Convective environments within Mediterranean cyclones

TL;DR

This study investigates the connection between Mediterranean cyclones and severe convective weather, revealing that a significant portion of lightning activity is cyclone-related and identifying key environmental factors that promote severe convection.

Contribution

It provides a climatological analysis linking Mediterranean cyclones with severe convection hazards using lightning data and reanalysis, highlighting cyclone features associated with high lightning potential.

Findings

20-60% of lightning hours are cyclone-related

Severe convection peaks before cyclone minimum pressure

Warm conveyor belts are key regions for lightning potential

Abstract

Understanding convective processes leading to severe weather hazards within Mediterranean cyclones is relevant for operational forecasters, insurance industry, and enhancing societal preparedness. In this work we examine the climatological link between Mediterranean cyclones and atmospheric conditions conducive to the formation of severe convection and convective hazards (convective precipitation, lightning and hail potential). Using ATDnet lightning detections we find that, from autumn to spring, 20 to 60% of lightning hours over the Mediterranean basin and adjacent land regions are associated with the presence of a nearby cyclone. Based on reanalysis data, severe convective environments, deep, moist convection (i.e., lightning potential) and related hazards are frequent in the warm sector of Mediterranean cyclones and to the north-east of their centres. In agreement with previous literature, convective processes and hazards peak approximately six hours prior to the time of minimum pressure of the cyclone centre. Moreover, severe convective environments are often detected in cyclone categories typical of transition seasons (especially autumn) and summer, while they are rarer in deep baroclinic cyclones with peak occurrence during winter. Finally, we show that dynamical cyclone features distinguish regions favourable to deep, moist convection. Warm conveyor belts of Mediterranean cyclones, characterised by large-scale ascent and located in regions of high thermodynamic instability, have the largest lightning potential. The potential is only half as intense along the cyclones' cold fronts.