The Analysis Of Forming Rainstorm And Research About Causing Mud-rock Flow And Landslide In Longnan

Using rainfall data from 1961 to 2000 in Longnan ,distributions of precipitation and rainstorm are analyzed .Using sounding data ,the large scale synoptic meteorology circulation patterns of rainstorm are catalogued.Using T106 data from 1995 to1999,the mean field of synoptic meteorology models are calculated.Combining single rainstorm,the rainstorm causes are analyzed .The mud-rock flow and landslide distributions and the relations with rainfall are analyzed. Corresponding prevent and fight against natural calamities countermeasures are posed.The main results are as follows:(1) In Longnan, rainstorms mainly take place in the east areas. They occupy 80 percent of all rainstorm days.They lessly take place in the west areas.The rainstorms take place from May to September.They mainly take place from July to August, occupy 80 percent of all rainstorms in this term.The duration of time and frequency of mud-rock flow and landslide and rainstorm are roughly the same.(2) The large scale synoptic meteorology circulation patterns of rainstorm are divided into southwest airflow pattern,irregular airflow pattern and northwest airflow pattern.In the first pattern, rainstorm frequency is the largest, occupy 80 percent of all rainstorm number of times.The frequency of the others is small,they occupy 17.8 percent and 9. 3 percent.( 3 ) The influential system of southwest airflow pattern is west wind slot. vertical ascending motion is deep,last more time. There are two vapor transportation passages,one is from Indian Ocean to the south of Himalayas and to Longnan.The other is from South Sea to Longnan.Cold airflow and warm airflow meet near Longnan and develop energy frontal areas and frontal system.( 4 ) The influential systems of irregular airflow pattern are shear line,low vortex and small slot near the east of Qinghai-Xizang plateau, vertical ascending motion is stong,mesoscale feature is obvious. There are two vapor transportation passages,one is warm southwest airflow from Bay of Bengal along the south of Himalayas to Longnan. The airflow from the East China Sea and South Sea meet in south China ,then toward Longnan.(5)Using divergence of Q-vector, Helicity and moist potentialvorticity(MPV),can diagnose rainstorm causes.Rainstorm usually appears when MPV1O in the middle and low tropospheric and MPV2>0 in the low tropospheric.The large negative number centre of divergence of Q-vector and Helicity are roughly the same as rainstorm centre.There must be not only advantageous circulation background and rich vapor,but alse deep instability condition in southwest and irregular airflow patterns.( 6 ) According to the disaster degree of mud-rock flow and landslide, the whole area is divided into four dangerous parts. Rainstorn grade is roughly the same as mud-rock flow and landslide grade.lt can be used to forecast mud-rock flow and landslide.