Regional Ocean-Atmosphere Feedback in Eastern Equatorial Pacific

Regional ocean-atmospheric coupled model has been developed to study regional scale air-sea interaction process. Its atmospheric component is Experimental Climate Prediction Center (ECPC)'s Regional Spectral Model (RSM) and ocean model is Regional Ocean Modeling System (ROMS). Using this coupled system, we attempt to reproduce recent observational evidence of rigorous air-sea coupling process associated with propagating meso-scale ocean eddies (or Tropical Instability Waves (TIWs) in eastern tropical Pacific. This study consists of two topics.

Firstly, following previous observational and numerical studies, we examine the response of atmospheric boundary layer (ABL) on meso-scale eddies and undulating SST fronts. It is shown that coupled model reasonably well reproduces observed patterns of ABL response to different phases of SST. SST by TIWs induces vertical stability adjustment within ABL, which results in accelerating (decelerating) cross-equatorial southeasterly trade winds, more (less) abundant water vapor amount, and stronger (weaker) turbulent flux over/near warm (cold) phase of SST. A close association between mesoscale SST features and ABL response of comparable scale give us an ample confidence in ability of the coupled modeling system. We are therefore motivated to examine the detailed mechanism of air-sea feedback associated with TIWs in this region.

As a specific focus, we study response of SST and dynamic topography of the equatorial Pacific Ocean to atmospheric feedback. TIWs-induced SST results in significant modification of surface turbulent flux as well as wind-stress. This implies that ABL forced by TIWs provides additional feedbacks onto ocean. To examine and quantify these effects, we introduce coupling parameters that adjust the intensity of the two modes of atmospheric feedback (thermal and dynamic). By doing so, we hope to understand the relative role and importance of each mode of feedback mechanisms on evolution of SST and dynamic structure of the equatorial Pacific Ocean. Detailed results will be discussed in the workshop.