Air-Sea Feedbacks onto the NAO on Decadal Timescales in Present Day and Last Glacial Maximum Simulations
The meridional overturning circulation (MOC) in several well-regarded global climate models contains a prominent 20-25 year oscillation. Previous studies suggest that the timescale for the oscillation is set by the ocean while the forcing is atmospheric, with an association to North Atlantic Oscillation (NAO) fluctuations. The NAO in these models also has an approximate 20-year oscillation. However, when the ocean in the Community Climate System Model (CCSM3) is replaced with a simple, slab-ocean mixed layer, the NAO lacks any self- sustaining oscillations, and thus, the oscillation requires feedback from ocean circulation. Other 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 adjustments. We suggest here 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 variability for the NAO. Additionally, the timescale for the MOC oscillation in a last glacial maximum (LGM) simulation of the CCSM3 is approximately half that found in the modern day simulation. Whether the same SST and sea ice feedback processes are active in the LGM simulation compared to the modern day simulation are investigated in this study. The technique used to uncover these relationships is linear inverse modeling (LIM). Using LIM, we are able to decipher which variables are important to the longer timescale NAO fluctuations and what the optimal patterns for the growth of that oscillation are.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 3305 Climate change and variability (1616;
- 4504 Air/sea interactions (0312;
- 4928 Global climate models (1626;