Aerosol-Cloud-Radiation Interactions in the Arctic

根据数字全球气候模型，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，变暖将在冬季最大。观测结果已经表明，北极地区的平均气温在春季、夏季和秋季显著上升。然而，冬季没有明显的温度变暖趋势，北极一些地区出现明显的降温。冬季温度趋势的缺乏与全球气候模型的预测相矛盾。在这项研究计划中，我们调查了一个过程，即脱水-温室反馈，可以解释冬季没有变暖。这一过程可概述如下。由于有利的大尺度大气环流，中纬度地区工业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具有较大尺寸的冰晶组成的云的形成（与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相反）。冰晶更有效地沉淀并使大气脱水。由于水蒸气是最有效的温室气体，大气中水蒸气的减少导致大气冷却。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北极冬季没有变暖的原因。本研究利用卫星遥感、实验室试验、现场观测和高分辨率气候模式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.