| By using precipitation data of monthly surface observation from China National Meteorological Data Service Center,the reanalysis data of specific humidity and horizontal wind from ECMWF,the precipitable water data of MODIS from NASA-EOS,and the cloud data from CERES SSF Aqua MODIS Edition 4A,the suitable conditions of artificial precipitation enhancement in the central region of Gansu province were analyzed.Using the hourly precipitation data,the radar base reflectivity image products,vertical accumulation of liquid water content products,hourly precipitation products and artificial precipitation operation examples in the study area from Gansu Meteorology Bureau,the precipitation as well as characteristics of base reflectivity echo before and after operation were analyzed.The results indicate that the average precipitation decreases from the southeast to the northwest of the study area.The most precipitation occured in July,145 mm,the least,1 mm,in December.The average precipitable water gradually decreases from southeast to northwest,moreover,the seasonal difference of which is significant.The water vapor flux is stronger from July to September.In September,the water vapor output of east boundary is more than 3.68 kg·m-1·s-1.Autumn witnesses the strongest net water vapor flux,0.98 kg·m-1·s-1.At the level of 850 hPa,the water vapor flow from southeast is much stronger than the rest,which can transfer water vapor from southeast to northwest in summer as well as autumn.The water vapor in the central region of Gansu mainly comes from the meridional moisture transportation.The precipitable water vapor gradually decrease from southeast to northwest.The most abundant precipitable water vapor is located in Minxian,while the least in Yongdeng.The water vapor in summer account for more than 58%of the whole year,however in winter,which is less than 4%.In July,the precipitable water vapor feature,636 mm,the most amount in the year,however,December feature the least,which is 77 mm.The precipitation efficiency decreases from southwest to northeast,which is higher during April-October,?13%,than that of November-March,?3%.The potential precipitation gradually decrease from southwest to northeast while the precipitation efficiency gradually decrease from southeast to northwest during June-September.In eastern MinXian and southlernTongWei,the precipitation efficiency is larger than other places.The spatial distribution of low cloud cover,liquid water content of low cloud,temperature difference of low cloud bottom and cloud top are basically consistent with precipitation efficiency,indicating a gradual decreasing distribution from south to north.The precipitation efficiency in each season is positively correlated to the cloud parameters,additionally,the correlation coefficients are between 0.61 and 0.92,as almost all of them passed the 5%significance level test.The base reflectivity echo??10 dBz?is the suitable operation condition of precipitation enhancement.when the base reflectivity echo is greater than 30 dBz,artificial precipitation operation could be effective.Above all,the water resource is abundant in the south of LinXia and KangLe,west of TongWei during March-September.In summer,the conditions,the low cloud over??0.5?,the cloud liquid water content??1.5×10-66 kg/kg?,the temperature difference of low cloud base and top??8 K?and the precipitation efficiency??18%?in the south of LinXia and KangLe as well as the west of MinXian,can be suitable for precipitation enhancement operation.In addition,the base reflectivity echo??10dBz?is the suitable condition for precipitation enhancement.While the base reflectivity echo is greater than 30 dBz,the artificial precipitation operation can be significantly effective. |
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