Numerical Simulation Of Tropical Cyclone's Intensity And Structure Changes In The Process Of Passing Through The Island Terrain In The Ideal Situation

The research mainly conducted on a case study basis which results in a lack of universality. In this paper, initially symmetrical bogus is created in the MM5 model by adopting the numerical simulation analysis, which develops into mature in the idealized environment and passes through an island abstracted from Taiwan, to deduce the influence on the intensity and structure. The result shows that, in the condition of the background flow and fixed SST, with a relatively weak cyclonic vortex as the initial field, we could form the TC, whose characteristics indexes as intensity, structure are in general agreement with the data gained from practical observation and research. The ideal simulation method proves to have high reliability and objectivity on the simulation of the TC intensity and structure changes. From landing to the island to ascending to summit of the mountain, the intensity of TC's centre is temporarily increased. This is because the uplifting of the terrain produces a partial narrow tube contraction effect vertically. When TC is passing over the island, the topography lifting and blocking functions undermine the vertical distribution of horizontal wind speed and the symmetry of the warm core and simultaneously narrow the maximum value scope of the two. During the process of TC passing over the island, the warm core structure in the middle-and-upper level splits into two parts, a great and a small; the warm core in the low level deviates from the TC's low pressure center toward the surface and the quasi-pressure system changes into the baroclinic system as well. The above causes the decrease of TC's overall intensity. During the process of TC passing over the island, the flows in the leeward side will be intensified and speed up almost to the maximum value of wind speed for the centre of TC. This phenomenon is mainly due to that the passing airflows are converted from sub-critical flow to super-critical flow after being compressed and flow in accelerating flow state in the leeward side. Meanwhile the wave breaking zone located in the leeward side reflects the low-level gravity waves also cause the acceleration of low-level stream's continual acceleration in the leeward side. In addition, the secondary low's absorb and amalgamation of the center of the TC which has passes over the mountain accelerates the northing process. The intensity of TC decreases notably after passing the island. This is because the terrain of island creates great friction resistance with the circulation, decreases and blocks the water vapor supply as well as damages symmetrical structure of TC.