沙尘扬升、对流层-平流层输送及远距离传输过程中的垂直分布及动力热力结构

The transportation of dust aerosols from troposphere to stratosphere and their stratified transmission in atmosphere are the key factors for the dust storm processes. CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) can reveal the vertical structure of dust aerosols and so makes it possible to deeply investigative this problem. Through the analysis of CALIPSO data, the synoptic and diagnosis analysis of weather observation, numerical simulation and trajectory analysis, a series of studies will be conducted in this project. Firstly, the dust storm processes occurred in China from 2006 to 2012 will be arranged and classified. The synoptic analysis will be conducted also on the typical processes among them to reveal their main characteristics. Secondly, the vertical distribution of dust aerosols and its dynamic and thermal construction in every stage of dust storm processes will be studied. Thirdly，the strength, distribution and evolution of dust aerosols in the procedures of dust transportation from troposphere to stratosphere and long distance transmission in troposphere and stratosphere, will be studied. Fourthly，a comprehensive using of CALIPSO data, numerical simulation and diagnosis analysis will be conducted to reveal the causes of dust rising, dust transportation from troposphere to stratosphere, stratified transmission of dust aerosol and dust settlement in the whole dust storm processes. Fifthly, the numerical simulation and sensitivity tests will be conducted to reveal the influence of topography, surface flux and cold air breaking out on the formation of dust storm and the vertical construction of dust aerosols. Sixthly, a comprehensive using of CALIPSO data and trajectory analysis will be conducted to reveal the characteristics of dust particles motion in the procedures of dust rising, dust transportation from troposphere to stratosphere, stratified transmission of dust aerosol and dust settlement. The dust particles size and dust concentration with different movement condition in these periods of dust storm process will be estimated also. Finally, a physical concept model that reveals the characteristics of dust aerosols distribution and dust particles movement will be put forward.

沙尘对流层-平流层输送及远距离分层传输是沙尘暴过程的关键环节，CALIPSO资料能反映沙尘垂直分布，使得对该问题的深入研究成为可能。本项目拟充分利用CALIPSO资料，结合天气和诊断分析、数值模拟及轨迹分析等方法，在对我国主要沙尘暴天气进行全面梳理、分类及天气分析的基础上，研究各类沙尘暴过程不同阶段沙尘垂直分布及三维动力热力结构；研究沙尘对流层-平流层输送及其平流层传输过程中的强度、分布及其演变特征；结合数值模拟、诊断分析方法研究沙尘暴过程中沙尘扬升、对流层-平流层输送、分层传输、沉降等动力过程的形成原因和动力学机理；研究地形、地面热通量等外强迫因素对沙尘暴发生及沙尘垂直分布的影响；综合CALIPSO资料和轨迹分析方法研究沙尘扬升、对流层-平流层输送、分层传输、沉降的运动规律；并对期间不同运动状态的沙尘粒径、浓度特征进行估计和估算；进而建立能够反映沙尘分布和运动特征的沙尘暴物理概念模型。

沙尘垂直分布及对流层-平流层输送问题是沙尘暴研究的重要课题，但大气内部垂直探测手段的缺乏使得这方面研究相对滞后。本项目利用CALIPSO资料结合常规、非常规气象观测资料，综合数值模拟、诊断分析等方法，针对沙尘扬升、对流层-平流层输送（TST）及远距离传输过程中的垂直分布和动力热力结构进行了全面分析，结果发现：（1）近年来沙尘暴出现波动减少，2013年后有所增多，浑善达克沙地已成为内蒙古另一沙尘暴多发中心。（2）沙尘暴发生前后往往伴随层结稳定度的增强；期间，与中小尺度涡旋相关的切线速度明显强于观测到的水平风速。（3）利用CALIPSO资料结合轨迹分析发现，沙尘暴发展阶段，沙源地附近沙尘集中在行星边界层中（内蒙古西部<4km）；沙尘传输阶段，沙尘分为两层且分别位于行星边界层（<3km）和自由大气，其中，后者在蒙古高原下游地区位于3-8km，青藏高原下游则位于3-7km或7-11km；且沙尘层始终为弱稳定度、弱垂直风切变的中性混合层，沙尘层之间则为稳定层结；有小范围孤立沙尘区出现在平流层低层可以成为沙尘TST的直接证据。（4）沙尘暴过程中，对流层顶经历漏斗状折叠到双漏斗状折叠直至折叠区与切断低涡（蒙古气旋型）趋于一致的变化过程；上升气流或与偏南、偏东气流结合，或准垂直穿越对流层顶进入平流层，位置越偏东、偏北，TST气流的强度和范围越大。偏西气流相继完成对流层至平流层，平流层至对流层的穿越，却难以形成有效TST。（5）降低萨彦岭山地高度可使对流层顶折叠减弱，及TST气流减弱；去掉地面加热则使天气系统强度和上升运动明显减弱，两者均导致沙尘TST减弱。（6）轨迹分析表明，（蒙古气旋、冷锋型）沙尘粒子到达对流层中层后，其中一支以气旋式轨迹在对流层中高层向下游传输，另一支则继续上扬并穿过折叠的对流层顶，以反气旋式轨迹在平流层低层向下游传输。（7）基于WEI方法的诊断分析表明，（蒙古气旋、冷锋型）天气系统发展前期均产生平流层-对流层净输送，中后期则出现TST净输送，且蒙古气旋型TST明显强于冷锋型。（8）进一步总结了沙尘上扬、TST及远距离传输概念模型。本项目成果可为沙尘暴成因、远距离传输、对流层-平流层交换等方面研究提供参考，同时能为沙尘气溶胶气候效应研究及应对气候变化工作提供指导。