Antarctic winter sea-ice seasonal simulation with a coupled model: Evaluation of mean features and biases

For Earth's climate system, the study of the seasonal variability of sea-ice is important as the sea-ice has a significant impact on the net radiative flux, which can influence the mean seasonal behaviours of the atmosphere and ocean. In this study, the seasonal hindcast of 14 austral winter seasons is conducted to assess the skill of a coupled model in simulating the seasonal Antarctic sea-ice and its connection with the other ocean and atmospheric variables. The GloSea4 set-up of the HadGEM3 coupled model is used for the seasonal simulations at the NCMRWF. The model could reproduce the sea-ice extent over the Antarctic for the Austral winter seasons with an average correlation value of 0.98. However, there are moderate biases in the sea-ice concentration. The sea-ice thickness in the model generally shows negative bias, which is not seen to be related to the surface air temperature biases in the coupled system. The moderate positive (warm) biases in the sea surface temperature extending into the upper ocean (30 m), combined with the sea-ice drift bias pattern away from the sea-ice region are the main reasons for the underestimation of sea-ice thickness in the model. The sea surface current bias pattern shows a poleward component that brings the warm water from the warm biased locations of the exterior region into the sea-ice region and explains the presence of warmer waters in the sea-ice regions. The anti-clockwise bias in the surface wind is seen to impact the surface current, Antarctic circumpolar current (ACC), having a similar anti-clockwise current bias. Despite these moderate biases in the model, the inter-annual variability of sea-ice extent is having a reasonably good skill. The model is suitable for extended/seasonal prediction of sea-ice during Austral winter for Antarctic.