岛屿地形对热带气旋强度影响的数值模拟研究

Numerical Simulation of Effect of the Island Terrain on Tropical Cyclone's Intensity

本文用理想数值模拟分析的方法,在MM5模式中构造对称初始涡旋,在理想的环境场中发展为成熟的TC并移动经过从台湾岛抽象出的岛屿地形,揭示岛屿对TC强度和结构影响的机理。结果表明,理想模拟试验的方法对TC强度及结构变化的模拟具有很好的可靠性和客观性;TC中心登岛至到达岛屿山顶过程中,由于岛屿地形的抬升作用使得垂直方向上产生了局地的狭管收缩效应,使得TC在通过时强度短暂加强;TC在过岛过程中,风速垂直结构以及暖心结构的对称性会因地形的抬升和扰动影响而破坏,同时二者的大值区范围缩小;TC在过岛时,暖心结构在中高层分裂成一大一小2个部分,低层暖心偏离TC低压中心而伸向地面,TC由准正压系统变为斜压系统,使得TC整体强度减弱;次生低压对翻山后的TC中心的吸引融合加速了其过山后的北折过程;TC过岛后强度减弱十分明显,这是由于岛屿地形对环流摩擦阻力较大,对水汽供应的减弱和阻断,以及对TC对称结构的破坏。

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,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.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.