Statistical analysis was performed on 404 samples of three-body scatter spike (TBSS) in 18 storm cells of 10 severe hailstorm processes in Changde and the surrounding areas,and the causes influencing TBSS observation were analyzed in detail.The conclusions can be drawn as follows.(1) Reflectivity intensity is the key factor for TBSS.As a factor causes TBSS features,the minimum reflectivity intensity should be 58 dBz.The more it is above this critical value,the easier TBSS will come into being.(2) The peak of TBSS can be reached under the following conditions:at altitude of 4 km or so,1.5° elevation,distance of 90 km or so,and the vertical distribution of the storm core echo intensity is a predominant impact factor during this process.(3) The frequency of TBSS is the most from 180° to 360°.Usually,longer length echo area in the leeward direction of wind storms can cause TBSS to be covered.This is the basic factor affecting the TBSS observation.The storm cells relative to the position and moving direction of radar usually decide whether there are echoes influencing TBSS observations in the radial outer side.(4) If intensity of TBSS echo and storm radial outer side weak echo are quite strong,the TBSS features can be identified from the storm radial outer side weak echo.%对常德及周边地区10次强雹暴过程中18个风暴单体产生的404次三体散射样本进行统计分析,并对影响三体散射观测的原因进行了详细分析.结果表明:(1)反射率因子强度是能否产生三体散射的关键因素,产生三体散射特征的最小反射率因子强度为58 dBz,在此临界值之上,反射率因子强度越强,越易产生三体散射;(2)风暴核回波强度的垂直分布是三体散射出现频数在高度4 km左右、仰角1.5°、距离90 km左右达到峰值的主要影响因素;(3)三体散射随方位分布在180°～360°出现频数最多,风暴单体移动下风方有径向长度较长的回波区时,导致三体散射特征被覆盖,是影响三体散射观测的根本原因,风暴单体相对雷达位置和移动方向通常决定径向外侧是否有影响三体散射观测的回波;(4)三体散射回波强度与风暴径向外侧弱回波相当或强时,三体散射特征能被识别.
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