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.