Simulation of the 1976/1977 Climate Transition over the North Pacific: Sensitivity to Tropical Forcing

Sea surface temperatures along the Kuroshio Current Extension in the 1000-year control run of the NCAR Community Climate System Model version 2 exhibit robust decadal variability, with statistically significant spectral peaks near 16 and 40 years. Heat budget analysis shows that these decadal SST variations are driven by anomalous geostrophic heat convergence in response to basin-scale stochastic wind stress curl fluctuations, with air-sea fluxes acting as a damping and Ekman currents acting as a positive feedback. The response of the atmosphere-ocean mixed layer system to the decadal variations in geostrophic heat convergence in CCSM2 is studied by means of an entraining ocean mixed layer model coupled to the atmospheric model component of CCSM2. Results from these experiments, with and without air-sea coupling in the tropics, will be described.