Air-sea coupling mechanisms in the North Pacific using a high-resolution mesoscale atmospheric model

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Thursday, 27 January 2011
Air-sea coupling mechanisms in the North Pacific using a high-resolution mesoscale atmospheric model
Washington State Convention Center
Ramesh K. Vellore, DRI, Reno, NV; and D. Koracin, I. Cerovecki, and C. E. Dorman

The air–sea interaction in the North Pacific, especially the air-sea coupling at ocean mesoscales between sea surface temperature (SST) and surface wind anomalies has been the subject of much debate during the past decade. Recent research studies have suggested that the mesoscale ocean-atmosphere coupling has the potential to force or change the large scale, low frequency oceanic variability (20-40 years). The air-sea coupling is strongest in the vicinity of the oceanic fronts, such as the Kuroshio Extension (KE) front. This is a region of intense winter ocean-to-atmosphere heat loss when cold, dry continental air passes over the warmer ocean. While observations reveal the strong air-sea coupling in the North Pacific, the global circulation models fail to reproduce a coherent coupled response of realistic strength. The objective of this study is to provide insight into the ocean-to-atmosphere feedback mechanisms using a regional (North Pacific) high-resolution atmospheric model (Weather Research and Forecasting model (WRF) with 0.1° horizontal resolution) with three different sets of SST estimates used as a lower boundary condition for the WRF model: 1) 1.4⁰ SST estimates from the Community Climate System Model version 3 (CCSM3), 2) 0.25° optimally interpolated (OI) Reynolds infrared-microwave based SST analyses, and 3) 0.1⁰ SST obtained from a stand-alone Parallel Ocean Program (POP) eddy-resolving model simulation driven by the Large and Yeager annually repeating “Normal Year” atmospheric forcing. We investigate the accuracy of the simulated air-sea coupling by analyzing the WRF model results' sensitivity to the spatial resolution of the SST and its influence on the simulated air-sea fluxes, surface winds, surface stability, and marine boundary layer structure. The preliminary results suggest that the effects of air-sea coupling are more pronounced on the surface heat and moisture fluxes than on the winds. In particular, we assess the accuracy of the model representation of the strength and frequency of wintertime cold air outbreaks compared to the observations, satellite data, and global reanalysis data products.