利用双多普勒雷达分析对流云垂直运动结构试验

对流云是我国南方地区主要的降水云系, 含有丰富的云水资源, 是南方人工增雨作业的主要对象。为了研究江淮地区对流云发生发展规律, 利用双多普勒雷达反演技术分析了发生在2004年7月31日的一块对流云不同发展阶段的垂直运动结构。对流云在发展阶段以上升气流为主, 底层辐合明显, 结构紧密; 成熟阶段的上升与下沉气流势力相当, 且比发展阶段强盛, 强回波位置下移, 结构较发展阶段松散; 减弱阶段上升和下沉速度均减小, 水平辐散增强。结果表明:反演的不同阶段对流云垂直运动结构合理, 可以利用双多普勒雷达反演技术进行对流云三维运动结构研究。

The Upright Motion Structure in Convection Cloud by Dual Doppler Radar

The convection cloud is the main precipitation system in south China, having abundant water resource. And it is the main modification object in south China too. A convective cloud development is closely correlated with the structure of the upright wind field, but it is hardly observed directly for the equipment limit. With the quick development in multiple Doppler radar synchronously observation and retrieved technique of the wind field, analysis is possible in the upright wind structure by dual-Doppler radar. The dual-Doppler radar data are retrieved for the upright wind structure analysis in such three different phases as the development, the intensification and the decaying in a convection cloud on July 31, 2004. In the development stage, a whole secondary circulation is found in 5—10 km height, and its center is at about 8 km height. In this phase, the updraft is more than downdraught obviously. All current is updraft under the secondary circulation, at about 5 km height. The convergence area on the VCS of Hefei Doppler radar is under 6 km height, the area of retrieved updraft. The transformation area from convergence to divergence is about 6—9 km height, which corresponds with the secondary circulation. In this phase, the heavy echo concentrates near the secondary circulation, and the heaviest echo at about 5—8 km height is underside of the center of the secondary circulation. In this phase, the echo dimension is small, about 10 km in longitude direction and 20 km in latitude direction. In the intense stage, the secondary circulation is strong. Its location is at 4—10 km height, near the center of cloud. The downdraught is almost under the secondary circulation and the updraft is above the secondary circulation. In this phase, the velocity of downdraught and updraft are bigger than the development stage, and their values are almost equal which is different from the dominant updraft in the development stage. The convergence area on VCS of Hefei Doppler radar is still at the bottom, and the wind tow ards Hefei radar is in higher layer corresponding with the retrieved result. In this phase, the heavy echo area is near the lower cloud and the heaviest echo is about 3 km height under the secondary circulation. The area of echo is obviously bigger than the development stage, about 30 km in longitude direction and 30 km in latitude direction. In the decaying stage, the secondary circulation has disappeared, that means the convection in cloud has become weak. The velocities of downdraught and updraft are both slow, and the strong out-flux is in the east and the north of the cloud top. The horizontal velocity is faster than in the intense stage but the upright velocity is slower than in the intense's. At this time, the horizontal radiation in cloud is increased. The wind direction on VCS of Hefei Doppler radar is toward the radar station in lower layer and outward in higher layer. And the observation and the retrieved result are similar. The echo in this phase is obviously weaker than in the development stage and in the intense stage. The heavy echo area is near the lower cloud, and the dimension of echo area is bigger than in the intense stage, about 50 km in longitude direction and 40 km in latitude direction. Result shows that it is possible and workable on the structure analysis in wind upright fields by dual-Doppler radar.