摘要
本次研究利用MODIS、CALIPSO等卫星观测资料以及MERRA-2再分析资料分析了2007–2017年撒哈拉地区气溶胶光学厚度的空间分布特征。结果表明,撒哈拉地区气溶胶光学厚度的空间分布具有明显的季节变化,夏季沙尘气溶胶光学厚度高值区位于撒哈拉北部地区,高达0.6以上;而冬季沙尘气溶胶光学厚度高值区位于撒哈拉南部地区,最大值约为0.5。此外,撒哈拉地区在不同季节的主要气溶胶类型均为沙尘,但在撒哈拉南部地区沙尘气溶胶光学厚度对总气溶胶光学厚度的贡献有明显的季节性差异。基于CALIPSO体积退偏比的研究结果表明,在撒哈拉南部地区,夏季人为气溶胶占比大,气溶胶粒子趋于球形,冬季气溶胶粒子的退偏比则明显高于夏季,粒子非球形程度更高。夏季撒哈拉北部地区位于脊前槽后的位置,以南地区近地面主要为偏西风,携带了大量水汽的气流由大西洋吹向撒哈拉地区,使撒哈拉南部地区进入雨季,增强了沙尘气溶胶的沉降,因此夏季撒哈拉地区沙尘气溶胶光学厚度分布北高南低;冬季高压控制着撒哈拉北部地区,撒哈拉南部地区近地面盛行偏东风,且冬季温度偏低,容易形成逆温,不利于沙尘气溶胶和局地污染物扩散,导致沙尘气溶胶光学厚度南高北低。此外,局地温度变化也进一步促进了撒哈拉地区沙尘气溶胶空间分布的季节性差异。
The spatial distribution of the aerosol optical depth(AOD)in Sahara regions from 2007 to 2017 is analyzed using Moderate Resolution Imaging Spectroradiometer(MODIS)and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations(CALIPSO)remote sensing,along with Modern-Era Retrospective analysis for Research and Applications,Version 2(MERRA-2)reanalysis data.We found that AOD in Sahara regions shows a significant seasonal variation,which is mainly attributed to dust aerosol.The higher dust AOD in summer is mainly concentrated in northern Sahara,with a maximum value of 0.6.In contrast,the higher dust AOD in winter is mainly located in southern Sahara,with a maximum of 0.4.According to the layer-integrated volume depolarization ratio retrieved by CALIPSO,there are mainly natural dust aerosols in summer,whereas anthropogenic dust aerosols are the major species in winter in southern Sahara.We found that northern Sahara located behind the trough and before the ridge,together with the weak westerly in near surface,leads to a large amount of water vapor flow from the Atlantic to Sahara,enhancing the settling of dust aerosols over southern Sahara.As a result,dust AOD is lower over southern Sahara whereas higher over northern Sahara in summer.In winter,a high-pressure system controls northern Sahara regions,whereas the easterly wind prevails in near surface over southern Sahara,along with the lower surface air temperature and easily formed inversion layer.These are the disadvantages for the diffusion of local air pollutants and dust aerosols,resulting in a higher dust AOD over southern Sahara regions.In addition,local temperature variations partly lead to the seasonal differences of dust aerosols in Sahara regions.
作者
邸文婧
牛笑应
陈子琦
刘俊
王鑫
DI Wen-jing;NIU Xiao-ying;CHEN Zi-qi;LIU Jun;WANG Xin(Laboratory for Semi-Arid Climate Change of the Ministry of Education,College of Atmospheric Sciences,Lanzhou University,Lanzhou 730000,China;Lanzhou Central Meteorological Observatory,Lanzhou 730020,China)
出处
《地球化学》
CAS
CSCD
北大核心
2021年第1期98-109,共12页
Geochimica
基金
国家重点基础研究发展计划(2019YFA0606801)
国家自然科学基金(41975157,41775144,41675065,41875091)。
