| In this paper, causes of debris flow disaster in mountainous region in shaanxi were preparatorily analyzed. The results showed that a lot of debris flow disaster occurred were induced by rainstorm. Based on kinds of conventional and non-conventional data, a sudden extremely heavily rainfall during June 8-9,2002 in the southern part of Shaanxi province was investigated by means of observation analysis, numerical simulation and diagnosis, and the effects of meso-scale landform to precipitation in Shaanxi province were discussed carefully. The following conclusions can be drawn.1. The main influence systems of causing this heavy rainfall are southwest vortex, shear line and southwest low-level jet.2. The meso- β scale system occurring on the low-level jet let to this rainfall. Water vapor coming from southerly and easterly flow which converge at the eastern of northwest district, high energy and potential instability are propitious to the form and maintenance of this rainfall.3. It is conditional symmetry instable at the middle troposphere and convective instable at the lower troposphere. The strengthening updraft due to the durable maintenance of southwest vortex, shear line and southwest low level jet triggers off instability and transfer vapor, head and cyclonic vorticity to rainstorm area which cause and intensify the rainfall. In addition, results show that moist potential vorticity (MPV), helicity and moist Q vector have explicit indication to forecast of heavy rainfall.4. It is suggested that increase of precipitation in the northern of Shanbei, in the ridge and the southing of Qinling Mountains and in the Hanjiang basin, and reduction of precipitation in the nouthing of Qinling Mountains, in the Guanzhong basin and in the Loess Tableland, because of the Qinling Mountains. Parts of Daba mountains are very important for the large precipitation in the Daba mountains, in the Hanjiang basin and in the Shanbei. |
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