Numerical study on impacts of the wet land boundary layer fluxes on the sustention of typhoon Nina and its rainfall

Typhoon Nina(7503) went deep inland and sustained for 4-5 days after it made landfall in south east coast of mainland China on 4 Aug.,1975. It re-strengthened over inland resulting in extreme rainfall of 1062mm/24 hours. Its underlying ground was almost saturated. Previous study (Chen, 2002) indicates that a landfalling typhoon could sustain a longer time if it stagnated over a huge water surface. Study (Kong, 2002) showed that the development of convection over a warm and wet ground likely contributed to the inland intensification of the remnants of the tropical storm Allison. Shen (2002) studied the impacts of the water surface in ground on the hurricane with GFDL Hurricane model and found that the water layer with 0.5m depth could obviously slow down the decaying rate of a hurricane over land. However, such effects of wet land are often neglected in the operational forecast. In this paper, the impacts of land-air fluxes in saturated wet land boundary layer have been investigated in order to get better understanding on the mechanism of typhoon sustention over land and its rainfall. The wet ground is favorable to Nina's sustention and its rainfall. Fluxes of latent heat and sensible heat in saturated wet land boundary layer are favorable to tropical cyclone intensification and rainfall increased, but the former would play a major role. On the other hand, momentum flux would weaken Rananim's intensification obviously but it is somewhat to increase the typhoon rainfall in local area.