GPS/MET误差分析及其在降水预报中的应用

GPS/MET反演的大气可降水量产品具有近实时、全天候等优点,可为全国水土保持领域的组网监测提供更多的数据支持,GPS/MET的数据质量对降水预报分析尤为重要.本研究将GPS大气可降水量与探空、微波辐射计进行对比,分析GPS/MET的数据质量;同时,分析GPS大气可降水量与地面降水的关系,探索GPS/MET在邻近降水预报中的作用.结果显示:1)2015年GPS大气可降水量与探空、微波辐射计的演变趋势总体一致,波峰和波谷有很好的对应性,全年看整层大气水汽含量存在着明显的月际变化,随时间呈单峰曲线分布;因此GPS/MET能较好的反映大气中可降水量随时间的变化.2)虽然GPS/MET与微波辐射计、探空2种探测手段的平均偏差较大,但是离散程度不大,说明GPS/MET与其余2种探测方法之间存在稳定的系统误差.3)大气可降水量在地面降水发生前十几个小时开始增大,随后维持在一个高值的水平上,说明在降水前大气中有一个明显的水汽积累的过程.地面降水发生时大气可降水量达到最大值,降雨强度的极大值与可降水量的极大值有很好的对应.地面降水过程结束后,可降水量量迅速下降.4)大气可降水量的极大值是降水产生的必要条件.综合考虑降水次数和降水概率后,选取大气可降水量连续4h增加6 mm以上为判断降水发生的依据之一;因此,GPS/MET数据质量较可靠且在降水预报中具有指示性作用,作为气象和水土保持学科交叉的纽带,可为水土保持业务和决策部门决策分析和制定方面提供数据支撑.

Error analysis of precipitable water vapor by GPS/MET and its application in precipitation forecast

Background] The products of Precipitable Water Vapor (PWV) retrieved by GPS/MET (GPS/Meteorology) have the advantages of near real-time and for all-weather,etc.,which provide more data sets for network monitoring in soil and water conservation field,thus,the data quality and the role of PWV is particularly important in precipitation forecast.Methods] Comparing the PWV retrieved by GPS/MET with those observed by sounding and microwave radiometer,the data quality of GPS/MET was analyzed.The relationship of PWV retrieved by GPS/MET and ground precipitation was analyzed,and the role of PWV in precipitation forecast was investigated.The PWV data sets used in the paper which contained GPS/MET,sounding and microwave radiometer detections were observed in 2015 at Zhangqiu station located at Jinan,capital of Shandong province,an eastern city of China.The data set of rain intensity recorded by ground automatic weather stations was also used.Results] 1) The evolution trend of PWV retrieved by GPS/MET,sounding and microwave radiometer in 2015 was consistent,and peaks and troughs presented a well correspondence.Throughout the year,there was a clear monthly variation of PWV,showing a single peak distribution with time.Therefore,GPS/MET may reflect the variation of PWV in the atmosphere over time.2) Although the biases between GPS/MET,microwave radiometer and sounding were large,the dispersion degree was not large,indicating that there was a systematic error between GPS/MET and the other two methods.3) PWV started to increase about 10 hours before precipitation to the ground,and then maintained at a large value,indicating that the there was an obvious process of water vapor accumulation before rainfall.PWV reached the max value while precipitation started,the max rain intensity corresponded to max PWV well.After precipitation ended,the PWV fell rapidly.4) The max PWV was the prerequisite of rainfall.The greater PWV value observed by GPS than average was,the larger the probability of precipitation was.For Zhangqiu station,considering the times and probability of precipitation comprehensively,the PWV increasing more than 6mm in consecutive 4 hours was selected to be an evidence of the precipitation happening.Conclusions] Based on the well matching of PWV observed by GPS with the other two detections (sounding and microwave radiometer),PWV data set retrieved by GPS/MET was reliable,and played an indicative role in precipitation forecast by analyzing the relationship between PWV and rain intensity.As an interdisciplinary link between meteorology and soil and water conservation field,GPS/MET may provide data support for decision-making section and in soil and water conservation practice.