A climatological perspective on cyclones and precipitation in the Eastern Mediterranean using potential vorticity-based classification

Eastern Mediterranean Cyclones (EMCs) are a major contributor to extreme weather in this region, including precipitation, strong winds, cold extremes or dust storms, significantly impacting the population and natural environment. Thus, understanding the relationship between EMC variability and associated impacts is key to understanding their predictability and forecasting these hazards. 

Previous approaches for cyclone classification over the Eastern Mediterranean region involved the cyclones’ location, intensity, or structure. Such approaches do not consider the involved processes and, therefore, result in limited physical interpretations of cyclone variability and associated impacts and predictability. 

Various processes come together to govern the genesis and development of EMC, and these processes have distinct signatures on the potential vorticity (PV) distribution. Here, we classify EMCs based on their associated upper-tropospheric PV structures into 6 clusters and analyse the impacts of resulting clusters.

We find that each cluster has its own signature of precipitation pattern. For each of the seasons, there are dominant clusters that bring extreme precipitation. In particular, two clusters of anti-cyclonic Rossby wave breaking PV patterns dominate the eastern Mediterranean's annual precipitation. Evidently, a strong ridge upstream of the PV trough has a greater impact on precipitation and temperature extremes than the PV pattern with a weak ridge upstream. Moreover, cyclones with low PV values, which correspond to heat-lows in the transition seasons, have an increasing trend in their occurrence frequency. 

This classification approach enhances our understanding of the link between cyclone variability and their surface impacts in the region through processes reflected in upper-level PV distributions. These findings could benefit strategies for managing the societal and environmental impacts of EMCs at weather and climate timescales.