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. The concept of cloud radiative forcing (CRF) is commonly applied to quantify the impact of clouds on the surface radiative energy budget (REB). Inthe Arctic, specific radiative interactions between microphysical and macrophysical properties of clouds and the surface strongly modify the warmingor cooling effect of clouds, complicating the estimate of CRF obtained from observations or models. Clouds tend to increase the broadband surfacealbedo over snow or sea ice surfaces compared to cloud-free conditions. However, this effect is not adequately considered in the derivation of CRFin the Arctic so far. Therefore, we have quantified the effects caused by surface-albedo–cloud interactions over highly reflective snow or sea icesurfaces on the CRF using radiative transfer simulations and below-cloud airborne observations above the heterogeneous springtime marginal sea icezone (MIZ) during the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign. The impact of a modified surfacealbedo in the presence of clouds, as compared to cloud-free conditions, and its dependence on cloud optical thickness is found to be relevant forthe estimation of the shortwave CRF. A method is proposed to consider this surface albedo effect on CRF estimates by continuously retrieving the cloud-freesurface albedo from observations under cloudy conditions, using an available snow and ice albedo parameterization. Using ACLOUD datareveals that the estimated average shortwave cooling by clouds almost doubles over snow- and ice-covered surfaces ( − 62  W m−2 instead of − 32  W m−2 ), if surface-albedo–cloud interactions are considered. As a result, the observed total (shortwave plus longwave) CRF shiftedfrom a warming effect to an almost neutral one. Concerning the seasonal cycle of the surface albedo, it is demonstrated that this effect enhancesshortwave cooling in periods when snow dominates the surface and potentially weakens the cooling by optically thin clouds during the summertimemelting season. These findings suggest that the surface-albedo–cloud interaction should be considered in global climate models and in long-termstudies to obtain a realistic estimate of the shortwave CRF to quantify the role of clouds in Arctic amplification.

Reassessment of shortwave surface cloud radiative forcing in the Arctic: consideration of surface-albedo–cloud interactions