Extinction of short -wave solar radiation due to El Chichon stratospheric aerosol



Using satellite-derived insolation (Tarpley, 1979), a method is developed to assess total short-wave radiation depletion due to El Chichon stratospheric aerosols under cloudless conditions. Seven daily digital images are mapped on a 1x1 longitude-latitude grid of Mexico from May 1982 to December 1983. Cloudless conditions are determined using hourly sunshine data at several of the points of the array. The spatial and temporal resolution of satellite-derived irradiance permits the study of the evolution of the aerosol layers through the extinction of solar radiation. The results are expressed as extinction anomalies with respect to the mean values of the corresponding digital images of 1984. During May 1982 high extinction values covered most of Mexico. From June to August 1982 solar irradiance returned almost to normal values as easterlies were well organized shifting the aerosol cloud westwards. After September 1982 solar radiation extinction increased reaching the highest values in December 1982 (27.5%). During January to May 1983 extinction remained high but variable, between 10 to 22%. From June to August 1983 solar radiation returned again to normal conditions in most of the country although some areas persisted with important extinction anomalies (13%). During September to December 1983 solar radiation extinction remained between 16 and 14% showing that the stratosphere still contained a large amount of residual aerosol. The decay of the perturbation behave as a dampened harmonic oscillator with seasonal oscillation, maximum and minimum occurring in local winter and local summer, respectively.


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