Analysis Of The Spatial Differences Of Surface Radiation In Central Tianshan Mountains,Xinjiang

Solar radiation is the main driving force of climate formation and change,which is of great significance in global change research.As solar radiation is weakened by atmosphere and redistributed by surface characteristics in the process of transmission,the spatial distribution of surface radiation is formed.The study of surface radiation is of great significance for further study of climate formation mechanism and surface energy balance.The terrain conditions of the mountainous areas make the redistribution of the solar radiation on the surface different from the plain areas,especially the strong altitude elevation,which leads to vertical gradient of mountain surface radiation.The harsh environments and difficult conditions make the area inaccessible and leads to difficulties in data collection,which is not conducive to mountain surface radiation balance research.In this paper,field observations in April 2014 and June 2016 were used to study and discuss the influence factors of surface radiation in central Tianshan Mountains,Xinjiang.The content of this study is established due to the needs of National Science and Technology Major Project "snow and ice monitoring and its evaluation based on high-resolution remote sensing data in Central Tianshan Mountains,Xinjiang"(Grant No.E0405/1112/05)to study the difference of surface radiation in Central Tianshan Mountains.Taking the Manasi River Basin of Central Tianshan Mountains as the study area,the surface radiation data obtained from two field observations were used to study the surface radiation characteristics in Central Tianshan Mountains.The differences of the components of surface radiation balance(downward radiation,upward radiation,net radiation,and surface albedo)were studied from three aspects:meteorological factors,underlying surface factors,and topographic factors.To explore the characteristics of surface radiation balance as reference for the study of surface radiation balance in mountainous area,the variation of each component of surface radiation balance with altitude is decipted and the vertical gradient of is obtained by using differential techniques.The main contents and conclusions of the paper are as follows.(1)Surface radiation observation data acquisitionIn April 2015 and June 2016,researchers went to the Central Tianshan Manasi River Basin Mountains of twice to conduct the field surface radiation observation.The underlying surface type and altitude of two factors were considered for the choice of field observation points in the case of accessibility.The basic information for each observation point is recorded.The surface radiation is measured by using the solar total radiation table under observation norms and a preliminary discussion is conducted according to the results.(2)Spatial distribution characteristics of upward and downward radiationBased on the field observations taken in Central Tianshan Mountains,the relationship between the spatial distribution of surface upward and downward radiation with solar altitude angle,distribution of cloud in the sky,type of the underlying surface,and terrain conditions are discussed.The results show that both the surface upward and downward radiation of different types of underlying surface increases with the increase of solar altitude angle under clear sky condition.Due to the severe influence of the cloud,the maximum value of the surface downward and upward radiation can exceed 18%and 40%of the maximum value in the clear sky condition,respectively.Snow upward radiation is affected by the physical properties of snow itself.Snow upward radiation is much greater than the grass,the absolute value of grass upward radiation is generally less than 200 W/m2.Surface downward radiation firstly increases then decreases with the increase of altitude,and the vertical radiation gradient is 7.91 W/m2·100m when downward radiation increases and 5.95 W/m2·100m when downward radiation decreases.While upward radiation shows a continuous increasing trend as altitude increases.The vertical radiation gradient is 14.60 W/m2·100m when altitude is between 1124?3324 m and 45.87 W/m2· 100m when altitude is between 3324?3879 m.The absolute value of the vertical gradient of the upward radiation is obviously greater than that of the downward radiation,which indicates that the spatial distribution of the upward radiation is much more complicated than the downward radiation.(3)Spatial distribution of surface net radiation and surface albedoThe relationship between the spatial distribution characteristics of surface net radiation and albedo obtained by field observation and the influencing factors is discussed.The four factors are solar altitude angle,distribution of cloud in the sky,type of the underlying surface,and the terrain conditions.The results show that the grass net radiation increases with the increase of solar altitude angle while the albedo of grass shows little change.Diurnal variation of the net radiation and albedo of the snow with the change of solar altitude angle is related to the physical properties of the snow itself.The surface net radiation is influenced by the clouds.The maximum grass net radiation in cloudy condition can exceed 14%of the clear sky condition.The fluctuation of the snow albedo curve is obvious.The net radiation of the grass surface is much greater than that of the snow under the same condition of sunny sky and solar altitude angle.The albedo of the snow surface is much greater than that of the grassland.The surface net radiation shows a decreasing trend with the increase of altitude.The vertical radiation gradient is-6.71 W/m2· 100m when altitude is between 1124?3324 m and-51.80 W/m2·100m when altitude is between 3324?3879 m.The surface albedo shows an increasing trend with the increase of altitude.The vertical albedo gradient is 0.01/100 m when altitude is between 1124?3324 m which means as the altitude increases by 100 m,the average albedo increases 0.01.This study presents the conditions of the twice field observations in Central Tianshan Mountains.Based on the observation data and conditions,the diurnal variation,cloud occlusion effect,horizontal distribution difference,and vertical distribution gradient of surface radiation are discussed from the perspective of solar elevation angle,cloud,underlying surface,and topography in the Central Tianshan Mountains.This study provides some reference for the study of climate research,surface radiation balance,and ice and snow ablation in mountainous areas.