一种新的综合物理指数构建及其在强降水预报中的应用

强降水是洪灾及相关衍生灾害的最主要原因之一,而过去单靠某一种变量诊断预报强降水,具有较大难度.本文在已有研究的基础上,根据强降水发生发展的物理机制,将引起降水的热力、动力和水汽条件综合考虑,尝试性地构建了一个新的综合指数THP(Temperature, Helicity and Precipitable water).然后针对两次强降水过程,利用NCEP/NCAR 1°×1°的再分析资料和地面常规观测资料,对THP指数进行了诊断分析,并选用2012年7月1日-8月15日的降水实况,对该指数进行了普适性检验.结果表明:(1) THP指数的变化可以有效表征强降水过程的发展和移动.对于降水落区的预报,THP指数的大值区与未来6 h的降水中心基本对应;对于降水发生时刻的预报,THP指数的位相变化超前于地面降水的变化,具有较好的指示性;(2) 对于高空槽前型降水,THP指数对降水强度也有一定的诊断意义,且普适性检验表明,该指数在我国中东部地区的盛夏期间具有良好的适用性;(3) 基于配料法的思想,THP指数将有利于强降水出现的、具有清晰物理意义的信号进行了集成,相比于表征单一物理量的指数,其稳定性得到了增强.

Construction of a new index and its application to forecasting heavy rainfall

Heavy rainfall is a severe weather occurring frequently in summer across China. It can not only bring urban waterlogging, landslides, but also cause huge losses of life and property. While it is difficult to forecast depending on the single physical parameters or only based on routine numerical weather prediction. At present the 6-hour-interval TS score of heavy rainfall is just 2.6% in China, much lower than the scores of the wind and temperature fields, so the forecast accuracy of strong precipitation still needs to be improved. From previous research, the occurrence of heavy rainfall has a very close relationship with convective parameters. Therefore it is of particular importance to find an integrated and convenient parameter to characterize the formation mechanism of heavy rainfall.#br#As the atmosphere is an organic combination of dynamic and thermal fluids, and precipitation is the result of many factors in the atmosphere, so the key of precipitation forecasting is data processing and mining strong signals from various early physical quantities. Base on the Ingredients-Based Methodology (IM), this paper introduces a new physical parameter THP (Temperature, Helicity and Precipitable water), which contains atmospheric thermodynamics, dynamics and moisture factors. Using NCEP/NCAR reanalysis data (time resolution every 6 h, spatial resolution 1°×1°) and ground observational data in China, the THP index was diagnosed and analyzed in two heavy precipitation processes in detail. And then, the universality of THP was tested according to precipitation observational data from July 1 to August 15, 2012.#br#The analysis and comparison show that the THP index can provide good direction to the distribution and the movement of summer heavy precipitation, and heavy rainfall is located in the high value area of THP. The variation of THP is ahead of changes in observational precipitation, so THP index can also give a good reference to the beginning and ending time of heavy rain. The THP value is of certain indicating significance to predication of rainfall intensity. Moreover, judging from the inspection effect, the THP index has a good applicability during summer in China mainland. Because the major affecting factors of rainstorms are considered in THP index, the stability of THP is superior to the method of using single physical parameters in forecasting analysis. And compared with some conventional physical parameters, the THP value shows a better correspondence to the precipitation rainfall area in the following 6 hours.#br#The THP index can reflect the characteristic and mechanism of heavy rainfall, and the bigger of the THP value, the bigger probability of rainstorms. Therefore, as a forecaster parameter, the THP index plays a positive role in forecasting heavy rainfall. Besides, the IM method has a clearly physical meaning, and can be used more widely to forecast the locations of other disasters, such as thunderstorms, wind gusts and hail, so as to improve the forecasting level of severe convective storms.