A determination of the infrared optical depth of the El Chichon volcanic cloud
- NASA Ames Research Center, Moffett Field, CA (USA)
Infrared transmission spectra of the atmosphere above 11-km altitude were obtained in December 1982 and April/May 1983 from a NASA Convair 990 aircraft. The observations on the first flight series encompassed low and middle latitude in the northern hemisphere, while observations on the second series covered a wide range of latitudes in both hemisphere. The authors have analyzed these data to derive the optical depth of the El Chichon volcanic cloud at a wavelength of 8.4 {mu}m. Comparison of these values with concurrent measurements by Dutton and DeLuisi of the cloud's optical depth at 0.5 {mu}m leads to the ratio of the cloud's infrared to visible optical depth, R. They analyzed the observed spectra by ratioing pairs of spectra taken at similar latitudes, but different air masses and comparing these ratio spectra with synthetic ones. The synthetic spectra allow for absorption by gases (O{sub 3}, H{sub 2}O, CO{sub 2}, CH{sub 4}, and N{sub 2}O) as well as extinction by the cloud particles. Extinction by the cloud particles is particularly important in the 8- to 9-{mu}m region. They obtain an average value for R of 0.25 {plus minus} 0.05. The data imply that concentrated sulfuric acid was the dominant source of aerosol extinction in the 8- to 12-{mu}m window region of the Earth's atmosphere and that the volume modal particle radius equaled 0.6 {plus minus} 0.1 {mu} at the time of the observations. At these times, the volcanic particles produced a significant warming of the lower stratosphere and had a nontrivial impact on the radiation budget of the troposphere and ground in the northern hemisphere.
- OSTI ID:
- 5600382
- Journal Information:
- Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 96:D2; ISSN 0148-0227; ISSN JGREA
- Country of Publication:
- United States
- Language:
- English
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