ESTIMATING POLYNYA CLOUDINESS

Abstract

Global cloudiness distributions, though an important component in radiative and hydrological budgets, are neither adequately known nor easily retrieved by the spatial and spectral resolutions afforded by current satellite instrumentation. At high latitudes, cold, high albedo surfaces present a particular challenge to cloud retrieval, offering little or no thermal or visible contrast for cloud-ice discrimination. It is in these frequently cloudy and climate-sensitive regions that changing cloud amounts and optical parameters enact the greatest influence, enhancing or suppressing melt through cloud base emission of longwave radiation or scattering of incident shortwave radiation. Polynyas and leads, seasonally ice-free areas characterized by intense air-sea fluxes of heat and moisture, are useful features for exploring the relationships between cloud cover and the underlying surface. Using polar-optimized CASPR (Cloud and Surface Parameter Retrieval) algorithms to process multi-channel AVHRR radiances, cloud amounts, microphysics, and surface forcing are evaluated and validated against in situ measurements collected in several polynyas and leads across the Western Arctic during the years 1992-2000