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Sea-ice forecasts with an upgraded AWI Coupled Prediction System
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  • Longjiang Mu,
  • Lars Nerger,
  • Jan Streffing,
  • Qi Tang,
  • Bimochan Niraula,
  • Lorenzo Zampieri,
  • Svetlana Loza,
  • Helge Goessling
Longjiang Mu
Alfred Wegener Institute for Polar and Marine Research

Corresponding Author:[email protected]

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Lars Nerger
Alfred Wegener Institute Helmholtz Center for Polar and Marine Research
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Jan Streffing
Alfred Wegener Institute for Polar and Marine Research
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Qi Tang
Alfred Wegener Institute Helmholtz Center for Polar and Marine Research
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Bimochan Niraula
Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung
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Lorenzo Zampieri
Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
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Svetlana Loza
Alfred Wener Institute for Polar and Marine Research
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Helge Goessling
Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research
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Abstract

A new version of the AWI Coupled Prediction System is developed based on the Alfred Wegener Institute Climate Model v3.0. Both the ocean and the atmosphere models are upgraded or replaced, reducing the computation time by a factor of 5 at a given resolution. This allowed us to increase the ensemble size from 12 to 30, maintaining a similar resolution in both model components. The online coupled data assimilation scheme now additionally utilizes sea-surface salinity and sea-level anomaly as well as temperature and salinity profile observations. Results from the data assimilation demonstrate that the sea-ice and ocean states are reasonably constrained. In particular, the temperature and salinity profile assimilation has mitigated systematic errors in the deeper ocean, although issues remain over polar regions where strong atmosphere-ocean-ice interaction occurs. One-year-long sea-ice forecasts initialized on January 1st, April 1st, July 1st and October 1st from 2003 to 2019 are described. To correct systematic forecast errors, sea-ice concentration from 2011 to 2019 is calibrated by trend-adjusted quantile mapping using the preceding forecasts from 2003 to 2010. The sea-ice edge raw forecast skill is within the range of operational global subseasonal-to-seasonal forecast systems, outperforming a climatological benchmark for about two weeks in the Arctic and about three weeks in the Antarctic. The calibration is much more effective in the Arctic: Calibrated sea-ice edge forecasts outperform climatology for about 45 days in the Arctic but only 27 days in the Antarctic. Both the raw and the calibrated forecast skill exhibit strong seasonal variations.