The Effect Of Dabie Mountain On Meso-scale Shallow Vortex During Heavy Rainstorms In Huaihe River Basin

In order to get the regional feature of rainfall for many years and the vorticity distribution over Huaihe River, this paper used average monthly precipitation during June and July from1979to2002and data four times a day’s relative vorticity during June and July from1979to2003for EOF and REOF analysis. Screening out multiple cases to analysis characteristics of the vortex through the mountain, pick up a typical vortex storm case for live analysis, diagnosis related physical fields of the Piedmont and after Mountain during the vortex eastward, and explore the mechanism of the vortex eastward when it through Dabie Mountain. Meanwhile, simulating numerical simulation test and designing two sensitivity tests about terrain changes of Dabie Mountain by the use of WRF model, researching the terrain effect on vortex and precipitation of Dabie Mountain. The results show:(1) The distribution of precipitation over Huaihe River showing an east-west rain belt, the rain belt located in the northern of Anhui and Jiangsu provinces, northern Anhui, after Dabie Mountain, more likely to occur precipitation.(2) Vortex over Huaihe River easily detour from the north of Dabie Mountain, there is a path southward turning around the Dabie Mountain, and the vortex are likely to get freshmen and strengthened after Dabie Mountain.(3) The lift and compression effect of Dabie Mountain’ terrain on airflow, the divergence at the lower troposphere of Dabie Mountain produce positive abnormal change, it also makes vortex strength which is in the piedmont of Dabie Mountain piedmont weakened.(4) Due to the peak of Dabie Mountain showing horizontal distribution, When the vortex is close to Dabie Mountain from the west, the high terrain of the main peak has a strong blocking effect on the northward meridional wind, When the value of the northward meridional wind is reduced, the speed of northward movement slows down.(5) Because of the lying of Dabie Mountain presents high from west to east, when the vortex moves over Dabie Mountain, terrain gradually increased along the wind has a good uplift to wind, the north side of Dabie Mountain depress, the vortex flow northward will strengthen.(6) The presence of Dabie Mountain strengthen the convergence field after the mountain, the center of divergence will rise eastward, which making the vortex after the mountain develop.(7) Because of Dabie Mountain, the vertical wind shear after the mountain at850hPa to500hPa strengthened, it leads to the transformation from the horizontal vorticity to vertical vorticity strengthen, and the vortex shifts from shallow system to deep system.(8) by WRF simulation and sensitivity test on the storm vortex, we found that the Dabie Mountain have a direct impact on the falling center of precipitation after the mountain, Simultaneously the distribution of precipitation presents two centers after the Dabie Mountains.