The Dynamic Analysis Of Doppler Radar Echo And The Improve Of Nowcasting Algorithm

Severe convective weather is one of major disastrous weather in China, with a small spatial scale, short-lived, breaking out suddenly, rapid evolution, destructive and other characteristics, and therefore has been concerned widely. Because of its high temporal resolution and spatial resolution, Doppler weather radar has become one of the effective facilities for forecasting meso-scale weather, and many extrapolation methods of radar echoes have been developed.But the methods of analyzing the echo development and moving are based on the of the radar reflectivity factor, the velocity data of Doppler radar has not been fully applied in the operation, and the dynamics process of echo development has not been researched enough. Therefore, extrapolation techniques often do not be taken the evolution of echo into account, which also makes a larger deviation for forecasting a rapid development echo, even for nowcasting.To solve the above problem, pyramid-delaminating theory and semi-Lagrangian extrapolation scheme are utilized for improving the optical flow method to retrieve wind fields and extrapolating the future 0-1h radar combined reflectivity factor. Results show that in the strong convective weather conditions, the improved optical flow method has certain advantages over the widely used cross-correlation (TREC, Tracking Radar Echoes by Correlation) technique.Studying the dynamics of echo, this paper analyzes the background, the echo evolution and vertical structure of squall line to understand the mechanism for the evolution of echo and the its relationship with divergence and vortex. Based on this, the radial velocity is used to retrieve divergence and vortex. A detailed analysis of the relationship between evolution process, the movement path of the echo and these two physical quantities is made to reduce extrapolation errors and improve the accuracy of forecasting strong convection weather.In the extrapolation process, due to the lagging relationship between strong echo center and the location of the convergence zone, it is difficult to decide where the echo will be modified. Therefore this research matches the positions of both first, and then extrapolates the convergence zone. The extrapolation results show that strong echo location is well consistent with the convergence center and it can be implications for correction of predicting strong echo locations.The primary issues of this paper are as following:1. Improving optical flow with pyramid-delaminating theory and semi-Lagrangian extrapolation scheme. Results show that in the strong convective weather conditions, improved optical flow method has obvious advantages.2. Analyzing the relationship between the radial divergence and vortex field and echo evolution in details. Results show the radial convergence zone and positive vortex area has indication of the strength, moving and deflection of echoes. Radial convergence zone can also guide the newborn or merger of a single echo.3. Matching the strong echo location and convergence areas. After matching, strong echo location is well consistent with the convergence center and it could correct the prediction locations of strong echo.