中国东部人为气溶胶气候效应的季节性特征研究

With the rapid economic growth and urbanization in East China, climate effects of anthropogenic aerosols have been paid more attention recently. The seasonality in anthropogenic aerosol effects on East China climate is noticed in many observational and modeling studies. However, the characteristics of its spatial distribution and cause of formation are still not well investigated.First, the seasonal variation of anthropogenic aerosol distribution and the influence of aerosol emissions and climate background on it will be analyzed. Then, the direct and indirect forcing of anthropogenic aerosols and their seasonal variation will be analyzed with new diagnostic methods. The impacts of large amount of mid-low level clouds in cold seasons and positive feedback between surface air temperature and low-level cloud amount in East China on aerosol radiative forcing will be investigated. Finally, with coupled ocean-atmosphere model simulations, the effects of response and feedback mechanism (including relatively position of rain belt and aerosol radiative forcing, anomaly of diabetic heating and Sea surface air temperature induced by anthropogenic aerosol forcing) on seasonal variation of precipitation and circulation will be analyzed.

随着经济的发展和城市化的推进，中国东部地区人为气溶胶气候效应已经成为一个研究热点。中国东部人为气溶胶及其气候效应的季节性特征已经被大量观测和模拟研究所注意，但是其分布特征和形成的原因还没有被很好地揭示。本项目将通过通过数值试验以及与观测的对比分析，揭示人为气溶胶分布的季节性特征,并分析排放源和气候背景场对其影响。利用新的辐射诊断方法，诊断中国东部人为气溶胶的直接和间接辐射强迫，揭示其季节变化特征，分析中国东部冷季节大量中低层云和“低云-地表温度”的正反馈机制对其影响。进而结合海气耦合试验，分析气候响应和反馈机制的季节差异性（包括气候雨带和辐射强迫的相对位置、人为气溶胶引起的非绝热加热和海温异常）对中国东部环流降水季节性特征的影响。

项目利用气候模式和观测资料研究了中国东部人为气溶胶气候效应的季节性特征，分析了人为气溶胶对东亚夏季风、东亚冬季风和春季气候影响,提出了新的可能的影响机制。研究发现人为气溶胶光学厚度(AOD)和直接效应在夏季最为显著，而气溶胶的间接效应却在冷季节最强，这与中国东部冷季节分布的大量中低层云有关。人为气溶胶使得东亚季风气候发生了显著变化：东亚夏季风减弱（南涝北旱），东亚冬季风的北方模态增强（欧亚大陆北部大范围变冷），华南春季降水显著极少(华南春旱)。人为气溶胶对东亚地区气候的影响机制存在着显著的季节差异性。夏季大尺度对流凝结潜热反馈是夏季风减弱的关键，人为气溶胶抑制中国北方对流的活动，减少对流层中高层凝结潜热的释放，减弱海陆热力对比，进而减弱季风环流和水汽输送，进一步抑制北方降水，形成一个正反馈。冬季风增强与黑碳的积雪反照率效应和大尺度瞬变活动反馈密切相关，黑碳引起的青藏高原增暖增强了高原北侧的大气斜压性，并通过瞬变扰动-平均流反馈使得冬季风北方模态增强，欧亚大陆北部大范围变冷。春季气溶胶间接效应起到了主导作用，它使得华南的降水显著减少。而地表温度-低云云量反馈会进一步增强人为气溶胶间接效应，加剧华南春旱的趋势。