A Study On Short-term Nowcasting Technology By Dopppler Radar

Using the conventional observation and Doppler radar data, this paper reached the convective weather processes from 2004 to 2008 in mid-south of Hebei province. We also analyzed the weather background, the characteristics of radar echo image of the convective weather processes, At the same time, we calculated the average divergence by the application of technology EVAD and analyzed the dynamic characteristics of the convective weather and judged the time of occurrence and the strength of the convective weather processes by the SRH. The specific content including:①Analyzing the weather background of the convective weather processes and summed up the climate and weather characteristics of the thunderstorms, hail and other weather disasters.②Analyzing the products such as the Doppler radar echo intensity and radial velocity and finding the Doppler radar image features of the convective weather processes. By analyzing the direction of the zero Doppler velocity contour on the PPI of the radial velocity and the difference of the positive and negative velocity values on the same distance from the radar, to qualitatively judge the convergence and divergence of the large-scale and the fixed height layer wind fields.③Computing the divergence value on different heights of the low-level using EVAD and according to the timing changes of the low-level divergence to Judge weather the environment fields were benefit to the development Analyzing the fifty convective weather processes which had been Scanned by the Shijiazhuang radar station from May to September of 2005 to 2008, and summing up the early warning indicators of the convective weather by the clear-air echoes.④Calculating the storm relative helicity (SRH) by the radar product of the vertical wind profile (VWP). Finding the relationship of the high-level SRH and the time of occurrence and the strength of the convective weather and summing up the early warning indicators of variety types convective weather such as hails, strong wind and short-time heavy rainfall by analyzing the twenty seven convective weather processes from 2007 to 2008.⑤We developped the "Convective Weather Automatic Alarm System" basing the statistical results of clear-air echoes. The system has been used since June to August in 2009. The system was easy to use and stable. The correct rate was 73.6%, the absent forecast quotiety was 19.5%, and the leak forecast quotiety was 6.9%. Overall, the leak forecasts were less than absent forecasts. It was also important to reduce the leak forecast quotiety and improve the capability of the nowcasting of severe convective weather.