| The 9806 TC(tropical cyclone) is a west-moving landing TC with diverse track and complex structure, which made landfall on Zhoushan archipelago. It brought disaster to Zhejiang Province. But few study focuses on orographic effects of small islands on TC. Therefore, it is worthy of studing. In this paper, the process of moving westwardly alone 30°N and landfall of the TC is simulated by using of the Penn-NCAR nonhydrostatic, two-way interactive, triply nested grid mesoscale model (MM5). And, the TC Bogusing scheme, the evolution of TC structure and the orographic effects of Zhoushan archipelago are discussed. In addition, a series of sensitive experiments are required to further demonstrate the orographic effects.In this paper, six experiments are designed. They are experiment B in which a a bogused vortex with tilted vertical structure is planted and the terrain of Zhoushan archipelago exists, experiment BT in which a a bogused vortex with right vertical structure is planted and the terrain of Zhoushan archipelago exists, experiment NB in which a a bogused vortex with tilted vertical structure isn' t planted and the terrain of Zhoushan archipelago exists, experiment BNZ in which a a bogused vortex with tilted vertical structure is planted and the terrain of Zhoushan archipelago is removed, experiment BLZ in which a a bogused vortex with tilted vertical structure is planted and the heights of terrain of Zhoushan archipelago are doubled, experiment BMZ in which a a bogused vortex with tilted vertical structure is planted and main islands of Zhoushan archipelago are set as a part of mainland. Some results of these experiments are shown as follows:In this paper, the orograpic effects of small islands on TC is firstly revealed. Comparing results of experiment B to experiment NB's, we find that the terrain of Zhoushan archipelago can leads the west-moving TC to deflect southward up to 15 km, and weakens it.Besides, the upward motion on the aweather slope of main mountains of Zhoushan archipelago can induce more precipitation and orographic highs. The interaction of orograpic highs with TC is one of main mechanisms of deflection of TC track, so is the interaction of deviating vorticity dips which are induced by air passing by mountains, with TC. Frictional dissipation and cutting off the water supply in the boundary layer by downslope adiabstic warming air are main mechanisms of terrain affecting TC intensity. These results supply a gap in study on.Results of sensitive experimentations reveal that the deflection of TC track increases, while variation of TC pressure is same as experiment B, if the height of Zhoushan archipelago terrain doubled. If bigger islands of Zhoushan archipelago are set as a part of mainland, the deflection of TC track is same as experiment B, while weakening of TC pressure is fast than experiment B. These result also confirm main mechanisms of terrain effects.In this paper, a bogused vortex with tilted vertical structure is firstly taken into account. Check results of experiment B , experiment BT and experiment NB, we find that the simulated TC track, center pressure and pattern of precipitation during landing in experiment B are better than others. So, a bogused vortex with asymmetrical horizontal structure and tilted vertical structure is good for a TC moving in mid-latitude, which may be a new way to initialize this kind of TC in numerical simulation.Results of experiment B demonstrate that a convergence zone of wind vector and water vapour with dense pressure gradient is formed alone the coast after TC's outer circulation encountering land, which results in more precipitation. When TC approaches to coast, under the squeezing effect between TC and land, convergences of wind vector and pressure gradient are intensified between TC' s center and coast, and, a new high wind domain forms. Therefore, the horizontal structure of TC changes. The vertial structure of TC tilts southwestward from lower level to higher level before landfall, and, it becomes more tilted as the TC ce...
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