Atmospheric Response to Arctic Sea Ice Loss in Low and High Resolution Coupled Experiments

• Main Authors: Chripko, Svenya, Msadek, Rym, Sanchez-Gomez, Emilia, Terray, Laurent, Moine, Marie-Pierre, Bessières, Laurent
• Format: Still Image
• Language: unknown
• Published: Zenodo 2019
• Subjects: Arctic; albedo; Sea ice
• Online Access: https://dx.doi.org/10.5281/zenodo.4507576; https://zenodo.org/record/4507576

Since the late 1970s summer Arctic sea ice extent has declined by more than 10% per decade and climate projections indicate a high probability of having ice-free summers by the middle to end of the century due to increasing greenhouse gas concentrations (Stroeve et al. 2012). Furthermore, climate model studies have shown that the decline of Arctic sea ice cover can affect weather and climate not only locally but also remotely through changes in the mid-latitude atmospheric circulation. However, the mechanisms beneath the Arctic-mid-latitude linkages are not completely understood. In this study, we investigate the atmospheric response in autumn and winter to Arctic sea ice reduction, using coupled ocean-atmosphere experiments based on the CNRM-CM6 model. We set the sea ice albedo to the ocean value, which yields a complete sea ice loss in summer, a large reduction in autumn and a moderate sea ice decline in winter. We run 100 members of 15 months initialized in January with two configurations: a low-resolution version based on a 130km atmosphere and a 1° ocean (CNRM-CM6-LR), and a high-resolution version which has a 50km atmosphere and a ¼° ocean (CNRM-CM6-HR). Both models have 91 levels on the vertical in the atmosphere (high-top). Comparing the atmospheric response to sea ice reduction in the two model experiments allows to assess the sensitivity of the response to horizontal resolution. Both models show comparable temperature and circulation response in the troposphere with a large polar amplification in autumn associated with a weakening of the mid-latitude westerlies and a narrowing of the subtropical jet stream. In both models we find a cooling over Central Asia in winter, which we interpret as a contribution from dynamical and thermodynamical changes due to the Arctic sea ice loss. In the stratosphere we find a weakening of the polar vortex in both models but occuring in different months: in December in CNRM-CM6-LR and in February in CNRM-CM6-HR. We analyse the differences in the mean state and variability between the two models and link these differences with the simulated response to Arctic sea ice decline.