The Numerical Simulation And Data Assimilation Research Of Typhoon Rainstorm

Through utilizing the NCEP reanalysis data of 1°×1°and the non-hydrostatic meso-scale model WRF, the numerical experiment are conducted to simulate typhoon "perl" (0601), Base on which, the reasons that leads to the typhoon rainstorm, the features of its spiral rain band, and the factors that causes its rupture are researched in-depth.From analysis, we found that: the deep convection is the direct reason for the heavy rainstorm on land; the thick and solid structure of the spiral band is a significant index of the typhoon rainstorm. The transmission of the cold air toward south and the advantageous orographic condition play a vital role in enlarging the intensity of the rainstorm. The interaction between the weather systems in both mid and low latitude is a key triggering mechanism. Further analysis indicates that the spiral rain bands at the northeast and southwest position of typhoon system locate symmetrically from the typhoon eye. The cyclonic vorticity, the vertical movement, the horizontal momentum and so forth all centered at the spiral rain area. The moisture mainly comes from the levels below 850hPa, and obviously from the unstable convective air outside, it which provides the unstable energy for the spiral rain band. A mesoscale strong wind band with velocity over 50m·s^-1 exists outside the spiral rain band, its birth relates to the accelerating function engendered by the pressure grads when the influe spiral rain band is inflowing.Two possible factors caused the rupture of the spiral rain band. One is the transformation of the upper and lower system; the other is the orographic influence. On one hand, the orographic forcing and uplifting function induced convection and further formed the rainstorm, on the other hand, the unstable energy gatherd near the windward slope and the effect of release of potential heat are capable of heating the mid and upper level and strengthening the upper level and thus be propitious to the upward spread and strengthening of the orographic vertical circle, formed the positive feedback and finally bring the strong enlargement of the quantity of rainstorm.In addition, the assimilation experiment of COSMIC GPSRO refrectivity data is further conducted to test its effect on improving typhoon forecast. It is concluded that after assimilation, the intensity and track are not obviously coordinated while the maximum quantity of typhoon rainstorm are significantly refined. Meanwhile the coodination of the presented variables mainly centred at the lower layers of troposphere.