Study Of Temporal And Spatial Characteristics Of Cloud Parameters And The Relationship To The Precipitation In Qilian Mountains Area

Northwest China belongs to the arid and semi-arid region,which is short of water resources.Water problem affects the social and economic development and the protection of the ecological enviroment.Qilian mountain is an important water source in northwest China due to its abundant water vapor supply and unique topographic conditions.To solve the water problem of northwest China needs to start from Qilian mountains area.There are a large number of glaciers in the Qilian Mountains which store water in the form of solid state,but it has been proved by practice that only glacial melting water can not fundamentally solve the water problem.Therefore,it is necessary to develop cloud water by artificial precipitation to solve the water problem.The formation and extinction of clouds is an important link in the generation of precipitation.The study of cloud physical characteristics and the relationship between cloud parameters and precipitation in Qilian mountains area is of great significance to the development of cloud water resources.This article uses MOD08-M3 data,grid ground precipitation data and FY-2 series satellite cloud parameter inversion products to analyze the spatial and temporal characteristics of cloud parameters(Cloud Amount,Cloud Water Path,Cloud Top Temperature,Cloud Top Pressure,Cloud Optical Depth and Cloud Particle Effective Radius)in Qilian Mountains area,and the suitable time and spatial region for artificial precipitation enhancement are analyzed in combination with the precipitation enhancement potential.In addition,the suitable conditions for artificial precipitation enhancement are also summarized.Finally,the relationship between cloud parameters and precipitation is studied by representative precipitation cases,and the reasons leading to weak precipitation are specially studied.The main results are as follows:(1)The regional average values of Cloud Amount,Cloud Water Path,Cloud Top Temperature,Cloud Top Pressure,Cloud Optical Depth and Cloud Particle Effective Radius in Qilian Mountains area are 55.50%,148.95 g/m2,-21.13?,456.56 hPa,12.64 and 21.04 um,respectively.From 2006 to 2015,Cloud Amount,Cloud Water Path,Cloud Optical Depth and Cloud Particle Effective Radius decreased by 2.3 %,21 g/m2,0.68 and 0.51 um,respectively.Cloud Top Temperature and Cloud Top Pressure increased by 1.9? and 65.2 hPa,respectively.Cloud water resources in the study area are abundant and suitable for the development of cloud water resources.(2)The main mountain area of Qilian Mountains is the region with the richest cloud water resources,and the cloud parameter condition in wushaling area is the best.The high value areas of Cloud Amount in four seasons are located in Xining surrounding,main mountain area,south of mountain,Lenghu area,respectively.The high value areas of Cloud Water Path in four seasons are located in the north and east of mountain,the north and middle of mountain,main mountain area,eastern side of Subei,respectively.The high value areas of Cloud Top Temperature and Cloud Top Pressure in four seasons are located in the northeastern part of study area.The high value areas of Cloud Optical Depth are located in the east of Subei in winter and in the southeast of study area in other seasons.The high value areas of Cloud Particle Effective Radius in spring are located in the region except Hexi Corridor.In other seasons they are located in between Lenghu and Subei,between Subei and Tuole,and in the northeast of mountain range,respectively.(3)The precipitation enhancement potential in summer is the largest 968.94 mm and the smallest in winter 118.53 mm.The monthly variation of precipitation enhancement potential shows obvious single peak pattern,which is the largest in July.The low value area of precipitation enhancement potential is located in the northern main mountain range area of Qilian Mountains,while the high value area is located in northeast and southeast corners of study area.The monthly precipitation is positively correlated with Cloud Amount,Cloud Water Path,Cloud Optical Depth,but negatively correlated with Cloud Top Temperature and Cloud Top Pressure.The relationship between Cloud Particle Effective Radius and precipitation is positive in January,April,July,November and December,but negative in other months.Cloud Amount and Cloud Particle Effective Radius are most correlated with precipitation in May and September,respectively.while the correlation between other cloud parameters and precipitation are the highest in January.(4)The suitable areas of artificial precipitation enhancement in April is located in southern Qilian Mountains,and in March and May they are located in southeastern side of Qilian Mountains.The suitable areas of artificial precipitation enhancement in June,July,August,September,October,November are also located in the southeast side of Qilian Mountains.The suitable areas of artificial precipitation enhancement in January is located in the northeastern side of Qilian Mountains,and the suitable areas of artificial precipitation enhancement in February and December are located in southern Qilian Mountains.(5)The suitability of artificial precipitation enhancement in each season in Qilian Mountains area is in the order of summer > autumn > spring > winter.The suitable conditions of artificial precipitation enhancement are as follows: The cloud physical condition is that the value of Cloud Water Path,Cloud Top Pressure,Cloud Optical Depth are large.The weather situation is South Branch Trough type,Strong Cold Air type and North-South Trough superposition type.The cloud types are Altostratus,Nimbostratus and Topographic cloud.The cold and warm configuration of cloud is cold layer and warm layer thickness are basically equivalent.(6)Before precipitation occurs,the supercooled layer becomes thicker,the cloud top becomes higher,the cloud layer becomes thicker,the convective becomes stronger,and cloud water increases.Cloud parameters fluctuate violently before and during precipitation.Cloud parameters can predict precipitation well before and during heavy precipitation,but not obviously in weak precipitation.The advance value of Cloud Optical Depth and Cloud Particle Effective Radius relative to precipitation is about 1h,and the advance value of other cloud parameters is about 2 h.The fitting effect between cloud parameters and precipitation is better in heavy precipitation stage.(7)When cloud parameters are poorly matched,heavy precipitation can not be formed.In the case of weak precipitation,the values of Cloud Optical Depth and Cloud Particle Effective Radius are dispersed,and the values of them are more dispersed when the rainfall value is smaller.The numerical values of Cloud Optical Depth and Cloud Particle Effective Radius are too small or too large will limit the actual precipitation.