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Re: Suivi de l'Oscillation Arctique AO - OA

Posté : 06 oct. 2014, 20:10
par Frosty
Il n'y a pas eu de mise à jour depuis longtemps sur l'AO et après une longue période positive et un vortex très concentré l'hiver dernier, ayant eu pour bonne nouvelle une banquise moins souffrante et nos amis Québécois renouant avec l'hiver, le vrai, l'AO semble en chute libre dans les jours à venir.

http://www.cpc.ncep.noaa.gov/products/p ... .sprd2.gif

Un changement de synoptique à attendre durant cette automne et pour l'hiver qui s'en vient ? :freeze:

Re: Suivi de l'Oscillation Arctique AO - OA

Posté : 06 oct. 2014, 23:40
par Wilfried
Frosty a écrit :
Un changement de synoptique à attendre durant cette automne et pour l'hiver qui s'en vient ? :freeze:
Au niveau de l'AO probablement car le QBO commence vraiment a devenir très négatifs ce qui risque d'avoir un impact conséquent sur le vortex polaire et donc sur l'AO et en même temps probablement sur la NAO qui pourrait alors devenir négative, déjà que sa phase négative est favorisé par la configuration des SST de l'océan Atlantique au mois d'août-septembre :D

Re: Suivi de l'Oscillation Arctique AO - OA

Posté : 07 oct. 2014, 18:19
par FredTDF
Voici la mise à jour de TDF ;-) La corrélation est toujours bien présente :!:


Image

Re: Suivi de l'Oscillation Arctique AO - OA

Posté : 07 oct. 2014, 22:10
par Wilfried
Fred Morti a écrit :Voici la mise à jour de TDF ;-) La corrélation est toujours bien présente :!:
C'est vrai que les corrélation sur le court termes sont très élevé mais il faudrait faire un bilan sur le très long termes pour que l'on puisse se rendre compte si les corrélations sont aussi forte.

Re: Suivi de l'Oscillation Arctique AO - OA

Posté : 07 oct. 2014, 22:49
par FredTDF
Wilfried a écrit :
Fred Morti a écrit :Voici la mise à jour de TDF ;-) La corrélation est toujours bien présente :!:
C'est vrai que les corrélation sur le court termes sont très élevé mais il faudrait faire un bilan sur le très long termes pour que l'on puisse se rendre compte si les corrélations sont aussi forte.
Tu as des graphiques sur les 60 dernières années en page 2 de ce topic. Et oui il y a également corrélation sur du long terme. On peut remarquer, par exemple, que l'indice ao était très largement en négatif dans les années 60. Décennie qui connu des hivers remarquables.

Re: Suivi de l'Oscillation Arctique AO - OA

Posté : 08 oct. 2014, 19:30
par romain86
Fred Morti a écrit :On peut remarquer, par exemple, que l'indice ao était très largement en négatif dans les années 60. Décennie qui connu des hivers remarquables.
Tout à fait. Et pas seulement les hivers, il y a eu pas mal d'étés très frais, beaucoup plus frais qu'aujourd'hui.

Re: Suivi de l'Oscillation Arctique AO - OA

Posté : 09 oct. 2014, 17:15
par Wilfried
romain86 a écrit :
Fred Morti a écrit :On peut remarquer, par exemple, que l'indice ao était très largement en négatif dans les années 60. Décennie qui connu des hivers remarquables.
Tout à fait. Et pas seulement les hivers, il y a eu pas mal d'étés très frais, beaucoup plus frais qu'aujourd'hui.
C'est sur que l'été 2014 ce n'est rien a côté de 1956 :hehe: , il y'a eu les années 70 ou il les étés étaient bien frais ;-)

Re: Suivi de l'Oscillation Arctique AO - OA

Posté : 18 janv. 2015, 20:45
par FredTDF
Voici une mise à jour avec l'influence météo de l'AO :

Image

Re: Suivi de l'Oscillation Arctique AO - OA

Posté : 18 juin 2015, 23:37
par williams
deux nouvelles études scientifiques nous disent que les relations entre le comportement de la banquise en fin d'automne et les conditions synoptiques dominantes l'hiver qui suit. Sommairement, une banquise tardive et fragile en fin d'automne en particulier du côté des mers de Kara et de Barents semble jouer comme un précurseur de conditions AO-/NAO- (plutôt froides en Europe) l'hiver suivant.
On the predictability of the winter Euro-Atlantic climate: lagged influence of autumn Arctic sea-ice

