Search

An operational synoptic-scale sea ice forecasting system for the Southern Ocean, namely the Southern Ocean Ice Prediction System (SOIPS), has been developed to support ship navigation in the Antarctic sea ice zone. Practical application of the SOIPS forecasts had been implemented for the 38th Chinese National Antarctic Research Expedition for the first time. The SOIPS is configured on an Antarctic regional sea ice–ocean–ice shelf coupled model and an ensemble-based localized error subspace transform Kalman filter data assimilation model. Daily near-real-time satellite sea ice concentration observations are assimilated into the SOIPS to update sea ice concentration and thickness in the 12 ensemble members of the model state. By evaluating the SOIPS performance in forecasting sea ice metrics in a complete melt–freeze cycle from 1 October 2021 to 30 September 2022, this study shows that the SOIPS can provide reliable Antarctic sea ice forecasts. In comparison with non-assimilated EUMETSAT Ocean and Sea Ice Satellite Application Facility (OSI SAF) data, annual mean root mean square errors in the sea ice concentration forecasts at a lead time of up to 168 h are lower than 0.19, and the integrated ice edge errors in the sea ice forecasts in most freezing months at lead times of 24 and 72 h maintain around 0.5×106 km 2 and below 1.0×106 km 2 , respectively. With respect to the scarce Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) observations, the mean absolute errors in the sea ice thickness forecasts at a lead time of 24 h are lower than 0.3 m, which is in the range of the ICESat-2 uncertainties. Specifically, the SOIPS has the ability to forecast sea ice drift, in both magnitude and direction. The derived sea ice convergence rate forecasts have great potential for supporting ship navigation on a fine local scale. The comparison between the persistence forecasts and the SOIPS forecasts with and without data assimilation further shows that both model physics and the data assimilation scheme play important roles in producing reliable sea ice forecasts in the Southern Ocean. [ABSTRACT FROM AUTHOR]

The sea ice cover has experienced substantial changes in Antarctica in the past decades, yet its responses to the long-term trend of the local atmosphere are still not clear. With the aid of an Antarctic coupled sea ice-ocean-ice shelf model, the sea ice seasonality in response to the long-term trend of the local atmospheric forcing has been quantified based on a sea ice budget analysis. Significantly spatial variabilities have been found in the Antarctic sea ice in response to the long-term trend of the local atmospheric forcing. The sea ice area and volume decrease in the Weddell Sea and increase in the Ross Sea throughout the year. In the Amundsen-Bellingshausen Seas sector, the sea ice area decreases from December to June and increases from July to November, while the sea ice volume decreases throughout the year. In the Indian-Western Pacific Oceans sector, the sea ice area decreases from January to May and increases from June to December, while the sea ice volume increases throughout the year. The long-term trend of the local atmospheric forcing modulates the sea ice loss in the melting period mainly through modifying the ice-ocean heat flux over the ice base, while it governs the sea ice growth in the freezing period by the combined effects of the ice-ocean heat flux and the atmosphere-ocean heat flux. Although the trend of the surface wind can also lead to distinct variations by the local sea ice convergence/divergence, the integrated contributions over the basin scale are relatively small. [ABSTRACT FROM AUTHOR]

Warm deep water intrusion over the Antarctic continental shelves threatens the Antarctic ice sheet stability by enhancing the basal melting of ice shelves. In East Antarctica, the Antarctic Slope Current (ASC), along with the Antarctic Slope Front (ASF), acts as a potential vorticity barrier to prevent the warm modified Circumpolar Deep Water (mCDW) from ventilating the cold and fresh shelf. However, mCDW onshore transport is still observed within certain shelf regions, such as submarine troughs running perpendicular to the continental shelf. This study focuses on the dynamic mechanisms governing mCDW intrusion within a submarine trough over the fresh shelf regions, East Antarctica. Based on an idealized eddy-resolving coupled ocean–ice shelf model, two high-resolution process-oriented numerical experiments are conducted to reveal the mechanisms responsible for the mCDW onshore transport. Three dynamic mechanisms governing cross-slope mCDW intrusion are identified: 1) the bottom pressure torque, 2) the topography beta spiral, and 3) the topography Rossby waves. These three mechanisms simultaneously govern the mCDW intrusion together. The bottom pressure torque plays a leading role in driving the time-mean onshore flow whose vertical structure is determined by the topography beta spiral, while the topography Rossby waves contribute to the high-frequency oscillations in the onshore volume and heat transport. The simulated spatial distribution and seasonality of mCDW intrusion qualitatively coincide with the observed mCDW intrusion over fresh shelf regions, East Antarctica. Both the topography beta spiral and the ASC play an important role in governing the seasonality of mCDW intrusion. [ABSTRACT FROM AUTHOR]