Busy-Hour Compared with Average Internet Traffic Growth Source: Cisco VNI Global IP Traffic Forecast, 20152020 Changes in traffic topology are being brought about by the increasing role of content delivery networks (CDNs) in data delivery. CDNs will carry 64.5 percent of total Internet traffic by 2020 (Figure 28). Although network performance is usually attributed to the speeds and latencies offered by the service provider, the delivery algorithms used by CDNs have an equal if not more significant bearing on video quality. Figure 28. Global Content Delivery Network Internet Traffic, 2015 and 2020 Source: Cisco VNI Global IP Traffic Forecast, 20152020 Speed is a critical factor in Internet traffic. When speed increases, users stream and download greater volumes of content, and adaptive bit-rate streaming increases bit rates automatically according to available bandwidth. Service providers find that users with greater bandwidth generate more traffic. In 2015, households with high-speed fiber connectivity generated 58 percent more traffic than households connected by DSL or cable broadband, globally (Figure 29). The average FTTH household generated 68 GB per month in 2015 and will generate 138 GB per month in 2020. Figure 29. Fiber-Connected Households Generate More Traffic Than Households with Other Sources of Broadband Source: Cisco VNI Global IP Traffic Forecast, 20152020 To limit the volume of traffic, service providers can institute use-based tiered pricing and data caps. On mobile networks, by looking at the use of more than 33,000 lines from Tier-1 mobile operators from 2010 to 2015, we found that monthly traffic from the top 1 percent of users is down to 18 percent of overall use compared to 52 percent in 2010, showing the effects of tiered pricing. With mobile penetration reaching a saturation point in many countries across all regions, the trend has been toward tiered plans as a way to monetize data and effectively manage or throttle the top users of traffic. On the fixed networks, data caps continue to increase to match subscribers growing appetite for video. In the United States, Tier-1 carriers are offering a variety of fair usage limits today, as high as 1 TB per month. A large provider in Japan has a 30-GB-per-day upload cap. In several countries, Netflix has a sizable percentage of the Internet video minutes and traffic. Wildcard traffic generators such as Twitch. TV, a live streaming service in which video gamers watch each other play, has established itself on many fixed networks around the world. Data caps affect a larger percentage of mobile users than fixed users. With Tier-1 carriers, approximately 12 percent of mobile users consume more than 2 GB per month (a common mobile data cap), whereas only 1.4 percent of fixed users consume more than 500 GB per month (a common fixed data cap). Other Trends to Watch Ciscos approach to forecasting IP traffic is conservative, and certain emerging trends have the potential to increase the traffic outlook significantly. Growth of smartphones as the communications hub for social media, video consumption, tracking IoEdigitization applications (et al.), as well as traditional voice. This trend demonstrates the impact that smartphones have on how consumers and businesses users access and use the Internet and IP networks. Internet gaming is seeing a resurgencethe traffic nearly doubled in 2015 and will grow seven-fold by 2020. Gaming on demand and streaming gaming platforms have been in development for several years, with many newly released in 2014 and 2015. With traditional gaming, graphical processing is performed locally on the gamers computer or console. With cloud gaming, game graphics are produced on a remote server and transmitted over the network to the gamer. If cloud gaming becomes popular, gaming could quickly become one of the largest Internet traffic categories. Virtual reality . With new hardware available to individuals, and a growing body of content to consume, virtual reality has experienced high growth in recent years. Traffic associated with virtual and augmented reality applications quadrupled in 2015 and is poised to grow 61-fold by 2020. This growth stems mainly from the download of large virtual reality content files and applications, but a significant wild card is the potential adoption of virtual reality streaming, which could raise our prediction of high-growth even higher. Immersive video . This emerging traffic type can cause significant new network design implications as it is a high-bandwidth consuming application. Social media platforms such as Facebook have launched support for spherical, or immersive video that integrates multiple camera angles to form a single video stream and can be watched from the viewers preferred perspective. It can generate bit rates 3 to 10 times greater than non-immersive HD bit rates. Video surveillance . New Internet-connected video surveillance cameras upload a constant video stream to the cloud for remote viewing. With a steady flow of video traffic from each camera, video surveillance is already having an impact on overall Internet traffic and accounts for 1.5 percent of total Internet traffic today, growing to nearly 4 percent by 2020. If such devices become mass market in the next five years, we could see video cameras generating a significantly higher volume of traffic, since Internet-enable cameras can produce up to 300 GB per camera per month for full HD-resolution monitoring of high-activity areas. For More Information For more information about the Cisco IP traffic forecast, refer to Cisco VNI: Forecast and Methodology, 20152020 and visit the other resources and updates at ciscogovni. Several interactive tools allow you to create custom highlights and forecast charts by region, country, application, and end-user segment. Refer to the Cisco VNI Highlights tool and the Cisco VNI Forecast Widget tool. For regional details about the VNI service adoption forecast, please visit the Cisco VNI SA highlights tool and Cisco VNI SA Graphing tool. Inquiries can be directed to trafficinquiriescisco . Appendix A: Cisco Global IP Traffic Forecast Table 8 shows a summary of the Cisco global IP traffic forecast. For more information and additional tables, refer to Cisco VNI: Forecast and Methodology, 20152020. Table 8. Global IP Traffic, 20152020There now follows an alphabetical list of some commonly used wordsphrasesabbreviations that you might see in the newsgroup (or via other weather-related sites on the WWW), but which may not be readily understood. The list has been prepared in association with Paul Bartlett, David Reynolds and many others: I would welcome suggestions for inclusion, but I will also scan the posts in the newsgroup and if I see a wordphraseabbreviation that is causing problems, I will include same. Where a longer explanation is required, a QA in the FAQ will be worked up, and referred to hereunder. For the professionalacademic community, these terms etc. will not be rigorous enough, but I ask for some understanding in this respect, as the list is intended to convey the idea of a concept, process etc. so that casual readers in the newsgroup can keep up with discussions without having to delve too deeply into a meteorological textbook. However, if Ive made a fundamental mistake, then by all means let me have a corrected entry for consideration. Glossary terms A-F Absolute drought A period of at least 15 consecutive days, to none of which is credited 0.01 inches 0.2 mm or more of precipitation. (See also drought partial drought dry spell ) Absolute vorticity (or total vorticity) of air particles at any particular point is comprised of two elements: (i) on the rotating earth, air adopts the local vorticity due to the earths solid-body rotation about its pole-to-pole axis, which is latitude dependent, and is known as the Coriolis parameter. This increases to a maximum over the poles and decreases to zero at the equator. The Coriolis rotation sense is always positive (or zero). (ii) the other element is known as the relative vorticity, the spin tendency of air particles due to their motion relative to the earth - driven by atmospheric forces. Relative vorticity can be either positive (cyclonic sense) or negative (anticyclonic). (See also: Vorticity Relative vorticity .) (abbr) Altocumulus (AC for METARSIGWX charts etc. Ac otherwise) a medium level, layer cloud type, but with varying levels of instability associated - the extreme event being ACCAST . (quot Alto-Q-Cast quot)(Altocumulus castellanus or castellatus the proper abbreviation for the Daily Register is Ac cas) These are medium level clouds (between circa 8000 and 18000 ft 2.5 to 5.5 km) which exhibit, at least in their upper parts, marked cumuliform turreted appearance - the convective towers are often taller than the width of the individual base the bases are connected and often appear to be arranged in lines or streets. These clouds are a good indicator of medium level instability and high moisture content - and often the precursor for widespread thundery activity within the following 24 to 48 hours. Observers used to SYNOP coding may also refer to these (along with Altocumulus floccusAc flo), as CM8 clouds. A process where temperature changes occur in a system, without heat being supplied to, or lost from that system. In meteorology, used in connection with changes involving air parcels moving vertically in the atmosphere. If heat exchange is involved, the process is non-adiabatic (or diabatic). Adiabatic lapse rate The change of temperature of an air parcel rising (cooling) or descending (warming) adiabatically. For dry (i. e. unsaturated) ascent or descent, the rate is 10degC km for moist or saturated processes, it varies but a useful average is 5 or 6degC km. The transfer by horizontal air movement of heat, moisture (or humidity), momentum etc. The atmosphere at all levels is usually in some form of motion at most times, thus it is necessary to identify areas of significant advection. For the lowmiddle troposphere thickness products (e. g. 500-1000 hPa) are often used. Solid particles suspended in the air. They include dust, salt particles, products of combustion etc. These are very important to the formation of water droplets or ice particles in the atmosphere, acting as nuclei for condensation sublimation. Ageostrophic effects An extensive volume of air possessing uniform physical characteristics at similar heights in terms of humidity and temperature structure. The proportion of solar incoming visible light (after passage through the atmosphere) reflected by a surface (e. g. sea, cloud-tops, ice etc.), expressed as a fraction or percentage of the incident light falling on that surface. Clouds have highly varying albedo, dependent upon thickness and composition. Old snow is about 55 (or 0.55), new snow around 80 (or 0.8). Water surfaces vary from very low (about 5 or so) at high sun elevation, to at least 70 (0.7) at low sun-angles: very smooth water surfaces with a low sun-angle can give rise to the phenomenon known as sun glint sometimes seen in visible satellite imagery where the albedo value is very high. (abbr) Above mean sea level. Anabatic wind A local-scale wind which blows up-slope, after strong heating of the hillmountain-side by the sun. Such upslope winds can sometimes drag fogstratus in the valley bottom (formed after a cold night) to upland areas that were previously clear of these phenomena. Airfields that were previously clear can suddenly fog-out well after sunrise due to this effect. When warm air ascends relative to the cold air at a frontal surface, the front is said to be an ana-front. Such fronts are normally active, in that thickprecipitation producing clouds (possibly with embedded instability), are usually located in the warm air associated with both a warm and cold front. Anticyclones A pressure feature where a maximum of pressure is surrounded by relatively lower values. On a synoptic chart, a system of closed isobars will be found, enclosing the central High. The circulation (of wind) is clockwise in the northern hemisphere (anticlockwise in the southern hemisphere). The structure of such features in the vertical is that high-level convergence coupled to gentle divergent-outflow at the surface leads to descent (or subsidence) of air within the anticyclone: this in turn leads to a decrease in humidity and an increase in the stability of the air, often producing an inversion close to the surface. Two types are defined: cold and warm see Cold anticyclone Warm anticyclone . Anticyclonic trough disruption If the northern (southern in the southern hemisphere) portion of an upper trough moves forward and warms out, leaving a quasi-stationary cut-off low in the base of the trough, the process is described as anticyclonic trough disruption - because the net result is a strong build of pressurenew high cell formation behind the retreating trough. (See also cyclonic trough disruption ) Arctic Oscillation The Northern Hemispheric broad-scale oscillation of long-wave type, of which the North Atlantic Oscillation (NAO) is our regional-scale component. (q. v. here ) (abbr) Altostratus (AS for METARSIGWX charts etc. As otherwise) a medium level, layer cloud type, formed by wide-scale rising motion in the troposphere, varying from thin, non-precipitating type through which the sunmoon can be seen, to thick layer(s) associated with frontal development giving persistent, significant precipitation, amp moderate in-flight turbulence amp icing. Over the many years that operational meteorology has developed, certain hours have been designated synoptic hours, and observation times standardised around these points the MAIN synoptic hours currently being 00, 06, 12 and 18 UTC(formerly GMT), with intermediate hours at 03, 09, 15 and 21 UTC. Increasingly however, observing systems (e. g. satellite, radar-networks, drifting buoys etc.) provide data at times other than these fixed hours - these are designated non, or asynoptic observations. NWP models can assimilate these observations during the initialisation process. Abbreviation used to stand for aviation. A term applied when a forecast wind direction changes in an anti-clockwise sense, i. e. from south back to northeast, via east. The opposite term is veering, thus quot southwest 4 veering north 5 or 6 quot, would imply a wind originally force 4 from the southwest, becoming a northerly force 5 or 6 by the end of the forecast period, passing via west. Baroclinic The temperature along a constant pressure surface (say 500 mbar) varies a thickness gradient exists. The degree of baroclinicity is given by the product of the layer thermal wind (q. v.) and the Coriolis parameter. For practical purposes, the strength of the thermal wind alone is a good guide. Baroclinic leaf An elongated cloud pattern formed within the jet stream zone associated with marked baroclinicity (i. e. strong thermal contrast). The boundary (in satellite imagery) on the polar air-mass side of the development is well defined, and has the look of a stretched-out quotSquot shape. The downstreamwarm air-mass edge is less distinct. This feature represents the initial (or frontogenetic) stage of a system development, certainly in the mid-troposphere, and often (but not always) at the surface. Not all baroclinic leaves lead to marked cyclogenesis although they will be the first stage of such. (See also Dry Intrusion ). Baroclinic zone Area where there is a marked contrast between cold and warm air masses. Can be determined on a thickness chart by a quotpacking togetherquot of thickness (q. v.) contours. Usually associated on a msl chart with classical fronts, and therefore an area for potential cyclonic development. Barotropic A (theoretical) state in which surfaces of constant pressure and constant temperature coincide at all levels. The atmosphere cannot sustain development, and thickness (q. v.) gradients are zero. If thickness contours are widely spaced (the realistic state), the atmosphere is said to be quasi-barotropic. (abbr) Patches (as in BCFG in METAR coding, meaning patches of fog). Beaufort wind scale This scale was originally devised by Francis Beaufort (later Admiral Sir Francis, Hydrographer of the Royal Navy), who lived from 1774 to 1857. He had a very active naval career and was also interested from an early stage in meteorological observations afloat. In 1805 amp 1806, he devised a scale for his own use, which was based upon the amount of canvas a sailing vessel could carry in the given conditions. The scale underwent various modifications and was not introduced into general RN use until the middle part of the 19th century but thereafter, it quickly gained world-wide acceptance. However, various versions developed. and in 1906, the UK Meteorological Office attempted to co-ordinate the usage, and at the same time provided the first definitive wind speed equivalents for each level of force, and since 1920, the scale has been used to define forecast wind conditions in the Shipping Forecasts for waters in the NE AtlanticNW Europe continental shelf. For a description of the current scale in use, see zetnet. co. uksigsweatherMetCodescodes. htm (abbr) quotBecomingquot, used in aerodrome (TAF) issues and others. A permanent change in conditions. (abbr) quotBrokenquot, 5 to 7 oktas (eighths) of cloud cover. (abbr) quotBlowingquot, used in connection with snow, sand etc. for the U. K. Met Office only - other services will have different criteria and the definition has changed over time it has not always been so strictly defined quotThe simultaneous occurrence of moderate or heavy snowfall with winds of at least force 7, causing drifting snow and reduction of visibility to 200 m or lessquot. (Moderate snow is said to occur when the visibility is substantially impaired, and the snow cover increases in depth at a rate up to about 4 cm per hour. Heavy snow should reduce the visibility to a low value (in the low hundreds of metres), and the snow cover increases at a rate exceeding 4 cm per hour. ) Blocked pattern Large scale obstruction of the normal west to east progression of surface cyclones in the mid-latitudes. The upper flow changes from predominantly zonal (q. v.) to meridional (q. v.). In a meridional block, the upper flow divides upwind of the block and flows around quasi-stationary vortices - one anticyclonic and the other cyclonic. In the omega block case the strongest flow is diverted to lower latitudes, leaving a slow-moving anticyclonic vortex on the poleward flank of the displaced zonal flow. Blocking anticyclone Acellular pattern of high pressure in the mid-latitudes, which diverts or prevents the normal west-to-east motion of depressions (areas of low pressure). A name applied to mid-latitude depressions which deepen violently. The term was coined by Sanders amp Gyakum (US Monthly Weather Review), in a 1980 paper dealing with such events, and requires a pressure fall in the depression centre of 24 hPa (or mbar) or more in 24 hours at latitude 60degN for the name to be applied. At latitude 45degN, the required value is 19hPa, and at 55degN, 23hPa. (see Explosive cyclogenesis .) Boundary layer In operationalsynoptic meteorology this is usually taken to be the layer at the bottom of the atmosphere wherein surface friction is important. It can vary in depth from as little as 100 m or less on a still, cold night to upwards of 1 km or more in a windy, well-mixed situation. Also known variously as the mixed layer or friction layer and is a function of wind speed, vertical temperature profile (i. e. stability) and surface roughness. (N. B: micrometeorologists regard the boundary layer as the first few cm of the lower atmosphere and this can lead to confusion when reading some texts. ) Mist (abbr. from French): vis gt1000m and not more than 5000m, where obscuration is caused by water droplets in suspension. Used in aviation reports, forecasts etc. Bright band effect As snow descends through the melting (or freezing) level, the melting snowflakes look like huge raindrops causing radar reflectance to increase sharply, implying heavier precipitation than is actually occurring. Corrections can be applied, provided the calibration system has some knowledge of the vertical temperature profile. The effect is usually confined to a layer about 1000 ft (300 m) thick. Buys Ballots Law As originally formulated, quot if you stand with your back to the wind (in the northern hemisphere), then low pressure lies on your left-hand side quot. For the southern hemisphere, then the low pressure is on the right-hand side. (Personally, I feel we should face the wind to see what is coming, so I would reverse these, i. e. face the wind, low pressure on right etc.) Prof. C. H.D. Buys Ballot (1817-1890) was a famous Dutch Meteorologist who founded the Royal Netherlands Meteorological Institute (KNMI) in 1854 and played an important role in establishing the first international organisation for meteorology - after the inaugural meeting of the International Meteorological Congress in Vienna in 1873. However, he is now best known for the Law as above it is possible that the credit for a rigorous treatment of the physics might be credited to Alexander Buchan, long-serving (1860-1907) Secretary of the Scottish Meteorological Society. cloud-to-air lightning flash Used when describing lightning which branches from a cumulonimbus cloud and terminates in clear air. This is an uncommon type of lightning.(See also CC. CG amp GC ) Calibration (radar) As well as de-cluttering for permanent echoes, and other adjustments, rainfall radar returns are calibrated (in real-time) against a network of telemetering rain gauges. This means of course that if the return is over areas without rain gauges (e. g. the sea), over-reading can occur, and caution is needed in blindly following radar imagery to assess rainfall ratesaccumulations for this reason. Convectively Available Potential Energy A measure of the energy released once convection is initiated, often from the surface (for high values), but mid-level convective initiation is also very important. Assessed on a thermodynamic diagram (e. g. a tephigram) by noting the area enclosed by the environment curve (i. e. actual temperature found by a radio-sonde), and the parcel-path curve where it intersects the environment curve at height. Used extensively in severe convective storm studies, although worth noting that just because high values of CAPE are observed, other factors need to be right for a severe storm to develop. (see also HERE ) Clear Air Turbulence Bumpy conditions in the upper atmosphere when no clouds are present to betray the possibility of such. Caused by sharp vertical and horizontal shear of wind, often (but not exclusively) in association with upper-level jet streams (see quotWhat are jetstreams quot). Can occur in, or be enhanced by mountain wave activity. Conservation of Absolute Vorticity -- The principle first outlined by Carl-Gustav Rossby in the 1930s which accounts for the tendency for upper atmospheric flow to take up a wave-like pattern. The theory can be used to predict the wavelength and speed of translation of the long-waves found in the atmosphere, which in turn govern the broad weather type at any one point. quot C eiling A nd V isibility OK quot: No CB, no cloud with base lt 1500m5000ft or below the highest minimum sector altitude, whichever is greater amp visibility 10km or more amp