2002 Annual

Tuesday, 15 January 2002: 10:45 AM
Determining Fog Type in the Los Angeles Basin Using Historic Surface Observation Data
Jeffrey A. Baars, Terabeam, Redmond, WA; and M. Witiw, A. Al-Habash, and J. Ramaprasad
Poster PDF (62.5 kB)
Statistics on fog occurrence and severity that have been gathered through historic observations are vitally important in the development of operating parameters for the deployment of free-space optics (FSO) equipment in a given location. However, the actual types of fog that have occurred during these observations is often not considered. Knowing the fog type is important when estimating low-visibility occurrences in locations where there are no observations. This is particularly true in a location such as Los Angeles (L.A.), where certain fog types will extend through the L.A. Basin, while others will be limited to ocean-side locations. Also, knowing the fog type could prove important for the seasonal forecasting of fog, inasmuch as certain fog types may be more correlated with large scale forcing such as the Pacific Decadal Oscillation (PDO) or El Niņo. A fog-type determination algorithm was developed using a single surface observation station. The algorithm considers wind direction, wind speed, exposure to the ocean, temperature, dew point, ceiling height, time of year, time of day, and precipitation occurrence. The algorithm was tailored for the L.A. Basin and was run using data from Los Angeles International Airport from 1961 to 1990. An independent, manual assessment of the results of the algorithm for two test years showed that over 95 percent of fogs were determined correctly. The findings show that 26.8 percent of fog types in the L.A. Basin were advection-radiation fog, 67.1 percent were advection or sea fog, 0.7 percent was precipitation fog, 1.1 percent were radiation fog and 4.3% were undetermined.

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