Atmosphere Ocean Science Colloquium

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Atlantic Multi-Decadal Variability as a Thermally Coupled Mode Enhanced by Cloud Feedback

Speaker: Amy Clement, University of Miami

Location: Warren Weaver Hall 1302

Date: Wednesday, October 22, 2014, 3:30 p.m.

Synopsis:

The causes of Atlantic multi-decadal variability (AMV) are currently unknown. Because of the multi-decadal timescale, most previous explanations have focused on an active role for ocean circulation in driving this variability, in particular changes in the Atlantic Meridional Overturning Circulation (AMOC). In this study, we show that the spatial characteristics of the AMV can be reproduced in models where ocean heat transport is prescribed and plays no active role in driving climate variability. These results show that the spatial features of the AMV can be understood as a thermally coupled mode of variability. Further, we hypothesize that the persistence of this mode of variability is enhanced by cloud feedbacks. Observational evidence and idealized modeling experiments show that a positive feedback between clouds, surface temperature, and atmospheric circulation can enhance this mode of variability, effectively extending its persistence on decadal and multi-decadal timescales. Current generation climate models do not robustly simulate this feedback. The results imply that correct simulation of cloud feedbacks is critical to the simulation of the AMV, and model deficiencies in cloud feedbacks can significantly impact near-term predictions.