no weather of significance i. e. DZ, RA, SN, SG, PL, IC, GR, GS, FG, BR, SA, DU, HZ, FU, VA, PO, SQ, FC, DS, SS. and variants (see this glossary for decodes). CB (strictly Cb) Abbreviation for cumulonimbus, the cloud type associated with a thunderstorm, when the upper portion of the cloud exhibits glaciation (supercooled water droplets converting to ice crystals). Broadly, there are two species: Cumulonimbus calvus (Cb cal) and Cumulonimbus capillatus (Cb cap). The former is used when glaciation has only just begun, and is often taken to be the start of the most active phase of development - transition from Cumulus congestus (Towering CU) the latter type exhibits the traditional anvil shape, when major activity may be (but not necessarily) beginning to wane. (See also TCU ) (abbr)cloud-to-cloud lightning flash Used when describing lightning that originates in cloud and terminates in cloud. Thus it describes lightning with passes from one cumulonimbus cloud to another and lightning which is contained within a single cumulonimbus cloud. This includes the diffuse lit from within (sheet) type lightning, as well as that whose channel is directly visible as it loops out of the cloud before returning back into it. (see also CA. CG amp GC ) (abbr) Cirrocumulus (CC in aviation reports etc. Cc otherwise) a high level, layer cloud type, with elements of instability, but rarely of significance for aviation or general meteorology. (abbr)convective condensation level Provided the dew-point of an air parcel is high enough, then during convective ascent the resultant cooling will lead to condensation at some altitude as the air temperaturedew point. The precise height this is achieved will depend upon the difference between the initial air temperature and dew-point of the parcel, and also the amount of mixing with the environment of the air through which the parcel is rising. The level where condensation is achieved (and thus the theoretical cloud base for cumulus clouds), is known as the Convective Condensation Level (CCL). to a rough approximation, the CCL is given by (T-D)400, where Tair temperature at the surface, Ddew point temperature (as the surface): the answer will be in feet. DONT use slavishly - regard as good to the nearest couple-of-hundred of feet at best. (abbr)Central England Temperature -- A series used to track temporal changes in the average temperatures over a large area of central England. see quotWhat is the Central England Temperature Series quot. CLICK HERE FOR LATEST DATA FROM THE HADLEY CENTRE. Abbreviation for cold front. (abbr)cloud-to-ground lightning flash Used when describing lightning which branches from the cumulonimbus cloud to the ground. It is sometimes referred to as fork lightning from its appearance. (see also CA. CC amp GC ) The lightning discharge process is complex it involves two discharges per stroke and there may be several strokes in one flash (which result in the flickering which is often observed). The initial and very weakly luminous discharge establishes a conductive (ionised) and usually highly-branched path through the air. The second and intensely luminous discharge moves in the opposite direction and drains the charge from the groundcloudair to the cloudground. For instance, a CG refers to a strokeflash where the initial discharge is from cloud to ground, although the intensely luminous discharge that we see is from ground to cloud. Channel Rat (Dutch Kanaalrat )An intense (small scale) developing depression that scuttles along the English Channel. It comes (and goes) in a matter of a couple of hours to half a day. Because of its speed of movement, coupled with its often rapid development (increase in wind speed), it can cause severe problems for areas adjacent to the Channel and southern North Sea. The term probably in use (in the Netherlands) since at least the early 1980s. Examples 12th May, 1983 amp 28th May, 2000. Average weather over fairly long intervals of time, usually greater than one year and often 30 years. Care should be taken to state (or ascertain) the period for which particular climate normals are applicable. Cloud head (strictly Baroclinic cloud head) During the early stages of explosive cyclogenesis (q. v.), a very marked area of dense layered cloud - convex away from the developing depression - can be observed in IR, VIS and WV imagery, detached from the cloud area associated with the development. This feature is the result of air rapidly ascending as the intense development gets underway. Studies have shown that all mid-latitude cyclogenetic events over oceanic areas giving rise to winds of hurricane force were preceded by such features. However, care is needed to correctly identify such and true detection is only possible with animated imagery. (See also Baroclinic leaf Dry intrusion .) In ensemble forecasting (q. v.), individual members often show strong grouping around a few results. Each grouping is referred to as a cluster. The more members making up a particular cluster, the higher is the confidence in that particular solution. (See also Ensemble Ensemble mean ) Cold advection The replacement (usually quasi-horizontally) of a warm air mass by a colder one. The process can be gradual or abrupt: the latter often occurring at well-marked cold-frontal boundaries. Cold anticyclone Area of high pressure with a cold core (relative to surrounding air), with the cold dense air dominant in the lower part of the troposphere contributing to the surface high pressure. Has a shallow circulation (i. e. high characteristics confined to lower layers), with a low warm tropopause etc. It often forms in the polar air behind a depression, moving with the synoptic-scale features with which it is associated. However, if a major change of type (from mobile to blocked) is underway, then the High may transform to a warm type. Persistent cooling of continental areas in winter at high latitudes (e. g. over Scandinavia, Russia, Siberia) produces semi-permanent cold anticyclones, with mean sea-level pressure often above 1050 hPa. (See Anticyclones Warm anticyclone ) Cold Occlusion If air (at the surface) behind an occluded front is colder than the air it is displacing (the usual case in the NE Atlanticmaritime NW Europe), then the front is known as a cold occlusion. The occlusion may be shown on synoptic charts as a linear extension of the cold front. (see also Warm occlusion ). An area where the atmosphere (in depth) is colder than its surroundings. The temperature is not measured by means of surface-based sensors (such as screen temperatures), but often (though not necessarily) by using thickness values (q. v.), with the 500-1000 hPa measure (roughly sampling the lower half of the troposphere) the most commonly used for this purpose. Closed centres with low thickness value (relative to adjacent regions) will define a cold pool. The opposite term (for a closed centre of high relative values), is quotwarm domequot, although this term will not be heard much nowadays. Cold-Front wave A secondary low pressure system forming on an extended cold front, where the thermal contrast across the front (in the troposphere) is large, and the upper pattern is conducive to falling pressure at the surface. The wave can move quite rapidly (in the direction of the general upper driving flow), and will lead to a hesitation in the clearance of the main cold front at the surface, or its return to areas that previously experienced a clearance. Not all such waves develop closed-low characteristics some will just run quickly along the length of the trailing cold front with little development, other than enhancing rainfall. Because of the small-scale of the initial development, NWP models dont always place and forecast these correctly. (See also warm-front wave .) Cold undercut A term often used in situations where advection of relatively milder air as traced by 850hPa variables (e. g. actual 850 temperature, ThetaE, ThetaW. partial thickness etc.) does not fully reflect events in the lowest 50 to 100hPa (i. e. within the planetary boundary layer). In winter amp spring especially, warm-air advection may be indicated by levels at above 850hPa, but the surface wind is well backed amp coming from a colder direction - the cold (relatively denser) air undercuts the overlying milder airstream: a decoupling occurs, depressing temperatures and creating a marked inversion potential cloudy mixing layer. The cold air may be either an airmass feed, or from a local source, e. g. cold air off the North Sea at the end of winter or early spring. Colour states METAR reports from military airfields operated by the RAF, some USAF and others may have a colour-code appended (usually only when ATC is open), which describes the airfield fitness: these run from BLU best, through WHT GRN YLO (1 and 2), AMB and RED . The colour is based on the lowest cloud base (usually 3 oktas or more cover, but some use 5 oktas) and the horizontal MET visibility. BLACK is also used, for airfield closed for non-weather reasons. Condensation The transformation of water vapour to liquid water in the process, latent heat (of vaporisation) is either released or absorbed. also see Evaporation Condensation nuclei Microscopic particles in the atmosphere that act as a focus or stimulant for cloud-drop growth. Conduction Heat transfer through a substance from point-to-point by means of the movement (or excitement) of adjacent molecular motions. When streamlines (q. v.) approach one another, the pattern is a confluent one. However, note that because streamlines only define the wind direction . and not the wind speed . a confluent pattern is not necessarily a con vergent pattern. The opposite of confluent is diffluent (often spelt difluent in North American texts.). This case denotes the spreading apart of streamlines. Again, such diffluent patterns are not necessarily divergent. (see also convergence. divergence .) Conservative property Meteorologists are always keen to label an air mass using a value that can be calculated from variables measured within that air mass (at various levels), but which remain constant, or nearly so in vertical (adiabatic q. v.) motion. Many properties are defined, such as potential temperature (Theta), equivalent potential temperature (Theta-e) and wet-bulb potential temperature (Theta-w). This latter measure is often used in operational meteorology in NW Europe: At the 850hPa level, it is used as a tracer for air masses, and is much used for defining frontal boundaries, and for defining the axes of warm plumes of air. (See also the entry under Wet Bulb Potential Temperature ) Lines on an upper air (constant pressure) chart (actual or forecast) joining places of equal height, 700 mbar 500 mbar etc. or of equal thickness. CONdensation TRAIL. Also abbreviated (from old coding practice) to COTRA. See quotWhy do some high flying aircraft leave white trails in their wake quot and MINTRA (this Glossary) Control run The principle of ensemble forecasting is to slightly perturb an analysis by small amounts and see what the outcome is for each change. Rather than use a centres operational model analysis and forecast output (which needs much computing time and maximum data ingress), an early look analysis and forecast run, using the same physics as the operational (OPOPER ) run, but performed at lower resolution (typically half-scale) is employed. This is known as the control run. Given the increase in computing power in recent years, the control can have higher specifications than some operational models of less than a decade ago Convection The transfer of heat by the actual movement of the heated substance, such as air or water. In meteorology, convection also means vertical transport through density imbalance, transporting mass, water vapour, and aerosols as well as heat. Convective condensation level Convective precipitation For precipitation production (rain, snow etc.), other conditions being satisfied, there must be a supply of upward motion through the cloud producing the rain, snow, hail or whatever. In convective precipitation, upward motion is provided by the release of convection in an unstable environment. (See quotStable and unstable air masses quot). Computer models in operational use cope with instability features via parametrisation schemes (q. v.), which model ideal convective towers within each model grid square, taking into account entrainment of dry air, moist convective vigour amp depth, temperature structure etc. Algorithms will assign model rainfall to either dynamic or convective: the type giving the greatest rate of rainfall is (usually) that which appears on the output chart.