Events / Media

Data Assimilation Seminar Series

Dr. Kohei Takatama (Apr. 17, 2018, 15:00-)

Affiliation R-CCS
Title Regional atmospheric data assimilation coupled with an ocean mixed layer model: a case of typhoon Soudelor (2015)
Abstract Meso-to-synoptic scale atmospheric phenomena with strong winds over the ocean or near the coast, such as typhoons, are often closely linked to sea surface properties. For example, stronger winds induce more heat fluxes from the ocean to the atmosphere when the sea surface is warmer than the surface atmosphere, and it may have a positive feedback loop to enhance a development of a low-pressure system. Simultaneously, there is a negative feedback mechanism to suppress the development due to decreased sea surface temperature (SST) by oceanic heat releases, cold-water upwelling by Ekman pumping, and vertical mixing induced by the strong winds. The decreased SST in turn will counteract the development of a low-pressure system. In the atmospheric model simulations, however, SST is usually given as a bottom boundary condition, and its temporal variation is considered in a simplified manner or even not considered at all.
This study investigates the effect of atmosphere-ocean coupling in a regional atmospheric data assimilation system for a case of typhoon. A simple ocean mixed layer model, known as the Price-Weller-Pinkel (PWP) model, has been implemented into a regional atmospheric data assimilation system SCALE-LETKF, composed of the regional atmospheric model SCALE-RM and the local ensemble transform Kalman filter (LETKF). It is expected that the ocean mixed layer model brings more realistic physics to the simulation and modifies the ensemble spread, particularly near the ocean surface. In this presentation, we will report the impact of the coupling effect in a case of Typhoon Soudelor (2015).
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