下沉气流对Z-I关系的影响

The Effect of Downdrafts on Z-I Relation

采用伽玛分布形式的雨滴谱表达式 ,讨论了下沉气流W对Z I关系的影响。发现随着W (向下为正 )增大 ,关系式Z=AIb 中系数A值减小 ,b值增大。利用地面实测雨滴谱资料计算出不同下沉气流下Z、I后回归得到的A、b值 ,以及根据由平均谱拟合得到的伽玛分布参数计算出A、b值 ,它们随W改变的变化趋势 ,均与理论分析结果一致。还讨论了环境气压场 p对Z I关系的作用 ,气压减小时 ,A值减小 ,b值增大 ,但变化不如W影响时的变化明显。此外 ,结合实测雨滴谱资料 。

The analysis using Gama type raindrop distribution show that the effect of downdrafts W on the relation between the radar reflectivity factor Z and the precipitation rate I should not be neglected when its dimension reaches or exceeds 5×10 1 cm·s -1.In the form Z=AI b,the coefficient A decreases and the exponent b increases as W increases,which is in agreement with the results from two cases computations well.The influence of the ambient pressure field p,which actually reflects the role of air density,is also analysed and the results indicates that A decreases and the exponent b increases as p decreases.In addition,some results of the discussion on the micro-physics characteristics of the raindrop spectra observed in two cases are presented.