(See also Dynamic and Orographic precipitation) Convergence When air flows in such a way that the area occupied by a particular group of air particles lessens (drawing together), the pattern is said to be convergent. Convergence in the atmosphere is associated with vertical motion, and hence development (or weakening) of weather systems. For example, convergent flow near the surface is coupled to, and may be the primary cause of, upward motion, leading to cloud formationshower initiation etc. (See also divergence. confluent .) Convergence zone Usually referring to a low-level feature, this is a narrow elongated area where two different airstreams are converging such that air within the zone must ascend, leading to enhanced cloud precipitation formation, particularly if the airmass is potentially unstable. The zone may propagate downstream with time, and its activity, location and extent will be governed by the synoptic patterns giving rise to the zone in the first place. Marked on a synoptic chart by a solid line along the axis of the zone, with angled branches indicating the convergence. In synoptic systems (e. g. a developing depression) airflow is not uniformly horizontal, and the system velocity (i. e. the speed of translation of the Low) must also be allowed for. High-velocity air aloft overtakes the synoptic feature, whilst lower down, the system often moves faster in a given direction than the low level airflow. To cope with all this, the concept of conveyor belts was adapted for use in synoptic and mesoscale meteorology as a means of explaining the movement of heat, moisture and momentum around such systems. For example, in a developingmobile depression, a warm conveyor belt (WCB) is assumed to rise from low levels in the warm sector just ahead of the surface cold front, to middle and upper altitudes over and well forward of the surface warm front. A compensating cold conveyor belt (CCB), descends from mediumupper levels well ahead of the surface warm front underneath the WCB then tucks around the backside of the low merging with the boundary layer flow. Coriolis effect As a consequence of earths rotation, air moving across its surface appears to be deflected relative to an observer standing on the surface. The deflection is to the right of movement in the northern hemisphere, to the left in the southern hemisphere. (also known as the Coriolis acceleration, or deflection) Coriolis parameter A important quantity in theoretical meteorology because it plays a major part in describing (mathematically) how air moves on our spinning planet under the influence of a pressure gradient. It is usually denoted as f . and defined as twice the product of the angular velocity of the earth and the sine of a particular latitude. The angular velocity of our spinning earth is (for practical purposes) constant, therefore the important variable is latitude: from the definition, f varies from a maximum at the poles (sine 90deg1) to zero at the equator (sine 0deg0). see also Absolute Vorticity Cross-contour flow (abbr) Cirrostratus (CS in aviation reports etc. Cs otherwise) a high level, layer cloud type, due to wide-scale ascent in the upper troposphere: of no significance for aviation but is a pre-cursor to frontal activity to come. (abbr) Cumulus (CU in METARSIGWX reports etc. Cu otherwise) a convective cloud type, with a base in the lower part of the troposphere, and varying from weak to vigorous vertical penetration, possibly into medium or upper levels. (see also TCU ) Cut-off time NWP models that are used in operational meteorology must have a nominal time at which the gates are closed to new data, and the forecast computation cycle is started. For models used for primary forecast guidance at short lead times, only a couple of hours at most is allowed after the nominal data time. So for example, the cut-off for 12UTC data might be around 1345UTC. For global models, i. e. those used for international aviation, a slightly longer time is allowed, but usually no more than 3.5hrs after data time. However, some centres (e. g. ECMWF ) with less demand for immediate products allow over 9 hours or more of data to be assimilated. Cyclogenesis The formation of a major low pressure system along a baroclinic zone (q. v.) (or frontal boundary), with primary forcing due to imbalances along the upper jet. (depressions) Weather systems characterised by low pressure and rising air flows. Wind circulation is anticlockwise in the northern hemisphere and clockwise in the southern hemisphere. Cyclonic trough disruption The southern (northern in the southern hemisphere) portion of a trough advances, perhaps developing a cut-off circulation, and slowly warming out, whilst the opposite (residual) portion of the trough becomes quasi-stationary, maintaining a cyclonic pattern at the surface. (also see: anticyclonic trough disruption ) (abbr) Dry Adiabatic Lapse Rate. The rate of cooling (for ascending air), or warming (for descending air) when air parcels are displaced by whatever mechanism. Usually taken to be 10degC1km (or 3degC1000ft). Dekametres (i. e. 10s of metres) - often used on upper air charts: thus a 500 hPa height quoted as 540 dam is equivalent to 5400 metres. (NB: although DM may still be seen on some model output, this is regarded as a non-standard abbreviation. dm should definitely not be used, as it is the abbreviation for decimetres, i. e. tenths of a metre) Daughter cell As the precipitation downdraught associated with a marked Cumulonimbus event meets the ground, it will spread out in all directions. Where this cold outflow current meets the low level inflow (relative to the cloud motion) head-on, then this is a point of maximum convergence, leading to forced lifting of the air at that point, and provided the air is unstable enough, and convection is not otherwise inhibited (e. g. widescale descent), then a new convective cloud event will be initiated - a daughter cell. Decoupling Even given the strongest pressure gradients, surface-based friction will slow airflow in the lowest 800 m or so of the atmosphere, leading to the familiar cross-isobaric flow (from high to low pressure). With strong free-air gradients (Vgr) (roughly above 25 knots or 12 ms), surface winds will bear some relationship to Vgr however, below these (approximate) levels, come nightfall under clear skies, surface cooling will lead to stabilisation of the lowest layers and the atmosphere finds it increasingly difficult to transfer momentum from the free-air levels to the near-surface. The surface wind may drop away completely as the surface-based inversion develops (often within the course of half-an-hour), allowing mist, fog or surface frost to form (other factors being in place): this process has come to be known as decoupling of the boundary-layer air from the flow inferred by the isobaric flow. Once the flow is decoupled, then the surface cools even more efficiently, thus reinforcing the nocturnal inversion. (See quotStable and unstable air masses quot for discussion of stability etc. and quotWhy does the wind blow quot for matters concerning surface wind-flow.) (used in METAR reports) - fog dispersal operations are in progress (probably obsolete now so included for historical purposes). Deterministic forecast A forecast that says rain will occur at such-and-such a place within a given time band, i. e. a yesno forecast, is an example of deterministic forecasting. (See also probability forecasting .) (strictly dew-point temperature) The temperature (of an air sample that contains water vapour), to which that sample must be cooled (Pressure and humidity content being held constant) to achieve saturation with respect to a water surface. It can be measured indirectly using a wet amp dry hygrometer (ordinary dry bulb thermometer, and anotheradjacent thermometer with its bulb covered in a damp muslin - hygrometric tables or calculator then being used to calculate the dew point, relative humidity, vapour pressure) also by a dew-cell type of instrument that measures relative humidity, from which the dew point can be calculated, or it can be measured directly by a dew-point hygrometer. The screensurface dew-point temperature is used in air mass analysis, and also in the calculation of night-minimum and fog-point temperatures, as well as being used in the estimation of convective condensation levels, human-comfort indices, probability of snow at the surface etc. Dew point values above the surface (from radio-sonde ascents) are used to define cloudy or potentially cloudy layers etc. in the upper air (see also Frost point ). Dew-point depression (DPD) The numerical difference between the temperature of a sample and its dew-point. The greater the difference, the lower the relative humidity. Values (deg. C) of less than 3 would be considered to indicate high relative humidity those of 7 or greater would indicate low relative humidity. (See quotWhat is the dew point depression quot) Discontinuity Where a steep gradient (i. e. sharp change over a small horizontal distance) occurs in a meteorological variable (i. e. temperature, humidity, wind direction etc.), there is said to exist a discontinuity in that variable. Diurnal cycle Changes which take place over the course of a 24hr period. The most obvious cycle is the rise and fall of surface temperature. Divergence When air flows in such a way that the area occupied by a particular group of air particles grows (spreads apart), the pattern is said to be divergent. Divergence in the atmosphere is also (along with convergenceq. v.) associated with vertical motion, and hence development (or weakening) of weather systems, depending upon the level where the divergence is dominant in a particular atmospheric column. For example, divergent flow aloft is coupled to, and may be the primary cause of, upward motion, leading to widespread cloud formationcyclogenesis etc. ( see also diffluent.) (obsolete abbreviation for dekametre - see entry for dam ) Downward penetration of Snow Falling snow modifies the temperature structure of the atmospheric boundary layer as both melting amp evaporation takes place. (See this question in the FAQ). Even if snow does not initially penetrate to the surface (after having fallen out of the parent cloud), if the Wet Bulb Freezing Level (q. v.) is low enough, the intensity of the precipitation is more than just light and the mean wind strength in the melting layer is not too strong, then the snow level can descend considerably below initial conditions. The depth of this downward penetration of snow as it is called, increases as the intensity of rain increases, andor the wind speed decreases. It will be immediately apparent that the prospect for error in snow forecasting due to these variables in marginal situations will be large Used in METAR