Impacts of Arctic Sea Ice on Cold Season Atmospheric Variability and Trends Estimated from Observations and a Multi-model Large Ensemble

• Published in: Journal of climate 2021-08, Vol.34 (20), p.1-64
• Main Authors: Liang, Yu-Chiao, Frankignoul, Claude, Kwon, Young-Oh, Gastineau, Guillaume, Manzini, Elisa, Danabasoglu, Gokhan, Suo, Lingling, Yeager, Stephen, Gao, Yongqi, Attema, Jisk J., Cherchi, Annalisa, Ghosh, Rohit, Matei, Daniela, Mecking, Jennifer V., Tian, Tian, Zhang, Ying
• Format: Article
• Language: English
• Subjects: Geophysics; Physics
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/JCLI-D-20-0578.1

To examine the atmospheric responses to Arctic sea-ice variability in the Northern Hemisphere cold season (October to following March), this study uses a coordinated set of large-ensemble experiments of nine atmospheric general circulation models (AGCMs) forced with observed daily-varying sea-ice, sea-surface temperature, and radiative forcings prescribed during the 1979-2014 period, together with a parallel set of experiments where Arctic sea ice is substituted by its climatology. The simulations of the former set reproduce the near-surface temperature trends in reanalysis data, with similar amplitude, and their multi-model ensemble mean (MMEM) shows decreasing sea-level pressure over much of the polar cap and Eurasia in boreal autumn. The MMEM difference between the two experiments allows isolating the effects of Arctic sea-ice loss, which explain a large portion of the Arctic warming trends in the lower troposphere and drives a small but statistically significant weakening of the wintertime Arctic Oscillation. The observed interannual co-variability between sea-ice extent in the Barents-Kara Seas and lagged atmospheric circulation is distinguished from the effects of confounding factors based on multiple regression, and quantitatively compared to the co-variability in MMEMs. The interannual sea-ice decline followed by a negative North Atlantic Oscillation-like anomaly found in observations is also seen in the MMEM differences, with consistent spatial structure but much smaller amplitude. This result suggests that the sea-ice impacts on trends and interannual atmospheric variability simulated by AGCMs could be underestimated, but caution is needed because internal atmospheric variability may have affected the observed relationship.