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The Weather Regimes

The large scale atmospheric circulation in middle latitudes is characterized by fluctuating jet streams between different quasi-stationary states, called weather regimes, and whose two best known ones are the zonal regime and the blocking. In Europe, the winter blocking is responsible for long period of advection of cold air coming from Scandinavia to Western Europe. In contrast, the zonal regime brings most extratropical cyclones over Europe and is especially responsible for winter storms over this part of the globe. Therefore, in our latitudes, these regimes affect the behaviour of synoptic eddies and, in particular, winter storms. Conversely, synoptic eddies feedback on the weather regimes that have given rise to them. Although this feedback is the subject of intense research since the 80s because of its role in climate dynamics, its precise nature is still unknown.

Many studies have shown that the storm-tracks or synoptic eddies tend to maintain or reinforce the weather regimes. However, other more recent studies emphasize the fact that synoptic eddies may also be responsible for transitions between regimes. In which case(s), synoptic eddies keep up the weather regimes and when are they responsible for their alteration? These are still unanswered questions that the meteorological scientific community tries to elucidate.