Overview of Indirect and Semi-direct Aerosol Campaign (ISDAC)—the influence of arctic aerosols on clouds (Invited Speaker)

Arctic haze is a well-known feature of the Arctic atmosphere, but the influence of the haze on clouds and the energy balance of the Arctic is poorly understood. To address this challenge the U.S. Department of Energy deployed the Canadian National Research Council Convair 580 loaded with 42 cloud and aerosol instruments to sample the atmosphere above the DOE site at Barrow Alaska during April 2008. The data reveals the formation of well-defined mixed-phase stratocumulus clouds on two of the flight days and a dense aerosol plume on another day. In the stratocumulus clouds the liquid droplets were confined to a thin layer near cloud top, with cloud ice distributed uniformly below. The composition of the particles that most ice crystals formed on was found to be dust. The dense aerosol plume was found to be composed of highly absorbing particles produced from biomass burning in Asia. On most other days the aerosol is hygroscopic. Cloud model simulations driven by large-scale boundary conditions are able to reproduce many features of the observed clouds.