10 Aug 2022
10 Aug 2022

Reanalysis representation of low-level winds in the Antarctic near-coastal region

Thomas Caton Harrison1, Stavroula Biri2, Thomas J. Bracegirdle1, John C. King1, Elizabeth C. Kent2, Étienne Vignon3, and John Turner1 Thomas Caton Harrison et al.
  • 1British Antarctic Survey, Cambridge, UK
  • 2National Oceanography Centre, Southampton, UK
  • 3Laboratoire de Météorologie Dynamique/IPSL/Sorbonne Universités/CNRS, UMR 8539, Paris, France

Abstract. Low-level easterly winds encircling Antarctica help drive coastal currents which modify transport of circumpolar deep water to ice shelves, as well as the formation and distribution of sea ice. Reanalysis datasets are especially important at high southern latitudes where observations are few. Here, we investigate the representation of the mean state and short-term variability of coastal easterlies in three recent reanalyses, ERA5, MERRA-2 and JRA-55. Reanalysed winds are compared with summertime marine surface wind observations from the ASCAT scatterometer and surface and upper air measurements from coastal stations. Reanalysis coastal easterlies correlate highly with ASCAT (r=0.91, 0.89 and 0.85 for ERA5, MERRA-2 and JRA-55 respectively) but notable wind speed biases are found close to the coastal margins, especially near complex orography and at high wind speeds. To characterise short-term variability, 12-hourly reanalysis and coastal station winds are composited using self-organising maps (SOMs), which cluster timesteps under similar synoptic and mesoscale influences. Reanalysis performance is sensitive to the flow configuration at stations near steep coastal slopes, where they fail to capture the magnitude of surface wind speed variability when synoptic forcing is weak and conditions favour katabatic forcing. ERA5 exhibits the best overall performance, has more realistic orography and a more realistic jet structure and temperature profile. These results demonstrate the regime behaviour of Antarctica’s coastal winds and indicate important features of the coastal winds which are not well characterised by reanalysis datasets.

Thomas Caton Harrison et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-693', Anonymous Referee #1, 15 Sep 2022
  • RC2: 'Comment on egusphere-2022-693', Anonymous Referee #2, 16 Sep 2022

Thomas Caton Harrison et al.

Thomas Caton Harrison et al.


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Short summary
Easterly winds encircle Antarctica, moving sea ice and helping drive ocean currents which shield ice shelves from warmer waters. Our most complete picture of how these winds behave comes from reanalysis datasets. In this paper we use satellite data, surface measurements and weather balloons to test how realistic recent reanalysis estimates are. The winds are generally accurate, especially in the most recent of the datasets, but important short-term variations are often misrepresented.