reports - low drifting (snow, sand etc.), not appreciably affecting the visibility, e. g. DRSN. Partial amp absolute droughts are terms that are no longer used in official summaries they were introduced in 1887 by G. J. Symons in British Rainfall, (with the term dry spell added in 1919) but ceased to be used circa 1960. Drought hydrology is a complex field of study and as statistical amp data-processing techniques have become sophisticated, there was no longer an official requirement for the use of these rather crude definitions. It is however useful to know what the definitions were, and even today, for hobby-use, defining periods of drought using these standards can be an interesting exercise. They are detailed elsewhere in this Glossary. (See Absolute drought partial drought dry spell). Droughts - types of Droughts as defined above are essentially meteorological in other words, they are defined in terms of the amount of rain (or rather lack of rain) that occurs. Hydrological drought episodes by contrast take account of the wider cycle of water use, with focus on the imbalance between precipitation input (rain, snow etc.) against water availability via aquifer storage, reservoir levels, land-surface run-off riverflow etc. Finally, agricultural droughts are usually defined in terms of the soil moisture deficit (SMD) across a growing season - the degree of irrigation (natural or artificial) needed to bring a particular soil type back to optimal production - balancing the outgoing moisture due to evaporation amp transpiration. Dry Intrusion (or dry slot) -- A narrow region, virtually cloud-free which separates a baroclinic leaf (q. v.). and the adjacent frontal cloud. This region is the result of abruptly descending upper troposphericlower stratospheric air into a rapidly developing and potentially damaging low pressure system -- hence the low humidity contentabsence of cloud. Water vapour imagery (see quotWhat are the various types of Satellite imagery available quot) in particular is used to diagnose this feature, and the rate of darkening of the dry slot gives a clue to the rate of development of the whole storm complex. A period of at least 15 consecutive days, to none of which is credited 0.04 inches 1.0 mm of precipitation. (See also drought. absolute drought. partial drought ). Duststorm (used in METARTAF reports etc.) visibility generally lt 1km due to dust raised by strong winds over a large area. Dust (widespread, in suspension) (used in METARTAF reports etc.) Visibility is 5000 m or less. Deutscher Wetterdienst (German Weather Service), based at Offenbach. Visit their web site at: dwd. de Dynamic precipitation For precipitation production, other conditions being satisfied (i. e. enough humidity, required temperature structure, sufficient depth of cloud), there must be a supply of upward motion through the cloud producing the rain, snow or whatever. In the case of dynamic precipitation, the primary agent for providing upward motion is broad-scale ascent due to, for example, short-wave troughs in the prevailing upper flow, jetstream developmental areas, mass convergence or strong warm advection. Computer models in operational use deduce dynamic precipitation by testing for super-saturation of a layer taking into account the total water content (all phases) in a layer: the excess found is precipitated out. The type (dynamic or convective) giving the greatest amount is (usually) that seen on output charts. (See also Convective and Orographic precipitation). Drizzle (as in METARTAF reports). Eclipse (of a geostationary satellite) The earths equator (and therefore a geostationary satellites orbit) is inclined to the orbit of the earth around the sun. This inclination allows sunlight to power the satellite on-board systems for most of the year. However, there is a period of about 3 weeks either side of the vernal and autumnal equinoxes when a satellite will be in the earths shadow for about 70 minutes each day (around local midnight). Because most of these platforms do not carry sufficient battery power to tide them over this gap, no imagery is generated and thus a local-midnight image is missing. European Centre for Medium Range Weather Forecasts, located on the southern outskirts of Reading, Berkshire, UK. Visit their web site at ecmwf. int Eden Winter Snow Index Embedded (in cloud, as in CB embedded in LYR cloud). A collection of NWP runs (typically in excess of 15, many having 50 or more) from the same start time (t0) and using the same model physics, but each run (or member) having a slightly perturbed (altered) set of initial conditions from the control run (q. v). The alterations are constrained within limits which are calculated in various ways - one example being that of performing a separate short-range model run and identifying the errors that would grow most over a 48 hr period. These errors are then applied in varying amounts to the initial conditions before performing the operational ensemble run. Another technique is to use (known) errors from a previous run and apply these in small amounts to the initial conditions of the new run. NB: these output are in addition to (and run some time after) the operational model output, i. e. the deterministic run which is the set of charts most often seen on web sites: it should not be assumed that the operational run (OPOPER: q. v .) is close to the ensemble mean (q. v.) or mode - significant deviations can and do occur at longer lead times. Also note that a particular centres operational model is often run at a higher spatial resolution than that used for the ensemble generation - the control . Ensemble mean An average of the ensemble output from a particular computer run - this is usually more accurate than just following one of the individual forecasts that make up the average. Further, by comparing the individual members spread about the mean, some estimate can be made of the reliability of the forecast: if there is strong agreement and therefore small divergence from the mean solution, then high confidence can be assigned to the average solution. Wide divergence, or clustering of groups of individual members well away from the mean will lead to considerable caution regarding using the output too slavishly and lower confidence in issued forecasts. Environmental Lapse Rate The actual plot of temperature against height (or equivalent) on a thermodynamic diagram. Evaporation The transformation of liquid water to water vapour - in the process absorbing latent heat (of vapourisation). (abbr)(also EWR) England and Wales Precipitation (or Rainfall). A data series combining the rainfall (and melted snowfall) amounts from a matrix of recording stations (well over 30) averaged to produce a single figure for an area taken to represent England and Wales. The series runs from 1766 - maintained (separately) by the Hadley Centre (EWR) and the University of East Anglia (EWP), though I understand that a unified data-set is to be (has been) produced. CLICK HERE FOR LATEST DATA FROM THE HADLEY CENTRE. Explosive cyclogenesis Sometimes, in an otherwise normal cyclogenetic situation, factors are conducive to rapid falls of pressure leading to very tight isobaric gradients extreme low pressure. These situations often give rise to damaging or stormy hurricane force winds: watch for 3-hourly pressure falls in excess of 10.0 mbar. (sometimes referred to as bombs , particularly in North American meteorological circles.) (abbr.) Funnel Cloud - (in METARTAF, this includes tornadowaterspout, so differs from the classical distinction between a funnel cloud not touching down, and one that does. See entry for Funnel cloud ). 1 or 2 oktas cloud amount, used in AviationMETAR reports etc. (see also SCT ) (abbr) Fog (vis lt 1000m, except when qualified by MI, BC, PR, VC) used in METARTAF reports etc. (abbr) Flight level (e. g. FL240. 24000ft amslstandard atmosphere) used in aviation reports, forecasts etc. Foehn (or Foumlhn) effect Mechanisms which give rise to a warm, dry wind on the leeward side of mountains or significant hills. Broadly, there are two: (i) the subsidence type where air at amp just above the hillmountain crest descends by lee-wave action, becoming even drier amp warmer than when it started out (ii) all air in a moist airstream on the upstream side of the hillmountain rises, leading to cloudprecipitation formation, thence lowering the humidity content, this air then descendingwarming adiabatically on the leeside. Reduction in visibility to under 1 km caused by suspension of minute water droplets (water fog) or ice crystals (Ice fog - q. v.). Water fogs are further sub-divided according to the process by which the fog forms, e. g. Radiation fog (caused mainly due to loss of surface heat from the ground at night in conditions of near-calm wind and high relative humidity) Advection fog (caused by movement of humid air over a relatively colder surface) Upslope fog (adiabatic cooling of air having high relative humidity as it climbs over high ground) and Evaporation fog (caused by evaporation into cold air which lies over a relatively warm water surface). ( If the visibility is below 200M but greater than 50M then it is usually referred to as Thick Fog (amp colloquially in the UK as motoring fog ) amp if below 50M then Dense Fog . However, there are different criteria for climatological stations, and other services will have different rules - treat this note as a guide only. ) (strictly fog-point temperature) The air temperature (as measured in a standard thermometer screen) at which fog is expecteddoes form. Its calculation (before an event) is usually based on empirical work which employs either the surface air temperaturedew point at some time earlier in the day, or by construction on a thermodynamic diagram. The fog point is lower than the air-mass dew point. because as air cools through the evening and night, moisture is condensed out on contact with the chilled land surface, and this lowers the dew point from afternoon values. Freezing fog As for the definition of fog (above), but the droplets are super-cooled (i. e. temperature below zero), and strictly, the fog should be depositing rime-ice. However, in METAR TAF coding, as long as the air temperature is below zero degC, then fog is coded as freezing irrespective of whether rime is observed. Freezing level Taken as the altitude where the air temperature is 0 deg. C. However, it should be carefully noted that in the free atmosphere, liquid water does not necessarily freeze at this level, or indeed at altitudes some way above this value -- it should more correctly be called the melting level, or as in operational aviation meteorology, the level (or altitude) of the zero degree isotherm. (see ZDL and Wet Bulb Freezing Level) . A boundary separating two air masses such as warm, moist air and cold, dry air. If the cold air pushes into a region of warm air, a cold front occurs and if the warm air advances relative to the cold, a warm front occurs. Frontal fracture During rapid cyclogenesis events, a weakness appears along the portion of the cold-front nearest to the depression centre, thought to be due to a combination of subsidence in this region, plus differential thermal advection, as, unlike in the Norwegian model. cold air is not advected so quickly eastwards to maintain the baroclinicity in this region. (See quotWhat is the Shapiro-Keyser cyclone model quot) Frontogenetic Any atmospheric process which leads to frontal formation, or an existing weak frontal zone to become enhanced, is termed frontogenetic. On charts issued by some national meteorological services, such fronts are shown with the normally solid line defining the front broken by spaces and large dots. Frontolysis