| The desert and Gobi Desert were widely distributed in Xinjiang,which made Xinjiang became one of the regions where had the largest amount of aerosol emissions in China.Since the 21 st century,the degree of desertification in arid areas had been aggravating,and the generation of aerosols had become more intense,which had seriously threatened the ecological environment and human health in Xinjiang.Relevant studies had done tons of analysis on aerosol emissions and hazards by using remote sensing technology,but there was less discussion on the relationship among aerosols,clouds and precipitation.Based on MODIS aerosol data and reanalysis data of long time series in Xinjiang,combined with geomorphology,cloud microphysical parameters and precipitation knowledge,this paper analyzed the influence of aerosol on cloud and precipitation in Xinjiang.The conclusions were as follows:(1)Through the comparison between AOD data and ground-based station data,the applicability of the data set in Xinjiang was determined,and the underestimation of AOD in Xinjiang was known to a certain extent;Affected by the parcel of land and climate conditions,the AOD of Xinjiang was higher within the fringe of Jungar basin and round the Taklimakan Desert,and also the lower within the high altitude mountainous space with dense vegetation and distributed population.The mean value of AOD over the years showed significant seasonal and regional differences,which was shown as follows:spring > summer > winter > autumn,and the distribution of AOD in southern Xinjiang was larger than Northern Xinjiang.The spatial distribution of cloud parameters within the study area were obviously variated,the COD and CWP were higher in northern part,while the CER had not obvious difference between northern and southern part of Xinjiang.The results showed that there were obvious differences in the distribution of the three cloud parameters in the four seasons,in which COD was within the order of winter > summer > autumn > spring,which was quite different from AOD;CER was mainly in autumn and winter,which higher than spring and summer.CER was primarily distributed in high altitude areas in spring,and low altitude areas in summer,and fall and winter;The main characteristics of CWP were the highest in summer and the lowest in winter.The spatial distribution of precipitation was high in the north and low in the south,especially in Urumqi and Yili Kazakh Autonomous Prefecture;The main seasonal difference was summer > spring > autumn > winter;The order of geographical division was "Northern Tianshan > Northern Xinjiang > Southern Tianshan > Eastern Tianshan >Southern Xinjiang".(2)The annual variation of AOD in the study area was relatively stable,but there were some differences within the year.The annual variation of AOD showed a single peak distribution.The peak value mainly appeared in March to may,and was lower from June to August.The lowest concentration of AOD was from December to January,showing a more obvious seasonal difference.The interannual variation of cloud parameters in Xinjiang was consistent with AOD.From 2003 to 2019,the m-k test statistics of COD and CWP were greater than 0,which indicated that the cloud optical thickness and cloud water path square measure increasing;The m-k test statistic of CER was less than 0,which indicated that the effective radius of cloud droplets had a significant decreasing trend.The results showed that the seasonal distribution characteristics of biomass in Xinjiang were as follows: Summer > Spring > Autumn > Winter.The maximum annual precipitation occurred in 2016,while the maximum precipitation in different seasons occurred in 2009 or 2010;The minimum of annual precipitation occurred in 2008,the minimum of spring and summer precipitation occurred in 2012 and 2016 respectively,and the minimum of autumn and winter precipitation occurred in 2013.(3)There was an extremely correlation between aerosol and cloud parameters,mainly showed by the correlation between AOD and COD,and an indirect correlation between aerosol and precipitation.At the same time,the negative effect between aerosol and precipitation had obvious geographical differences,mainly in the southern Tianshan Mountains;Secondly,there was a negative correlation between AOD and CWP,and the main effect on precipitation was that the precipitation would larger when the concentration of AOD was between 0.1 and 0.4;Based on the spatial autoregressive model,it was found that AOD had significant regression relationship with three cloud parameters,and the regression coefficients of AOD to COD,CER and CWP were-1.37,-0.11 and-0.13,respectively.At the same time,three cloud parameters were used as explanatory variables for spatial autoregressive analysis:Average annual precipitation = 247.683 ×[ Annual mean cloud optical thickness] +869.779 ×[ Annual average cloud water path]-861.928The spatial autoregressive models of different seasons are as followsRRE(spring)= 0.016 ×[ Cloud optical thickness(spring)] + 110.762 ×[ Cloud water path(spring)]RRE(summer)= 104.595-19.138 ×[ Cloud optical thickness(summer)]-212.444×[ Cloud water path(summer)]The parametric statistic showed that each COD and CWP had a positive relationship with precipitation in spring,whereas COD and CWP had a negative impact on Precipitation in summer.Through the structural equation model,the direct or indirect relationship between the factors was discussed,and the size and direction of the path coefficient were obtained.The results showed that AOD was a negative path to other factors,and cloud parameters were a positive path to precipitation;The most significant was the negative path of the potential variable "cloud" constructed by AOD for cloud parameters,and the path coefficient was-0.710.The most significant cloud parameter was CWP,and the path coefficient was-0.708.CWP was also the most important positive path affecting precipitation,and the path coefficient was 0.678.Therefore,it was concluded that aerosol affects precipitation not only directly,but also mainly by changing the water content of clouds. |
PDF Full Text Request