基于西南涡加密探空资料同化的一次奇异路径耦合低涡大暴雨数值模拟研究

A numerical study on a heavy rainfall caused by an abnormal-path coupling vortex with the assimilation of southwest China vortex scientific experiment data

中文关键词:  西南涡  高原涡  WRFDA  西南涡加密探空资料  涡度方程

英文关键词:SWCV  TPV  WRFDA  Intensive sounding data of SWCV  Vorticity equation

中文摘要:

      利用WRF模式及WRFDA同化系统，引入业务探空资料和西南涡加密探空资料，对一次四川盆地奇异路径低涡耦合大暴雨过程进行了数值试验，对比检验不同同化试验对本次过程降水和低涡移动路径的模拟能力，分析了加密探空资料同化对西南涡结构及其降水演变的影响。结果表明：在同化业务探空资料的基础上，引入西南涡加密探空资料能改善模式对本次降水和低涡移动路径的模拟，而仅同化业务探空资料对模拟结果的改善作用有限；引入西南涡加密探空资料，一方面能在初始风场上产生气旋式扰动，增加初始高原涡和西南涡的强度，另一方面通过调整初始四川盆地上空大气温、湿度结构，使模式在积分初期就能产生出实况量级的降水；西南涡加密探空资料的同化试验揭示了仅靠高层的高位涡不足以激发和维持700 hPa的西南涡，需要通过低层水平辐合引起正涡度增加并向上输送来增强700 hPa的气旋式环流，进而促进西南涡的移动和发展，而模拟初期降水的潜热释放也起重要作用，加深了对西南涡及其降水成因的认识。

英文摘要:

      Using the Weather Research Forecast (WRF) model and WRF data assimilation system (WRFDA), sensitivity experiments are conducted to simulate a heavy rainfall caused by the coupling of the Tibetan Plateau vortex (TPV) and an abnormal-path southwest China vortex (SWCV) in Sichuan Basin with assimilation of operational sounding data and the intensive observed data obtained through the SWCV Scientific Experiment. The model simulations of precipitation and the vortex moving path using different initial conditions are compared, and the impacts on the structure evolution of the SWCV and associated precipitation by assimilating intensive sounding data are analyzed. The results show that the model capability for the forecast of precipitation and the moving paths of TPV and SWCV is improved by assimilating both intensive sounding data and conventional sounding data, while the forecast is less satisfactory with assimilation of only the conventional sounding data. By introducing intensive sounding data, the intensities of initial TPV and SWCV are enhanced due to the increased cyclonic perturbation on the initial wind field. In addition, the more unstable stratification adjusted by data assimilation makes it easy for the model to produce large precipitation with a magnitude that is consistent to observation at the initial time. The experiment reveals that the generation and maintenance of the SWCV at 700 hPa in this case not only rely on high potential vorticity in the upper levels, but also rely on increases in positive vorticity caused by horizontal convergence in the lower levels and its upward transport, which is favorable for the SWCV to develop and move. Latent heat release associated with precipitation at the beginning of the simulation also plays an important role in the development of SWCV. Results of the present study are helpful for better understanding the mechanisms for the development of SWCV and associated precipitation process.