When fronts weaken markedly due to, for example, marked anticyclonic subsidence across the front, then the feature is undergoing frontolysis. On charts issued by some national meteorological services, such fronts are shown with the line defining the front struck-through by short inclined strokes. Frost point (strictly frost-point temperature) The temperature (of an air sample that contains water vapour), to which that sample must be cooled (Pressure and humidity content being held constant) to achieve saturation with respect to an ice surface. (see also dew point ). (abbr) Frequent (hardly or not separated, as in FRQ CB in aviation forecasts). (abbr) Smoke (as used in METARTAF reports etc.) Funnel cloud (FC) A visible rotating tube of condensation particles, formed as the pressure falls in an intensifying vortex (extending below a cumulonimbus cloud) - perhaps reaching the groundsea. It should be noted that the funnel cloud simply betrays the zone where the pressure is low enough and humidity high enough for cloud to form - the vortical circulation may well be in contact with the ground, but of such relatively weak intensity that it either causes little or no damage, or is detected only by surface dust soil disturbance. There are well documented cases where tornadoes (as defined elsewhere) do not have cloudy funnels all the way to the surface. (based on Doswell, C. A. III, 2001) (abbr) Freezing (used in connection with rain, drizzle, fog, all giving rise to ice deposition due to supercooled water droplets impacting upon surfaces with temperatures below 0.0degC, OR when temperature lt 0.0degC anyway, whether or not ice deposits are observed.) Glossary terms G-L The word gale is used in everyday speech in a rather loose way to describe any strong wind, for example. quot its blowing a gale outsidequot, when it may be just a strong blow in inland areas of the southern Britain. Meteorologists must work to a strict definition of a gale. For operational forecasting (UK Met Office practice) both for land and sea use, a gale Force 8 on the Beaufort scale is defined as a mean wind (over 10 minutes) of 34 knots (39mph, 63 kmhr, 17 ms ) or more, or gusts of 43 knots (49 mph, 79 kmhr, 22 ms) or more. This definition is also used for verifying Shipping Forecasts and Gale Warnings. Isolated gusts accompanying squalls or thunderstorms are not counted. However, for climatological purposes (i. e. post-event analysis), only the mean wind is considered, i. e. a mean wind of 34 knots or more, as specified in the Beaufort wind scale (q. v.). see also definitions for Severe Gale. Storm. Violent Storm and Hurricane Force. (abbr)ground-to-cloud lightning flash Used when describing lightning which branches from the ground to the cloud. The upward branching often results in an appearance like a trident, etc. This is an uncommon type of lightning. (See also CA. CC amp CG ) (abbr) Global Ensemble Forecast System (of NCEP q. v.) Geopotential quotPotential energy per unit mass of a body due to the earths gravitational field, referred to an arbitrary zeroquot (The Meteorological GlossaryUK in meteorology, mean sea level is the reference level). A geopotential metre (by this definition) is related to the dynamic metre (straightforward unit of length) by the expression: 1 gpm0.98 dynamic m. Geopotential height differs from geometric height where the value of the gravitational constant (g) departs from 9.8 ms2. Gravity does vary, both by altitude and latitude, but for practical purposes, when looking at NWP output on the web, you can ignore these slight differences. Geopotential heights are used in meteorology because flow along a geopotential surface involves no loss or gain of energy, whereas flow along a geometric surface may do so - so for strict physical mathematical calculations within computer models, the distinction between the two must be maintained. Geostrophic wind Defined as the (theoretical) wind that would blow on a rotating planet which results from a balance between the pressure gradient causing the initial displacement of the air, and the apparent (to us on the earth) deflecting force due to the planetary rotation. Many corrections are needed to find the true wind vector amongst which are the effects of friction and the several forces involved when the pressure pattern changes - which is the usual case. However, by this definition we get the general statement that the speed of the geostrophic wind is proportional to the pressure gradient, or inversely proportional to the distance between isobarscontours. Curvature of the flow must also be taken into account. see Gradient wind . Global Forecast System The primary forecast model (NWP ) from the US NCEP service (q. v.). The model suite is run to T 384 hr, in two bursts one to T 120 (5 days) then a further run to the 16 days (384hr). The model is run four times daily, though not all WWW sites hold all runs (or full output for each run). Hail (abbr. from French) dia: gt 0.5 cm used in METAR aviation reports etc. Gradient wind When the path that an air parcel takes is curved (relative to the earths surface), as so often in meteorology, that airflow is subject to an additional force necessary to maintain a curved path. For cyclonic flow, the true wind that blows will be less than the theoreticalgeostrophic wind for anticyclonic flow the true wind is greater, subject to a limiting maximum. This is why, for example, around what initially looks like a dramatically intense depression, the wind may not be quite so excessive: cyclonic curvature will account for substantial negative correction to the theoretical value. Around a surface ridge, the wind is often surprisingly stronger than might be implied by isobaric spacing. Small hail dia: lt0.5cm used in METARaviation reports etc. Given that the wind in the surface boundary level varies markedly about the mean wind (q. v.), it is often necessary to report the accompanying instantaneous maximum (or gust speed) in a defined period. For METAR reports, then the period over which this peak wind is reported is between 2 and 10 minutes (depending upon the country). For SYNOP reports, the period is either the last hour (most likely in NW Europe), or the period covered by the past weather group in the report - reference to the accompanying amplifying groups will usually sort this out. Hectopascal Horizontal vorticity Even the classical vertical vorticity term (q. v.) has some upward downward component, but this is usually ignored for practical synoptic-scale meteorology. However, when coming down a scale or two, to local mesoscale development, ( e. g. severe convective storms ), then vorticity about a horizontal axis is most important. It is often assessed in the lowest 3 km of atmosphere, and is driven by two terms: vertical speed shear (increase decrease of wind with increasing altitude) and directional (twisting) shear, the change of direction with increasing altitude. If, in the lowest 3 km of atmosphere (up to 700 hPa), there is both a sharp increase of wind speed and a directional veer of wind with height, then horizontal vorticity will be potentially significant, provided it is coupled to the vigour of a developing cumulonimbus complex. (See also Vorticity Vertical vorticity and quotWhat is Helicity quot (abbr) Hectopascal - equivalent to a millibar (q. v.). An attempt to use SI units without doing away with the idea of millibars (from the c. g.s. system). 1 hPa100 Pa (or Nm 2 ) Hurricane Force This term (in UK Met Office use) is only used in shipping bulletins and associated GaleStorm warnings in the form quotHurricane Force 12quot, from the modified Beaufort scale. It is strictly defined as a mean (10 minute) wind of 64 knots or more. (Gusts not defined) (See also comments at Severe Gale ). Please note carefully that just because an area of low pressure produces winds to hurricane force as defined here, it does NOT make that feature a Hurricane For more on this, see this question on the October 1987 storm Haze: used in METARTAF reports etc. when visibility is reduced in a dry atmosphere. (visibility gt 1km, relative humidity roughly lt 90). (abbr) Ice crystals (also known as diamond dust) used in METARaviation reports. When used in aviation weather reportsforecasts, implies aircraft superstructure icing. A period of 24hr (conventionally beginning 0900UTC), during which the air temperature is less than 0 degC. Visibility reduced to less than 1000 m by suspension of minute collection of ice crystals in high concentration. The crystals will glitter and may give rise to optical phenomena. (NB: this is NOT the same as freezing fog, which is composed of water droplets - see definition elsewhere.) Initialisation The process whereby a model analysis is produced by utilising model fields from an earlier run, and integrating synoptic, and asynoptic observations to produce the initial state at t0. The model analysis may not be the same (in detail), as a hand-drawn analysis, and intervention (q. v.) is sometimes needed as a result to preserve some small scale features which can influence the forecast run. Insolation Radiant energy received from the sun on any particular surface. Often used when discussing receipt of infra-red radiation on the surface of the earth. Instant Occlusion or pseudo-occlusion The name that has been coined to label the cloud mass associated with an active trough in the cold air, that comes close to, and interacts with a pre-existing baroclinic zone, forming a pattern that looks superficially as if it was part of a traditional occlusion process. Intertropical Convergence Zone (usually abbr. ITCZ) A zone (often rather broad, but sometimes quite narrow), which separates the air-masses brought together by the low-level outflow from the sub-tropical high pressure belts north and south of the equator. Over the oceans, the zone can be well marked over land, sensible heating usually leads to breaks or other anomalies, and the regional-scale monsoon circulations also distort, or swamp the idealised structure of the ITCZ. Cloudiness (and hence precipitation activity) can vary sharply over a period of 24hr. Day-to-day change of position is often small, but the zone migrates north amp south through the course of a year, roughly in sympathy with the changing position of the sun. Intervention A process where forecasters force acceptance of a report rejected in the model initialisation routine (supporting), or use bogus observations to input a conceptual model observed in imagery. (abbr) Intensifying (as used in SIGMETs for a phenomenon becoming more intense or extensive). Inversion (of temperature) A layer in the atmosphere (usually very shallow lt 0.4 km), where temperature rises with increasing height. Two of the best-known in operational meteorology are the nocturnal inversion (formed due to strong cooling of land surfaces after sunset), and the subsidence inversion (due to descent amp adiabatic warming of air associated with anticyclones). Another near-surface type is that formed when warm air travels over a cold surface (e. g. cold seas or icesnow). (abbr) Isentropic Potential Vorticity - the product of the absolute vorticity of an air parcel, and its static stability, calculated along a constant surface of theta (potential temperature), hence the isentropic. Anomalies in IPV around the level of the tropopause (and hence in the region of the driving jet stream) can be related to developments through the troposphere, leading to cyclogenesis. Because IPV is a highly conservative property for any sample of air, it is found to be particularly useful for tracking the path that stratospheric air (high IPV values) will take as it enters the upper troposphere during rapid cyclogenesis