Bates, S. C., University of Washington, Seattle, USA, email@example.com
Bitz, C. ., University of Washington, Seattle, USA, firstname.lastname@example.org
Battisti, D. ., University of Washington, Seattle, USA, email@example.com
Barsugli, J. ., CIRES-University of Colorado, Boulder, USA, firstname.lastname@example.org
ATLANTIC MERIDIONAL OVERTURNING CIRCULATION VARIABILITY IN MODERN AND LAST GLACIAL MAXIMUM SIMULATIONS OF CCSM3
The Atlantic meridional overturning circulation (AMOC) in several modern day global climate simulations contains a prominent 20-25 year oscillation. We find the timescale for an AMOC-like oscillation in a last glacial maximum (LGM) simulation of the CCSM3 is approximately half that found in the modern day simulation. Previous studies suggest that the oscillation timescale is set by the ocean while the forcing is atmospheric, with an association to North Atlantic Oscillation (NAO). The NAO in the CCSM3 modern simulation also contains an approximate 20-year oscillation. Previous research shows that the NAO forces a delayed flux of subtropical gyre water into the Nordic Seas, where deep water forms, due to subpolar gyre (SPG) adjustments. We suggest that the resulting SST and sea ice anomalies in the Nordic Seas provide a feedback to the atmosphere, which, being delayed from the initial NAO forcing, may set the longer timescale for the NAO. Preliminary results indicate a strong correlation between the NAO and the barotropic streamfunction in the SPG as well as an SST pattern consistent with the SPG adjustment. Differences in feedbacks in the LGM climate give rise to key differences in the AMOC-like mechanism in the LGM simulation. Using linear inverse modeling, we are able to decipher which variables are important to the longer timescale fluctuations, the optimal patterns for growth, and the differences in predictability of the NAO and AMOC within the LGM and modern scenarios.
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