The Study On Numerical Simulation Of A Severe Rainstorm Brought By A Landing Northward Tropical Cyclone (Typhoon)

A briefly summarization for the general law of rainstorms in northeast China was presented in this paper. And the scientific research situation about heavy rain in both China and abroad was outlined. Using fifty years typhoon annals data, we analyzed the statistic characteristics about spatial and temporal distribution of typhoon, which may influence Liaoning province.A severe rainstorm over Liaoning occurring from August 19th to 21st in 1997 by a landing northward tropical cyclone (9711) was simulated by MM5 non-hydrostatic model. Through comparing the simulate results with the real weather, the different layer synoptic-scale circulation, height field, temperature field and precipitation were successfully reappeared.The main synoptic background in the case was as follow. Firstly, subtropical high center lay to the north than usual, and forms a blocking high in combination with land high in eastern Asia. Secondly, on account of the strong southwest current which occurred at the west side of the subtropical high and dynamic effect of the typhoon itself, the landing northward tropical cyclone (9711) landed in Liaoning again. Thirdly, a trough with some weak air from Ural Mountain and the northeast cold air entering into the tropical cyclone showed that the systems in different latitudes had some effects each other.In order to make clear the changing situation about various meteorological element fields during the heavy rain. The diagnostic analysis in three aspects was done in this text: the vapor conditions, in which the difference of the temperature and dew point, relative humidity, vapor flux and the divergence of vapor flux were discussed; the dynamic and thermodynamic conditions, vorticity, divergence and vertical velocity were analyzed; the vertical layer condition, which included potential temperature, static stability, convective (potential) instability and the vertical profile of eight physical fields over the observatory of Shenyang.The diagnostic analysis indicated that the main factor resulting in the large area rainstorm in Liaoning was the lower level jet. It provided not only continuously vapor but also the heat energy and momentum, and induced several meso-β scale vertical circulations, in the meantime, it was helpful to maintains the strong upward motion in the rain area. The wind velocity pulse in jet axis made lower level convergence strongly too. The coupling of low-level (convergence area lay ahead of jet on the left) and upper-level (divergence area lies rear of jet on the right) jets played an important role in the course of vertical motion developing. The westerly cold air in middle to low layer made the baroclinic function become stronger, further lead to the enhancement of precipitation by accumulating and discharging the energy of instability. While the southerly low-level current was detained by the easterly cold air, which resulted in the ascending motion and influenced on the shear intensity and its resultant precipitation. The action that weak cold air penetrated into the tropical cyclone made the low pressure become vortex potential instability, and finally turned into kinetic energy. The results were that the center pressure of low became lower, the wind velocity around the cyclone was stronger and the precipitation became more.