A regional climate system model, ARCSyM, was used to investigate the formation and maintenance of a sensible heat polynya in the Antarctic. As a first step, the model was implemented for the Antarctic region and the large-scale atmospheric and sea ice circulation was validated against available analyses and satellite derived products. The coupled atmosphere-ice model performed well in comparison to other atmosphere-only regional models.
To determine some of the smaller scale biases from the large-scale atmospheric model, the atmospheric fields and surface energy budget were compared to point measurements at surface stations on the Antarctic continent. This comparison determined some significant biases over the high plateau in the large-scale model simulations due to physical parameterizations and topography in the model. The results near the coastal areas were more credible and hence added confidence could be placed in the finer scale simulations near the margins of the continent.
A finer resolution atmosphere-sea ice simulation of the Cosmonaut Sea region determined that the small-scale atmospheric circulation contained no significant biases given limited data, yet the sea ice simulation exhibited a significant overestimation of sea ice concentration. One possibility was an error in the atmosphere-ice energy exchange, in which case a good atmospheric simulation was obtained for the wrong reasons. Otherwise, there was a lack of oceanic heat, which emphasized the importance of the oceanic heat flux in regulating the sea ice cover, and that a polynya is not likely to develop under atmospheric forcing alone.
Finally, ARCSyM was used to determine the possibility of deep ocean convection or upwelling and the role of the atmosphere. In simulations with a one-dimensional mixed-layer model, the threshold for deep mixing of the water column was found to be unrealistic compared to limited observations. This model result and the findings from the analysis of observations provided evidence that deep convection is not likely in the Cosmonaut Sea. Indications are that dominant oceanic forcing in the region appears to be an upwelling driven by surface divergence. Thus, the atmosphere-sea ice model was used to determine the relative roles of the ocean and atmosphere. The results evinced that a polynya formed through sea ice divergence and the sea ice divergence was correlated with the atmospheric divergence. Also, a polynya was not maintained over a large region of excessive oceanic heat. These assertions suggest that oceanic upwelling by itself is not sufficient to form and sustain a polynya in this region and that the atmospheric divergence provided the driving mechanism for the formation of the Cosmonaut Sea polynya.