Dim Comou, Potsdam Institute for Climate Impact Research, Germany


Persistent summer circulation: Risks, Impacts & drivers


Summer, with most biological and agricultural production, is probably the season when future changes in extremes will have the most-severe impacts on humanity. Summer extremes are particularly devastating when they persist for several days: Many consecutive hot-and-dry days causing harvest failure, or stagnating wet extremes causing flooding. Despite this importance, we are far from a comprehensive understanding of the mechanisms involved in the formation and the potential future changes of persistent weather conditions in summer.

In this presentation, I will summarize some recent research on persistent circulation regimes in the Northern Hemisphere mid-latitude summers. I will discuss (1) the observed and climate model projected changes in summer persistence, (2) observed and climate model projected changes in summer circulation and the likely implications for persistent circulation regimes, and (3) important drivers of persistent circulation patterns. The latter includes low-latitude monsoon forcing, mid-latitude sea-surface temperature patterns, Arctic drivers and early-season soil moisture content. These remote and regional drivers have in principle the potential to interact in a positive reinforcing manner that favors persistent circulation regimes. Due to feedback mechanisms between soil moisture, snow cover changes, and continental-scale circulation, summer weather in western Europe and the interior North America is likely to become more continental as seen in models and possibly also in observations. The presentation will highlight the robust evidence (based on observations, climate models and a solid physical understanding) as well as the knowledge gaps, discussing a possible way forward with a coordinated research agenda.


Tuesday June 11, 11:30 - Note the later time!


Rossbysalen C609, Arrhenius laboratory, Svante Arrhenius väg 16C, 6th floor