摘要
在北京2004年的45次降水过程中,基于DISDROMETER仪器测量的雨滴谱资料计算每次降水的强度R和雷达反射率因子Z。结果表明,不同降水过程中,雷达反射率因子Z与降水强度R的幂指数关系中的指数b和系数a是不同的,这与不同降水过程的雨滴谱分布不同密切相关。综合分析这45次降水过程中的指数b和系数a,得到指数b和系数a呈正相关。接着,分别就指数b和系数a与平均降水强度、平均雷达反射率因子、平均特征直径和雨滴平均数密度之间关系做了详细的讨论。另外,基于这一年的降水雨滴谱资料,讨论了Z-R幂指数关系中指数b和系数a的月变化特征。分析结果表明,从4月到12月系数a和指数b呈现逐月递减的年变化特征。最后,文章就12个个例的特征直径Dm的特征进行了分析。结果显示,当特征直径Dm随时间保持不变时,降水强度R和雷达反射率因子Z之间存在线性相关的关系,即当特征直径Dm为常数时,Z-R关系的指数b为1。
The rain rate R and radar reflectivity factor Z were calculated based on the raindrop size distribution data of 45 precipitation events measured in Beijing during 2004 by a Disdrometer, which has 20 channels and measures the raindrop diameter from 0.35 mm to 5.0 mm. For different precipitating clouds, the relationships between R and Z, or coefficient a and exponent b, are quite different, that maybe attribute to different raindrop size distributions. At the same time, the Z-R relationship over land is also different from that over the sea. There is a positive correlation between a and b in these 45 events of precipitation. The relationship between coefficient a （or exponent b ） and some physical quantities, such as rain rate R, radar reflectivity factor Z, characteristic diameter Dm and raindrop number density NT is analyzed, respectively. When R 〈 5 ram/h, or NT〈1000 m^- 3, or Z〈 2000 mm^6 / m^3, coefficient a （or exponent b） changes greatly, and when R, or NT, or Z gradually increases, coefficient a （or the exponent b） approaches to a constant value. Both coefficient a and exponent b decreased from April to December in 2004. Moreover, the characteristics of Dm derived from the raindrop size distribution data of 12 precipitations are analyzed, and the results show that there is a linear correlation between R and Z, in other words, exponent b is 1, when Dm is a constant.
出处
《气象学报》
CAS
CSCD
北大核心
2008年第1期125-129,共5页
Acta Meteorologica Sinica
基金
973项目“空间微波遥感地海表和大气数据验证”课题(2001CB309402)
国家基金委项目(40428006和40227001)
