Continental heat anomalies and the extreme melting of the Greenland ice surface in

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/2014JD021470 ©2014 American Geophysical Union. All rights reserved. Recent decades have seen increased melting of the Greenland ice sheet. On 11 July 2012, nearly the entire surface of the ice sheet melted; such rare events last occurred in 1889 and, prior to that, during the Medieval Climate Anomaly. Studies of the 2012 event associated the presence of a thin, warm elevated liquid cloud layer with surface temperatures rising above the melting point at Summit Station, some 3212 m above sea level. Here we explore other potential factors in July 2012 associated with this unusual melting. These include 1) warm air originating from a record North American heat wave, 2) transitions in the Arctic Oscillation, 3) transport of water vapor via an Atmospheric River over the Atlantic to Greenland, and 4) the presence of warm ocean waters south of Greenland. For the 1889 episode, the Twentiet