摘要
利用国产对流层Ⅱ型风廓线雷达资料对2012年3月17日北京地区经历的雾霾雨雪多相态天气过程进行了诊断分析,结果表明风廓线雷达探测产品能够很好地判别上述天气的发展转变过程,可以揭示降水过程的细节变化。雾霾维持时,风廓线雷达一般能够探测到非常弱的水平风和大气垂直运动,大气折射率参数很小,而近地面层信噪比则表现出较强的信号,高度一般在850 hPa以下,其上层大气的信噪比很弱,表现为晴空状态,上下对比度非常明显。同时,风廓线频谱高度图表现为无降水特征。降水发生前,对流层的信噪比会明显增强,风廓线雷达垂直波束的径向速度V_r首先在中高层出现正值,反映出下沉运动的不断增强现象,同时其他两对对称波束V_r不再维持对称形态。降水发生时,5个波束V_r自地面向上均转变为正值,且最大速度一般位于近地面层,同时最大V_r也不集中在垂直波束,反映了降雨过程中存在着风的影响。此时,谱宽一般稳定维持在1~2 m·s^(-1)。当降水发生相态转变时,谱宽会有明显的减小,信噪比增强,频谱图中V_r有所减弱,这种变化通常发生在整个边界层到对流层。降水结束时,上述现象成相反变化,谱宽增加,信噪比减弱,5个波束V_r呈对称形态。
A multi-phase weather process with fog,haze,rain and snow seen in Beijing on 17 March 2012 is analyzed by using wind profile radar data.The results show that the profiler products are good at diagno-sing and distinguishing weather change and evolution,and can reveal the detailed variation of precipitation. The profiler is usually used to detect weak horizontal wind and weak vertical movement of atmosphere in case of fog.Its air refractive index is small while signal noise ratio (SNR)below 850 hPa is strong.Simul-taneously,the profiler frequency spectrum shows the features of clear weather.Before it rains,the SNR in troposphere remarkably strengthens,the profiler vertical beam radial velocity (Vr)firstly presents positive values,in the mid-and high-levels,which indicates the air sinking motion is enhanced.At the same time the other two double beams (Vr)are not symmetrical anymore.When it rains,all the five beams (Vr)of profiler turn positive from surface to upper air,and the largest Vris near surface,not concentrated in the vertical beam.Correspondingly,spectrum width maintains in 1 - 2 m · s-1 .When precipitation phase changes,spectrum width diminishes obviously while SNR strengthens,and the Vrgets weakened.These changes usually occur in the whole boundary layer to troposphere.When rain stops,the above changes show reverse features,including spectrum width increases,SNR weakens,and all the five beams return to symmetrical state.
出处
《气象》
CSCD
北大核心
2014年第8期992-999,共8页
Meteorological Monthly
基金
公益性行业(气象)科研专项(GYHY201306076)资助
关键词
多相态
风廓线雷达
特征分析
multi-phase weather
wind profiling radar
feature analysis
