毫米波云雷达功率谱密度数据的检验和在弱降水滴谱反演中的应用研究

Examination and Application of Doppler Spectral Density Data in Drop Size Distribution Retrieval in Weak Precipitation by Cloud Radar

本文首先利用数值模拟的方法,分析了利用毫米波云雷达功率谱密度反演雨滴谱时,降水粒子米散射效应、空气湍流、空气上升速度等对雨滴谱和液态水含量等参数反演的影响;建立了功率谱密度处理及其直接反演雨滴谱、液态水含量、降水强度和空气上升速度的方法;并利用2012年7月在云南腾冲观测的二次弱降水数据,采用毫米波雷达和Ku波段微降水雷达观测的回波强度、径向速度垂直廓线以及780 m高度上的功率谱密度对比的方法,以及毫米波云雷达观测的780 m高度上功率谱密度、回波强度与地面雨滴谱计算得到的这些量的对比方法,分析了毫米波雷达数据的可靠性;并将780 m高度上毫米波雷达反演的雨滴谱与地面雨滴谱数据进行了对比,分析了毫米波雷达反演的雨滴谱的准确性;分析了毫米波雷达回波强度偏弱的原因,讨论了该高度以下降水对毫米波雷达衰减的影响。结果表明:空气湍流对弱降水微物理参数反演影响不大,而空气上升速度和米散射效应均对反演结果有一定影响;毫米波雷达观测到的径向速度和功率谱密度与微降水雷达比较一致,回波强度的垂直廓线的形状与微降水雷达也比较一致,但毫米波雷达观测的回波强度偏弱;与雨滴谱计算值相比,毫米波雷达观测的低层的回波强度也偏弱,天线上的积水是造成毫米波雷达回波强度变弱的主要原因。毫米波雷达观测的低层的功率谱密度与地面雨滴谱观测的数据形状比较一致,但有一定的位移。毫米波雷达反演的雨滴谱与地面观测的谱型和粒子大小也比较一致。这些结果初步验证了毫米波雷达观测的功率谱密度及其反演方法的可靠性。

The effects of Mie Scattering, air turbulence, and air vertical speed on drop size distribution （DSD） retrieval from Doppler spectral density data observed by cloud radar are discussed in this study. The processing algorithm for the Doppler spectral density data and retrieval algorithm for DSD, liquid water content （LWC）, rain rate, and air vertical speed with Doppler spectral density data are presented. The two weak precipitation cases observed by vertical-pointingKa-band cloud radar, Ku-band micro-rain radar, and disdrometer in July 2012 at Tengchong, Yunnan Province, are used to examine the cloud radar data quality and retrieval algorithm. The vertical profiles of reflectivity and velocity observed by cloud radar and micro-rain radar are compared. The Doppler spectral density data at an altitude of 780 m observed by cloud radar, micro-rain radar, and disdrometer calculation are compared. In addition, the DSD and rain rate are retrieved by Doppler spectral density data and compared with disdrometer data. The effect of water over the cloud radar antenna on reflectivity measurement is also discussed. The results indicate that although the effects of air turbulence on precipitation microphysical parameters are negligible, those of air vertical speed and Mie scattering are obvious. The velocity, Doppler spectral density data, and variational pattern of reflectivity with altitude observed by cloud radar and micro-rain radar show good agreement; however, the reflectivity measured by the cloud radar was weaker than that observed by the other methods. The water over the cloud radar antenna significantly reduced the reflectivity. The Doppler spectral density data and DSD observed by the cloud radar were similar with that observed by disdrometer. Therefore, this study has verified the effectiveness of Doppler spectral density data measurement by cloud radar and retrieval parameters.