" s! F% \7 F& L) ?3 _9 K $ Q$ c- s' h* c+ `The heat wave that struck Greenland in July 2012 melted surface ice across virtually the entire ice sheet, causing extensive flooding. Ice core data suggest that such events occur only about once every 150 years on average, with the last one in 1889. Ralf Bennartz and colleagues have examined the physical mechanisms behind the 2012 event. At high elevations thin liquid-bearing clouds had an important role in enhancing surface warming, as they were optically thick enough and low enough to significantly enhance the downwelling infrared flux at the surface. At the same time they were thin enough to allow sufficient solar radiation through to raise surface temperatures above the melting point. The cover shows formations known as fog bows, or cloud bows, over the NSF mobile laboratory at Summit Station, Greenland. Fog bows are similar to rainbows but less colourful as they are caused by smaller liquid water droplets. Cover photo by Dr. Brant Miller, University of Idaho, taken in July 2012." Q4 ]5 z' J; T K/ y- u# M) e5 J
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