Spatial And Temporal Variation Of Cloud Water Resources And Assessment Of Precipitation Efficiency Over The Qinghai-Tibet Plateau

Clouds are one of the important components of the atmosphere.Clouds affect regional precipitation and radiation budgets through macroscopic and microscopic physical characteristics such as cloud cover,cloud water content,and cloud particle radius,which play a crucial role in climate change.As the global climate warms,glaciers on the Qinghai-Tibet Plateau melt away,and the area of lakes expands,which has a profound impact on regional water resources and the ecological environment.Clouds are the source of precipitation,which can supplement the water resource reserves of the Qinghai-Tibet Plateau.Therefore,it is of great significance to study cloud water resources and precipitation efficiency in the Qinghai-Tibet Plateau.This study analyzes the temporal and spatial distribution of cloud characteristic parameters over the Qinghai-Tibet Plateau using Cloud Sat satellite data and CERES fusion products from 2006 to 2019;The accuracy and applicability of TRMM 3B43 satellite precipitation data on the QinghaiTibet Plateau were verified using ground observation data,and the precipitation efficiency on the Qinghai-Tibet Plateau was calculated;Using atmospheric circulation data and ERA5 reanalysis data,the factors affecting precipitation efficiency over the Qinghai-Tibet Plateau were analyzed and evaluated.The results show that:(1)The high annual cloud cover values of the Qinghai-Tibet Plateau are located in the northwest and southeast of the plateau,showing a "seesaw" spatial variation characteristic on both sides of the north and south,and the cloud cover gradually decreases from the middle to the southeast and northwest sides;Temporarily,the cloud cover is high in summer and low in winter.The Qinghai-Tibet Plateau has the highest frequency of single-layer clouds(28.7%)and the thickest average thickness(2.75 km);As the number of cloud layers increases,the thinner the cloud thickness,the lower the probability of occurrence.The characteristics of different types of clouds in the QinghaiTibet Plateau vary.Altostratus is the dominant cloud system in the Qinghai-Tibet Plateau,with the highest frequency of occurrence among all types of clouds;Cirrus has the highest cloud base height,while cumulus has the lowest cloud base height;The thickness of deep convective clouds is the largest,and the thickness of stratus is the thinnest.(2)The spatial distribution of the cloud water path in the Qinghai-Tibet Plateau is characterized by high in the central region and low in the east and west sides;In terms of time distribution,the cloud water path showed an upward trend from 2006 to 2019.The radius of cloud ice water particles on the east and west sides of the Qinghai-Tibet Plateau is large,while the radius in the middle is low;Cloud liquid water particles have a large radius in the central part of the Qinghai-Tibet Plateau and a low radius in the surrounding area.In the Qinghai-Tibet Plateau region,ice water mixed-phase clouds are mostly present at altitudes of 4.8 to 7.7 km,and ice clouds are mostly present at altitudes above7.7 km;The highest cloud ice water content occurs at an altitude of 7.4 km in May,and the highest cloud liquid water content occurs at an altitude of 6 km in September.Compared with cloud ice water and cloud liquid water,cloud ice water has a larger range of changes in water content and particle concentration,and there are significant differences in size between ice and particles.(3)The fitting accuracy of TRMM 3B43 precipitation data and surface meteorological station precipitation data on the Qinghai-Tibet Plateau from 2006 to 2019 is high,with a correlation coefficient of 0.99.The average annual precipitation on the Qinghai-Tibet Plateau is 567.9 mm,showing an increasing trend with an increasing rate of 30.5 mm/10 a during the study period.The precipitation on the Qinghai-Tibet Plateau exhibits a spatial distribution characteristic of high in the south and low in the north,and the precipitation on the Qinghai-Tibet Plateau exhibits a reverse variation characteristic on both sides of the north and south and in the middle.The precipitation in most areas of the Qinghai-Tibet Plateau shows an increasing trend,while the precipitation in some areas of the northern Qinghai-Tibet Plateau shows a decreasing trend.The precipitation over the Qinghai-Tibet Plateau is greatly influenced by the regional cloud water path content and cloud water particle radius.(4)The spatial distribution of precipitation efficiency in the Qinghai-Tibet Plateau is characterized by high in the south and low in the north,and the precipitation efficiency in the eastern and central regions is characterized by reverse changes.The precipitation efficiency in the Himalayas and Kunlun Mountains on the Qinghai-Tibet Plateau varies greatly.Precipitation efficiency increased significantly in the central and eastern regions while decreasing significantly in the northern and western regions.Among the influencing factors of precipitation efficiency,the change of cloud water path has a significant impact on precipitation efficiency on the north and south sides of the Qinghai-Tibet Plateau;The North Pacific Index has a significant negative correlation with precipitation efficiency;The closer to the ground,the higher the correlation between meteorological element fields and precipitation efficiency.The precipitation efficiency of the Qinghai-Tibet Plateau is mainly influenced by regional relative humidity and wind.