Thirty - one cases of p recip itation p rocess in July to August of 2007 over Qilian mountains have been classified using the dominant air currents at the level of 500 hPa and cloud patterns of FY - 2D satellite images. The difference between the 500 hPa average geopotential height for grid point on 110°E (H1) and that on 90°E (H2) in the range of 30°N - 45°N was used as criterion of classification, and the p recip itation p rocesses have been classified as three main types, including southwest air current, northwest air current and flatwest air current type. Southwest air current type is also divided into moving and blocking two subtypes and northwest air current type into cold advection and Hetao cold vortex two subtypes. Using p recip itation data from automated weather stations in the experimental region, the circulation characters and p recip itation intensity for each synop tic type have been analyzed. It is found that the total p recip itation of the south slope ismore than that of the north slope about 44% in the same sea level elevation in summer 2006 over Qilian mountains, but for climatic state and the year of 2007, the total p recip itation of the north slope wasmore than that of the south slope, and the dominant southwestwind in 2006 but northwestwind in 2007 at the level of 500 hPa overQilian mountains.

The regional distribution features of daily mean net radiation，sensible heat flux，latent heat flux and soil heat flux density in summer over central Gansu were derived from the Surface Energy Balance A1gorithm for Land(SEBAL)using micrometeorological ob．servations over a wheat field at Dingxi station，solar radiation observations at Dingxi and Lanzhou stations．observations of 34 meteoro-logical。hydrological and rainfall stations over the Maxian Mountain region，combining with NOAA一16 AVHRR data，as well as the land surface reflectance an d vegetation coverage retrieyed from NOAA一16 AVHRR data．the efects of land surface process on precipi．tation were also analyzed in this paper．Th e results show that the regional distribution of annual mean precipitation corresponds well to vegetation coverage in summer。the correlation coeficient is 0．722．and the correlation coeficients of annual mean precipitation and soil heat flux ．1atent heat flux density are 一0．65 and 0．615．respectively．It is showed that the forest can not only increase net radia-tion but also decrease sensible and soil heat fluxes by decreasing surface reflectance and temperature．More solar energy can bere·ceived and mostly used for evapotranspiration over forest regions．which makes vapor content increased there．For this reason precipita—tion over forest regions is much more than that of semi—arid regions with sparse vegetation

The regional distribution features of daily mean net radiation，sensible heat flux，latent heat flux and soil heat flux density in summer over central Gansu were derived from the Surface Energy Balance A1gorithm for Land(SEBAL)using micrometeorological observations over a wheat field at Dingxi station，solar radiation observations at Dingxi and Lanzhou stations．observations of 34 meteoro-logical。hydrological and rainfall stations over the Maxian Mountain region，combining with NOAA一16 AVHRR data，as well as the land surface reflectance an d vegetation coverage retrieyed from NOAA一16 AVHRR data．the efects of land surface process on precipi．tation were also analyzed in this paper．Th e results show that the regional distribution of annual mean precipitation corresponds well to vegetation coverage in summer。the correlation coeficient is 0．722．and the correlation coeficients of annual mean precipitation and soil heat flux ．1atent heat flux density are 一0．65 and 0．615．respectively．It is showed that the forest can not only increase net radia-tion but also decrease sensible and soil heat fluxes by decreasing surface reflectance and temperature．More solar energy can be received and mostly used for evapotranspiration over forest regions．which makes vapor content increased there．For this reason precipitation over forest regions is much more than that of semi—arid regions with sparse vegetation