ASCOS - The Arctic Summer Cloud-ocean Study

Clouds play a key role in the Arctic climate, by regulating the surface energy fluxes that affect freezing and melting of sea ice. The Arctic is dominated by low-level optically thin clouds and the radiative properties of these thin low-level boundary layer clouds, shortwave reflectivity as well as longwave emissivity, are dependent on the number concentration of cloud droplets. This depends on the availability of aerosols and changes in the aerosol climate due to climate change therefore have the potential to alter the surface energy balance as well as the structure of the atmospheric boundary layer and therefore the local mixing. This in turn can affect the melting and freezing of the sea ice and also feed back to the changes in surface albedo through changes in melt pond formation. Models handle these interactions poorly, mostly because they are poorly understood; such understanding must be built on observations.

With an integrated study from ocean mixed layer through the ice and the troposphere, the Arctic Summer Cloud Ocean Study (ASCOS) was designed to identify and understand controlling factors of the optically thin low-level clouds. ASCOS main activities commenced during an ice-drift operation when the Swedish icebreaker Oden was moored to an ice floe close to 87°N 05°W and drifted passively for three weeks in the transition from summer melt to freeze up late August and early September 2008.

ASCOS attracted the participation from seventeen research groups from eleven countries and was the fourth in a series of expeditions in the same region carried out in 1991, 1996 and 2001. We are not aware of any other similarly extensive expedition during the IPY to the central Arctic Ocean, north of 80°. The presentation will provide a brief overview of ASCOS and show examples of the benefits of its interdisciplinary and international approach.