单多普勒雷达反演热带气旋近中心风场的VAP扩展应用方法

An extended application of the VAP method for wind field retrieval near the tropical cyclone center with single Doppler radar data.

中文关键词:  单多普勒雷达，风场反演，热带气旋

英文关键词:Single-Doppler radar,Wind retrieval,Tropical cyclone

中文摘要:

      在尝试运用VAP方法和扩展VAP（EVAP）方法，对“韦帕”台风期间移动天气雷达（CINRAD/CCJ）观测基数据进行单雷达风场反演时，发现部分区域出现风向、风速不合理的情况。分析认为，在热带气旋近中心区域风向风速变化均较剧烈，而上述两种算法的假定条件难以准确代表风场的实际变化。根据热带气旋发展成熟阶段的气旋环流近似轴对称的特点，文中提出一种新的假定条件，即在与热带气旋中心等距离的圆周上局地风速不变、风向均匀变化，对VAP方法进行扩展应用，称为EVAPTC（EVAP for Tropical Cyclone）方法。对理想模型流场试验及对实际个例的反演结果表明，EVAPTC方法简便，反演误差相对较小，能够基本反映出台风近中心的环流特点，尤其是螺旋云带上的风场特征。例如“韦帕”台风螺旋云带内侧有明显的辐合气流进入螺旋云带，螺旋云带尾部的外围气流绕着云体移动，螺旋云带上的强回波区存在着风场扰动等。

英文摘要:

      In the attempt to employ the VAP and extended VAP (EVAP) method for retrieving wind fields based on observation data from the mobile weather radar (CINRAD / CCJ) during the typhoon “Weipa”, some unreasonable wind directions and velocities have been found after the retrieval. The reason might be attributed to the assumptions assumed by the above methods that are not well representative for the actual situation of violent change of wind speed and direction near the tropical cyclone center. According to the characteristics of approximately axial symmetry circulation of a tropical cyclone, especially in its mature stage, this paper presents a new assumption, namely, the assumption of uniform change of wind direction with stationary wind speed on the circle equidistant from the tropical cyclone center. The authors called it as EVAPTC (EVAP for Tropical Cyclone) method under the new assumption. The experimental results of an ideal model and the retrieval results of an actual case all show that the EVAPTC method is simple and convenient with relatively small retrieval error. It can basically reflect the circulation features near the typhoon center, especially the wind field in the spiral band. As an example, in the case of typhoon “Weipa”, there are obvious convergent airs flowing into the inner side of spiral band with the flow on the periphery of the spiral tail shifting around the clouds and wind disturbance existing in the strong echo areas of spiral band, etc.