Airborne observations of surface cloud radiative forcing over different surface types of the Arctic Ocean during late summer/early autumn

Clouds can cause a significant change to the radiative energy budget of the Earth's surface compared to clear-sky conditions, which is referred to as surface cloud radiative forcing (CRF). The CRF in the Arctic strongly depends on the surface properties (absorbing open ocean vs. strongly reflecting sea ice) and is affected by the low or even absent sun and the special thermodynamic conditions. Therefore, in contrast to the mid and low latitudes, in the Arctic, clouds mostly warm the surface on annual average. However, the CRF will change as the sea ice retreats in a warming climate, which might be accelerated due to the enhanced warming of the Arctic, known as Arctic Amplification. Thus, to quantify the contrast of the CRF over sea ice-covered and sea ice-free ocean surfaces, several airborne campaigns have been conducted in the vicinity of Svalbard in the recent years. The measurements of cloud macrophysical and microphysical properties as well as radiative and turbulent fluxes cover different seasons (spring to early autumn).

Airborne broadband radiation measurements under all-sky conditions were used to calculate the surface CRF during low-level flight sections. In this study, observations from the concurrent campaigns Multidisciplinary drifting Observatory for the Study of Arctic Climate – Airborne observations in the Central Arctic (MOSAiC-ACA) and MOSAiC-Icebird, conducted in August/September 2020, are presented. First results of the CRF over open ocean and the marginal sea ice zone (MIZ) of late summer/early autumn conditions are assessed and compared to the previous airborne spring and early summer campaigns to analyse the seasonal variability of the CRF.