Causes and Evolution of Winter Polynyas North of Greenland
The causes and evolution of winter polynyas north of Greenland are investigated using the limited weather station and remotely sensed sea ice data together with output from the fully coupled Regional Arctic System Model (RASM), including one hindcast and two ensemble simulations. We find that the extreme atmospheric wind forcing is primarily responsible for sea ice redistribution and transport offshore, which accounts for the majority of sea ice loss within the observed winter polynyas. This modeling study confirms that strong southerly winds (>10 m s-1) blowing persistently over the study region for at least 2 days or more are required to mechanically transport some of the thickest Arctic sea ice out of the region and thus to create open-water areas (i.e., a latent heat polynya).
Based on results from two RASM ensemble simulations produced by dynamical downscaling of the Community Earth System Model (CESM) Decadal Prediction Large Ensemble (DPLE) simulations, the frequency of winter polynya occurrence is insensitive to the initial sea ice thickness in the study area. This implies internal variability of atmospheric forcing and not a forced response to climate warming as a dominant cause of winter polynyas north of Greenland.
During 1979–2020, only four winter polynyas occurred north of Greenland, in December 1986 and February 2011, 2017, and 2018 according to the observations and RASM hindcast. The extreme wind forcing resulted in greater ice transport offshore and opening of these polynyas. The anomalous warm air intrusion was not a factor in generating these polynyas, as no sea ice melt was diagnosed. Two decadal RASM ensemble runs were completed and analyzed, one representing thicker ice in the 1980s and one with thinner ice in the 2010s. A comparison of results from these two ensemble runs indicates that a dominant cause of these winter polynyas stems from internal variability of atmospheric forcing rather than from the forced response to a warming climate.