GFI/BCCR Seminar: Revisiting Atlantic-European weather regime

Christian M. Grams (IAC, ETH Zurich):

Revisiting Atlantic-European weather regimes

Abstract

The large-scale midlatitude flow is dominated by Rossby wave activity along the upper-level midlatitude wave guide and jet stream. In the Atlantic-European region this activity occurs in preferred quasi-stationary persistent states, so-called weather regimes, which here explain most of the atmospheric variability on sub-seasonal time scales. In this presentation Atlantic-European weather regimes are revisited in order to elucidate their linkage to the eddy-driven jet, atmospheric blocking, and the physical and dynamical processes governing their life cycles. For the latter, the focus is on "diabatic outflow" driven by cloud-condensational processes in synoptic-scale weather systems. Furthermore, the role of weather regimes in extreme weather events is discussed with focus on their influence onatmospheric river occurrence in Europe and recent examples of severe flooding and heat waves. Finally, challenges in predictability are exemplarily demonstrated for a recent forecast bust.