The overarching objective of this study is to reduce the large uncertainty in the effects of aerosols and clouds on the Arctic surface energy balance and climate. This will provide a sound foundation for making improved predictions of future Arctic climate. Specific project objectives are:
- Understand the microphysical properties of Arctic clouds and their dependence on aerosol properties: Very low CCN concentrations in the Arctic result in clouds that are optically thinner than commonly found at lower latitudes, having fewer but larger droplets. They are also commonly mixed phase, containing low concentrations of ice crystals.
- Determine the natural and anthropogenic sources of aerosol within the Arctic boundary layer: Aerosol within the Arctic boundary layer (BL) may originate from local surface sources (either directly or via nucleation from precursor gases), advection within the BL, or entrainment into the BL from the free troposphere from distant sources. None of these sources are well quantified with the result that global aerosol models fail to reproduce observed aerosol distributions within the Arctic (Korhonen et al. 2008). The measurements made here will provide a robust basis for understanding how the sources will change with changing ice conditions
- Determine boundary layer structure and turbulent mixing properties: Low cloud droplet concentrations result in different shortwave warming and longwave cooling profiles than for midlatitude stratocumulus; thus the radiatively driven dynamics of Arctic clouds are also expected to differ, affecting coupling with the surface (a source of aerosol and moisture) and entrainment of air from above the boundary layer (also a potential source of aerosol)
- Quantify the feedbacks between clouds, aerosol, sea ice and the wider climate system: Cloud radiative properties affect the surface energy budget and thus changing ice cover; the ice fraction and extent influence the surface production of aerosol; and the aerosol in turn affect cloud microphysical properties. Changes to atmospheric thermodynamic structure affect the surface longwave radiation budget via the emission temperature of cloud and the water vapour content of the lower atmosphere.
Korhonen, H; K. S. Carslaw, D. V. Spracklen, D. A. Ridley, J. Strom, 2008: A global model study of processes controlling aerosol size distributions in the Arctic spring and summer, J. Geophys. Res, 113. doi:10.1029/2007JD009114