Characterization of the unprecedented polynya events north of Greenland in 2017/2018 using remote sensing and reanalysis
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Characterization of the unprecedented polynya events north of Greenland in 2017/2018 using remote sensing and reanalysis data Ruibo Lei1*, Dawei Gui1, 2, Zhouli Yuan1, Xiaoping Pang2, Ding Tao1, Mengxi Zhai1 1 MNR Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai 200136, China 2 Chinese Antarctic Center of Surveying and Mapping, Wuhan University, Wuhan 430072, China
Received 22 May 2019; accepted 20 August 2019 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
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. Key words: sea ice, ice concentration, ice motion, polynya, Greenland, Arctic Ocean Citation: Lei Ruibo, Gui Dawei, Yuan Zhouli, Pang Xiaoping, Tao Ding, Zhai Mengxi. 2020. Characterization of the unprecedented polynya events north of Greenland in 2017/2018 using remote sensing and reanalysis data. Acta Oceanologica Sinica, 39(9): 5–17, doi: 10.1007/s13131-020-1643-8
1 Introduction Polynyas are regions of open water and/or thin ice that occur within sea ice zones at locations where a more consolidated and thicker ice cover might be expected climatologically (Martin, 2001). They differ from leads, which are linear openings that appear ephemerally, and they tend to occur randomly from a spatial perspective (Tamura and Ohshima, 2011). Polynyas have gen
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