According to the data of ground - based observation from 1951 to 2008 at Dunhuang national standard climate station, the spatio - temporal change of sand - dustweather in Dunhuang area was analyzed. The result reveals that the sand - dust weather obviously decreased. It occurred most frequently in the 1950 s, and in a year, it occurred most in sp ring and least in autumn. The annual wind days decrease and wind speed becoming smallwere the main reasons for sand - dustweather reduction in Dunhuang area. Meanwhile, the circulation causing sand - dustweather there was classifyed in the paper. Amp le resources of sand - dust and regional effects p rovide essentialmaterial conditions for sand - dustweather occurrence.

Based on the reflectivity factor of CINRAD ( the constant altitude p lan data) interpolated with 3D - Barnes scheme assuming that the reflectivity factor of solid water drop would accord with the experiential relation of the reflectivity factor induced by the liquid water drop, Vertically IntegratedWater Content (V IWC) including solid and liquid water was calculated with the method of discrete sum instead of vertical integral. The ratio ofV IWC and the up right height of hail cloud is defined asVertically IntegratedWater Content Density(V IWCD) , the maximum V IWCD ( shortened form: V IWCDmax) is identified by use ofMAX function. With methods of statistic and regression equation, the correlation between the V IWCDmax of hail cloud during hailing p rocess and the maximum hail diameter on the ground is analyzed in detail for 54 hail clouds observed by Lanzhou CINRAD during 2004 - 2006. Results show that the magnitude about number density of hail pellet coming from hail embryo in hail clouds with the same maximum diameter is equivalent during hailing p rocess, and hail pellet scale is an important factor which determined hail cloud echo intensity and hail size on the
ground; the p iecewise function (6) which is affected by two important factors of hail cloud tilted structure and radar scanmodel reflects the correlation between the V IWCDmax of hail cloud during hailing p rocess and the maximum hail diameter.

Based on FY - 2 infrared images and the reanalysis data for six hours ofNCEP (1°×1°) , the heavy dust storm p rocess occurred on 13 Ap ril 2007 in the middle west part of Hexi corridor is analyzed, particularly the cloud head of the descending jet was tracked and the gravitational instability, conditional symmetric instability and conditional instability are diagnosed in detail. Results show that a high speed descending jet resulted in this heavy dust storm and the jet triggered strong convection in frontal region, and conditional instability occurred in themiddle part of troposphere first, then developed downwards. The release of conditional instability energy at the level of 700 hPa caused rap id development of convective circulation in boundary and brought on this heavy dust storm.