GWDO Parameterization Scheme And Terrain Influences On A Heavy Rainfall Case In Dabie Moutain

A mesoscale shear-lined rainfall process in the Dabie Mountain between 21:00 on June 20th,2008 and 06:00 June 21st,2008 is simulated and analyzed, which is based on NCEP/NCAR 1°×1°analyzed data, conventional as well as unconventional ground observations and WRF V3.1.1 version of the mesoscale non-hydrostatic equilibrium model. Due to sensitivity tests, the impact of GWDO(Gravity Wave Drag by Orography) parameterization scheme and the topography on the heavy rainfall.By using NCEP/NCAR analyzed data, in the high latitudes, the maintenance of the blocking high and the broad band of low pressure at Lake Baikal and Lake Balkhash forms straight zonal flow. In the low latitudes, the moving westward of Subtropical high leads to the production of deep shear line system production at Yangtze-Huaihe region. The maintenance of the shear line provides strong convergence field for the rainfall. Before the rainfall, by the control of southwest air at the Dabie Mountain area leads to the air temperature to raise, which offers heat for the rainfall. The Water vapor derived from the South China Sea in the saddle pressure field favorable situation, is transported to Dabie Mountain area by southwesterly flow, which offers favorable water vapor condition for the rainstorm. The downdraft at the right side of upper level jet zone produces the north wind, while the downdraft in the south of SAH (South Asian High) produces the south wind. The convergence of the two air flow emerge a strong upward motion in the Dabie Mountain area, which provides a favorable convergence field, and this is also the main reason for the formation of the shear line.The comparison between with and without GWDO parameterization scheme outputted by the model, without GWDO parameterization scheme in rainfall drop position is worse, but the change is smaller in the position of systems. Forecasting precipitation area can be greatly improved by adding the drag coefficient. Without GWDO parameterization scheme in this precipitation, the disturbance is stronger, the gravity waves are more active, and precipitation is heavier in a gravity wave strong area.In order to find out the terrain influence considering GWDO parameterization scheme on the shear-lined heavy rainfall, sensitivity tests are carried out to remove the Dabie Mountain and Huangshan Mountain, Tianmu Mountain. When removing the Dabie Mountain terrain, the precipitation intensity is dramatically increases on the whole shear line. The biggest increase region is in the west of the rain band (in the east of the Dabie Mountain). In the west of the rain band, vapor flux also greatly enhances. In the middle of the rain band, vapor flux decreases, while in the east of the rain band the vapor flux is also increases. This strengthen or weaken of rain band consistent with the change of the disturbance in the shear line. However, changes in circulation compared to the changes in precipitation are much smaller. In the not taken into account in Huangshan Mount and Tianmu Mount's terrain sensitivity test, generally speaking vapor flux greatly reduces in the rain region, only the east rain band with a clear increasing leads to heavier precipitation. Overall, the terrain of this shear line rainfall has a weakened impact. The effect is especially obvious in near the removal of the terrain. However, by using GWDO parameterization scheme, disturbances on the shear line also have changes, which leads to different distribution of the rainfall. Analysis of the vertical circulation shows that, in the meridional circulation, the southwest and northwest flow convergence produces a strong upward motion at the shear line, a monsoon circulation exits on the middle troposphere to the south of the shear line. There are a number of secondary circulations in the monsoon circulation. No matter removing the Dabie Mountain terrain or removing the Huangshan Mountain, Tianmu Mountain terrain, the results are all the same. In the test of gravity wave drag coefficient, disturbances are weak, while disturbances in the control experiment obviously upward spread. To the north of the shear line, dominated by northerly flow, disturbances are obvious on the middle troposphere.