Variability and extremes of poleward breaking Rossby waves over the North Atlantic - European Region (VARNAER)

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In the extratropics Rossby waves play an important role in determining the general circulation, especially in the upper troposphere / lower stratosphere region. It is known that events of poleward breaking Rossby waves are often observed over the North Atlantic-European region in wintertime. In this project we investigate the influence of the observed background flow in the upper troposphere on poleward Rossby wave breaking events and the link to severe weather. We will study the intra-seasonal and interannual variability of events of poleward breaking Rossby waves over the North Atlantic-European region and diagnose the extreme cases of the wave breaking events for each season, based on ECMWF Reanalysis (ERA-INTERIM) and analyses. The predictability of such events is investigated by using different forecasts data sets. Furthermore, the expected influence of the different zonally varying background flows on poleward Rossby wave breaking will be examined in simplified global ECHAM5 model simulations in order to improve the understanding of this process. A further key investigation is the diagnosis and mesoscale modelling (WRF) for implications of poleward Rossby wave breaking events on the change of the Grosswetterlage (large scale flow) in the lower troposphere, in order to examine different acting mechanisms, and to understand the sub-seasonal differences of the influence and of the impact on severe weather over Northern Europe.