Dynamical systems insights on cyclonic compound “wet” and “windy” extremes in the Eastern Mediterranean

Extreme weather, such as heavy precipitation and strong winds, can co-occur, resulting in larger socio-economic impacts than the linear sum of their components. These are termed “compound extremes” and are challenging to forecast even a few days before. With this aim, we investigate the “wet” and “windy” extremes associated with Eastern Mediterranean cyclones in winter. We combine insights from a synoptic classification algorithm, traditional atmospheric analysis techniques, and dynamical systems theory. In phase space, the latter quantifies atmospheric states' co-recurrence ratio (α) and persistence (Θ⁻¹). We base the analysis on ERA5 at various pressure levels and time lags. Our analysis is two-fold; first, we define compound dynamical extremes (CDE) based on upper and lower deciles of α and Θ⁻¹, linking them to the synoptic patterns. We find that CDEs are related to the depth and location of the surface cyclone and upper-level trough. Then, we show that high co-recurrence and persistence are associated with heavier precipitation and stronger wind speed. Second, we define compound extremes (CE), the upper 5% of precipitation intensity and wind velocity co-occurring simultaneously. We link these back to the dynamical system metrics anomalies. Finally, we compare CEs with individual extremes and cyclone climatology. We find that CEs display significantly higher co-recurrence and persistence than individual extremes. Indeed, days with high co-recurrence and persistence anomalies are ∼2–18 times more likely to be allied with extreme weather, depending on the extreme type, than low co-recurrence and persistence. Moreover, we show that the upper levels are significantly more persistent than the surface flow during a CE. The mid-February 2012 “wet” and “windy” CE case-study strengthened the abovementioned climatological findings. To conclude, the dynamical systems viewpoint is a valuable complement to understanding the dynamics of CEs in the Eastern Mediterranean. We foresee it to be fruitfully applied to other CEs and regions.