Regional atmospheric patterns and the delayed sea-ice freeze-up in the western Arctic
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The western Arctic sea ice cover has dramatically changed since the late 1970s, particularly the timing of the autumn freeze-up. While atmospheric dynamic and thermodynamic processes associated with synoptic-scale weather patterns largely impact the onset of regional ice formation, linkages between the subseasonal occurrences of these patterns, across interannual to multidecadal time scales, and the freeze-up are not well understood. This manuscript takes a synoptic climatological atmospheric pattern (AP) classification approach to evaluate the role of warm season-dominant (i.e., May-October) mean sea-level pressure (MSLP) and 1000–500 hPa thickness APs, derived from daily NCEP/NCAR reanalysis fields, on the passive microwave-derived freeze-up dates for the marginal Beaufort/Chukchi Seas and western Arctic Ocean from 1979 to 2013. Analysis of the respective classifications’ frequencies and their relationships to the freeze-up reveals that approximately one-third of freeze-up variance may be explained by early/middle warm season Beaufort Sea High surface pressure pattern frequency changes. A similar amount of freeze-up variance is explained by the occurrence of mid-warm season dominant thermal patterns, either earlier or later than their predominant season. Both results suggest that pattern changes may be associated with changing ocean–atmosphere heat exchanges affiliated with lengthened periods of melt conditions.
KeywordsWarm Season Atmospheric Pattern Western Arctic Ocean Freeze Date Thickness Pattern
The authors would like to thank Jeffrey Miller (NASA Cryospheric Sciences Laboratory/Wyle, Inc.), Stephen Howell (Environment Canada), Mary Haley (NCAR/CISL), and Cameron Lee (Kent State University, Department of Geography) for their assistance with aspects of data acquisition/processing and figure creation.
The NCEP/NCAR reanalysis data is obtained from the NOAA/ESRL Physical Science Division (http://www.esrl.noaa.gov/psd/data/reanalysis/ reanalysis.shtml), while the freeze-up data is acquired from the NASA Cryosphere Science Research Portal (http://neptune.gsfc.nasa.gov/csb/index.php?section=54) with updates for 2012 and 2013 supplied by Jeffrey Miller.
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