Characterization of the unprecedented polynya events north of Greenland in 2017/2018 using remote sensing and reanalysis data

Based on an ice concentration threshold of 90%,it has been identified that two polynya events occurred in the region north of Greenland during the 2017/2018 ice season.The winter event lasted from February 20 to March 3,2018 and the summer event persisted from August 2 to September 5,2018.The minimum ice concentration derived from Advanced Microwave Scanning Radiometer 2(AMSR2)observations was 72%and 65%during the winter and summer events,respectively.The occurrence of both events can be related to strengthened southerly winds associated with an increased east-west zonal surface level air pressure gradient across the north Greenland due to perturbation of mid-troposphere polar vortex.The relatively warm air temperature during the 2017/2018 freezing season in comparison with previous years,together with the occurrence of the winter polynya,formed favourable pre-conditions for ice field fracturing in summer,which promoted the formation of the summer polynya.Diminished southerly winds and increased cover of new ice over the open water were the dominant factors for the disappearance of the winter polynya,whereas increased ice inflow from the north was the primary factor behind the closure of the summer polynya.Sentinel-1 Synthetic Aperture Radar(SAR)images were found better suited than AMSR2 observations for quantification of a new ice product during the polynya event because the SAR images have high potential for mapping of different sea ice regimes with finely spatial resolution.The unprecedented polynya events north of Greenland in 2017/2018 are important from the perspective of Arctic sea ice loss because they occurred in a region that could potentially be the last“Arctic sea ice refuge”in future summers.