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

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.