OPTICAL EXTINCTION PROPERTIES OF VOLCANIC STRATOSPHERIC AEROSOL DERIVED FROM GROUND-BASED LIDAR AND SUN PHOTOMETER MEASUREMENTS

Measurements of lidar-integrated backscatter and Sun photometer optica l thickness made at Mauna Loa, Hawaii (19.5 degrees N), were used to c ompute the bulk columnar value of the extinction-to-backscatter ratio S-c of stratospheric aerosol during a period of major stratospheric ae rosol contamination following the eruption of El Chichon (Mexico, 17.3 degrees N, March-April 1982). Values of S-c were also calculated usin g observations of integrated backscatter and aerosol optical thickness collected from various sources in the northern midlatitude region. Th e calculated values of S-c were found to range between 40 and 70 sr at a wavelength of 0.694 mu m during periods when high and moderate stra tospheric aerosol concentrations were observed. Variations of S-c with time of approximately 20-30% are noted in the results. Similar S-c re sults obtained by other investigators are compared with the results of this investigation. Overall, the agreement among the various results was found to be consistent within their uncertainties. Values of S-c w ere also calculated for the stratospheric aerosol from the eruption of Mount Pinatubo (Philippines, 15 degrees N, June 1991). The Mount Pina tubo results were about 15% lower than the El Chichon results during t heir early stages. Differences between the El Chichon and the Pinatubo results are within their error bounds.