Study On Characteristics Of Velocity Field Of Doppler Radar In Precipitation

The space resolution of radial velocity product in the CINRAD (China new generation Doppler weather radar) reaches 0.25 km * 0.25 km and the radar makes one volume scanning per 6 minutes, then the horizontal wind products of different height in the range of dozen kilometers to about 100 or 200 kilometers can be retrieved, whose spatiotemporal resolution can reach 6 min* dozen kilometers that conventional information amounts to less than the resolution. Since CINRAD network applied to operation, it is discovered that the velocity echo images of Doppler radar in the rainfall process have obvious characteristics. If the features of velocity echo data can be adequately dug out to apply to weather forecasting, the efficiency and accuracy of weather forecasting will be enhanced. As a result, mainly according to the Doppler weather radar data during 2004-2007 in Nanjing, and combined with the rainfall information of the automatic weather station and the routine weather charts, the characteristic parameters of radial velocity echo before precipitation and VWP products in the precipitation process are designed and statistically analyzed in the article. There are four sections mainly in the paper.(1) The characteristics and statistic analysis of radial velocity echo images before precipitation. The convergent and divergent features of non-precipitation are introduced, and it is concluded that the convergent and divergent features have strong indication for the appearance of precipitation by using the method of statistic analysis.(2) The characteristics and statistic analysis of VWP product. The features of VWP product are introduced, and the detailed analysis is made for the reliability of wind field and the ability in representing atmospheric humidity, then the relationship between the change of wind direction and speed and the rainfall intensity is also studied, meanwhile, the index of weather forecasting is roughly devised.(3) The characteristic analysis of VWP product in spring large scale rain course. The different characteristics at different stages of rainfall development (formation, development and dissipation) are studied in detail, which are meaningful for this kind rainfall in the future.(4) Case analysis. The detail analysis is made for the features of the velocity echoes and VWP product during a spring large scale rain course occurred in Nanjing on April 22 2007.