两次降水过程的微降雨雷达探测精度分析

Precision Evaluation of Micro Rain Radar Observation in Two Precipitation Events

垂直指向微降雨雷达(MRR)能够测量从近地面至高空的雷达反射率因子和雨滴谱分布特征,对认识降水微物理结构,改进雷达定量降水估计精度有重要作用。为评估MRR探测的雨滴谱分布、降水和雷达回波精度,利用南京地区夏季观测的两次降水过程,将MRR与业务S波段天气雷达、二维视频雨滴谱仪、常规雨量筒观测进行层状云降水和对流性降水下的定量对比分析。结果表明,MRR垂直探测的雷达反射率因子与S波段雷达观测在中低层(<4 km)平均差异<1 dB,但高层(>4 km)出现显著低估,且该现象随降水强度增强更明显,这主要是雷达回波衰减导致。MRR在回波强度<35 dBz时对降水率的探测精度较高,但在>35 dBz时低估降水。其中,层状云降水的降水率比对流性降水更接近雨量筒观测。常规雨量筒对0.1 mm以下的降水无探测能力,而MRR探测敏感度较高,对于微弱降水率的估计效果也很好。由于MRR最大探测范围的限制,相对于2DVD而言,MRR探测的最大粒子直径低估、最小粒子浓度高估,但在中间段的探测效果和2DVD雨滴谱观测一致性较高。总体而言,MRR是一个有效的降水探测仪器,其探测结果在层状云降水过程中优于对流性降水过程。

MRR is a vertically pointing Micro Rain Radar which can measure vertical profiles of radar reflectivity and drop size distribution(DSD).It plays an important role in understanding precipitation microphysical structure and improving quantitative precipitation estimation.In this study,the observations from an S-band Doppler radar,a 2D-Video-Disdrometer and a rain gauge during two summer precipitation events in Nanjing are used to assess the performance of MRR.The intercomparison analyses of these four instruments in stratiform and convective precipitation are also performed.The results show that,the vertical profile of reflectivity measured by MRR and S-band radar has a good agreement below 4 km with the mean difference less than 1 dB.Above 4 km,however,MRR tends to underestimate the reflectivity due to the precipitation attenuation.The difference of reflectivity between MRR and S-band radar increases with the height.Furthermore,MRR can accurately estimate the rain rate with the reflectivity below 35 dBz,but underestimate the rain rate with the reflectivity above 35 dBz.The rainfall estimation for stratiform clouds is more accurate than that for convective clouds.Especially,MRR exhibits good performance for the weak rainfall below 0.1 mm·h^(-1),which cannot be measured by rain gauge.Due to the inherent limitation of MRR and the precipitation attenuation,MRR shows high consistency with 2DVD for raindrops with size from 1 mm to 5 mm,but underestimates the concentration of drops larger than 5 mm and overestimates the concentration of drops smaller than 1 mm.Overall,MRR is an effective instrument for the precipitation measurements,especially suitable for quantitative estimation of stratiform.