Atmospheric blockings and downstream cyclones in the Euro-Mediterranean sector

Weather extremes in Europe and the Mediterranean can have a significant effect on societies across the region. These weather extremes include heatwaves, cold spells, windstorms, and intense rainfall events. In a climate that is continuously changing, their impact, both socio-economically and environmentally, can worsen with an increase in the frequency and intensity of these extremes. As recent studies have highlighted, some extremes such as heatwaves in the northern hemisphere are connected to atmospheric blocking, while heavy precipitation has been associated with intense cyclones occurring in the Mediterranean basin which are more commonly known as Mediterranean Cyclones (MCs). However, the connection between atmospheric blocking and MCs is still understudied, despite evidence suggesting their mutual importance for exacerbating and synchronizing surface extremes. The aim of the present study is the systematic investigation of how often MCs develop downstream of atmospheric blocks over the Euro-Atlantic region, and how the Atlantic storm track is modulated under such conditions. To this end we employ the combined ‘best tracks’ MCs dataset with objectively identified (using potential vorticity anomalies) blocking features in ERA5 for the 1980-2020 period. We find that in the presence of atmospheric blocks, MCs that develop downstream tend to be more intense and more persistent than other MCs. Moreover, MCs that develop under this scenario form particular subsets of MCs, with preferred seasonality and geographical distribution, compared to all MCs. The results have important implications for the predictability of MCs and their various impacts in the region on both weather and climate time scales.