Joint Seminar: What Controls the Overturning Circulation of the Stratosphere? ... and the Specter of Abrupt Climate Change!

I will explore the role of the troposphere and stratosphere in regulating the Brewer-Dobson Circulation, the meridional overturning circulation of the stratosphere, and its response to anthropogenic climate change with an idealized atmospheric general circulation model.  A series of controlled experiments suggest that the tropospheric planetary wave activity sets the total amplitude of the BDC, while stratospheric conditions set its depth. The two factors have comparable impact on mass transport through the stratosphere. I'll then probe the impact of anthropogenic forcing in the idealized model, focusing how the circulation response varies as a function of the warming amplitude.  For moderate warming, the response of the simple model is remarkably similar to comprehensive models: the Hadley cell widens, the tropospheric mid-latitude jets displace poleward, and the Brewer-Dobson Circulation increases. However, when the warming of the upper tropical troposphere exceeds a critical threshold, the climate changes abruptly due to a regime transition in the eddy driven circulation.  These results suggest the possibility that dynamics alone could cause abrupt climate change, or at least amplify other nonlinear elements of the climate system.




13:30 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Edwin P. Gerber, Courant Institute, NYU


Hauke Schmidt

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