| In the context of global warming,the ecosystem of arid and semi-arid regions is very fragile and sensitive.Climate change plays a decisive role in the survival and sustainable development of human beings in this region,which has attracted widespread attention in recent years.As one of the important factors regulating climate,clouds are the main cause of changes in meteorological factors such as sunshine hours,relative humidity,temperature and precipitation.The formation and change of clouds play an important role in regulating the Earth's climate,water cycle processes and the balance of the Earth's radiation budget.These effects are mainly achieved through macroscopic and microscopic characteristics such as cloud cover,cloud type,cloud water content,cloud height,cloud thickness,and the size of cloud droplets and crystals,and the characteristics of different cloud types vary greatly in space and time.Based on CloudSat data,ERA5 reanalysis data,TRMM precipitation data and ground observation data,this paper selects the Qilian Mountains and the surrounding areas as the study area,which are highly sensitive to climate change,and takes clouds as the research object.From the perspective of the earth-atmosphere system,we analyze the horizontal and vertical distribution characteristics of cloud characteristic parameters in the Qilian Mountains and the surrounding areas,as well as the response relationships between cloud characteristic parameters and various meteorological elements,and draw the following conclusions.(1)The total cloud amount in the Qilian Mountains and surrounding areas showed an increasing trend from 2006 to 2017(7.4%/10a),with high and low clouds contributing to the total clouds with weak fluctuations,and low clouds changing less.The seasonal variation of cloud amount is obvious,with the highest in summer and the lowest in winter.In terms of the spatial distribution,the highest total cloud amount(53%)was found in the Qinghai Lake area,followed by the western Qilian Mountains(33%),and the lowest cloud amount was found in the Qaidam Basin area.Cloud liquid water content showed a decreasing trend from2006 to 2017(-1.6 mg·m-3/10a)and cloud ice water content showed an increasing trend(2 mg·m-3/10a),but none of the trends were significant.The seasonal variation of cloud liquid(ice)water content is also higher in summer and lower in winter.In terms of the spatial distribution,the highest cloud liquid(ice)water content was found in the Qinghai Lake area,followed by the western Qilian Mountains,and the lowest in the Hexi Corridor area.(2)The vertical distribution of cloud amount in the Qilian Mountains and the surrounding areas has obvious seasonal variations,with the highest cloud amount at 6-11 km from March to May.After May,the clouds begin to decrease at 8-11km and increase at 5-8 km.The cloud liquid water content and cloud ice water content both have obvious seasonal changes,showing that the cloud liquid(ice)water content is the most in summer and autumn,and the least in winter.The existence of clouds is in the following forms:water clouds are dominant below 5km,water in 5-10 km clouds is mostly solid and liquid coexistence,and ice clouds are dominant above 10 km.Among the regions,the cloud amount and cloud liquid(ice)water content are the highest in the Qinghai Lake area and the western Qilian Mountains.The clouds in the study area are mainly single-layer clouds,and as the number of cloud layers increases,the frequency of clouds decreases,the cloud layers become thinner,and the vertical distance between adjacent cloud layers decreases.The frequency of upper-level clouds is the highest among all types of clouds,followed by cirrus clouds,and cumulus clouds are the lowest.For deep convective clouds,the cloud top height is higher,the cloud base height is lower,and the cloud average thickness is larger.The cloud top height of rainlayer cloud is slightly lower than that of deep convective cloud,and its average thickness is only second to that of deep convective cloud.For cirrus,cumulus and stratus cloud,the distance between cloud top height and cloud base height is smaller,and the cloud layer is thinner.(3)The Meridian and Zonal distribution of cloud parameters in the Qilian Mountains and its surrounding areas are obvious.The longitude distribution of cloud amount and cloud liquid(ice)water content is higher than the regional average between 90°E-93°E and 98°E-101°E.The zonal mean distribution of cloud amount and cloud liquid(ice)water content is higher in the higher elevation mountains,and lower in the lower elevation areas north of the Qilian Mountains.In the number of cloud layers,1-layer clouds have no obvious meridional distribution,and 2-3 layers appear more frequently in the eastern Qilian Mountains.In the zonal distribution,1-layer clouds and 2-layer clouds appear more frequently in the area south of 38°N,and 3-5-layer clouds appear more frequently in the area slightly southward than 1 and 2-layer clouds.The meridional and zonal distribution of each cloud type is more complicated by the influence of topography and water vapor.The correlation between most of the circulation and cloud properties is not very high,and the variation of cloud properties in this region may be more influenced by local geothermal conditions.The high value of water vapor content is mainly distributed in the eastern part of Qilian Mountains,which indicates that the formation and development of clouds in the Qilian Mountains and surrounding areas are the result of the interaction between water vapor and topography.(4)The annual mean temperature in the Qilian Mountains and surrounding areas showed an increasing trend(0.53°C/10a)during 2006-2017,and precipitation also showed a weak increasing trend.The average annual temperature is lower in the Qilian Mountains and the inner plateau,and higher in the Qaidam Basin and the areas north of the Qilian Mountains.The precipitation shows a decreasing trend from southeast to northwest.The influence of cloud amount on temperature has more obvious geographical characteristics,the increase(decrease)of cloud amount in the Qilian Mountains,north of Altun Mountains and the central and western regions of Qilian Mountains is always accompanied by the increase(decrease)of temperature in the Qilian Mountains,north of Altun Mountains and Qaidam Basin,conversely,the decrease(increase)of temperature in the southern and eastern fringes of Qaidam Basin.There is also a significant coupling pattern between the cloud content and the temperature field. |
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