Study On Characteristics Of Atmospheric Water Resources And Precipitation Efficiency Over Typical Regions In Northwest China

It's well known that there is severe drought in Northwest China.To develop atmospheric water resources reasonably so as to alleviate the shortage of fresh water over the Northwest China based on precipitation enhancement techniques,it is necessary to understand the characteristics of atmospheric water resources in typical regions systematically and integrally.Based on the high resolution reanalysis dataset ECMWF ERA5,MODIS and CloudSat satellite data,the features of water vapor transport,macro and micro physical characteristics of cloud in typical regions of Northwest China were studied by statistical analysis methods,and the hydrometeor precipitation efficiency was estimated.The atmospheric water resources and precipitation efficiency of Liupan Mountain,a small mountainous area located in the eastern part of Northwest China were studied firstly,then the research area was extended to four wider typical regions: the monsoon boundary zone in the eastern part of Northwest China,Qilian Mountain region,Tianshan region and Three Rivers' Headstream region,with emphasis on the vertical structure of macroscopic and microscopic physical characteristics of clouds in each typical region.Precipitation efficiency in Northwest China was also estimated.The main conclusions are as follows:Compared with other mountainous areas in Northwest China,Liupan Mountain area,which located in the monsoon boundary zone,has abundant atmospheric precipitable water and stronger water vapor transport,especially in summer.The clouds fraction reaches 70%over the Liupan Mountain in the afternoon of spring,summer and autumn,and the cloud water path and the optical thickness in summer are significantly larger than those over the surrounding areas.The dynamic field caused by topography has a significant impact on summer precipitation,the more intense the ascending motion is,the stronger the corresponding rainfall intensity is.During the typical precipitation processes in summer,with stratus clouds embedded in convective systems moving from west to east through Liupan Mountain area,the average precipitation efficiency of hydrometeor is 48.1%.There is still a considerable amount of hydrometeor in the air fails to become precipitation,and there is certain potential in this areafor developing the atmospheric water resources.The water vapor flux,atmospheric precipitable water,cloud cover and cloud water path in summer in Northwest China are larger than those in other seasons.Affected by the Asian monsoon,the physical values of the monsoon boundary zone are significantly larger than those in Qilian Mountain region,Tianshan region and Three Rivers' Headstream region,which means the atmospheric water resources over the monsoon boundary zone are more abundant.The proportion of ice cloud,mixed cloud and water cloud in the monsoon boundary zone is similar,while the other three typical regions tend to form more ice cloud and mixed cloud in summer.The vertical distribution of cloud water content in the four typical regions decreases as altitude increases,while the ice water content increases first and then decreases;the effective radius of liquid water does not change significantly with altitude,while the effective radius of ice water varies relatively large but concentrates in the range of 47-68 um;the distribution of cloud water particle number concentration decreases with the increase of altitude,while that of ice particles decreases.There are obvious differences in macro physical characteristics such as cloud type,cloudtop and cloudbase height between different regions.The summer hydrometeor precipitation efficiency is unevenly distributed in Northwest China.Compared with the one over the west of Inner Mongolia and the southern Xinjiang,the precipitation efficiency over the monsoon boundary zone,the eastern part of Qilian Mountain region,the middle and western part of Tianshan region and the southwestern part of Three Rivers' Headstream region is relatively higher.However,the high value area is small and the precipitation efficiency over the northwest of the monsoon boundary zone,east of Tianshan,west of Qilian Mountains and northeast of Three Rivers' Headstream region are relatively lower,which reduced from 60% to about 30%.There is certain potential for development and utilization of atmospheric water resources in Northwest China.