Analysis And Study Of Two Strong Convective Weather Precess Mechanism In ShanDong Province Of China

Strong convective system usually contain severe weather such as thunderstorm,windstorm,hail,and rainstorm et al. The strong convective system is very important but defficult to forecast for it's local and sudden nature. Observation and simulation study are done to two strong convective system which occurr on 28 April 2006 and 28 May 2007 in Shandong province of China by using the satellite, radar data, mesoscale auto-meteorology stations observational net data and PSU/NCAR mesoscale meteorology nonhydrostatic model MM5. The wavelet analysis method is used to transform the 4.28 process simulation results into continuous wave structures and the structures is analysed. By all those analysis, such results are found:(1) By using the right physical option and data processing method, the 4 km model resolution can get the relatively well result for the 4.28 squall line which is a relatively large mesosclae convecive system while the 10 km model resolution result deviation is a little big compares with the observation result. The 4 km model resolution result deviation is still obvious compares with the observation result for the 5.28 convective process, even by using the same physical option and data processing method. The initiation and evolution of the very small scale local convective system like this is usually connect closely with meso-γscale weather systems and have relation to the interaction of weather systems in different scales. It is also affected by complicated boundary layer terrain,local thermodynamics and dynamics action. The simulation results of the two strong mesoscale convective system show the dependence of mesoscale convective system's predictability to the scale of the weather system and resolution of the model.(2) The mesoscale terrain has important affection to the initiation of both the two strong convective weather process. For the 4.28 process, the mesoscale convergence line, which is formed by downslope wind from the Taihang mountains converging with the southwest warm humid wind , releases the Convective Available Potential Energy, initiates the convection and organizes the convective cells into squall line. In addition, the lee wave which exists for a long time generating from the Taihang mountain is one of the initiation mechanism of this process. For the 5.28 process, Coupled with the action of mesoscale convergence line within the surface obverse trough, and coorperate with the low troposphere shear line and high troposphere cold advection, the cold wet air from the ocean arise after meet the Shandong central mesoscale terrain initiate the convection.(3) The wavelet analysis method can depict the modes of gravity waves, the time and space characters of the gravity waves'evolution. The analysis of the 4.28 system simulation result shows, there are gravity waves of many kinds of wavelength, the range of the wavelength is 20 ~ 200 km and most of the wave energy between the wavelength of 50 ~ 100 km. In the whole evolution process of the squall line, there are gravity waves of 50 km and 100 km wavelength no matter in high troposphere or low troposphere, and both of them have two or three wave periods. The phase speed of the gravity waves which have the same wavelength are nearly the same, but the phase speed of the 50 km wave is a little faster than the 100 km wave, obviously, it is different from the analysis of the linear model. The waves which have different wavelengths form into a wave packet and it's group speed is 14 ~ 28 m/s. The gravity waves propagate forward and backward after being initiated, and those waves usually initiate new convective cells during the propagation and dispersion process, the new convective cells will initiate the new gravity waves again. The interaction of convection and gravity waves makes the propagation of the squall line into discrete way.