A Numerical Simulation Research On The Generation And Development Mechanism Of A Heavy Precipitation Supercell In Northern Jiangsu On 22 July 2008

Supercell storm causes extreme strong convective severe weather, strong local characteristics, fast generation and disappearance and complex development mechanism make the forecast of the supercell storm process is difficult, the study has important significance. A numerical simulation on the generation and development mechanism of a heavy precipitation supercell storm in northern Jiangsu on 22 July 2008 is implemented by using conventional observation data, NCEP reanalysis data, FY2C satellite products, CINRAD-SA Doppler radar data, a high resolution mesoscale numerical model Weather Research and Forecast (WRF) and cycling 3-D variational (3DVar) assimilation technique of radar data.Firstly, the radar echo features are investigated on the basis of numerical simulation results and Doppler radar observation. The results show that at its mature stage the heavy precipitation supercell displays a low-level weak echo and associated front "V" notch echo, with the larger radar reflectivity factor sloping toward the low-level inflow from low level to high level, the vertical structure is presented as an inclined upward and downward flow pair. Corresponding radial velocity images show a well-developed mesoscale cyclone coincident with the heavy rain area at the surrounding of the front "V" notch echo.Secondly, the analysis of thermodynamical structure show that, strong positive and negative horizontal rotation are associated with srong vertical motion from 700 hPa to 250 hPa in the cloud. The release of the instability energy release at low layer and the deep wet neutral layer play an important role in the strong development of the supercell storm. The configuration of vorticity and divergence at the strong convective center and its surrounding is conducive to the formation of a wide range of cold cloud field and the temperature field of cold at high and low level and warm at middle level. During the period of the supercell storm generation and development, the low-level convergence and updraft in the front of the storm under the impact of heavy low- and middle-layer vertical wind shears that forms strongly rotating updraft, which is favorable to strengthening and maintaining of the supercell storm.Thirdly, moist potential vorticity conservation principle and slantwise vorticity development theory are used to investigate the generation and development mechanism of a heavy precipitation supercell. The results show that there are close relationships between the evolution of supercell storm and the moist potential vorticity at 650 hPa; the cold air sliding down along the moist isentropic surface confluences with the slantwise upward motion warm and moist air on the wet isentropic surface, both of them experience a stability decreasing process, promotes the development of convection and heavy rains, and the condensation latent heat release on the isentropic surface, further facilitate the development of the cyclonic vorticity and supercell storm; mesocyclone occur and develop easily on the place of isentropic surface slope, and the isentropic surface is more slant, the intensity of mesocyclone is greater, its development is more intense.Overall, detailed observational analysis and numerical simulation are conducted on a typical heavy precipitation supercell in northern Jiangsu, the three-dimensional structure and the generation and development model of the process are established, which is helpful to improve the prediction quality of the supercell storm in northern Jiangsu.