NUMERICAL SIMULATION OF MESOSCALE STRUCTURES OF TYPHOON AND OROGRAPHIC EFFECTS USING MM5

The track, landfall, dynamic and thermodynamic and cloud-rain physical mesoscale structuresand their evolution of typhoon HERB 1996 in 36 h from 0000 UTC 31 July to 1200 UTC 1 August1996 were simulated by using the non-hydrostatic mesoscale model MM5. This period covered theprocess of typhoon HERB landfall at Taiwan and Fujian Provinces. Results show that the model successfully simulated the landfall process of typhoon HERB,revealed the most important characteristics of the mesoscale dynamic and thermodynamic andcloud-rain physical structure during its landfall. The simulated typhoon track was close to theobservation. The center of cyclonic circulation simulated at 0000 UTC on 1 August 1996 (24 hintegration) was located in shore near Fuqing, Fujian Province at which the typhoon was reportedto landfall two hours later. It shows that strong upward motion formed by low level convergenceexisted in the eye-wall and subsidence at the eye. The wind field shows clear asymmetricalstructure near the typhoon center. The cloud and rainband was screw-typed distributed aroundtyphoon center, and consisted of meso-β scale rain cores. During the period of typhoon HERBstaying near and passing over Taiwan, the lower cloud was developed in the eye region so that theprevious clear typhoon eye on the satellite pictures became fuzzy. Observation shows that thetyphoon center was "warm", but the model simulations with higher space resolution show that inthe mid-troposphere the region of eye-wall with stronger upward motion and more cloud-and rain-water was warmer than the eye. During the period of typhoon passing over Taiwan and its following landfall at Fujian, thetrack of model typhoon deviated about 30 km northward (i. e., rightward) because of theorographic effects of Taiwan Island, but the strength of the typhoon was not affected remarkably.The amount of rainfall on Taiwan in the 36 h simulations was enhanced more than six times by theorographic lifting of Taiwan Mountain.