北京一次对流暴雨过程的干冷空气活动及作用

Activities of Cold-Dry Air and Its Impact on Convective Heavy Rain Process in Beijing

利用常规观测资料、1°×1°NCEP再分析资料、微波辐射计及风廓线雷达等加密观测资料,针对2011年6月23日北京地区发生的一次强对流暴雨过程,对高低层干冷空气活动及其作用进行了分析。结果表明:北京地区高低层配置符合干侵入三维模型,中层以上的干区与水汽图像的暗区相吻合,同时配合有自高纬向低纬传播的高位涡带,北京地区干侵入特征明显。微波辐射计与风廓线雷达观测能够实时追踪干冷空气造成的温度、湿度和风场变化,6 km高度以上的温度和湿度变化最为显著,两者下降到最低点的时间与强对流的触发时间有较好的一致性,高层干冷空气对强降水有一定激发作用。干侵入降低了大气稳定度,造成高层θse低值中心垂直位于低层θse高值中心之上,探空曲线呈典型的喇叭形开口结构。回流干冷空气与气旋前部暖湿气流形成准静止锋,850 h Pa以下低层温度锋区显著,为对流的发展加强提供了热动力条件,回流冷空气形成的东部高压有利于雷暴系统在北京地区滞留,延长了降水时间。

By using conventional observation data,radar reflectivity,1° × 1° NCEP reanalysis data and unconventional observations including wind profile radar and ground-based radiometer data,the cold air and its influence was studied according to a strong convective storm in Beijing area on 23 June 2011. The main results are as follows: The dry zone and high potential area above middle-level corresponded well with dark zone in WV image,which showed the dry intrusion was obvious. The temperature,humidity and wind changed instinctly which was observed by the ground-based radiometer and profile radar,the storm was triggered just after the temperature and humidity above 5 km decreased to the lowest. The dry intrusion caused the lowθsecenter just over the highθsecenter,which led to strong convective instability. The lower level northeast airflowwas cold and dry,and the corresponding temperature front was distinct under 850 h Pa,which provided dynamical and thermal effect for the development of the convective system. The backflowcold formed anticyclone on the east of Beijing,which was good for the convective system to stay at Beijing and the rainfall to sustain longer.