Atmospheric science

Low-level clouds

Geophys. Res. Lett.http://doi.org/hwk (2012)

Credit: © ISTOCKPHOTO / THINKSTOCK

Sea ice is a vital component of the Arctic climate system, with recent losses thought to affect the properties of clouds in the region. Observations indicate that low-lying clouds are less frequent in ice-free areas of the Arctic Ocean during autumn.

Kazutoshi Sato of the Japan Agency for Marine-Earth Science and Technology and colleagues analysed the height of the autumnal cloud base in ice-covered and ice-free regions of the Chukchi and Beaufort Seas of the Arctic Ocean, using radiosonde and ceilometer data collected between 1998 and 2010. Low-lying clouds with a base below 500 m were 30% less frequent in ice-free regions, compared with ice-covered areas. In contrast, clouds characterized by a base height exceeding 500 m were about 20% more frequent in ice-free areas. Conditions in the boundary layer between the ocean and the atmosphere also varied with sea-ice coverage: ice-free areas were characterized by a larger thermal contrast between the air and sea, and greater warmth in the lower troposphere.

The team suggests that it is these boundary layer conditions, and associated heat fluxes, that determine cloud-base height over the Arctic Ocean.

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Armstrong, A. Low-level clouds. Nature Geosci 5, 368 (2012). https://doi.org/10.1038/ngeo1492

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