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Marine Stratocumulus Cloud Fields off the Coast of Southern California Observed Using LANDSAT Imagery. Part I: Structural Characteristics

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  • a Institute of Atmospheric Sciences, South Dakota School of Mines and Technology, Rapid City, South Dakota
  • | b Atmospheric Sciences Division, NASA/Langley Research Center, Hampton, Virginia
  • | c Department of Mathematics and Computer Science, South Dakota School of Mines and Technology, Rapid City, South Dakota
  • | d PRC/Kentron Inc., Aerospace Technologies Division, Hampton, Virginia
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Abstract

The structural characteristics of stratocumulus cloud fields off the coast of southern California are investigated using LANDSAT Multispectral Scanner (MSS) imagery. Twelve scenes in this area are examined along with three other stratocumulus scenes near San Francisco, over central Oregon, and in the Gulf of Mexico.

Results from this initial study of stratocumulus clouds indicate that 1) cloud-background threshold selection techniques based upon edge detection gradient assumptions are not appropriate for cloud segmentation and classification algorithms; 2) cloud size distributions obey a power law; 3) cell horizontal aspect ratio increases with cell diameter, 4) stratocumulus clouds are bifractal in nature with fractal dimension of about d ≈ 1.2 for cells with diameter D < 0.5 km and d ≈ 1.5 for cells with D > 0.5 km; 5) stratocumulus cloud fields appear to be homogeneous over regions of about 100 km × 100 km, a much smaller region than the 2.5° × 2.5° boxes to be used in the ISCCP regional averaging algorithms; and 6) structural properties of stratocumulus clouds observed off the coast of southern California are similar to those properties observed for stratocumulus clouds at three other locations.

Abstract

The structural characteristics of stratocumulus cloud fields off the coast of southern California are investigated using LANDSAT Multispectral Scanner (MSS) imagery. Twelve scenes in this area are examined along with three other stratocumulus scenes near San Francisco, over central Oregon, and in the Gulf of Mexico.

Results from this initial study of stratocumulus clouds indicate that 1) cloud-background threshold selection techniques based upon edge detection gradient assumptions are not appropriate for cloud segmentation and classification algorithms; 2) cloud size distributions obey a power law; 3) cell horizontal aspect ratio increases with cell diameter, 4) stratocumulus clouds are bifractal in nature with fractal dimension of about d ≈ 1.2 for cells with diameter D < 0.5 km and d ≈ 1.5 for cells with D > 0.5 km; 5) stratocumulus cloud fields appear to be homogeneous over regions of about 100 km × 100 km, a much smaller region than the 2.5° × 2.5° boxes to be used in the ISCCP regional averaging algorithms; and 6) structural properties of stratocumulus clouds observed off the coast of southern California are similar to those properties observed for stratocumulus clouds at three other locations.

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