A comparison of the atmospheric response to the Weddell Sea Polynya in AGCMs of varying resolutions

Abstract. The Weddell Sea Polynya (WSP) is a large opening within the sea ice cover of the Weddell Sea sector. It has been a rare event in the satellite period, appearing between 1973 and 1976, and again in 2016/17. Some studies have suggested that there may be a large-scale atmospheric response to the WSP. Here, we use high and low-resolution atmosphere-only experiments with the HadGEM3 UK Met Office model, the ECHAM5 Max Planck Institute model and the OpenIFS ECMWF model, to isolate the atmospheric response to the WSP. Results show a large (~100–200 Wm^-2) turbulent air-sea flux anomaly above the polynya. The response to the WSP is local and of short duration (barely outlasting the WSP) with a similar magnitude and spatial pattern of lower tropospheric warming and increase in precipitation in all 6 configurations. All models show a weak decrease in surface pressure over the WSP, but this response is small (~2 hPa) in comparison to internal variability. The dynamic response is inconsistent between models and resolutions, notably above the boundary layer, suggesting a weak or null response that is covered by internal variability aloft. The high resolution does alter the pattern of the response but increases its magnitude by up ~50 % in two of the three models. The response is influenced by natural variabilty of the westerly jet. The models perform well against ERA5 reanalysis data for the 1974 WSP in spatial response and magnitude, showing a turbulent heat flux of approximately 150 Wm^-2.