events. NWP models can be programmed to output the height of a particular IPV value - defined such that it samples air in the model stratosphere. These patterns are then overlaid on water vapour imagery, and any mis-match between model and reality are quickly seen and allowed for. (See also Potential Vorticity ) and also this article on Water Vapour Imagery. (abbr) International Standard Atmosphere. A standard reference for temperature, pressure, and relative density structure in the troposphere and lower stratosphere, used for the calibration of (pressure) altimeters. A line on a synoptic chart joining points of equal atmospheric pressure. Isolated (as in ISOL CB etc.) Abbreviation used in aviation work to stand for quotover-landquot. Lapse rate (of temperature) The decrease of temperature with height in the atmosphere. Confusingly, the opposite case, an increase in temperature with height, is known as a negative lapse rate. Latent heat The amount of energy needed to accomplish a phase change. Latent heat of fusion is the amount of energy required to melt ice, and at 0degC is 3.34 10 5 J kg -1 (or about 80 calg). The latent heat of vaporisation is the amount of energy needed to evaporate liquid water. It is equivalent to 2.50 10 6 J kg -1 (or about 600 calg) at 0degC. The latent heat of sublimation is the energy needed to carry out a change from solid (ice) to gas (vapour). It is the sum of the latent heats of fusion and vaporisation, i. e. 2.83 10 6 J kg -1 (or about 680 calg) at 0degC. When water freezes, condenses or changes from a gas to a solid, 80 calg, 600 calg and 680 calg are released to the environment respectively. The processes are all reversible. Lies on the cold side of the jet axis, in the region of marked deceleration of flow. A preferred region for cyclonic development. Lenticular clouds These form within the crest(s) of orographic (or lee) wave-trains, over and downwind of hills mountains islands, provided of course that the air is humid enough. The clouds are formed because air cools as it is forced to rise and if condensation takes place, lens-shaped clouds are observed with clear space in between the elements. The cloud forms within the upwind leg of each wave-crest and dissipates (evaporates) on the downwind leg: the air is therefore flowing through the cloud, with the cloud itself staying quasi-stationary change in the cloud requires an alteration in the windflow or temperature humidity environment. Sometimes, under very special circumstances, a pile of plates is observed, where lenticular clouds are stacked vertically. The most common form of wave-forced cloud is perhaps Altocumulus lenticularis (Ac len), but lenticular cloud forms are found at all levels. Standing wave motion can also lead to a previously uniform sheet of cloud developing a lenticular appearance, and on occasion, complete dispersal. (See also MTW ). Loaded gun scenario On a day of instability through a great depth of the troposphere, and high values of CAPE (q. v.), rising surface temperatures will at some point ensure that convection parcels leave the surface, the condensation level will be reached, cloud will grow (given sufficient moisture), and a heavy shower, or even a thunderstorm will result. It sometimes happens though that although the atmosphere is markedly unstable above, say, 2 km a lid opposing surface-based convection exists at or below this level, due often to a layer of warmdry air that has become entrained in the airflow from some source. This means that surface temperatures must become very high to overcome this lid, often requiring additional triggers, such as low-level convergence or release of medium level potential instability by a mid-level trough, thus lifting the whole column and releasing the pent-up energy in a sudden burst. and the loaded gun will be fired, perhaps leading to a severe stormsupercell event. (see Spanish plume ). Layer(s) (as used in cloud forecasting in aviation products). Glossary terms M-R Operational model A term used to differentiate the primary NWP output from a particular centre from any ensemble products from the same source. The operational model will almost always be run at a higher resolution than that used for ensemble output. It must not, however be assumed that the OpOPER is necessarily the best outcome, particularly beyond 3 days or so. (see Ensemble ) Orographic forcing An airstream encountering a barrier to its passage is forced to go around or over the obstacle. The upward deflection of the airflow is sufficient to give rise to adiabatic cooling, and if the air is moist enough, the formation of clouds, precipitation etc. In addition, convergence of the flow on the windward side (due to a rapid decrease in velocity) when the air encounters a sharply graded barrier not only enhances the vertical motion, but also leads to a deformation of the flow which in turn alters the vorticity of the air particles. Thus, hill and mountain ranges are most important in a study of meteorology. Orographic rainfallsnowfall For precipitation to occur, other conditions being satisfied (i. e. enough humidity, required temperature structure, sufficient depth of cloud etc.), there must be a supply of upward motion through the cloud producing the rain, snow or whatever. In orographic precipitation, the forcing agent is provided by large ranges of hillsmountains blocking the flow of humid air in such a way that vertical (upward) currents of air are produced, leading to adiabatic cooling gtgt condensation gtgt cloud formationenhancement gtgt precipitation element growth. Orographic forcing OF ITSELF usually only produces small amounts of precipitation, but can be the means of enhancing or triggering other mechanisms (e. g. convective activity), and is one of the important elements in the seeder-feeder model (q. v.). Computer models in operational use do now have sufficiently realistic orography and vertical resolution to model such, but the output (usually) does not explicitly define orographic precipitation. Orographic waves (in an NWP ensemble suite) When considering a collection of solutions at a particular lead time (from a single-centre, or as part of a Poor Mans ensemble ), some clustering is usually observed - i. e. a large number of members pointing to a similar outcome. However, as lead times get longer (especially beyond 72 hours), one or two members may depart significantly from the ensemble mean, (andor mode of larger clusters) - these are termed outliers such indications carry small weight, but cannot be totally ignored. In particular, at extended range (beyond about 7 days), there may be no clear clustering signal, and an outlier is just as likely to be right as a solution nearer the meanmedian of the output. (See also ensemble. clusters. ensemble mean etc.) (abbr) Overcast 8 oktas (cloud amount, as used in aviation reports, forecasts etc.) Overconvection The promise of a fine, sunny day is sometimes spoiled because cumulus cloud builds and spread out into an almost unbroken sheet of stratocumulus by late morning - which then refuses to break up for the rest of the day. For this to occur, there must be a marked inversion (see quotWhat is an inversionquot ) within 100 to 300 hPa of the surface, which must be intense enough to stop convective currents breaking - through the inversion even at maximum temperature the convective condensation level (CCL ) must be at least 60 hPa below the inversion level, and the layer between CCL and inversion must have a reasonably high relative humidity. For some rather obscure reason, this phenomenon has come to be called overconvection (at least in the UK, probably originating within the gliding community) - possibly because convective cumulus spills-over to cover the sky ( though, other conditions being right, the cloud may disperse around or just after dusk.) Over-running trough An active, mid-latitude frontal system is associated with a marked short-wave trough. The active weather associated with the front lies forward of the trough, driven by the dynamics associated with it. At some stage in its life though, the trough (or a portion of it) will relax (and effectively weaken), allowing the trough to run well ahead of the lower-tropospheric portion of the frontal system - it over-runs the (surface) location of the front, and the activity at that position will decay. Note however that the upper trough will still have weather associated with it - and may be the means of driving an uppersplit frontal structure well away from the classical surface front as drawn on conventional analyses. See also quotWhy fronts die quot. Pascal - allocated in honour of Blaise Pascal, to a unit of one Nm 2. the basic unit of pressure in the SI system. Parametrisation Some atmospheric processes are below the grid-scalewavelength of operational meteorological computer models and cannot be handled explicitly by such schemes - for example individual showers, which are not only important for local weather, but have a feedback effect within the atmosphere that needs to be included in the NWP routines to maintain a realistic model of the real atmosphere. Larger scale model parameters (e. g. wind vector, temperature, humidity) are used to diagnose and represent the effects of such sub-gridscale processes: this is know as parametrisation. See HERE Partial drought A period of at least 29 consecutive days, whose mean daily precipitation does not exceed 0.01 inches 0.2 mm. (See also drought absolute drought dry spell ). Is the study of times of naturally occurring events, such as the first blossom appearance in a long established species, or the departure of migratory birds. From 1875 to 1948, a register of such events was maintained by the Royal Met. Society, but after a period when the science was in the doldrums, the Woodland Trust and Centre for Ecology amp Hydrology combined in the late 1990s to kick-start the observing network, recognising that such data can complement studies into long-term climate change. For more detail, see:- phenology. org. uk (abbr) Ice Pellets (was PE) used in aviation weather reports. (abbr) Polar mesospheric clouds (or Noctilucent clouds ). (abbr) Pressure at mean sea level: often seen in connection with NWP model products. (abbr) Well developed sanddust swirls as used in aviation weather reports. Polar front A boundary that separates polar air masses from tropical air masses . Polar mesocyclones A term now used to encompass the whole family of disturbances resulting from arctic air flowing equatorward over progressively warmer seas the term Polar Low (q. vabove) is now often used only for extreme systems where gale or near gale-force winds are observed. Polar mesospheric clouds quot Poor Mansquot Ensemble Technique A true NWP ensemble (q. v.) is the product of multiple iterations of a single atmospheric model on a single centres computer: the individual members of the ensemble run are obtained by perturbing the initial conditions very slightly to simulate the uncertainty that is always present at analysis time. However, long before these techniques were perfected, operational forecasters would (and still do) absorb the differing output from various international centres (e. g. EC, NCEP, DWD etc.) and or different runs from the same centre - treating all the various outputs as members of what has been dubbed a Poor Mans Ensemble. As with true ensembles, the more model runs that agree at a certain lead time, the higher is the confidence in that particular solution. Potential Instability (also known as Convective Instability) Said to exist when forced lifting (e. g. ascent over mountains or broad - scaledynamic ascent) causes a layer, initially (just) stable to such forced ascent to become unstable. Decreasing