地基GPS/PWV在降水过程中的突变与缓变性特征

Mutation and gradual variation characteristics of ground-based GPS/PWV during precipitation

用江苏省2009—2011年57个地基GPS/MET监测网获取的逐时大气可降水量(PWV)和同期降水及JMA(Japan Meteorological Agency)再分析资料,探讨了PWV的日际和逐时变化与不同时间尺度和强度的降水间的关系。结果表明:PWV日际变化与降水日变化具有显著相似的形态特征和演变趋势,两者存在较为一致的同步性,总体呈单峰分布,强降水集中期对应着PWV最大时段;PWV在入梅和梅汛期内强降水过程中存在明显突变现象,并提炼了以GPS/PWV突变事件为依据的入梅和梅雨期暴雨预报指标;在不同强度的降水过程中,PWV值域局限在一个特定量值区间,其中20 mm/h以下各级强度降水对应PWV区别明显,GPS/PWV值对应的特定量值随降水强度增大而增大,但20 mm/h以上的各级强降水对应PWV特定量值区别较小;在短时强降水的预报中,除充分的水汽条件外,其强度将取决于天气系统对周边水汽的辐合能力和将入流水汽抬升而成云致雨的动力条件;降水发生前存在水汽的连续、缓变蓄积过程,蓄积过程至少可推前12 h。

Based on the hourly atmospheric precipitable water vapor （PWV）, the rainfall amount in the same period and Japan Meteorological Agency （JWA） reanalysis data from 57 ground-based GPS/ MET monitoring net during 2009-2011 in Jiangsu province, the relation between the diurnal, hourly var- iation of PWV and the precipitation with different time scales and intensities was preliminarily discussed. Results showed that firstly, the diurnal variation of PWV had significant similar morphological character- istics and evolution trend with the daily variation of precipitation, both of which had a synchronous con- sistency and a unimodal distribution was obvious, the precipitation centralized period corresponded to the maximum period of PWV. Secondly, at the beginning and during the Meiyu period, an obvious mutation apeared in PWV and the forecasting index of heavy rainfall was developed, based on the GPS/PWV mu-tation events. Thirdly, in the processes of precipitation with different intensities, PWV value was limited in specific range. For the precipitation amount below 20 mm/h, their corresponding PWV were obviously different. With the precipitation intensity strengthening, the corresponding specific value of GPS/PWV increased. However, for the precipitation amount over 20 mm/h, their corresponding PWV were almost similar. Fourthly, in short-term rainfall forecasting, the rainfall intensity not only depended on abundant water vapor, but on the surrounding water vapor convergence ability of weather system and the dynamic condition of cloud and rainfall formation by uplifting the inflow of water vapor. Finally, precipitation had a continuous, gradual accumulation process of water vapor, which would at least last 12 hours.