Thank you Regulattor. I didn't know this phenomenon.
Here is a portion of an article translated into English by a translator :
Here is a portion of an article translated into English by a translator :
Stratospheric sudden warming
Sometimes the vortex air heats up in circumstances other than those governing normal building cycle - destruction of the vortex. These phenomena, abbreviated SSW (Sudden Stratospheric Warming) see the vortex air warm by several tens of degrees in the space of a few days, resulting in a massive vortex of destabilization and upheaval of stratospheric winds that depend on it. It should nevertheless distinguish two types of SSW by importance:
- The SSW minors who have a limited impact on the dynamics of the vortex.
- Major SSW who manage to permanently change the entire operation of the vortex to move or do explode into several lobes.
These SSW to stay simple, due to forcings from the troposphere or the mesosphere. Considering the troposphere, we need to incorporate the notion of Rossby wave. These waves are formed by the corrugations of the jet stream which delimits the tropospheric polar vortex its environment. When a wave of great importance advects a powerful breath of hot air towards the pole, energy and transported to the polar regions can affect the stratosphere as far as this energy is sufficiently large. The stratospheric vortex of air starts to warm up brutally from its periphery, several tens of degrees in the space of a few days. But we have seen that the thermal winds dependent on the temperature gradient between the intra- and extra air vortex-vortex air. Given that the gradient is decreased due to intra-vortex air warming, thermal winds decrease in strength, the stratospheric vortex enters an unstable phase. Two events can then occur: a motion event or division event.
Event movement or displacement event
During the displacement event, the warming of the polar stratosphere is not enough to pop the vortex. This is simply driven by a stratospheric high pressure that tends to take its place at the pole. The consequences of displacement events are less important than that of a splitting event which we will discuss in the next section.
The animation below is a forecast made by the GFS model December 27, 2012 for a period from January 3 to 7, 2013. It shows the wave "hot" attacking the vortex (blue - purple) from Siberia. The latter is ejected from its usual quarters and pushed Europe while weakening. A week after this modeling, many winter offensive and failover tropospheric air stream operated on the Old Continent. We shall return to the impacts of a disruption of the polar vortex.
_http://shrani.si/f/2S/CQ/4OuojmzW/strat.gifHere is a direct link to track the phenomenon : _http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=6&mode=10&carte=1
According to forecasts, we can expect this kind of scenario in the coming days with a likely drop in temperature in western Europe.
Event division or splitting event
The splitting event is the most extreme phenomenon: the warm impulse eventually explode the vortex into two lobes. Therefore, the circulation of stratospheric winds is completely disturbed, they will eventually stop and even change direction.
The image below shows a splitting event in January 2013. The hot drive, anticyclonic, invaded the pole and has shattered the vortex into two lobes, one of them laying on the near Atlantic, resulting profound changes in stratospheric and tropospheric circulations in the Northern Hemisphere. At the same time, it was snowing heavily on Western Europe.
_http://climatedata.e-monsite.com/medias/images/gfsnh-2013011806-10-6.png
Here is a 3d animation :
_https://www.youtube.com/watch?v=bminxfVGa5w
The consequences
The events (splitting or displacement) are not rare, but they are not very common either. In its highest form, they are able to cause profound changes in the weather, for several weeks. Between the time when the phenomenon is triggered and its impact observed on the surface, it takes about two weeks. This is interesting because it allows to see the big changes coming in the weather, mainly winter offensive and cold waves. During the winter of 2012-2013 the event of displacement and forecasts of splitting event allowed to consider, about 20 days in advance, a sudden attack of winter.
The stratospheric polar vortex disturbances are indeed not without consequences for its ground-level counterpart that ends up being destabilized in turn. Normal traffic from west to east is indeed greatly disturbed by the direction of changes in stratospheric winds, the worst case being the reversal of the direction of the latter following a splitting event. In turn, the ground-level polar vortex eventually present high waves, consequently resulting in a change of surface winds and troposphere. In January, February and March 2013, these winds met regularly oriented to the north or northeast, bringing cold air and snow from 2012 to 2013 that will give a tough winter, abnormally cold and endless.
Conversely, in the winter of 2013-2014, the polar vortex has also undergone a SSW, relocating it to North America that has undergone an impressive cold snap while Europe bathed in sweetness and 'moisture.
_http://infometeobelgique.blogspot.fr/2013/12/vortex-polaire-et-rechauffement.html
Apparently, given the recent severe winters in the northern hemisphere, this happens more and more often. Perhaps because of differences with increasing temperatures between these 2 layers of atsmophère.