The Asymmetry of Daily Sea Ice Variations and Its Impacts on Surface Shortwave Radiation over Arctic during Summer

Arctic sea ice loss can affect surface energy balance during summer, but it is unclear how surface shortwave (SW) radiation can respond to natural variations of sea ice cover (SIC). Here, we propose a decomposition framework to approximately isolate the impact of daily SIC variations on surface net SW (SW_net) radiation mainly through the sea ice–cloud and sea ice–albedo feedbacks. Using model simulations under preindustrial conditions, we show that daily SIC anomalies exhibit an asymmetry in amplitude and occurrence frequency during June–August. Specifically, negative SIC anomalies occur less frequently but with larger amplitudes over north of the marginal ice zone (MIZ), similar to positive SIC anomalies over south of the MIZ. Regions with large negative SIC anomalies exhibit reduced lower-tropospheric stability, higher evaporation, and thus higher near-surface specific humidity, which increase low-level relative humidity and cloud fraction. These cloud anomalies lead to decreased mean surface downward SW (SW_dn) radiation over north of the MIZ. Regions with large positive SIC anomalies show roughly the opposite over south of the MIZ. This asymmetric effect ultimately causes a seasonal-mean SW_net change over the Arctic. In reanalysis, the mean change of Arctic summer SW_net between two historical periods can also be decomposed into the asymmetric impact of daily SIC variations and the impact of the mean SIC change based on the proposed framework, which is qualitatively consistent with the model results. Our findings suggest that the asymmetry of daily SIC variations and the associated other anomaly fields can cause mean-state changes in Arctic surface energy fluxes during summer.