面向业务应用的上海地区毫米波云雷达观测质量评估

Operational usage-oriented evaluation of millimeter radar observations in Shanghai

摘要:

基于宝山国家基本气象站部署的毫米波云雷达2019年的观测数据,辅以激光雨滴谱、微雨雷达、探空资料、风云四号卫星产品、地面雨量计等多元观测数据,从探测稳定性、探测能力、基数据和产品数据探测合理性等方面开展了毫米波云雷达观测质量评估。结果表明:毫米波云雷达在试验期间仅出现单次软件故障,且基数据全年获取率高于95％,探测稳定性较好;毫米波云雷达各高度最小可测回波强度位于-40～-20 dBZ,并随高度呈现出与理论相符的指数递减;9 km高度以下最小回波强度变化小于2 dB,最小回波探测能力稳定性较高,在降水率达到4～5 mm/h时,毫米波云雷达会出现强衰减导致的虚假晴空区。虽然多部毫米波云雷达的基数据存在差异,但与地面雨滴谱计算回波强度和微型雨雷达观测回波强度具有一致的垂直分布及时间演变特征。毫米波云雷达探测云顶云底高度与探空资料估算云顶云底高度、风云四号卫星反演云顶高度具有一定的一致性。拼接缝和距离旁瓣虚假回波是较为直观且能够对业务化应用产生直接影响的问题。

Abstract:

The observational stability,observational ability,and rationality of both the base data and products of the millimeter cloud radar (MCR) installed at Shanghai Meteorological Service during “The study and experiment of vertically integrated meteorological observation technology in mega-cities” (MCME) are evaluated using observations from a ground-based lidar distrometer,a micro-rain radar,a radiosonde,FY-4A's products,and a surface rain gage.The results show that the observational stability of the MCR is considerably high,with only one software failure during the MCME and a data acquisition rate greater than 95％.The minimal detectable reflectivity of the MCR is generally distributed within -40 to -20 dBZ and has an exponential distribution in the vertical direction,which fits well with the theory.The minimal detectable reflectivity of the MCR changes little (less than 2 dB for heights lower than 9 km) during the MCME.A false “No Cloud” region is seen in the MCR's observation when the rain rate is larger than 4—5 mm/h.Although the raw data of the two MCRs have certain differences,the pattern of reflectivity in the time-height cross-section is highly reasonable,as indicated by comparisons between the reflectivity from the MCR's observation,the reflectivity calculated with the lidar distrometer's observation,and the reflectivity from the micro-rain radar's observation.The cloud top height and cloud base height retrieved by the MCR are also evaluated by the cloud top and base height calculated by the radiosonde and the cloud top height retrieved by the FY-4A satellite,and the results show a certain degree of consistency among the three observations.The inconsistency of reflectivity caused by the merging of multiple pulses with different pulse widths used in the MCR's base data processing and the false “clear sky area” caused by strong attenuation are two evident issues that may have significant impacts on the operational usage of the MCR.The paper concludes with recommendations on how to improve the current MCR in light of the requirements for the development of the Shanghai Meteorological Service.