humidity aloft is required within the layer, and heavy rainthunder can be the result. Theta-W or Theta-E (q. v.) difference charts are often used to find such areas of potential instability: the usual levels used are at 850hPa and 500hPa. The value at 850hPa is subtracted from that found for 500hPa, and negative values so found indicate potential instability. Only slightly negative differences can lead to some significant convective activity. all other factors being favourable of course. Such layers can also be inferred using a thermodynamic diagram (or tabular listing of Theta E or Theta W), noting where values decrease with increasing altitude within the low-to-middle troposphere (roughly up to 400hPa). Potential Vorticity The ratio of the absolute vorticity (q. v.) of an atmospheric column to the (defined) pressure difference across the column. This quantity is used to label air in much the same way as we use other conservative properties. As a column of air moves along, it shrinks vertically (due to mass divergence) in just the right amount to decrease its absolute vorticity as it expands vertically (due to mass convergence), its absolute vorticity increases. Therefore, Potential Vorticity tends to remain constant following the motion of the flow, for adiabatic motion. Precipitation Anything precipitated by clouds (rain, snow, hail, drizzle etc.) is covered by this noun. Often abbreviated to ppn or pptn. (for definitions of various types of precipitation, see:- quotBeaufort Lettersquot ) Pressure Gradient The difference in atmospheric pressure over a defined (usually horizontal) distance. (See quotWhy does the wind blowquot ) Pressure Gradient Force (abbr. PGF)The force exerted on the air due to a pressure gradient, causing a tendency for movement (i. e. wind) from areas of high pressure to areas of low pressure.(See quotWhy does the wind blowquot ) Prevailing visibility Prevailing wind The most frequent wind direction for any particular location in a given period, e. g. a day, month, year or climatological period. Partial fog (i. e. fog quotbanksquot substantial portion of airfield covered by fog - but not completely visibility lt 1000m.) Probability (as used in aviation forecasts, e. g. TAFs in the latter, under current 2002 rules, only PROB30 or PROB40 are allowed, e. g. moderate probability of an event occurring. Probability forecasting Given that there is always a measure of uncertainty in forecasting the weather, the likelihood of an event happening can be expressed as a probability: thus a 70 chance of rain, 20 chance of thunderstorms etc. Often useful in finely balanced situations i. e. rain vs. snow severe storms vs. no storm etc. (see also Deterministic forecasts). Progression When large scale features in the upper air, such as a 500 or 300 hPa troughvortex drift west-to-east this is said to be a normal progression of the pattern. (See also retrogression). (abbr: Polar Stratospheric Clouds) During the polar night (i. e. the period in the middle of the winter when insolation does not penetrate to ultra-high latitudes), the stratosphere cools significantly leading to closed-loop circulations (both vertical and horizontal) which virtually isolate these polar stratospheric regions - the quotPolar night vortexquot is found, within which temperatures can be found well below (minus)75degC. In these extremely cold conditions, clouds are observed to form in the stratosphere, which appear to be composed of a combination of nitric acid and water. Stratospheric clouds can also form from ordinary water ice (i. e. as in the troposphere) but these are much less common at these high altitudes as the stratosphere is normally very dry and water-ice clouds only form at the lowest temperatures. The presence of PSCs and the part they play in the chemical interactions at these levels have been a subject of much debate in recent years. (See main FAQ here for the Stratospheric Night Jet and here for Stratosphere amp various web-sites dealing with upper atmosphere ozone depletion.) Pulse storms (a term often used in North America) Random air-mass thunderstorms forming in an environment of little or no vertical wind shear, which appear as individual returns (without any obvious organisation) on radarhigh-resolution satellite imagery systems. They usually last 20 to 30 minutes, perhaps up to 60 minutes, and give rise to small hail, sometimes heavy rain and perhaps weak tornadoes. They can be regarded as a more intense version of the single-cell convective type discussed in the main FAQ here. i. e. higher CAPE values are involved than for an ordinary shower. PVA region An area where marked advection (movement) of positive, or cyclonic vorticity (q. v.) is occurring - hence P ositive V orticity A dvection often associated with a small upper trough running through the broadscale upper pattern. Cyclonic development will occur - other factors being favourable. Pressure at airfield level set on an aircraft (pressure) altimeter when height above local aerodrome level (strictly the official threshold elevation) is required. Pressure at mean sea level (reduced according to actualmean temperature). Pressure at mean sea level (reduced according to ISA profile) set on an aircraft (pressure) altimeter when height above local mean sea level is required. (abbr) Rain as used in aviation (e. g. METARTAF) reports. This is the transmission of energy by electromagnetic waves, which may be propagated through a substance or through a vacuum at the speed of light. Electromagnetic radiation is divided into various classes on the basis of wavelengths these are, in order of increasing wavelength: gamma radiation, X-rays, ultra-violet (UV) radiation, visible (VIS) light, infra-red (IR) radiation and radio waves. Radiosonde ( sometimes abbreviated to RS ) An instrument that measures temperature, pressure and humidity of the atmosphere as it is carried aloft on a balloon. The quotsondequot transmits its measurements to a ground-based radio receiver via radio signals, and by accurate tracking (radar or satellite) of the sonde unit, upper winds can be deduced. A period of 24hr, conventionally beginning at 09UTC, during which precipitation of 0.2mm or more has been recorded. (See also Wet day ). Relative humidity (RH) See the main FAQ here . Relative Vorticity The vorticity (or tendency for air particles to spin) relative to the earth. It can be considered for practical purposes (and crudely assessed on meteorological charts) as the combination of two factors: (i): the spin imparted due to the curved path that air takes in its passage through the atmosphere (cyclonically curved contourspositive, anticyclonically curved contoursnegative). (ii) the other factor is due to the shear developed along the flow due to the differing velocities of the moving particles. Swiftly moving air will generate a twist element relative to the lower-velocity flow on either side shear vorticity : where the twisting generated is in a cyclonic sense, that is counted as positive where in the anticyclonic sense then it is negative. ( See also Vorticity Absolute Vorticity .) Relaxation When the amplitude of a trough decreases with time, the trough is said to have undergone relaxation. The change is usually measured in terms of a latitude change of a chosen contour or thickness line. Retrogression When an upper trough (or ridge) moves against the normal west-to-east flow in mid-latitudes, the feature is retrogressing, or undergoing retrogression. (abbr)Relative Humidity (expressed as a value). See Upper ridge Ridge amplification When contour heights along the axis of an upper ridge increase, the ridge is amplifying. Right entrance On the warm side of the jet core, in the region of maximum acceleration of flow. Often associated with marked cyclogenesis. (abbr) Saturated adiabatic lapse rate. The rate of cooling (variable) of a saturated air sample rising in the atmosphere. (see quotStable and unstable air massesquot ) Saturation The condition air reaches when it contains the most water in the vapour state that it is capable of holding at any particular temperature. If any more vapour is injected into the sample (or if the sample is cooled), then condensation will occur. (abbr) Stratocumulus (SC in METARSIGWX charts etc. Sc otherwise) a low-level cloud type, varying from thin, well broken layers with little impact for aviationgeneral weather, to deep, sometimes unstable character giving rise to persistent PPN, and a risk of moderate turbulence amp moderate (some situations severe) icing. (abbr) Scattered (3 or 4 oktas) cloud amounts used in aviation reports, forecasts etc. (of historical note, SCT used to mean 1 to 4 oktas, until the introduction of FEW on revamp of the METAR code in the 1990s). In mid-latitudes, we are used to the idea of the four seasons: spring, summer, autumn and winter. For climatological accounting purposes, these are defined using three calendar month blocks thus:- March, April amp May spring June, July amp August summer September, October amp November autumn and December, January amp February winter. (For more, see quotHow are the seasons definedquot ) Seclusion process During the process of rapid cyclogenesis (q. v.), the standard Norwegian theory of development leading to an occluded front is not appropriate. What appears to happen is that the original cold front becomes weakill-defined (close to the low centre), and a new cold front appears further to the west. (This is effectively what has been drawn in the past as a back-bent occlusion). So, what happens to the warm air associated with the warm frontal zone near the low centre Around and immediately to the equatorward side of the low, it becomes trapped or secluded from the rest of the development in a discrete region enclosed by relatively colder air encircling the development - a so-called seclusion. (This is therefore a different process from that producing the classical occlusion whereby warm-sector air is lifted by the advancing cold air.) (see quotWhat is the Shapiro-Keyser clyclone modelquot ) Seederfeeder mechanism When very moist (e. g. tropical maritime) air flow is forced to rise over upland areas, thick layers of stratus or stratocumulus cloud form. As noted elsewhere, these orographic clouds of themselves produce relatively little rainfall (in a thermally stable environment). If however rain is already occurring from medium layer cloud (thick altostratus, nimbostratus) seeder clouds, it will have to fall through the low-level feeder cloud, with collisioncollection processes markedly enhancing the net rainfall rate at the surface. This effect often produces prolonged heavy rainfall in the warm conveyor regime within a warm sector, particularly if the system is slow-moving. Sensible heat transfer The transfer of heat by conduction and convection (i. e. it can be sensed or detected directly). (abbr) Severe (as in SEV ICE, for severe icing). Severe Gale The definition of a Severe GaleForce 9 is strict for operational (UK) forecasting for maritime purposes. Either the mean (10 minute) wind must be 41 knots or more, up to 47 knots or the gusts must be 52 knots or more, up to 60 knots. The term will also be heard on broadcast weather forecasts, although its arguable that the general population cannot be expected to know what this definition is, and the practice now is to explicitly forecast gust values rather than just relying on the adjective severe to imply possible problems. (See also Gale. Storm and notes at the Beaufort wind scale .) Part of the WMO header code used in bulletins that carry atmospheric reports, more commonly known as sferics, or SFLOCS. (See quotWhat are sfericsquot ) (abbr) Snow grains as used in aviation weather reports.