Isolating the influence of aerosols on Arctic cloud radiative effects during a polluted warm air mass intrusion

Abstract. Arctic warm air mass intrusions are key to the region's energy balance because they transport large amounts of heat and moisture from lower latitudes. The resulting changes in heat and moisture content influences cloud properties, the thermodynamic structure of the boundary layer, and surface radiation. Warm air mass intrusions can also carry significant amounts of aerosols into the Arctic, including aerosols from anthropogenic sources at lower latitudes, which could influence the radiative impacts of such events. In this study, we examine the role of aerosol transport during a warm air mass intrusion that occurred in the central Arctic in April 2020. We use a version of the regional chemistry-climate model WRF-Chem adapted for Arctic conditions (WRF-Chem-Polar), to investigate the radiative impact of aerosol-cloud interactions associated with the event. We isolate the effects of the high aerosol burden by running the model with and without anthropogenic emissions. Anthropogenic emissions increase cloud droplet number concentration by 117% and liquid water content by 52%. However, the net surface radiative impact of these aerosol-cloud interactions is limited over sea ice. The high albedo of the underlying sea ice limits shortwave cloud cooling, while the longwave effects of cloud perturbations are small. Over open ocean regions, the surface radiative impacts of the aerosols are stronger. Overall, these results show that the net effect of an extreme aerosol transport event is sensitive to the season in which the event takes place, due to strong dependence on the surface state and the background Arctic haze conditions.