Satellite-derived sea-ice concentration (SIC) and re-analysed atmospheric data are used to explore the predictability of the winter Euro-Atlantic climate due to autumn SIC variability over the Barents-Kara Seas (SIC/BK). The period of study is 1979/80-2012/13. Maximum covariance analyses show that the leading predictand is undistinguishable from the North Atlantic Oscillation (NAO). The leading covariability mode between September SIC/BK and winter North Atlantic-European sea level pressure (SLP) is not significant, indicating that no empirical prediction skill can be achieved. The leading covariability mode with October or November SIC/BK is moderately significant (significance levels<10%), and both predictor fields yield a cross-validated NAO correlation of 0.3, suggesting some empirical prediction skill of the winter NAO index; sea-ice reduction in the Barents-Kara Seas being accompanied by a negative NAO phase in winter. However, only November SIC/BK provides significant cross-validated skill of winter SLP, surface air-temperature, and precipitation anomalies over the Euro-Atlantic sector, namely in south-western Europe. Statistical analysis suggests that November SIC/BK anomalies are associated with a Rossby wavetrain-like anomaly across Eurasia that affects vertical wave activity modulating the stratospheric vortex strength, which is then followed by downward propagation of anomalies that impact transient-eddy activity in the upper-troposphere helping to settle and maintain the NAO-like pattern at surface. This stratospheric pathway is not detected when using October SIC/BK anomalies. Hence, only November SIC/BK, with a one-month lead-time, could be considered as a potential source of regional predictability.
L'article complet est disponible ici mais n'est pas en libre accès (payant).
A negative phase shift of the winter AO/NAO due to the recent Arctic sea-ice reduction in late autumn

This paper examines the possible linkage between the recent reduction in Arctic sea-ice extent and the wintertime Arctic Oscillation (AO)/North Atlantic Oscillation (NAO). Observational analyses using the ERA interim reanalysis and merged Hadley/Optimum Interpolation Sea Surface Temperature data reveal that a reduced (increased) sea-ice area in November leads to more negative (positive) phases of the AO and NAO in early and late winter, respectively. We simulate the atmospheric response to observed sea-ice anomalies using a high-top atmospheric general circulation model (AGCM for Earth Simulator, AFES version 4.1). The results from the simulation reveal that the recent Arctic sea-ice reduction results in cold winters in mid-latitude continental regions, which are linked to an anomalous circulation pattern similar to the negative phase of AO/NAO with an increased frequency of large negative AO events by a factor of over two. Associated with this negative AO/NAO phase, cold air advection from the Arctic to the mid-latitudes increases. We found that the stationary Rossby wave response to the sea-ice reduction in the Barents Sea region induces this anomalous circulation. We also found a positive feedback mechanism resulting from the anomalous meridional circulation that cools the mid-latitudes and warms the Arctic, which adds an extra heating to the Arctic air column equivalent to about 60% of the direct surface heat release from the sea-ice reduction. The results from this high-top model experiment also suggested a critical role of the stratosphere in deepening the tropospheric annular mode and modulation of the NAO in mid to late winter through stratosphere-troposphere coupling.
L'article complet, qui est au passage vraiment très bien fourni, est en accès libre sur ce lien.
Investigation of the atmospheric mechanisms related to the autumn sea ice and winter circulation link in the Northern Hemisphere

The relationship of Barents–Kara sea ice concentration in October and November with atmospheric circulation in the subsequent winter is examined using reanalysis and observational data. The analyses are performed on data with the 5-year running means removed to reduce the potential effects of slowly-varying external driving factors, such as global warming. We show that positive (negative) Barents–Kara sea ice concentration anomaly in autumn is associated with a positive (negative) North Atlantic Oscillation-like (NAO) pattern with lags of up to 3 months. The month-to-month variations in the lag relationships of the atmospheric anomalies related to November sea ice concentration are presented. Further analysis shows that the stratosphere-troposphere interaction may provide the memory in the system: positive (negative) sea ice concentration anomaly in November is associated with a strengthened (weakened) stratospheric polar vortex and these anomalies propagate downward leading to the positive (negative) NAO-like pattern in the late December to early January. This stratosphere mechanism may also play a role for Barents–Kara sea ice anomaly in December, but not for September and October. Consistently, Eliassen-Palm, eddy heat and momentum fluxes suggest that there is strong forcing of the zonal winds in November.
Lien (article complet payant)

Williams

Re: Suivi de l'Oscillation Arctique AO - OA

Posté : 18 juin 2015, 23:56
par Wilfried
williams a écrit :deux nouvelles études scientifiques nous disent que les relations entre le comportement de la banquise en fin d'automne et les conditions synoptiques dominantes l'hiver qui suit. Sommairement, une banquise tardive et fragile en fin d'automne en particulier du côté des mers de Kara et de Barents semble jouer comme un précurseur de conditions AO-/NAO- (plutôt froides en Europe) l'hiver suivant.
On the predictability of the winter Euro-Atlantic climate: lagged influence of autumn Arctic sea-ice

