河北省雷暴大风的雷达回波特征及预报关键点

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

应用河北省石家庄新乐CINRAD-SA雷达资料对2006—2008年河北省中南部地区262个站雷暴大风的雷达回波特征进行统计。分析发现,雷暴大风的主要雷达回波特征有弓形回波、阵风锋和径向速度大值区,出现其中一个或多个特征均可发布雷暴大风预警。根据以上雷达回波特征能够对66%的雷暴大风发布预警,34%的雷暴大风仅仅依据雷达资料无法预警,其中孤立块状回波占39%,带状回波占61%。弓形回波仅占雷暴大风的19.8%,能够观测到的阵风锋回波仅占16.8%,65.3%的雷暴大风观测到径向速度大值区,径向速度大值区是雷暴大风最重要的雷达回波特征。径向速度大值区的形成一般早于弓形回波和阵风锋回波,依据径向速度大值区可更早发布雷暴大风预警。

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 16.8M of cases, and thunderstorm gales high speed value area can be observed 65.3%of ca- ses. Therefore, the high speed value area is the most important characteristics of radar echoes. The forma- tion 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 ra- dar. 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 thun- derstorms 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 he verified in the future.