Monthly Mean Low Cloud Frequency Maps

Maps of the monthly mean low cloud frequency were produced using Geostationary Orbiting Environmental Satellite (GOES) measurements and a cloud detection algorithm. The cloud detection algorithm is based on the CERES Cloud Mask (pdf available here) which uses visible and infrared radiance measurements to first determine if each satellite pixel is clear or cloudy. If a pixel is found to be cloudy, the algorithm then assigns the cloud to one of several different cloud types. Cloudy scenes identified as low clouds have relatively warm cloud top temperatures signifying that the top of the cloud is not too far above the surface. Nearly all marine stratus clouds (i.e., marine layer clouds) fall into this category.

Instruments on the GOES satellites measure radiances in 5 wavelength channels (1 visible and 4 infrared) which differ slightly from those used in the original CERES cloud mask. As a result, minor modifications to some of the coeffiecients in the algorithm were made by calibrating the cloud mask results to surface based observations of cloud cover.

The table below contains links to maps of low cloud frequency over the Southern California Bight region. Maps showing monthly climatology of low cloud frequency based are based on the 1996-2008 period. Maps of low cloud frequency for individual months contain two plots; the top plot is the actual mean low cloud frequency for that month and the bottom plot is the difference from the long-term mean (anomaly). The bottom plot is helpful for determining if a given month was more or less cloudy than normal.

Year May Jun Jul Aug Sep
Climatology
1996-2008		 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
1996 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
1997 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
1998 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
1999 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
2000 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
2001 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
2002 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
2003 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
2004 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
2005 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
2006 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
2007 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
2008 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
2009 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
2010 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM
2011 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM 7AM 2PM

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