Anomalous blocking over Greenland preceded the 2013 extreme early melt of local sea ice

Ballinger, Thomas J., Hanna, Edward, Hall, Richard J. , Cropper, Thomas E., Miller, Jeffrey, Ribergaard, Mads H., Overland, James and Hoyer, Jacob L. (2017) Anomalous blocking over Greenland preceded the 2013 extreme early melt of local sea ice. Annals of Glaciology . ISSN 0260-3055

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The Arctic marine environment is undergoing a transition from thick multi-year to first-year sea ice cover with coincident lengthening of the melt season. Such changes are evident in the Baffin Bay-Davis Strait-Labrador Sea (BDL) region where melt onset has occurred ~8 days decade-1 earlier from 1979-2015. A series of anomalously early events has occurred since the mid-1990s, overlapping a period of increased upper-air ridging across Greenland and the northwestern North Atlantic. We investigate an extreme early melt event observed in spring 2013 below the 1981-2010 melt climatology), with respect to preceding sub-seasonal mid-tropospheric circulation conditions as described by a daily Greenland Blocking Index (GBI).

The 40-days prior to the 2013 BDL melt onset are characterized by a persistent, strong 500 hPa anticyclone over the region (GBI >+1 on >75% of days). This circulation pattern advected warm air from northeastern Canada and the northwestern Atlantic poleward onto the thin, first-year sea ice and caused melt about 50 days earlier than normal. The episodic increase in the ridging atmospheric pattern near western Greenland as in 2013, exemplified by large positive GBI values, is an important recent process impacting the atmospheric circulation over a North Atlantic cryosphere undergoing accelerated regional climate change.

Keywords:Greenland, blocking, GBI, sea ice, melt onset, sea surface temperature
Subjects:F Physical Sciences > F860 Climatology
Divisions:College of Science > School of Geography
ID Code:28776
Deposited On:29 Sep 2017 08:15

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