Effects And Analysis Of Radiation By Aerosol Particles In Seasonal Snow In Arid Region

Snow cover is the most important water resource in arid and semi-arid regions.After the aerosol particles settle on the snow through dry and wet,such as Black Carbon(BC),it can effectively reduce the albedo of snow and increase the solar incident radiation.The absorption of radiation,which then changes the shape of snow,accelerates the melting of the snow,reduces the snow cover,and ultimately affects regional and global water cycles and climate change.The arid region of central Asia is the largest non-zonal arid zone in the world,it is also one of the focal points of international water conflicts.The impact of climate change on the water cycle in the region has become a hot spot in international water research.Water resources have become a constraint factors on the "One Belt and One Road".In recent years,some studies have pointed out that the direct radiative forcing of BC has surpassed CH4,making BC’s contribution to global warming second only to CO2.The hydrological effect and climate effect caused by BC in snow have attracted the attention of scholars.This study uses remote sensing technology to analyze the temporal and spatial variability of snow cover information in the arid regions of central Asia,obtain the overall evolution of snow cover in the region from 2001 to 2018,explore the changes between snow cover and elevation,and reveal the snow and ice variation law of the belt in the arid regions of central Asia;the analysis of the AOD variation characteristics of autumn and winter in northern Xinjiang and the observation and spatial distribution of BC in seasonal snow in the northern Xinjiang region,which is typical of water resources and climate change in the arid regions of central Asia.Discusses correlation between latitude,altitude,AOD and BC in autumn and winter,and assessment of the chemical composition of the absorbent particles in snow and their possible anthropogenic and natural sources.Based on meteorological conditions such as temperature,air pressure,relative humidity,horizontal and vertical wind speed,the HYSPLIT model is used to simulate the main airflow direction of each sampling point,and then analyze the potential transport path of BC and its potential diffusion characteristics.using SNICAR model to simulate the change of snow albedo under different conditions,to explore the sensitivity of BC and snow particle size to snow spectrum and the influence of the mixed state on snow albedo;through model continuous simulation and remote sensing data,inversion of planar radiative forcing in northern Xinjiang based on MODIS data,the following conclusions were obtained:(1)The study area is divided into six typical regions(the five countries of Central Asia and the Xinjiang region of China).The rate of decline of SCP during the snowmelt period has obvious regional differences.The cyclical changes of SCP during the year are obvious,and the interannual variation is slightly decreasing.Similar to the SCP change,SCD also showed a slight downward trend,with 32.2%of the area showing a downward trend,30.9%of the area showing an increasing trend,and 36.9%of the area remaining stable.Below 1000m above sea level,the SCP changes with the seasons in a U-shape,with significant interannual variations.In the 1000-4000m region,the SCP exhibits a V-shape with seasonal changes during the year,and the interannual changes show stability fluctuations;more than 6000m is a permanent product.Snow,seasonal,spatial and temporal changes are not obvious.There is a clear correlation between snow cover and elevation in most areas of Xinjiang.The percentages of extremely low,low,medium,high and extremely high correlation are 0.86,16.84,11.67,36.22 and 34.41%,respectively.The significant correlation between regional snow cover and temperature is between-0.546 and-0.910,which has a great relationship with the special underlying surface conditions and the background of global warming.(2)Both SCP and SCD in Xinjiang showed a decreasing trend.According to the possible reasons for the decrease of snow information,the distribution of BC in the atmosphere and snow in Xinjiang was analyzed.The spatial distribution of AOD in winter in northern Xinjiang is relatively consistent from 2002 to 2018.The Altay region is in a low-value area.The high-value area is concentrated in the central and eastern regions of Jinghe County,Wusu City and Tianshan North Slope Economic Belt in the southeast of Aibi Lake.In autumn and winter,the overall AOD of northern Xinjiang has a slight upward trend,with 54.2%of pixels showing an increasing trend.Combined with the BC concentration and AOD in surface snow which collected in the field in 2018,the BC concentration ranged from 44.08 to 1949.9 ng/g,with an average of 536.71 ng/g,using optical methods to obtain CBCequiv,CBCmax,CBCest,and Atot data.The spatial distribution characteristics of each region and the relative contribution of BC and non-BC absorbing particles to light absorption,quantitative analysis of the correlation between AOD and BC content in snow,the correlation coefficient R2 can reach 0.705.To a certain extent,it is indicated that the aerosol particles in the winter atmosphere of northern Xinjiang are mainly BC.