Convective environments and hazards in Mediterranean cyclones

In the Mediterranean region the presence of warm sea surface temperatures and of complex topography favour per se the development of deep convection. This study shows how the presence of Mediterranean cyclones (MEDCs) further enhances the frequency of thunderstorms and how the synoptic and mesoscale features around the cyclones’ low-pressure centres organise the distribution of convective environments. The results are based on ERA5 reanalysis environmental variables, hail and lightning probabilities (modeled from ERA5 predictors) and a lightning detection dataset called ATDNet. Furthermore, a recent classification of MEDCs into nine clusters based on upper-level dynamical structure (Givon et al., 2024) serves as a framework for assessing the relationship between cyclone type and convection.

For each MEDC cluster, we characterise the frequency, intensity, spatial distribution and time evolution of convective environments and hazards. Convective activity typically develops to the northeast of the cyclone centre and within the warm sector, peaking before the cyclone reaches its minimum central pressure. Among the various cyclone types, small and deep systems occurring during autumn in the Northern Mediterranean exhibit the highest potential for the development of severe convection, followed by weaker cyclone systems propagating mainly in the Southern Mediterranean during transition seasons and summer. We further examine feature objects that correspond with different dynamical processes within the cyclones, finding that regions of warm conveyor belt ascent are more strongly associated with deep convection than cold frontal zones. The pattern holds across all cyclone clusters. These findings advance the understanding of mesoscale processes associated with MEDCs and offer useful insights for improving operational weather forecasting and risk communication regarding MEDC-related hazards.

Givon, Y., Hess, O., Flaounas, E., Catto, J. L., Sprenger, M., and Raveh-Rubin, S.: Process-based classification of Mediterranean cyclones using potential vorticity, Weather Clim. Dynam., 5, 133–162, https://doi.org/10.5194/wcd-5-133-2024, 2024.