Aerosol-Cloud-Radiation Interactions in the Arctic

根据全球气候数值模型，北极将是温室气体增加导致的变暖幅度最大的地区。这些气候模型还预测，变暖将在冬季达到最大值。观测已经表明，在春季、夏季和秋季，北极上空的平均温度显著上升。然而，在北极的一些地区，冬季没有明显的温度变暖趋势和明显的降温。冬季气温趋势的缺失与全球气候模式的预测相矛盾。在这个研究项目中，我们研究了一个可以解释冬季没有变暖的过程，即脱水-温室反馈。这个过程可以概括如下。由于有利的大尺度大气环流，工业在中纬度地区排放的人为气溶胶在冬季被输送到北极上空。这些气溶胶是强酸性的。实验室实验和实地观察表明，天然气溶胶上的酸性涂层改变了某些气溶胶（冰核）形成冰晶的能力。冰核浓度的降低导致形成由较小浓度的冰晶和较大尺寸组成的云（与未污染气团中由较大浓度的冰晶和较小尺寸组成的冰云相反）。冰晶更有效地沉淀，使大气脱水。大气中水蒸气的减少导致大气冷却，因为水蒸气是最有效的温室气体。这一过程发生在受污染的北极气团中，可以解释过去几十年冬季北极没有变暖的原因。本研究采用卫星遥感、实验室实验、原位测量和高分辨率气候模型来研究这一过程。

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.