期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：37
页码：11490-11495
DOI：10.1073/pnas.1510937112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceFuture-greenhouse simulations, and evidence of frost-intolerant species in high-latitude continental interiors during past equable climates, show significantly amplified warming at high latitudes over land in winter, with physical mechanisms that are still not understood. We show that the process of Arctic air formation, in which a high-latitude maritime air mass is advected over a continent, cooled at the surface, and transformed into a much colder continental polar air mass, may change dramatically and even be suppressed in warmer climates due to an increase in the duration of optically thick low clouds. This leads to two-degree warming over the continent in response to each degree of warming over the nearby ocean, possibly explaining both past and future continental warming. High-latitude continents have warmed much more rapidly in recent decades than the rest of the globe, especially in winter, and the maintenance of warm, frost-free conditions in continental interiors in winter has been a long-standing problem of past equable climates. We use an idealized single-column atmospheric model across a range of conditions to study the polar night process of air mass transformation from high-latitude maritime air, with a prescribed initial temperature profile, to much colder high-latitude continental air. We find that a low-cloud feedback--consisting of a robust increase in the duration of optically thick liquid clouds with warming of the initial state--slows radiative cooling of the surface and amplifies continental warming. This low-cloud feedback increases the continental surface air temperature by roughly two degrees for each degree increase of the initial maritime surface air temperature, effectively suppressing Arctic air formation. The time it takes for the surface air temperature to drop below freezing increases nonlinearly to [~]10 d for initial maritime surface air temperatures of 20 {degrees}C. These results, supplemented by an analysis of Coupled Model Intercomparison Project phase 5 climate model runs that shows large increases in cloud water path and surface cloud longwave forcing in warmer climates, suggest that the "lapse rate feedback" in simulations of anthropogenic climate change may be related to the influence of low clouds on the stratification of the lower troposphere. The results also indicate that optically thick stratus cloud decks could help to maintain frost-free winter continental interiors in equable climates.
