吸收性气溶胶辐射强迫对青藏高原热源及东亚水循环的影响机制

The heat source of the Tibetan Plateau (TP) and its thermal forcing play an important role in the radiative budget and hydrologic cycle over East Asia. The absorbing aerosols could strongly absorb solar radiation, which ranked behind only CO2 as the second largest warming factors in the atmosphere. Moreover, the absorbing aerosols deposited on snow can reduce the snow albedo and further accelerate the snow melting, resulting in a series of climate feedbacks. The TP has the largest glacier except the polar region, which is located close to regions over South and East Asia that have been and are predicted to continue to be the largest sources of black carbon and dust in the world. Due to the unique geographical location and climatic characteristics of TP, the influence of the TP absorbing aerosols on the TP heat source and East Asia climate have become a hot issue of Earth Science in recent years. Based on the WRF-Chem model (Weather Research and Forecasting model coupled with chemistry), coupled with SNICAR (SNow, Ice, and Aerosol Radiative model), combined with ground-based observations and satellite retrievals, the aim of this project is to develop the dust emission scheme in different types of land cover over the TP and surrounding regions; estimate the emission, transport and dry/wet deposition of absorbing aerosols over the TP; elucidate the influence of absorbing aerosols in heating up the TP; explore the mechanism of absorbing aerosols influencing atmospheric circulation and hydrologic cycle over East Asia by changing the TP heat source.

青藏高原热源变化及其热力强迫对东亚乃至全球气候变化具有重大影响。吸收性气溶胶具有强烈的吸光性。大气中的吸收性气溶胶是仅次于CO2的最重要的大气升温因子；沉降到冰冻圈表面的吸收性气溶胶可以降低冰雪反照率，导致冰雪的加速消融，引发一系列大气反馈效应。高原是除极地外拥有冰川最多的地区，毗邻东亚和南亚两大主要吸收性气溶胶排放源，其独特的地理位置和气候特征使得吸收性气溶胶对高原热源及东亚气候的影响成为近年来地球科学领域的热点问题之一。本项目拟采用耦合了SNICAR模块的WRF-Chem模式，将野外观测、地面台站和卫星遥感资料作为观测约束，评估和改进数值模式中高原及周边地区大气和积雪中吸收性气溶胶的模拟效果；揭示高原吸收性气溶胶的潜在来源及输送路径；阐明高原大气和积雪中吸收性气溶胶及其相互作用对高原热源的贡献；探讨吸收性气溶胶对东亚大气环流和水循环的影响机制。

高原吸收性气溶胶的特征、来源及传输过程，及其气候效应的研究是近年来地球科学研究领域的热点问题之一。本项目以高原吸收性气溶胶为研究核心，基于改进后的数值模式、卫星遥感和地面观测，系统探讨了高原吸收性气溶胶的特征、来源及其输送机制，揭示了高原吸收性气溶胶辐射强迫对高原热源、亚洲气候和空气污染的影响。主要研究成果如下：（1）系统揭示不同季节高原吸收性气溶胶的来源及其输送机制，提出了夏季塔克拉玛干沙尘向高原输送的经向传输机制，基于卫星遥感和数值模拟发现，春季西风急流中心位于高原上空，西风偏强，高原沙尘以局地起沙为主；夏季西风急流北移并减弱，加之高原及塔克拉玛干感热加热增强，导致沙尘聚集在高原北坡。（2）阐明东亚冬季风对高原黑碳分布的影响及其环流机制。研究表明，在冬季，当东亚冬季风偏强时，高原南侧西风气流增强，东亚大槽东移，来自印度北部、四川盆地和中国中部的黑碳气溶胶会抬升传输到青藏高原东部。分析了高原大气中沙尘和黑碳气溶胶的辐射强迫和加热率，量化高原吸收性气溶胶对高原热源的加热作用。（3）揭示了揭示了高原大气和沉降到积雪中吸光性杂质对南亚和东亚的温度、环流场和水汽循环都有重要影响；重点分析青藏高原沙尘气溶胶对积雪的影响机制，发现沉降到积雪的沙尘可增加地表吸收短波辐射0.75 W m-2，并通过快速融雪使高原西部和北部积雪减少8%。（4）发现冬季青藏高原异常增可进一步导致南亚和东亚污染物聚集。冬季高原温度异常增加使得经向温度梯度增加，通过加强大气斜压性，北支西风增强。南亚北部出现异常下沉气流导致的下沉逆温和异常偏北气流带来的干冷空气，温度平流所致的逆温和减弱的冬季风出现在东亚东部，有利于南亚和东亚污染物聚集。该研究的实施对更加全面认识高原吸收性气溶胶时空分布，及其热源变化以及对中国乃至东亚灾害天气和气候变异预测的影响具有重要意义。在项目资助下在JC、ES&T、ERL、JGR等大气科学领域权威期刊发表学术论文13篇。