基于GNSS实时水汽信息的暴雨短临预报研究

It is very difficult to accurately monitor and forecast precipitation time, precipitation intensity and precipitation area of local torrential rainstorms due to their limitations of radiosonde, microwave radiometer and weather radar respectively. In this contribution, a new approach including theories and methods for rainstorm nowcasting is presented, which uses the real-time water vapor information from GNSS observations. To resolve the real-time problems of undifferenced precise point positioning (PPP) for the rainstorm nowcasting, this subject focuses on the study of estimation of real-time satellite clock biases and acquisition of real-time water vapor information. Based on the real-time water vapor information, the variation characterizations of water vapor and its horizontal gradient are analyzed. Meanwhile, the congruent relationship between the accumulation time, increment variation and high-level duration time of water vapor and the rainstorm information including precipitation time and precipitation intensity is ascertained. On the basis of the spatial and temporal distribution of water vapor, the variation characterization of horizontal gradient of water vapor and the atmospheric dynamics and thermodynamic conditions, the quantitative indexes of precipitation time, precipitation intensity and precipitation area are abstracted to improve the precision rate of rainstorm nowcasting under the existing weather forecast system, and to provide the reliable theoretical basis for rainstorm nowcasting by using GNSS.

由于探空仪、微波辐射计和天气雷达在暴雨短临预报应用中各有局限，实时监测并准确预报局地特大暴雨的降水时间、强度及其落区成为难点。本课题提出一种基于GNSS实时水汽信息进行暴雨短临预报的理论与方法。针对非差精密单点定位（PPP)在暴雨短临预报应用中需要解决的实时性问题，课题拟重点研究高精度卫星钟差实时估计、实时水汽信息快速获取等方法。在快速获取水汽信息的基础之上，实时监测并分析水汽及其水平梯度变化特点，探明暴雨来临之前水汽积累时间、增降速率和维持在高水平状态的时长与后续暴雨降水时间及强度之间的对应关系；依据水汽时空分布以及水平梯度变化特点，结合大气动力和热力条件，提炼短临预报暴雨发生时间、降水强度及落区的定量指标，提升现有天气预报系统的暴雨短临预报准确率,为基于GNSS观测进行暴雨短临预报提供可靠的理论依据。

由于探空仪、微波辐射计和天气雷达在暴雨短临预报应用中各有局限，实时监测并准确预报局地特大暴雨的降水时间、强度及其落区成为难点。项目负责人及项目组成员查阅了国内外与实时PPP-ZTD获取、ZTD到PWV转化和PWV平面与动态变化显示分析等方面的相关研究资料，并申请获取了本项目研究所需的部分相关数据（主要包括区域参考站网的GNSS观测数据及其相应的气象观测数据）。主要研究内容包括高精度水汽信息的实时获取理论与方法；开发一套可实时监测与分析水汽时空动态变化特征的GNSS/PWV动态变化监测与分析系统；建立一套适合湖南地区的加权平均温度Tm本地化估算模型；对高频水汽信息进行时间序列分析，探明暴雨来临之前水汽的积累时间、增降速率以及维持在高水平状态时长与后续暴雨降水时间和强度之间的对应关系，归纳暴雨发生前后的变化特点和规律。结合大气热力和动力条件，分析水汽时空分布图及其水平梯度变化，总结降水范围及其发展规律。提炼短临预报暴雨发生时间、降水强度及落区的定量指标，提升现有天气预报系统的暴雨短临预报准确率,为基于GNSS观测进行暴雨短临预报提供可靠的理论依据。