Dept. of Geosciences Colloquium - Ph.D. seminar: The North Atlantic-Mediterranean Dynamical Chain: Bridging Large Scale Flow and Local Winter Weather

Zoom: https://tau-ac-il.zoom.us/j/87073901428?pwd=Zay3aB8aBEigEH9SC4iEU9pByK9FCN.1

Abstract:

The Mediterranean is considered one of the most cyclogenetic regions on the planet. This is sustained by a unique combination of dynamical and thermodynamical factors, from its sharp land-sea temperature differences to the topographic forcing of its surrounding mountain ranges. The basin is also crucially located downstream of the North Atlantic Ocean, a major source of both moisture and energy. The interaction between the North Atlantic and Mediterranean regions spans multiple scales (from large scale jet streams to synoptic storms) and incorporates many dynamical components, e.g., extratropical cyclones, Rossby wave packets and potential vorticity (PV) streamers. The mechanistic understanding of this connection still has significant gaps, especially for the eastern Mediterranean where storms are relatively smaller and further downstream. Advancing our knowledge of this topic is essential, as projected changes in large-scale circulation patterns—such as the poleward shift of the Atlantic jet stream—will likely affect the distribution, intensity, and frequency of Mediterranean storms in the future. This work presents a multiscale analysis of the Atlantic-Mediterranean chain and its impacts on cyclonic activity and precipitation in Israel and the Levant. Using several datasets of objectively tracked features along the chain (cyclone tracks, streamers, wave breaking events), we identify different North Atlantic flow regimes that significantly influence winter conditions in the Mediterranean on a subseasonal scale. This unfolds through a specific chain of events: upper-level flow perturbations upstream cause Rossby wave breaking events along the jet stream, which in turn develop into PV streamers. These streamers reach the Mediterranean, and through increased baroclinicity they enhance cyclonic activity in the region. Finally, we establish the connection to Mediterranean cyclones more explicitly with Finite Amplitude Wave Activity, a local diagnostic of flow waviness.

Event Organizer: Dr. Ariel Lellouch