(3)According to the analysis of the concentration and spatial distribution characteristics of the chemical components of the absorbent particles in snow in majority samples,while combined with the dependence of each ion concentration and BC,which can be found that the economic belt of the northern slope of Tianshan is located in an area of anthropogenic emissions sources.Desert,western and northern of Ebinur Lake may mainly affected by local natural dust sources.Using the HYSPLIT diffusion model to simulate the BC backward trajectory in different regions,the BC potential transport path is obtained.In the backward trajectory of the Ebinur Lake Basin,with a proportion of 48-67%,the main path is the northeast direction of Bole-Jinghe-Ebinur Lake,which has a great influence on the BC concentration of the sampling point;In the northern slopes of the Tianshan Mountain,mainly moving to the northeast along the direction of Jinghe-Shihezi-Urumqi,with a proportion of 50%-75%,the local emissions are more serious and contribute a large proportion to BC;in the Altay area,the backward trajectory of the Altay region is mainly transported along the southern part of Russia-northern Kazakhstan-East Kazakhstan,accounting for 43%to 82%,the local pollution contribution is less;in the Karamay region,mainly comes from the east and west of Kazakhstan,accounting for 57%-65%,the pollution in some areas is not obvious;in the desert area,the transmission path is mainly in the southwest direction.(4)Different concentrations of absorbent particles in snow have a great influence on the albedo of snow.The SNICAR model is used to simulate the albedo change under different conditions,in order to provide data for subsequent radiative forcing.The results show that:The solar zenith angle has a great influence on the albedo in the near-infrared band.In the snow spectral curve,the solar zenith angle changes from 0° to 80°,and the albedo at 600 nm in the visible light band increases by 0.045.The albedo at 1000nm,1200nm and 1300nm in the near-infrared region increased by 0.16,0.225 and 0.249,With the increase of snow particle size from 100 to 800 microns,the corresponding albedo reduction can reach 0.15,The decrease of albedo caused by snow particle size in the range of 100-300 um is larger than that in the range of 400-800 um.,and the increase of the snow particle size can enhance the light absorption effect of the light absorbing particles.With the increase of BC concentration,the snow albedo will decrease significantly.The influence of BC concentration on spectral albedo is small in near infrared band,and the range of influence is mainly concentrated in visible band.In the presence of BC,the increase of snow particle size will increase the light absorption effect of BC,and the higher the concentration,the more the absorption increase.From the perspective of spectral index,it is shown that BC and snow particle size are sensitive in the visible light band of 350-740nm and near-infrared,and the correlation coefficient is high;Increasing the mixing proportion of BC and snow particle size will increase the reduction of snow albedo,and the higher the concentration of BC,the more significant the increase.If the BC is mixed with the uniform shape of the snow particle size,the albedo will gradually decrease.When the value in the snow is low,the albedo of the SNICAR simulation is in good agreement with the measured albedo.(5)Using SNICAR model to simulate continuous band information,combined with MODIS remote sensing data to invert the RFMODISIlaps generated by ILAPS,Reff and BC in seasonal snow in Xinjiang,analyze its spatial distribution characteristics,and analyze the factors affecting radiative forcing and discuss its uncertainty finally verified the radiative forcing based on remote sensing data inversion.The results showed that the average ILAPS,Reff and RFMODIS Ilaps in northern Xinjiang region were 0.273,241.38μm and 20.43≈7.3Wm-2,respectively.The spatial distribution of ILAPS and RFMODIS Ilaps shows obvious regional differences.The highest value of ILAPS appears in the neighboring Tacheng area of Kazakhstan-Kelamayi area and the eastern three counties of northern Xinjiang.The higher value of RFMODIS Ilaps is mainly distributed in the economic belt of the northern slope of Tianshan.There is no obvious regularity in the distribution of Reff in northern Xinjiang.By analyzing the correlation between BC emission data ILAPS,Reff and RFMODIS Ilaps,the distribution of RFMODIS Ilaps is dominated by ILAPS and BC emission data,and the correlation is up to 0.89.The BC emission data shows that local pollution emissions contribute to local ILAPS,which in turn affects RFMODIS Ilaps.Spatial distribution,while snow particle size has no significant effect on RFMODIS Ilaps.Using RFsite estimate data to verify the average absolute error of RFMODIS Ilaps,RFsite estimate and RFMODIS Ilaps inversion of remote sensing data is 24.05 W m-2;the error of RFMODIS Ilaps data is inversely proportional to the concentration of BC in snow,when RFMODIS IlapsBC is small,RFMODIS Ilaps error is large.The deviation of RFMODIS Ilaps in the MODIS data inversion in northern Xinjiang is between 24.3%and 326%.