Preprints
https://doi.org/10.5194/tc-2021-279
https://doi.org/10.5194/tc-2021-279

  29 Sep 2021

29 Sep 2021

Review status: this preprint is currently under review for the journal TC.

Causes and Evolution of Winter Polynyas over North of Greenland

Younjoo J. Lee1, Wieslaw Maslowski1, John J. Cassano2,3, Jaclyn Clement Kinney1, Anthony P. Craig4, Samy Kamal5, Robert Osinski6, Mark W. Seefeldt2,3, Julienne Stroeve2,7, and Hailong Wang8 Younjoo J. Lee et al.
  • 1Naval Postgraduate School, Monterey, California, USA
  • 2National Snow and Ice Data Center, Boulder, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
  • 3Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado, USA
  • 4Independent Researcher
  • 5RedLine Performance Solutions, College Park, Maryland, USA
  • 6Institute of Oceanology of the Polish Academy of Sciences, Sopot, Poland
  • 7University of Manitoba, Winnipeg, Manitoba, Canada
  • 8Pacific Northwest National Laboratory, Richland, Washington, USA

Abstract. During the 42-year period (1979–2020) of satellite measurements, only three winter polynyas have ever been observed north of Greenland and they all occurred in the last decade, i.e. February of 2011, 2017 and 2018. The 2018 polynya was unparalleled by its magnitude and duration compared to the two previous events. Combined with the limited weather station and remotely-sensed sea ice data, a fully-coupled Regional Arctic System Model (RASM) hindcast simulation was utilized to examine the causality and evolution of these recent extreme events. We found that neither the accompanying anomalous warm surface air intrusion nor the ocean below had an impact on the development of these winter open water episodes in the study region (i.e., no significant ice melting). Instead, the extreme atmospheric wind forcing resulted in greater sea ice deformation and transport offshore, accounting for the majority of sea ice loss. Our analysis suggests that strong southerly winds (i.e., northward wind with speeds of greater than 10 m/s) blowing persistently for at least 2 days or more, were required over the study region to mechanically redistribute some of the thickest sea ice out of the region and thus to create open water areas (a latent heat polynya). In order to assess the role of internal variability versus external forcing of such events, we additionally simulated and examined results from two RASM ensembles forced with output from the Community Earth System Model (CESM) Decadal Prediction Large Ensemble (DPLE) simulations. Out of 100 winters in each of the two ensembles, initialized 30 years apart, one in December 1985 and another in December 2015, respectively, 17 and 14 winter polynyas were produced over north of Greenland. The frequency of polynya occurrence and no apparent sensitivity to the initial sea ice thickness in the study area point to internal variability of atmospheric forcing as a dominant cause of winter polynyas north of Greenland. We assert that dynamical downscaling using a high-resolution regional climate model offers a robust tool for process-level examination in space and time, synthesis with limited observations and probabilistic forecast of Arctic events, such as the ones being investigated here and elsewhere.

Younjoo J. Lee et al.

Status: open (until 24 Nov 2021)

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Younjoo J. Lee et al.

Younjoo J. Lee et al.

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Short summary
During 1979–2020, three winter polynyas occurred in February of 2011, 2017 and 2018 north of Greenland. The anomalous warm air intrusion had no impact on melting of ice. Instead, the extreme wind forcing resulted in greater ice transport offshore. Based on the two ensemble simulations, representing a 1980s thicker ice vs a 2010s thinner ice, a dominant cause of these winter polynyas stems from internal variability of atmospheric forcing rather than from the forced response to warming climate.