A New Quantitative Framework for Mediterranean Cyclogenesis: Local Wave Activity and Cross-Basin Dynamics

The North Atlantic–Mediterranean region hosts a complex interplay of two storm tracks, linked by multiple weather systems interacting across scales, such as the interplay of low-level cyclones and anticyclones with upper-level Rossby waves. Compared to the well-known inherent cyclogenetic properties of the Mediterranean itself, the role of crossbasin processes, mainly from the North Atlantic, in shaping Mediterranean cyclones remains insufficiently understood. In this study, we use the local wave activity (LWA) framework, applied for the first time to the Mediterranean, for quantifying the relative cyclogenetic contributions of physical processes within and outside the basin, and to assess their impact on cyclone characteristics. Our analysis shows that the waviness of the North Atlantic atmospheric flow enhances the frequency of Mediterranean cyclones and the occurrence of the upper-level streamers that drive them. Eddy momentum flux divergence over the northern Mediterranean coast, combined with local baroclinic LWA sources, plays a central role in cyclone dynamics, affecting storm trajectories and precipitation on subseasonal to monthly time scales. On a broader scale, our analysis demonstrates how wavy flow propagates from the North Atlantic into the Mediterranean basin, transforming throughout the process over the course of 5–10 days. The novel application of the LWA perspective establishes a new dynamically grounded framework for analyzing Mediterranean cyclogenesis and the physical processes that drive it. It also provides new insights into the cross-basin interactions that shape cyclone development, with potential implications for extreme winters and future climate trends in the basin.