Radar Echo Characteristics of Thunderstorm Gales and Forecast Key Points in Hebei Province

Using Xinle CINRAD-SA radar data at Shijiazhuang about 262 cases of thunderstorm from 2006 to 2008, radar echo characteristics of thunderstorm gales in Hebei Province are analyzed. It is found that the main characteristics can be divided into three categories, including the bow echo, band echo and bulk echo. The band echo accounts for 66.8%, the bow echo is 19.8%, and the isolated bulk cell echo is 13.4%. So the band echo is the main echo of thunderstorm gale. The main radar echo characteristics of thunderstorm gale are bow echo, gust front and radial velocity large value area, and all of them are thunderstorm gale warning indicators. Based on the above radar echo features, 66% thunderstorm gales can be forecasted. All bow echo thunderstorm gales can be forecasted, but they only account for 19.8%. Gust fronts can be observed only 16.8% of cases, and thunderstorm gales high speed value area can be observed 65.3% of cases. Therefore, the high speed value area is the most important characteristics of radar echoes. The formation rate of high speed value area is generally earlier than bow echo and gust front, so the thunderstorm gale can be forecasted earlier by using this characteristic.There are some limitations in the thunderstorm gale warning based on radar echoes. Sometimes the gust front echo will cause velocity less than 17 m/s, when the early warning may be false alarm. The gust front echo mainly concentrates in the boundary layer, and cannot be detected if it's far away from the radar. But when it's close to the radar, the gust front echo are difficult to identify solely due to clutter noise. Therefore, thunderstorms warning based on the gust front echo only will lead to missing alarms. For small scale isolated bulk echo, there are no significant differences between the reflectivity characteristic of gale, precipitation and thunderstorm. If the gamma scale convergence appears on the radial velocity, it's not the unique features to the thunderstorms gale. Therefore, the isolated blocky echoes cause thunderstorms more difficult to make the gale warning.At present, the radial velocity of the large value area is a warning indicator of the thunderstorm gale. Whether there is an exceptional case needs to be verified in the future.