Variation of Direct Beam Solar Radiation in the United States Due to the El Chichon Debris Cloud

Abstract

Direct beam hourly solar radiation values, measured near solar noon under clear skies, were used to show the decrease in radiation in the United States caused by the debris cloud from the El Chichon volcanic eruption of March/April 1982. Maximum decreases of mean monthly direct beam occurred in December 1992, at Phoenix. Ariz., Boulder, Cola., and Bismarck, N.D. They were 11%, 17%, and 25% below the average December 1978?81 levels, respectively, at those locations. Data were taken from the National Oceanic and Atmospheric Administration solar radiation network. The El Chichon cloud ?arrived? at Boulder and Bismarck in August and October 1982, respectively, as determined by the first 1982 mean monthly radiation that was significantly below (5% level) the background data regression line. The arrival time at Phoenix was most likely in August. Cloud residence time was at least 11 months at Boulder. At Bismarck and Phoenix, cloud density had not yet begun to decrease in December 1982 after three and four months residence time, respectively. An anomalous, strong, and sudden short-period (7-day) drop in radiation was recorded in mid-May 1982 at Phoenix but not at Boulder or Bismarck. Similar mid-May drops were found, however, at Albuquerque, N.M., Las Vegas, Nev. and El Paso, Texas. Volcanic clouds causing large percentage decreases in direct beam radiation below expected climatological levels, such as observed in 1982 with the El Chichon cloud, when combined with the long cloud residence time, would be of considerable economic concern to solar energy systems, especially those depending primarily on direct beam radiation for energy input.