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Report on Atmospheric Effects (1980-1989) — February 1984

Atmospheric Effects (1980-1989)

Scientific Event Alert Network Bulletin, vol. 9, no. 2 (February 1984)
Managing Editor: Lindsay McClelland.

Atmospheric Effects (1980-1989) Lidar still detects aerosols but dawn/twilight colors decrease

Please cite this report as:

Global Volcanism Program, 1984. Report on Atmospheric Effects (1980-1989) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 9:2. Smithsonian Institution.

Atmospheric Effects (1980-1989)

All times are local (unless otherwise noted)

Lidar data. Lidar data from Mauna Loa, Hawaii showed a substantial decrease in total aerosol backscatter between measurements on 1 and 15 February. Total backscatter as well as altitudes and values of peak backscatter were nearly identical on 15, 22, and 29 February but shapes of aerosol profiles varied somewhat. A broad, single layer without fine structures was detected over Fukuoka, Japan on 11 March. Two distinct layers had been seen from Fukuoka a month earlier. Total backscatter over Hampton, Virginia remained at roughly double the Mauna Loa values. Three distinct layers were observed 8 February, but the aerosol profile showed a single broad layer on 21 February and 1 March.

Unusual sunrises and sunsets. From Boulder, Colorado, Richard Keen reported that unusual twilights were not seen during December. However, Keen notes that clear skies for 1,500 km to the west of the observation site are necessary to generate double twilights, and December weather was usually poor. Double twilights, with salmon color at 4° SDA followed by persistent deep red secondary color, were observed on 2, 4, 6, and 7 January. Double twilights were also observed on 24, 28, and 30 January, and 5-6 February, but were not as bright as those in late 1983 or early January 1984. The secondary twilights of late January-February were also not as persistent; at the end of red secondary glow, SDA was 16° on 4 January, 14° on 28 January, 13° on 30 January and 12° on 6 February. Keen notes that these observations imply a thinning and/or lowering of the aerosol layer. No double twilights have occurred at Boulder from 6 February through early March, but skies west of Boulder were again frequently cloudy.

Optical effects at Jeddah, Saudi Arabia were often weak in late January and February. From sunset 25 January to sunrise 28 January dusk and dawn observations by Edward Brooks indicated that aerosol scatterers were nearly absent. Only early dawn colors (higher altitude aerosols) were seen 1, 2, and 4 February. Of the twilights between 1 and 9 February, only on the 6th did colors indicate a strong scattering layer. Brighter dusks and dawns were more frequent from mid-February, but scattering effects remained inconsistent. No dawn colors were visible 21, 25, and 27 February and colors were subdued on many other mornings and evenings late in the month.

Fred Schaaf reported that twilight effects at Millville, New Jersey in February and early March were the weakest since aerosols from the March-April 1982 El Chichón eruption first arrived over the area. Frequent cloudy weather limited observations. Little or no high-altitude aerosol material appeared to be present and colors produced by lower altitude material had diminished.

Information Contacts: T. DeFoor, MLO; W. Fuller, NASA; M. Fujiwara and M. Hirono, Kyushu Univ., Japan; R. Keen, Univ. of Colorado; E. Brooks, Saudi Arabia; F. Schaaf, Millville, NJ.