The Rainstorms Characteristics Of Climate And The Numerical Simulation And Diagnostic Analysis Of Rainstorm Cases In The Middle Yellow River Under The Background Of Global Change

In order to study the characteristics of rainstorms in the middle Yellow River under the global change, the trends and periodic oscillation of the rainstorm days of overall and in July and August were analyzed by using1981-2010ground precipitation data. The results show that: either overall or in July and August, the trends are slightly growth, but this growth is not obvious; the overall and in July and August rainstorm days all have8a periodic oscillation, and the overall has3-4a periodic oscillation in1990-2000, while in July and August the low frequency oscillation is not similar. The rainstorm days have2-3a periodic oscillations in the early1980s and the late1990s in July.But in August they have4a periodic oscillations between the late1980s and late1990s, after2004they have3-4a periodic oscillation.Although the rainstorm days have the better climate characteristics, but each rainstorm process is randomly distributed in the rainstorm season, and add the reason of the complex topography of the region, we still can’t accurately forecast the rainstorm. In order to cope with heavy rain disaster better and grasp the trigger mechanism of the rainstorm in this region for forecasting, we will study the characteristics of two rainstorm processes in the middle Yellow River on22July2010and27July2012by using the1°×1°NCEP/NCAR reanalysis data,observed surface precipitation data,TRMM3h data,black-body temperature(TBB) data from FY-2E satellite and and radar data.The rainstorm processes are simulated by WRF(Weather Research Forecasting) mesoscale numerical model and diagnostic analysis is made by using WRF model outputs.Results show that the "10·7" rainstorm was the result of the combined effect of the Western Pacific Subtropical High and the cold vortex in Hetao area. A large number of water vapor from the Indian Ocean and the South China Sea as amoisture source for the rainstorm. The "12·7" rainstorm took place in regions between the northwest marginal zone of the western Pacific subtropical high and the Baikal cyclone. In the middle and low layers, the water vapor originated from the Bay of Bengal, passed the eastern Tibetan Plateau and arrived in north Shaanxi. The process from the small non-organized cloud clusters to self-organized cloud clusters stimulated the development of mesoscale convection system. Near and behind the trough line, the mesoscale gravity wave could be caused by geostrophic adjustment in the right of jet stream exit region at200hPa. By using the divergence fields, cloud water distribution is able to determine the existence and moving of mesoscale gravity wave. The energy of downward propagation of mesoscale gravity wave was absorbed by the atmospheric neutral layer near surface, which leaded to the convection development in lower atmosphere layer, and promoted the genesis and development of rainstorm. Based on the direction of the upper-level jet and the value distribution of the nonlinear balance equation (NBE) the area and direction of movement of gravity wave can be determined which can be used to forecast the rainstorm.