Causes and Evolution of Winter Polynyas over North of Greenland
- 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
- 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.
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Younjoo J. Lee et al.
Status: final response (author comments only)
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RC1: 'Comment on tc-2021-279', Frank Kauker, 24 Nov 2021
The comment was uploaded in the form of a supplement: https://tc.copernicus.org/preprints/tc-2021-279/tc-2021-279-RC1-supplement.pdf
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AC1: 'Reply on RC1', Younjoo Lee, 04 Apr 2022
We sincerely thank the reviewer for taking the time to provide helpful comments and have addressed them carefully in the revised manuscript.
As the reviewer suggested, the major revision of this manuscript is the expanded analysis of observed polynyas including the December period from 1979.
Also, we expanded the analysis of RASM ensembles for the winter months from December to March.
Please see attached the pdf files for the detailed responses.
Thank you.
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AC1: 'Reply on RC1', Younjoo Lee, 04 Apr 2022
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RC2: 'Comment on tc-2021-279', Axel Schweiger, 15 Feb 2022
- AC2: 'Reply on RC2', Younjoo Lee, 04 Apr 2022
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AC3: 'Comment on tc-2021-279', Younjoo Lee, 04 Apr 2022
Dear Dr. Christian Haas,
Thank you for your comment on ice deformation and thickening during the 2018 polynya period.
In the revised manuscript, since this study more focuses on the development of polynyas, we briefly mentioned the work by von Albedyll et al. (2021) in the discussion, regarding the contribution of dynamic and thermodynamic processes in sea ice thickness change.
Best,
Younjoo
Younjoo J. Lee et al.
Younjoo J. Lee et al.
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