垂直指向的Ka波段云雷达观测的0℃层亮带自动识别及亮带的特征分析

Characteristics of Bright Band and Automatic Detection Algorithm with Vertical Pointed Ka Band Cloud Radar

利用2013年垂直指向的Ka波段云雷达在广东观测的弱降水个例,分析了回波强度Z、径向速度Vr和退偏振因子L_(DR)在0℃层附近的变化规律,利用建模样本提出了基于云雷达垂直观测Z、Vr和L_(DR)数据的0℃层亮带自动识别方法,并利用独立观测样本进行了识别算法的检验,分析了Vr数据对识别效果的影响,与每天四次探空得到的数据进行了对比。结果表明,在0℃层亮带内,Z和L_(DR)的极大值的高度和Z、Vr、L_(DR)这三个物理量在垂直方向上的突变范围都一致,0℃层亮带的厚度与Z、Vr和L_(DR)的变化量有一定的关系,在0℃层亮带特征较明显的回波上部也存在明显的空气上升运动。Vr和L_(DR)是识别0℃层亮带的关键因子,而Z可能因云的位置和复杂的云层而产生剧烈的垂直变化。该算法可以较好识别典型的0℃层亮带,正确提取主要参数,而云的边缘和多层云等情况会影响0℃层亮带的识别。为利用Ka波段云雷达数据分析弱降水的性质提供了算法。

Reflectivity（Z）,radial velocity（Vr） and depolarization ratio（L_（DR）） in weak precipitation in Guangdong were observed by vertical pointed Ka band cloud radar in 2013.The statistical characteristics of bright band（BB） are analyzed and the automatic algorithm to detect BB is developed based on the vertical profiles of Z,Vr and L_（DR）.The sounding data are used to examine the detection algorithm.The results show that the sharp variations patterns of Z and L_（DR） with height and positions with maximum Z and L_（DR） are similar.The ranges with sharp variations of Z,Vr and L_（DR） are corresponding well.The thickness of BB is obvious correlation with Z,variations of Vr and L_（DR） within BB.The updrafts often exist in the top of cloud for bright band case.Vr and L_（DR） are key factors for detection of BB,however sharp variations of Z often occur in the edge of cloud system.The detection algorithm could detect the typical BB and non-BB,the cloud edge and multi-layer cloud could affect the detection algorithm.This work provides the productions for cloud physical research.