Analysis Of Mesoscale Mechanism Of Remote Heavy Rainfall In Sea Typhoon Steering

In this paper, we use the WRF model and FNL data to simulate the heavy rain process in Shandong area from 12:00 August 1 to 00:00 on August 4, 2011, which is caused by the interaction between typhoon and the large scale circulation, the period which typhoon turning and strengthening. The results shows that:(1) Due to the interaction between the typhoon "Muifa" and the mid-latitude system, there was a heavy rainstorm in Shandong. Heavy rainfall in Shandong present a northeast to southwest elongation zonal distribution, there are four heavy rain centers. The occurrence of heavy rainfall is the result of high and low level jet,low level cold vortex, subtropical high and tropical cyclone "Muifa". The high-level jet has enhanced the divergent suction effect, and the low-level jet has increased the water vapor and heat transport in the lower level, and the southward airflow on the north side of the typhoon and the southwest of the subtropical high has strengthened the water vapor transport in Shandong. All those provide abundant water vapor for the production of heavy precipitation.(2)Heavy rainfall occurred in the typhoon inverted trough reach to the south of Shandong, with the typhoon strengthened, the inverted trough with mesoscale vortex generated and developed, the eastern part of Shandong Peninsula also has a mesoscale vortex generated and developed, precipitation is located on the west side of the inverted trough , between two mesoscale low vortex. Strong convection occurs in the process of mesoscale low vortex development, the typhoon inverted trough has played an important role in this process.(3)During the process of typhoon intensification, before intensification, the wind speed in heavy rain occurred area is large and associated with low level divergence.When the typhoon is strengthened, the wind speed in the rainstorm area is weakened,the southeastern airflow in the east of the typhoon and Jiangsu are enhanced,especially on the east side of the typhoon Southeast airflow enhanced more obviously. When the strong convection occurs, the southeast jet in the east of typhoon and southwest jet flow in the north branch trough at low 850hPa converges in the rainstorm area. It can be seen that, with the strengthening of typhoons, the two airflows are strengthened and converged in Shandong, which is conducive to the transmission and convergence of water vapor and energy.(4) Analysis of the effect of dry and cold air can be seen that: before the occurrence of heavy rain,the dry air is above the wet air in atmosphere, and the wind vertical shear between high and low is larger. When the storm is strengthened, the dry and cold air behind the westerly trough has arrived in the western part of Shandong from Hebei Province, and moved eastward slowly. During the period of strong convection, the dry and cold atmosphere stratified associated with the wet and warm air from the east side of the typhoon at 850hPa forms an unstable stratum in the storm area.