气溶胶辐射效应和海洋反馈作用对东亚夏/冬季风的影响机制研究

With the rapid growth of pollutant emissions, the climatic effects of aerosols have been paid more attention recently over East Asia, although great uncertainties are still remain. Firstly, the seasonal features of aerosol climatic effects and the cause of formation were not well evaluated in literature. Secondly, the mechanism of aerosol climatic effects on East Asian summer monsoon was still controversial, and their impacts on East Asian winter monsoon was rarely investigated. Thirdly, because of the restricted research conditions, the only regional atmospheric model was used by previous studies to assess the aerosol climatic impacts. Because the oceanic feedbacks are neglected, therefore the accurate results of aerosol radiative impacts on East Asian monsoon are difficult to obtain. In this study, on the basis of previous research, by using a regional coupled atmosphere-ocean-land model, the seasonality of climatic effects by the different aerosol species and the mixed total aerosol are identified. Furthermore, the possible mechanism of radiative effects by different aerosol components and the mixed total aerosols on the land sea temperature contrast, the sea temperature gradient, and the final East Asian summer/winter monsoon and hydrological cycle could be quantified. By considering typical aerosol species and discussing the results from the coupled atmosphere-ocean-land model and the only atmospheric model, we can also obtain the possible impacts of oceanic feedbacks on East Asian summer/winter monsoon.

随着排放的增加，东亚地区气溶胶的气候效应已成为当前研究的热点，但仍存在很大不确定性。首先，已有研究未能揭示东亚地区气溶胶气候效应的季节性变化特征及其产生原因；其次，已有研究对气溶胶影响东亚夏季风的机制还存在争议，对其影响东亚冬季风还不清楚；最后，以往研究受条件限制，仅采用区域大气模式研究气溶胶的气候效应，屏蔽了海洋的反馈作用，因此难以获得气溶胶影响东亚季风的准确结果。本项目基于前期研究，利用最新的区域海陆气耦合模式，得到各种气溶胶/总气溶胶气候效应的季节变化特征；讨论各种气溶胶/总气溶胶如何通过影响海陆温差、海温梯度，进而影响东亚夏季/冬季季风环流和降水的物理机制；选取典型气溶胶，通过讨论耦合或不耦合海洋模块模拟结果的差异，定量评价海洋的反馈作用对东亚夏季/冬季季风的可能影响。

气溶胶直接辐射强迫（RF）及海洋的反馈作用，是影响东亚夏季和冬季季风的重要因子。本项目利用区域海陆气-气溶胶耦合模式，结合卫星和再分析数据，研究了东亚黑碳、有机碳、硫酸盐、海盐、沙尘RF的分布、季节变化、相对贡献及气象因子对RF的影响；重点讨论了黑碳、硫酸盐、总气溶胶（黑碳、有机碳、硫酸盐外部混合）辐射效应对东亚夏季和冬季季风的影响机制；以总气溶胶为例，研究了可变海温对东亚夏季和冬季季风的影响。研究发现，总气溶胶大气顶（TOA）和地表RF主要由沙尘、黑碳、硫酸盐贡献；沙尘和黑碳贡献了大气加热的96%。春季和夏季，沙尘TOA RF及大气加热强于黑碳；秋季和冬季，黑碳强于沙尘。云使沙尘、黑碳TOA RF增强，其他气溶胶TOA RF减弱；云使各种气溶胶地表RF都减弱。相对湿度（RH）导致粒子膨胀效应使各种气溶胶TOA和地表RF都增强。相对云的影响，RH对RF的影响在垂直方向上更均一。云对气溶胶TOA和地表RF的影响大于RH。黑碳夏季大气热泵效应（EHP效应）起主导作用，使夏季风增强，中国大陆地区降水增加；冬季地表降温效应更显著，北风异常导致冬季风增强，中国大陆地区降水减少。硫酸盐的直接效应以地表降温作用为主，夏季其地表降温效应较弱，除中国北方外其他地区降水减少；冬季硫酸盐地表降温效应显著增强，冬季风增强，中国大陆地区降水减少。总气溶胶使东亚夏季风减弱，水汽向北输送受阻，中国南方降水增加，中国北方受EHP效应影响降水增加，中国中部和东部降水减少，呈“+ − +”分布型；总气溶胶冬季地表降温效应，使冬季风增强，中国大陆地区降水减小。对于总气溶胶，相较单独大气模拟结果，夏季，可变海温减弱了夏季风增强的趋势，使中国南方的降水异常偏大，中国中部、东部和北方的降水异常变小；冬季，可变海温导致更强的北风异常，冬季风更强，使中国中部、东部、南方的降水异常变大。