Aerosol-Cloud-Radiation Interactions in the Arctic

根据数值全球气候模型，北极将是与温室气体增加相关的变暖最大的地区。这些气候模型还预测，全球变暖将在冬季达到最大值。观测已经表明，北极的平均气温在春季、夏季和秋季显著上升。然而，冬季没有明显的气温变暖趋势，北极一些地区的气温显著下降。冬季气温趋势的缺失与全球气候模型的预测相矛盾。在这个研究项目中，我们研究了一个过程，即脱水-温室反馈，可以解释冬季没有变暖的原因。这一过程可以概括如下。由于有利的大尺度大气环流，该行业在中纬度上空排放的人为气溶胶在冬季经北极输送。这些气雾剂是高度酸性的。实验室实验和野外观测表明，天然气溶胶表面的酸性涂层改变了某些气溶胶(冰核)成核冰晶的能力。冰核浓度的降低导致由较小浓度的较大尺寸的冰晶组成的云的形成(而不是由较大浓度的较小尺寸的冰晶组成的未受污染的气团中的冰云)。冰晶的沉淀效率更高，使大气脱水。由于水蒸气是最有效的温室气体，大气中水蒸气的减少会导致大气降温。这一过程发生在被污染的北极气团中，这可以解释为什么在过去几十年里，北极的冬季没有变暖。本研究采用卫星遥感、实验室实验、现场测量和高分辨率气候模型等方法对这一过程进行了研究。

According to numerical global climate models, the Arctic will be the region where the warming associated to the increase of greenhouse gases will be the largest. These climate models also predict the warming will the maximum during winter. Observations already show that the mean temperature over the Arctic has increased significantly during spring, summer and autumn. However, there is no significant temperature warming trend during winter and a significant cooling over some regions of the Arctic. The absence of wintertime temperature trend contradicts the predictions of global climate models. In this research program, we investigate a process, namely the dehydration-greenhouse feedback, that could explain the absence of warming during winter. This process may be summarized as follows. Anthropogenic aerosols emitted by the industry over the mid-latitudes is transported over the Arctic during winter due to the favorable large-scale atmospheric circulation. These aerosols are highly acidic. Laboratory experiments and field observations have shown that acid coating on natural aerosols alters the ability of some aerosols (the ice nuclei) to nucleate ice crystals. The decrease of the ice nuclei concentration leads to the formation of clouds composed of a smaller concentration of ice crystals with a larger size (as opposed to ice clouds in an unpolluted air mass composed of a large concentration of ice crystals of smaller size). Ice crystals precipitate more efficiently and dehydrate the atmosphere. The decrease of water vapor in the atmosphere leads to an atmospheric cooling since water vapor is the most efficient greenhouse gas. This process occurring in polluted arctic air mass could explain the absence of warming over the Arctic during winter over the last decades. In this research, satellite remote sensing, laboratory experiments, in-situ measurements and high-resolution climate models are used to investigate this process.