This paper was presented at the Art, Science and Applications of Reflectance Spectroscopy Symposium sponsored by ASD Inc. and IEEE GRSS, February 23-25, 2010 in Boulder, Colorado.

Author: Dan Lubin
Affiliation: University of California—San Diego

Abstract

The Arctic is home to some of the most dramatic manifestations of recent climate warming, including rapid retreat of sea ice cover that has been stable for the past five millennia. Attribution of the precise mechanisms governing the climate warming is challenging because many factors are at play, including greenhouse gas increases, the ice-albedo feedback, changes in atmospheric circulation related to climate warming, changing oceanic energy flux, and anthropogenic sources of pollution in the Arctic. All of these affect the surface energy balance, and require suitable measurements to ascertain their respective roles. Global climate models are becoming sophisticated enough to incorporate detailed physical processes relevant to the Arctic, including heterogeneous properties of sea ice, and the roles of aerosol, liquid water, and ice in clouds. The latter are particularly relevant because the Arctic experiences stratiform cloud cover throughout most of the year, particularly during the spring sea ice melt season. Climate studies now recognize the importance of thermodynamic phase in clouds, as well as how anthropogenic aerosols interact with clouds to change the energy balance at the surface. During spring 2008, a Department of Energy (DOE) experiment was conducted in Alaska and over the Beaufort Sea to study these issues. This experiment, the Indirect and Semi-Direct Aerosol Campaign (ISDAC), included deployment of an ASD spectroradiometer at the DOE Atmospheric Radiation Measurement (ARM) site at Barrow. The instrument recorded downwelling irradiance spectra every minute, in the wavelength interval 350-2200 nm. In the near-infrared windows, these spectra clearly show the influence of liquid water versus ice particle cloud microphysics on the surface radiation balance. Thus, while ISDAC made numerous instrumented aircraft flights sampling cloud microphysics and aerosol properties, the measurements by the ASD instrument are the "lynch pin" that link these in situ atmospheric observations with changes in the surface energy budget.