微波辐射计反演大气廓线精度及降水预报应用

利用2018年6月—2021年7月陕西西安泾河站MWP967KV型地基微波辐射计反演数据和L波段探空数据, 分析晴天和云天(低云、中云、高云)微波辐射计反演的大气温度、相对湿度、水汽密度的精度, 探讨相关产品在降水过程中的应用能力。结果表明:晴天和云天微波辐射计与探空的温度相关系数均为0.99, 水汽密度相关系数均为0.97, 相对湿度相关系数均低于0.50, 均达到0.01显著性水平;晴天和云天的温度差异较小, 但云天相对湿度均方根误差超过25%, 较晴天的19.54%明显偏大, 且3种参数均越接近地面反演精度越高。在不同云类型条件下, 3类云的温度差异较小, 低云相对湿度均方根误差和偏差最大, 分别为26.85%和9.51%。对降水个例分析表明:在临近降水发生前空中相对湿度、液态水含量、大气可降水量和液态水路径均明显增长, 这可作为降水可能发生的指示因子。降水前1 h大气可降水量达到4 cm, 液态水路径达到0.2 mm, 可作为判断降水发生的参考阈值。

Accuracy of Atmospheric Profiles Retrieved from Microwave Radiometer and Its Application to Precipitation Forecast

Real-time and effective detection of atmospheric profiles is of great significance in understanding the evolution of climate system. Ground-based microwave radiometers can provide atmospheric temperature and humidity profiles with extremely high temporal and spatial resolution. Domestic MWP967KV microwave radiometer has effectively made up for problems of imported microwave radiometers, but there are relatively few studies on the performance evaluation and application of this microwave radiometer. In order to better apply data and products of MWP967KV microwave radiometer, inversion data from June 2018 to July 2021 at Jinghe Station of Xi'an are compared with L-band radiosonde observation. The accuracy of atmospheric temperature, relative humidity and vapor density retrieved from microwave radiometer under clear skies and different cloudy skies (classified as low cloud, middle cloud and high cloud, respectively) are analyzed, and the applicability of the related products in precipitation is further explored. Results show that correlation coefficients of temperature between microwave radiometer and radiosonde are 0.99, correlation coefficients of vapor density are 0.97, and correlation coefficients of relative humidity are less than 0.50 under clear skies and cloudy skies, all passing 0.01 significant test. The difference of temperature between clear and cloudy skies is small, but root mean square error of relative humidity in cloudy skies is more than 25%, which is significantly larger than that in clear skies. It indicates that the presence of clouds reduces the accuracy of the humidity inversion, causing large errors, and the inversion accuracy is higher near the ground. Under different cloud types, the temperature difference is small, while root mean square error and bias of relative humidity in low cloud are the largest, which are 26.85% and 9.51%, respectively. In addition, a case analysis shows that relative humidity, liquid water content, atmospheric precipitable water vapor and liquid water path increase significantly before the occurrence of precipitation, which can be used as indicators of the possible occurrence of precipitation. Statistic results show that the atmospheric precipitable water vapor reaches 4 cm and liquid water path reaches 0.2 mm during several precipitation cases, and these indexes can be used as the reference threshold for judging the precipitation of Xi'an.