环境地转基本气流的计算及热带气旋运动与其偏差的统计分析

利用国家气象中心T63L16的1.875×1.875经纬网格点资料和中央气象台编号的热带气旋实时中心位置资料,计算了1996年全年25个热带气旋,共126个时次的环境地转基本气流,分析了环境地转基本气流的垂直分布特征,并对热带气旋的实际运动与环境地转引导气流的偏差(后文将称其为引导偏差,即热带气旋的实际中心位置与按引导气流推算出的位置之间的偏差)进行了分析,发现引导气流的计算区域不同,其引导偏差是不一样的。得到了引导气流的最佳计算区域,并且发现热带气旋运动与环境地转基本气流的垂直切变结构的关系以及引导偏差与引导气流的速度、气旋本身的初始纬度位置和强度等有关。结果还表明,200～1000 hPa的深层加权平均的基本气流的引导效果最佳,可作为最佳引导气流使用。了解这些规律和特征,对热带气旋运动预报具有一定的参考意义。

CALCULATION OF THE ENVIRONMENTAL GEPSTROPHIC BASIC FLOW AND STATTISTICS ON THE DEVIATION OF TROPICAL CYCLONE TRACK AND FROM IT

Using the T63L16 analysis data with the resolution of 1.875×1.875 degree of latitude and longitude obtained from National Meteorological Center (NMC) and the real central position information of tropical cyclone numbered by NMC,the environmental geostrophic basic flow at 126 times of 25 tropical cyclones in 1996 are calculated. The vertical distribution features of the environmental geostrophic basic flows are analyzed. Besides,the deviation of real TC tracks from the environmental geostrphic basic flow (referred as steering flow hereafter,namely the deviation between the real central position of TC and the position calculated according to the steering flow) is also investigated. The result shows that the steering deviation would be different if the domain used to calculate the steering flow is different. The present paper obtains the optimum domain size to calculate the steering flow. It is found that the steering deviation has relationship with the velocity of steering flow and the initial latitude and intensity of tropical cyclone itself,and that tropical cyclone motion has relationship with the vertical shear structure of environmental geostrophic flow. The result also shows that the optimum steering flow is the deep layer averaged basic flow from 1000 hPa to 200hPa. Having the knowledge of these principle and features would help to make accurate forecast for tropical cyclone motion.