NUMERICAL STUDY ON IMPACTS OF BOUNDARY LAYER FLUXES OVER WETLAND ON SUSTENTION AND RAINFALL OF LANDFALLING TROPICAL CYCLONE

Typhoon Nina(1975) moved into inland and then stagnated and sustained for 4-5 days after it made landfall in Fujian province of China on Aug. 4,1975. Nina restrengthened over inland resulting in severe flooding with the extreme rainfall of 1062 mm in 24 hours. Previous analysis indicated that the landfalling TC could sustain a longer time if it stagnated over a huge surface of a lake, reservoir or saturated wet land. Severe rainfall disaster may be arised from a certain TC remnant sunstained over land. The impacts of land-air fluxes in saturated wet land boundary layer on TC sustention have been discussed. The PSU/NCAR non-hydrostatic mesoscale model MM5v3 and its TC Bogus scheme were employed to perform several sets of numerical simulation. Bidirectional feed-back double nested grid mesh was used and Grell and Kain-Fritsch convective parameterization schemes were adopted for coarse and fine mesh respectively. Reiser's scheme and the Blackadar PBL parameterization were employed in those experiments.The results have shown that the vertical transfer of the physical quantities of the boundary layer over saturated wet land would affect the structure, intensity and rainfall of a landfalling typhoon to a great degree. Fluxes of latent and sensible heatings are favorable to tropical cyclone sustention and intensification, but the latent heat flux would play a major role in tropical cyclone intensification and sustention of spiral rain-band. They also affect the rainfall distribution. On the other hand, momentum flux would weaken TC circulation obviously and consume TC energy remarkably, but it somewhat increases the TC rainfall in local area.