| The northeast Qinghai-Xizang plateau is margin area which topographic altitude is precipitate, and which has the high frequent interaction between synoptic system in plateau and westerlies system. The heavy-hard rainfall in this area is strong outburst, lasting short time, which consists the singularity of the plateau being its especial geography position, topography and underlying surface. The mechanism is difficult to be make out by conventional weather analysis and statistical forecast, and couldn't find the correspond criterions of these paroxysmal disaster weather forming. These puzzled the forecasters, and leaded to the lower accuracy rate of forecast. The weather analysis and climatic characteristics of the heavy-hard rainfall in this area, structure characteristics during the rainstorm, the mechanism and structure of mesoscale systems bringing rainstorm and etc. are studied by conducting diagnostic analysis, theory of dynamics and numerical simulation. The influence on the rainstorm causing by mesoscale topography piling on the plateau, the particular valley topography in northeast plateau and complex surface vegetation are researched by numerical experiments. The heavy-hard rain in northeast Qinghai-Xizang plateau is that precipitation in 24h 25. 0 mm. The regional one is that there are three stations whose precipitation in 24h 25. 0 mm .Detailed diagnoses is made on a heavy-hard rain in the Northeast Qinghai-Xizang Plateau using NCEP data of 1 X 1 with 6h intervals, more complete and integrated conventional observational data and the data set of automatic meteorological stations in plateau and new generation Doppler radar data and satellite images and etc. The following conclusions can be drawn:1. The distribution of heavy-hard rain, which is characteristics of valley topography in northeast Qinghai-Xizang Plateau is obviously effected by topography. The distribution of yearly mean precipitation and the frequencies of heavy-hard rain in this area are descending from east to west. There are two greater value centers: one is the valley region in northeast of the plateau, the other is the north of Sichuan province.2. The characteristics of rainstorm in this area are occurring at one station, strong local, greater intensity, concentrating on the period from Jun. to Sep., and more occurring in July and Aug.. There is a distinct inter-decadal trend in numbers of station and days of heavy-hard rainfall and the frequencies of it increased in recent decade. The heavy-hard rainfall usually occurs at night with greater relative intensity.3. The main relative systems of heavy-hard rainfall in northeast plateau are Western Pacific Subtropical High, South Asia High, Low Latitude Systems, Upper Level Jet(ULJ) , Low Level Greater Wind Speed Axes, Westerly Trough and Plateau Trough, Low Level Vortex, Cold Frontal, Occluded Front in Qinghai Lake, Mesoscale Low Pressure, Heat Low-Pressure in Qinghai, shear line and convergence line, mesoscale cloud cluster, etc. The west subsidiary model of South Asia High is the main circulation type of heavy-hard rainfall in this area. The low latitude systems such as typhoon, etc.affect the rainstorm in plateau through direct and indirect action. The synoptic systems within heavy-hard rainfall stagnated in the most of this area.4. The main characteristics of satellite images for the regional heavy rain are overlapping of the different cloud systems. One of reasons leading to heavy-hard rain during the overlapping is that the overlapping leads to unstable development of the inertial-gravity waves.5. The heavy-hard rainfall in transitional season is brought by mixed cloud systems whose movements are slow and less, and the echo depth are about 5 km and horizontal distance of strong echo are within 10km. The one is brought by meeting and overlapping of mixed and high level trough moving eastward cloud systems whose echo depth is about 12 km, and the horizontal distance is within 10~20km and the intensity is up to about 50dBz. The intensity is les...
|
PDF Full Text Request