标题：An Overview of Antarctic Sea Ice in the Community Earth System Model Version 2, Part I: Analysis of the Seasonal Cycle in the Context of Sea Ice Thermodynamics and Coupled Atmosphere‐Ocean‐Ice Processes
期刊名称：Journal of Advances in Modeling Earth Systems
电子版ISSN：1942-2466
出版年度：2021
卷号：13
期号：3
页码：e2020MS002143
DOI：10.1029/2020MS002143
出版社：John Wiley & Sons, Ltd.
摘要：We assess Antarctic sea ice climatology and variability in version 2 of the Community Earth System Model (CESM2) and compare it to that in the older CESM1 and (where appropriate) real‐world observations. In CESM2, Antarctic sea ice is thinner and less extensive than in CESM1, though sea ice area is still approximately 1 million km 2 greater in CESM2 than in present‐day observations. Though there is less Antarctic sea ice in CESM2, the annual cycle of ice growth and melt is more vigorous in CESM2 than in CESM1. A new mushy layer thermodynamics formulation implemented in the latest version of the Community Ice Code (CICE) in CESM2 accounts for both greater frazil ice formation in coastal polynyas and more snow‐to‐ice conversion near the edge of the ice pack in the new model. Greater winter ice divergence in CESM2 (relative to CESM1) is due to stronger stationary wave activity and greater wind stress curl over the ice pack. Greater wind stress curl, in turn, drives more warm water upwelling under the ice pack, thinning it and decreasing its extent. Overall, differences between Antarctic sea ice in CESM2 and CESM1 arise due to both differences in their sea ice thermodynamics formulations and differences in their coupled atmosphere‐ocean states. Plain Language Abstract Sea ice is a central part of the Antarctic climate system, and Earth system models are an indispensable tool for studying the climate of the Antarctic. Advances in modeling are essential for understanding and projecting future changes in the region as the globe warms. Here, we describe Antarctic sea ice climatology in the state‐of‐the‐art Community Earth System Model, version 2 (CESM2). CESM2 incorporates several modeling advances which collectively improve representation of Antarctic climate compared to previous model versions. Among these is a “mushy layer” treatment of sea ice, where the ice is modeled as a mixture of solid ice and salty water. Modeling sea ice as a mushy layer changes the way that Antarctic sea ice grows in CESM2, in a manner more closely resembling how Antarctic sea ice has been observed to grow in the real world. Antarctic sea ice area in CESM2 also more closely matches observed sea ice area, due primarily to differences in atmospheric winds and ocean heating. In conjunction with observations and other state‐of‐the‐art global climate models, CESM2 will be an important tool for furthering understanding of Antarctic climate at present and in the future.
