Atmospheric blockings and downstream cyclones in the Euro-Mediterranean sector

Societies across the Mediterranean and wider European region can be significantly affected by weather extremes such as heatwaves, cold spells, windstorms and intense rainfall events. Temperature extremes are connected to atmospheric blocking, while heavy precipitation and windstorms have been associated with Mediterranean Cyclones (MCs). However, the connection between atmospheric blocking and MCs is still understudied, despite evidence suggesting their mutual importance for cyclone development and for exacerbating and synchronizing surface extremes. The aim of the present study is the systematic investigation of the frequency of MC development downstream of atmospheric blocks over the Euro-Atlantic region, and to examine how different cyclone track characteristics along with cyclone-attributed-precipitation might be 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 1970-2020 period. We find that in the presence of atmospheric blocks, MCs that develop downstream tend to be more intense and to be associated with increased precipitation compared to other MCs. Moreover, under blocking conditions, the distribution of precipitation varies geographically between the north-west and south-east Euro-Mediterranean region, with moisture transport contributing to this difference. MCs developing under this scenario form particular subsets of MCs, with preferred seasonality and geographical distribution, compared to all MCs. Lastly, certain MCs tend to be more static, while their mobility exhibits variability under blocking conditions. These results have important implications for the predictability of MCs and their various impacts in the region on both weather and climate time scales.