Cold-Season Arctic Amplification Driven by Arctic Ocean-Mediated Seasonal Energy Transfer

Abstract

© 2020. The Authors. Earth's Future published by Wiley Periodicals LLC on behalf of American Geophysical Union.The Arctic warming response to greenhouse gas forcing is substantially greater than the rest of the globe. It has been suggested that this phenomenon, commonly referred to as Arctic amplification, and its peak in boreal fall and winter result primarily from the lapse-rate feedback, which is associated with the vertical structure of tropospheric warming, rather than from the sea-ice albedo feedback, which operates mainly in summer. However, future climate model projections show consistently that an overall reduction of sea-ice in the Arctic region leads to a gradual weakening of Arctic amplification, thereby implying a key role for sea-ice albedo feedback. To resolve this apparent contradiction, we conduct a comprehensive analysis using atmosphere/ocean reanalysis data sets and a variety of climate model simulations. We show that the Arctic Ocean acts as a heat capacitor, storing anomalous heat resulting from the sea-ice loss during summer, which then gets released back into the atmosphere during fall and winter. Strong air-sea heat fluxes in fall/winter in sea-ice retreat regions in conjunction with a stably stratified lower troposphere lead to a surface-intensified warming/moistening, augmenting longwave feedback processes to further enhance the warming. The cold-season surface-intensified warming/moistening is found to virtually disappear if ocean-atmosphere-sea ice interactions are suppressed, demonstrating the importance of ice insulation effect and ocean heat uptake/release. These results strongly suggest that the warm-season ocean heat recharge and cold-season heat discharge link and integrate the warm and cold season feedbacks, and thereby effectively explain the predominance of the Arctic amplification in fall and winter.