干旱区一次春季沙尘过程的大气气溶胶垂直分布结构及其特征

采用微脉冲激光雷达(Micro-Pulse Lidar,MPL)对干旱荒漠代表站张掖站上空一次春季沙尘暴过程的边界层和自由大气的气溶胶分布和大气环境进行了观测。结果表明,气溶胶的垂直廓线可分为高、中、低3层,高层气溶胶出现在5～9km,主要是通过上风方向的高海拔区域或低层气溶胶通过对流等过程突破边界层顶进入自由大气输送而来,其分布高度在一天中随着时间的推移逐渐降低;中层气溶胶位于2.5～4.5km,其消光特性随高度的增加没有明显的变化,具有垂直混合现象;低层气溶胶在2.5km以下,其消光特性随着高度增加反而降低;中、低层气溶胶主要来源于外部源区或当地沙尘源区和沙壤土起沙。气溶胶垂直分布表现出3种形式:在大气稳定条件下,气溶胶随高度增加呈单峰型减小趋势;不稳定条件下随高度增加指数型降低;混合层中随高度增加而保持稳定。由于受边界层日变化的影响,气溶胶分布的上界出现单峰型日变化特征,具体表现为下午较高,早晨较低。

Vertical Distribution Structure and Characteristic of Aerosol over Arid Region in a Dust Process of Spring

Direct observation of vertical distribution of aerosol and atmospheric condition in the free troposphere are made using the surface Micro-Pulse Lidar(MPL) at Zhangye station(39.08°N,100.27°E) in the spring of 2008.The results show that the vertical profiles of aerosol over Zhangye can be divided into three parts,namely high layer,middle layer and low layer.Aerosol in high layer is appeared from 5 km to 9 km at 08:00～24:00,and it is down trend with time.Aerosol in middle layer is small height gradient with time that show well-mixed aerosol layer,and ranged from 2.5 km to 4.5 km.The aerosol in low layer is decreased with height increasing.The aerosol in high layer is come from outer original,due to being lifted from higher altitude region on upwind direction,and is transported on higher level.The aerosol in middle and low layers are from outer original or local,due to multi-sand originals and local sand texture.There are three aerosol distribution shapes,aerosol profile shows exponent decreased with height increasing under the stable condition,a small height gradient is well-mixed dust layer,vertical profile of aerosol shows single peak with height increasing under the unstable atmospheric condition.Due to effect of the top of atmospheric boundary,up-boundary of extinction coefficient shows diurnal change of single peak,which is higher in the afternoon and lower in the morning.