Reduced Sea Ice Enhances Intensification of Winter Storms over the Arctic Ocean

Abstract

Abstract The ideal environment for extratropical cyclone development includes strong vertical shear of horizontal wind and low static stability in the atmosphere. Arctic sea ice loss enhances the upward flux of energy to the lower atmosphere, reducing static stability. This suggests that Arctic sea ice loss may facilitate more intense storms over the Arctic Ocean. However, prior research into this possibility has yielded mixed results with uncertain cause and effect. This work has been limited either in scope (focusing on a few case studies) or resolution (focusing on seasonal averages). In this study, we extend this body of research by comparing the intensification rate and maximum intensity of individual cyclones to local sea ice anomalies. We find robust evidence that reduced sea ice in winter (December–March) strengthens Arctic cyclones by enhancing the surface turbulent heat fluxes and lessening static stability while also strengthening vertical shear of horizontal wind. We find weaker evidence for this connection in spring (April–June). In both seasons, lower sea ice concentration also enhances cyclone-associated precipitation. Although reduced sea ice also weakens static stability in September/October (when sea ice loss has been especially acute), this does not translate to stronger storms because of coincident weakening of wind shear. Sea ice anomalies also have little or no connection to cyclone-associated precipitation in these months. Therefore, future sea ice reductions (e.g., related to delayed autumn freeze-up) will likely enhance Arctic cyclone intensification in winter and spring, but this relationship is sensitive to simultaneous connections between sea ice and wind shear. Significance Statement Sea ice is a barrier between the ocean and atmosphere, limiting the exchange of energy between them. As the amount of sea ice in the Arctic Ocean declines, the ocean can transfer more heat to the atmosphere above in fall and winter. It is theorized that this extra energy may help intensify storms that pass through the Arctic. We examine individual storms over the Arctic Ocean and what sea ice conditions they experience as they develop. We find that storms intensify more when sea ice is lower than normal in the winter season only. This relationship may contribute to stronger Arctic winter storms in the future, including heavier precipitation and stronger winds (which can enhance wave heights and coastal erosion).