The Simulation of Typhoon Krovanh Using a Coupled Air－Sea Model

In order to investigate the mechanism of impact of sea surface temperature (SST) cooling on typhoon intensity and the ocean response to typhoon, a mesoscale coupled air－sea model is developed based on the non-hydrostatic mesoscale model MM5 (the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model) and the regional ocean model POM (Princeton Ocean Model). In this study, two experiments are performed, one used the coupled model and the other MM5, in which the SST field at the model initial time is fixed so that the typhoon-induced cooling is ignored. Results reveal that the level of intensity prediction is improved including typhoon-induced SST cooling, the simulated minimum surface pressure and maximum surface wind in the coupled model are better consistent with observation than that in the uncoupled model, and the simulated central pressure from the latter is 20 hPa deeper than that from the coupled model result. The SST simulated by POM in the coupled experiment is also in good agreement with that from the TRMM/TMI-derived data. The maximum SST cooling is 5.8°C, which is about 95 km away from the right side of the typhoon track. Corresponding to the SST cooling, the depth of mixed layer deepens in the meantime, indicating the effect of entrainment on SST cooling. Analysis shows that SST cooling reduces the sensible and latent heat fluxes from ocean to the vortex, especially in the inner-core region. In this study, the averaged total heat fluxes in the inner-core region of the typhoon decrease by 32.1%, which causes reduction of the moist static energy and the radial gradient of moist static energy, resulting in weakening of the typhoon.