Seo, H., R. Murtugudde, M. Jochum and A. J. Miller, 2008:
Modeling of mesoscale coupled ocean-atmosphere interaction and its feedback to ocean in the western Arabian Sea.
Ocean Modelling, sub judice.
Abstract. The observations of the western Arabian Sea in the recent decade have revealed the rich filamentary eddy structure in the ocean with a large horizontal SST gradient in response to the southwest monsoon winds. This summertime oceanic condition triggers the intense mesoscale coupled interaction, whose overall influence on the regional ocean remains uncertain. In this study, a high-resolution regional coupled model is employed to explore this feedback effect on to the long-term dynamical and thermodynamical structure of the ocean.
The observed relationship between the near-surface winds and mesoscale SSTs generate the Ekman pumping velocities on the scales of cold filaments, whose magnitude is order of 1 m/day both in the model and observations. This additional Ekman velocity made possible by the wind-eddy interaction accounts for approximately 10-20% of the oceanic vertical velocity in the western Arabian Sea. This implies that nonlinear Ekman pumping arising from the mesoscale coupled feedback makes a nontrivial contribution to the vertical structure of the upper ocean and the evolution of the mesoscale eddies.
Furthermore, mesoscale SST features enhance the latent heat flux input to the ocean. The long-term latent heat flux change due to the eddies in the model is estimated approximately 10-15 W/m2 over the cold filaments, which is consistent with the previously reported estimates based on the short-term in situ measurement. Given the shoaled mixed layer, this additional surface heat flux warms the cold filament at the rate of 0.3-0.4C/month for a single season with a strong eddy activity, and 0.1-0.2C/month in a 12-year mean. This long-term mixed layer heating by the surface flux is approximately +-10% compared to the lateral surface heat flux by the eddies, yet it can be comparable to the vertical heat flux, rendering overall low-frequency modulation of SST possible. Potential dynamic and thermodynamic impacts of this observed air-sea interaction on the monsoons and regional climate are yet to be quantified given the strong correlation between the Findlater Jet and the Indian summer monsoons.
Preprint (pdf)