Wintertime Cloud Cover: A Contributor Towards Inter-Annual Sea Ice Variability

The role of cloud forcing on Arctic sea ice is fundamental but also complex, serving as an accelerant or antagonist to ice growth on a hemispheric scale. Though sea ice decline in recent decades is largely attributed to arctic amplification, plunges in ice extent and restorative winter refreezes occurring on a year-to-year basis cannot be adequately explained by this general trend. For improved understanding and prediction of these inter-annual fluctuations in ice area, cloud forcing effects on surface energy budgets must be seen as an important factor for ice growth and melt. For example, the significant rebound of arctic sea ice from the record minimum of September 2012 was aided by the surface cooling effects of negative winter cloud cover anomalies (fewer clouds), according to a recent study using satellite and reanalysis data.

For this study, the ERA-Interim reanalysis is used to diagnose and quantify the contribution of surface radiative forcing by wintertime cloud cover on sea ice during years with anomalous total ice areas. Comparisons between reanalysis of cloud forcing from September through March and passive microwave-derived ice concentrations in September demonstrate a significant inverse correlation between cloud cover during winter and the ice extent at the end of a melt season. Cloud re-emission of longwave radiation in winter months acts to curb the process by which polar seas radiatively cool to space and freeze, so that less winter cloud generally results in thicker sea ice. Here we investigate the role of winter cloud cover as a predictor and contributor to anomalous ice extent over the past 32 years. Our results stand to improve climate model projections of sea ice melt and assign some cause to large year-to-year ice area variability in a warming arctic regime.