Estimating high latitude radiative fluxes from satellite data: problems and successes

Surface-based observations of polar radiative fluxes are limited to a small number of coastal stations in both polar regions, a few Arctic Ocean drifting ice stations, and a few interior Antarctic stations. Long-term monitoring of the surface and top of the atmosphere radiation balances and the factors that affect them, as well as an analysis of their spatial patterns, will therefore require the use of satellite data. The authors consider whether one can estimate the radiation balance accurately enough for climate change studies, say to within 5 W m^-2. To answer this question they first address how well one can retrieve those geophysical parameters that are used in the estimation of the radiative fluxes: surface temperature and albedo, cloud and aerosol properties, and atmospheric temperature and humidity profiles. The highly reflective snow/ice surface, frequent temperature inversions, persistent ice crystal precipitation, and absence of solar radiation for many months are a few of the factors unique to polar regions that result in ambiguous solutions in the retrieval of cloud, aerosol, and surface properties. The authors present a method of estimating surface and top of the atmosphere radiative fluxes from visible, near-infrared, and thermal satellite data. A procedure is described and applied to AVHRR imagery of the Beaufort Sea during the March-April 1992 Leads Experiment (LEADEX). This combined satellite-in situ data set allows to assess the accuracies with which the radiation balance components can be measured, and provides guidance for future research.