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GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L08503, doi:10.1029/2008GL033451, 2008

The contribution of cloud and radiation anomalies to the 2007 Arctic sea ice extent minimum

Jennifer E. Kay

Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado, USA
Department of Atmospheric Sciences, Colorado State University, Fort Collins, Colorado, USA


Tristan L'Ecuyer

Department of Atmospheric Sciences, Colorado State University, Fort Collins, Colorado, USA


Andrew Gettelman

Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado, USA


Graeme Stephens

Department of Atmospheric Sciences, Colorado State University, Fort Collins, Colorado, USA


Chris O'Dell

Department of Atmospheric Sciences, Colorado State University, Fort Collins, Colorado, USA


Abstract

Reduced cloudiness and enhanced downwelling radiation are associated with the unprecedented 2007 Arctic sea ice loss. Over the Western Arctic Ocean, total summertime cloud cover estimated from spaceborne radar and lidar data decreased by 16% from 2006 to 2007. The clearer skies led to downwelling shortwave (longwave) radiative fluxes increases of +32 Wm−2 (−4 Wm−2) from 2006 to 2007. Over three months, simple calculations show that these radiation differences alone could enhance surface ice melt by 0.3 m, or warm the surface ocean by 2.4 K, which enhances basal ice melt. Increased air temperatures and decreased relative humidity associated with an anti-cyclonic atmospheric circulation pattern explain the reduced cloudiness. Longer-term observations show that the 2007 cloudiness is anomalous in the recent past, but is not unprecedented. Thus, in a warmer world with thinner ice, natural summertime circulation and cloud variability is an increasingly important control on sea ice extent minima.

Received 29 January 2008; accepted 13 March 2008; published 22 April 2008.

Keywords: Arctic sea ice; radiation; clouds.

Index Terms: 1621 Global Change: Cryospheric change (0776); 1610 Global Change: Atmosphere (0315, 0325); 1640 Global Change: Remote sensing (1855); 3310 Atmospheric Processes: Clouds and cloud feedbacks; 3349 Atmospheric Processes: Polar meteorology.

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Citation: Kay, J. E., T. L'Ecuyer, A. Gettelman, G. Stephens, and C. O'Dell (2008), The contribution of cloud and radiation anomalies to the 2007 Arctic sea ice extent minimum, Geophys. Res. Lett., 35, L08503, doi:10.1029/2008GL033451.