Aerosols in the central Arctic cryosphere: Satellite and model integrated insights during Arctic spring and summer

Abstract. The central Arctic cryosphere is influenced by the Arctic Amplification (AA) and is warming faster than the lower latitudes. AA affects the formation, loss and transport of aerosols. Efforts to assess the underlying processes determining aerosol variability are currently limited due to the lack of ground-based and space-borne aerosol observations with high spatial coverage in this region. This study addresses the observational gap by making use of total aerosol optical depth (AOD) data sets retrieved by the AEROSNOW algorithm over the vast cryospheric region of the central Arctic during the Arctic spring and summer. GEOS-Chem (GC) simulations combined with AEROSNOW retrieved data are used to investigate the processes controlling aerosol loading and distribution at different temporal and spatial scales. For the first time, an integrated study of AOD over the Arctic cryosphere during sunlight conditions was possible with the AEROSNOW retrieval and GC simulations. The results show that the spatial patterns observed by AEROSNOW differ from those simulated by GC. During spring, which is characterised by long-range transport of anthropogenic aerosols in the Arctic, the GC underestimates the AOD in the vicinity of Alaska. At the same time, it overestimates the AOD along the Bering Strait, Northern Europe, and the Siberian central Arctic sea ice regions, with differences of -12.3 % and 21.7 %, respectively. In contrast, the GC consistently underestimates AOD compared to AEROSNOW in summer, when transport from lower latitudes is insignificant and local natural processes are the dominant source of aerosol, especially north of 70° N. This underestimation is particularly pronounced over the central Arctic sea ice region, where it is -10.6 %. Conversely, the GC tends to overestimate AOD along the Siberian and Greenland marginal sea ice zones by 19.5 %, but underestimates AOD along the Canadian Archipelago by -9.3 %. The differences in summer AOD between AEROSNOW data products and GC simulated AOD highlight the need to integrate improved knowledge of the summer aerosol process into existing models to constrain its effects on cloud condensation nuclei, ice nucleating particles, and any effects on the radiation budget over central Arctic sea ice during the developing AA period.