Satellite-derived sea-ice concentration (SIC) and re-analysed atmospheric data are used to explore the predictability of the winter Euro-Atlantic climate due to autumn SIC variability over the Barents-Kara Seas (SIC/BK). The period of study is 1979/80-2012/13. Maximum covariance analyses show that the leading predictand is undistinguishable from the North Atlantic Oscillation (NAO). The leading covariability mode between September SIC/BK and winter North Atlantic-European sea level pressure (SLP) is not significant, indicating that no empirical prediction skill can be achieved. The leading covariability mode with October or November SIC/BK is moderately significant (significance levels<10%), and both predictor fields yield a cross-validated NAO correlation of 0.3, suggesting some empirical prediction skill of the winter NAO index; sea-ice reduction in the Barents-Kara Seas being accompanied by a negative NAO phase in winter. However, only November SIC/BK provides significant cross-validated skill of winter SLP, surface air-temperature, and precipitation anomalies over the Euro-Atlantic sector, namely in south-western Europe. Statistical analysis suggests that November SIC/BK anomalies are associated with a Rossby wavetrain-like anomaly across Eurasia that affects vertical wave activity modulating the stratospheric vortex strength, which is then followed by downward propagation of anomalies that impact transient-eddy activity in the upper-troposphere helping to settle and maintain the NAO-like pattern at surface. This stratospheric pathway is not detected when using October SIC/BK anomalies. Hence, only November SIC/BK, with a one-month lead-time, could be considered as a potential source of regional predictability.
L'article complet est disponible ici mais n'est pas en libre accès (payant).
A negative phase shift of the winter AO/NAO due to the recent Arctic sea-ice reduction in late autumn

This paper examines the possible linkage between the recent reduction in Arctic sea-ice extent and the wintertime Arctic Oscillation (AO)/North Atlantic Oscillation (NAO). Observational analyses using the ERA interim reanalysis and merged Hadley/Optimum Interpolation Sea Surface Temperature data reveal that a reduced (increased) sea-ice area in November leads to more negative (positive) phases of the AO and NAO in early and late winter, respectively. We simulate the atmospheric response to observed sea-ice anomalies using a high-top atmospheric general circulation model (AGCM for Earth Simulator, AFES version 4.1). The results from the simulation reveal that the recent Arctic sea-ice reduction results in cold winters in mid-latitude continental regions, which are linked to an anomalous circulation pattern similar to the negative phase of AO/NAO with an increased frequency of large negative AO events by a factor of over two. Associated with this negative AO/NAO phase, cold air advection from the Arctic to the mid-latitudes increases. We found that the stationary Rossby wave response to the sea-ice reduction in the Barents Sea region induces this anomalous circulation. We also found a positive feedback mechanism resulting from the anomalous meridional circulation that cools the mid-latitudes and warms the Arctic, which adds an extra heating to the Arctic air column equivalent to about 60% of the direct surface heat release from the sea-ice reduction. The results from this high-top model experiment also suggested a critical role of the stratosphere in deepening the tropospheric annular mode and modulation of the NAO in mid to late winter through stratosphere-troposphere coupling.
L'article complet, qui est au passage vraiment très bien fourni, est en accès libre sur ce lien.
Investigation of the atmospheric mechanisms related to the autumn sea ice and winter circulation link in the Northern Hemisphere

The relationship of Barents–Kara sea ice concentration in October and November with atmospheric circulation in the subsequent winter is examined using reanalysis and observational data. The analyses are performed on data with the 5-year running means removed to reduce the potential effects of slowly-varying external driving factors, such as global warming. We show that positive (negative) Barents–Kara sea ice concentration anomaly in autumn is associated with a positive (negative) North Atlantic Oscillation-like (NAO) pattern with lags of up to 3 months. The month-to-month variations in the lag relationships of the atmospheric anomalies related to November sea ice concentration are presented. Further analysis shows that the stratosphere-troposphere interaction may provide the memory in the system: positive (negative) sea ice concentration anomaly in November is associated with a strengthened (weakened) stratospheric polar vortex and these anomalies propagate downward leading to the positive (negative) NAO-like pattern in the late December to early January. This stratosphere mechanism may also play a role for Barents–Kara sea ice anomaly in December, but not for September and October. Consistently, Eliassen-Palm, eddy heat and momentum fluxes suggest that there is strong forcing of the zonal winds in November.
Lien (article complet payant)

Williams
Merci pour se partage Williams mais il me semble que certaine étude avait aussi prouvé ce lien cependant parfois certaine personne ont affirmé le fait que le Dipôle Arctique pouvait avoir de l'influence sur la l'AO mais le problème c'est que je comprend mal comment fonctionne le Dipôle Arctique, quelqu'un pourrait m'en dire plus s'il vous plait, merci! :o