| This paper systematic analyzed the large-scale environmental field, as well as water vapor, power, thermal conditions for formation and development of typhoon "sepat". It is suggested that, after landfall, the circulation of "sepat" had maintained for a long term, its path changed, and the strong rain areas are mainly located at the left side of the typhoon's path. The main reason is that the mainland's subtropical high dynamic stability, not available for storm to hit the southwest after landfall. By the influence of low pressure near 160°E , the West Pacific subtropical high pressure withdrew east, and southern not obviously, which is not conducive to the typhoon. At the same time, the easterly flow system was weak. A long time control and the latitudinal development of the middle latitude mainland's high pressure were good for the provision of high-altitude rainstorm divergence conditions. And the east area was controlled by the west side of the Western Pacific subtropical high southerly flow and the southwest summer monsoon. In particular, the stable maintain of the mid-latitude high pressure and the southwest monsoon formatted a favorable circulation field. And the southwest low-level jet transported large warm instability energy to heavy rain area. In the typhoon circulation, north (south) was dry (wet) and high (low) temperature. These two different nature air encountering, and the strong convergence of low-level jet of left side formattedα-scale andβ-scale strong rainfall convective clouds, causing heavy rainfall. As the typhoon in-depth inland, it mostly moves along the river valley area of low-lying. And land-rich vapor transport is conducive to typhoon after landing to maintain for a long term.Using the NCEP analysis data, this paper simulated the typhoon "sepat" from 1318082007 to 1918082007 with WRF, and analyzed it. It suggested that the storm relative helicity corresponded well to the heavy rainfall district in the initial time. And the strong rainfall areas corresponded to the low-level (high-level) negative (positive) moist potential vortex, which is available to the occurrence and maintenance of strong convection. Around the centre of the heavy rainfall, there is always positive potential vortex. And, the high potential vortex anomaly is a useful occurred mechanism of the development of heavy precipitation.And also, through the analysis the spiral rain bands using the output the numerical simulation, results show that the kinetics and thermodynamics vertical structure of spiral rain bands indicated that the cyclonic vorticity, vertical movement, and horizontal momentum and heat of typhoon are concentrated in the spiral rain bands, namely, the typhoon brought heavy rain and strong wind with the accompanying of spiral rain bands. And it can be seen that the vertical distribution of the kinetics and thermodynamics physical quantities are almost upright cylindrical, slightly tilted outward with a high degree, which is probably a strong outflow of the high-level. Spiral rain bands structural analysis also showed that its main water vapor is from below 850 hPa,.There are Sorthwest and Northeast convergence flow separately from outside and inside to spiral bands,and they are very near .so heavry convergence occur. The acceleration of water vapor which transports upwardly at lower layer is advantagcous to the counter-flow development. The pressure gradient force of spiral rain bands lateral convergence flow accelerated the formation of meso-scale strong winds of spiral rain bands lateral.
|
PDF Full Text Request