科尔沁沙地对流起沙及对区域沙尘气溶胶贡献的数值模拟研究

Dust emission process is an important basic of the processes of dust transport and deposition, and it can be divided into two classifications based on dust emission mechanisms, i.e., saltation bombardment and/or aggregation-disintegration dust emission (SADE), and convective turbulent dust emission (CTDE). CTDE is mostly generated under atmospheric conditions with strong convective turbulence, and it occurs more frequently than dust-storm events (SADE) which require specific weather conditions. The effects of CTDE on regional dust aerosols and the earth system is very significant on a longer time scale. Based on the WRF-Chem model implemented with a CTDE module (KS14 scheme) and in combination with CTDE field observational data, this project focuses on one of the classical dust source regions, the Horqin Sandy Land area in Inner Mongolia of China, and aims to quantitatively descript the effects on CTDE by various meteorological factors and soil parameters, to improve and complete CTDE criteria through introducing more CTDE impact factors, to simulate and analyze the spatial and temporal distribution features and evolution of CTDE, and to quantitatively evaluate the CTDE’s contribution to dust aerosols in the regional atmosphere. It can provide important scientific reference for the improvement on the CTDE modelling, and better understanding of the evolvement mechanism of dust aerosols as well as their effects on climate and environment.

沙尘起沙过程是决定沙尘输送和沉降的重要基础，可分为跃移起沙和对流起沙。大气对流运动较强时经常发生对流起沙现象，相对特定天气条件下发生的跃移起沙（如沙尘暴），对流起沙发生更加频繁，在中长时间尺度上对区域大气沙尘气溶胶及地球系统具有重要的影响。本申请拟利用中尺度大气-化学耦合模式WRF-Chem耦合对流起沙模块 (KS14方案)，结合对流起沙野外实测资料，定量研究内蒙古科尔沁沙地地区对流起沙过程气象和土壤因子的影响和作用，改进对流起沙判据；模拟和分析对流起沙的时空分布特征和演变规律，定量评估对流起沙对大气沙尘气溶胶的贡献。研究结果为改善对流起沙的数值模拟、理解大气沙尘气溶胶的演变机制及其气候和环境效应提供重要科学依据。

本项目拟研究科尔沁沙地对流起沙特征及其对区域大气沙尘气溶胶的贡献。为此，本项目利用内蒙古科尔沁沙地沙尘天气观测和监测站多年的沙尘和气象要素实测资料进行了以下研究：1）考虑临界起沙阈值存在季节变化，进而改进已有的对流起沙判据，为后续对流起沙研究奠定重要基础；2）深入研究不同气象和土壤因子（尤其是相对湿度和土壤含水量）在不同时间尺度上对起沙过程的影响；3）分析对流起沙过程中沙尘气溶胶的粒径分布特征；4）基于观测建立简单适用的对流起沙参数化方案，并开展不同方案之间的对比和模拟研究；5）定量评估不同起沙机制（对流起沙和跃移起沙）对大气沙尘气溶胶的贡献。研究发现：科尔沁沙地地区环境湿度的变化在不同时间尺度上对起沙过程的影响有所不同，随着时间尺度的增加（小时-日-季节）环境湿度对起沙过程的影响趋于减弱。对流速度尺度是决定对流起沙通量的重要因子，观测表明二者存在较好的幂指数变化关系，在此基础上建立的对流起沙参数化方案相比基于物理机制建立的复杂方案(MK14方案)模拟效果相近,但形式更加简单且参数更易于获取。从全年尺度上而言，对流起沙和跃移起沙过程向区域大气中分别贡献了约40%和60%的沙尘气溶胶，表明对流起沙在较长的时间尺度上对沙尘气溶胶的贡献不可忽略。