Fourteenth ARM Science Team Meeting Proceedings, Albuquerque, New Mexico, March 22-26, 2004 Derivation of Seasonal Cloud Properties at ARM-NSA from Multispectral MODIS Data D. A. Spangenberg Analytical Services and Materials, Inc. Hampton, Virginia P. Minnis National Aeronautics and Space Administration Langley Research Center Hampton, Virginia T. Uttal National Oceanic and Atmospheric Administration Environmental Technology Laboratory Boulder, Colorado Q. Z. Trepte and S. S.-Mack Science Applications International Corporation Hampton, Virginia Introduction Improving climate model predictions over earth’s Polar Regions requires a complete knowledge of polar cloud microphysics. Over the Arctic, there is minimal contrast between the clouds and background snow surface observed in satellite data, especially for visible wavelengths. This makes it difficult to identify clouds and retrieve cloud properties from space. Variable snow and ice cover, temperature inversions, and the predominance of mixed-phase clouds further complicate cloud property identification. For this study, a solar-infrared infrared near-infrared technique (SINT) first used by Platnick et al. (2001) and a visible-infrared solar-infrared split-window technique (VISST) developed by Minnis et al. (1995) are used to retrieve cloud properties over the Atmospheric Radiation Measurement (ARM) North Slope of Alaska (NSA) Barrow site. Because of the large uncertainty in VISST optical depth τ retrievals using the 0.65-µm channel over bright, highly variable scenes, SINT is used instead. In the SINT algorithm, more accurate optical depths can be achieved using the 1.6-µm channel instead of the 0.65-µm channel due to the relatively dark background surface reflectance and lower sensitivity of τ with reflectance at 1.6 µm. In this paper, the operational Clouds and the Earth’s Radiant Energy System (CERES) cloud mask (Trepte et al. 2002) is first used to discriminate clouds from the background surface in Terra Moderate Resolution Imaging Spectroradiometer (MODIS) data. For those pixels tagged as being cloudy, either SINT or VISST is run to obtain both cloud macro and microphysical properties including τ, particle 1