Aerosol-Cloud-Radiation Interactions in the Arctic

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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.