关键词: 华北暴雨, 数值模拟, 急流, 干侵入, 动力场耦合

Abstract:

A heavy rainstorm occurring in North China during 18-19 August 2010 was simulated by using WRF3.2 (Weather Research and Forecasting Model for version 3.2) and NCEP reanalyzed meteorological data with 1° × 1° grid. Based on reasonable simulation results, the dynamical, thermal mechanism of the heavy rain formation and the interaction of the mesoscale weather systems were analyzed. Results show that under the beneficial circumstance of the high, medium and low system configuration, the northern cold air driven by high altitude vortex met with warm wet air from the edge of the subtropical high in North China, which provided the favorable weather conditions for the heavy rain. The strong rainfall took place on the left front side of the low jet, and the low jet played an important role in this case. The strengthening of a high-level jet stream and its momentum downward spreading made the maintenance of the low level jet, and the coupling of the high and low-level jets provided a proper dynamical condition for the occurrence and development of the torrential rain process. The atmospheric air presented convective instability below 650 hPa during the period of heavy rainfall, at the same time the K index was more than 35 ℃ in North China, strong precipitation appeared in the process of K index gradient increasing significantly. The cold air from upper troposphere invasion in the middle and lower layer was one of the reason causing the strong precipitation, and the strong precipitation occurred when the low-level warm advection was upward and upper-level cold advection was downward.

Key words:  heavy rainfall in North China, numerical simulation, jet, dry invasion, coupling of dynamic field