Theweather systems and a relatedmesoscal convective systems, causing severe heavy rain in the south-eastGansu Province during 27-28 Aug 2006, are successfully simulatedwithMM5 models. Trumpet-shaped topography prominently increased rainfall in Gangu county. The rise of the terrain enhanced the low level convergence and verticalmovementover thewindward side of the terrain.The dynamical enforced rise of the terrain emerged at the prophase and the time of the rainfal.l
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Firstly,the working p rincip le and measurement p recision of the Airda - 3000Q type atmospheric wind p rofiler (AWP) were introduced. Then, a contradistinctive analysis on the wind p rofile data acquired by both AWP and synchronous balloon sounding was conducted to estimate the reliability ofAWP for detectingwind field. The results show that under the stable weather condition, the p rofiler’s detection ofwind direction and wind speed had some deviation compared by the balloon’s detection from the ground to 200 m height due to the detecting blind spots of the AWP and the ground clutter, but above 200 m, both wind field p rofiles correlated well;Under the comp lex weather condition, theirwind p rofiles had obvious deviation because the wind information on the different height acquired by AWP is a temporal average of wind field in a time period, but the wind data measured by sounding balloon on a specific height is the instantaneous value while balloon passed by.

By using global reanalysis data from NCEP /NCAR, the durative of a floating dust overBeijing during 7 - 10 in Ap ril of 2006 was analyzed. Itwas found that the impact systems of the floating dustweatherwereWest Siberia cold eddy, Okhotsk warm high and Tibetan Plateau high ridge at the level of 500 hPa; the dry - cold air at the level of 700 hPa transferred to Beijing ceaselessly, and the cold advection and baroclinic instabilitywere strong, the gale and dust storm occurred in the strong cold advection area; the weak instability stratification in surface layer and mid - low level in the south ofNorth China resulted in weak ascending air flow, then transported dust particles to Beijing depending on the easterlywind in front of the surface low p- ressure. Because of the neutral or instability condition atmid - low level over Beijing, the dust particleswere difficult to go down, and the floating dustweather lasted for four days.