Report on Atmospheric Effects (1980-1989) — October 1984
Scientific Event Alert Network Bulletin, vol. 9, no. 10 (October 1984)
Managing Editor: Lindsay McClelland.
Atmospheric Effects (1980-1989) Lidar data from Italy and Germany
Please cite this report as:
Global Volcanism Program, 1984. Report on Atmospheric Effects (1980-1989) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 9:10. Smithsonian Institution.
Atmospheric Effects (1980-1989)
All times are local (unless otherwise noted)
Lidar at Garmisch-Partenkirchen, Germany continued to detect remnants of the stratospheric aerosols from the El Chichón eruption. Peak backscattering ratios were somewhat lower in the summer and early autumn than they had been in the spring. At Firenze, Italy (43.8°N, 15.25°E), lidar data were collected April 1982-March 1984 by the Istituto di Ricerca Sulle Onde Electromagnetiche (figures 9 and 10). Integrated backscattering increased from just after the El Chichón eruption through early 1983, then declined gradually. At Hampton, Virginia, integrated backscattering was about the same in late October as in mid-September. A relatively weak secondary layer appeared to be present above the main layer of El Chichón material. Integrated backscattering varied considerably in October at Mauna Loa, Hawaii. An intense layer observed 30 October between a double tropopause at 15 and 15.3 km was probably cirrus cloud; below 13 km several layers appeared on the lidar data and cirrus were visible to the naked eye. At Fukuoka, Japan, increases in peak and integrated backscattering were noted for several days beginning 8 October between 9 and 22 km. Values rose to about 1.8 times seasonal means, then returned to previous levels.
M. Patrick McCormick and Thomas Swissler provided the following information about the relationship between backscattering ratios measured by lidar at wavelengths generated by ruby (0.6943 µm), and Nd-YAG (1.064 and 0.532 µm) laser transmitters. For any two wavelengths, the relationship can be expressed as:
(1) (R1-1) = (N1/N2)4-x (R2-1) where R1 and R2 are backscattering ratios produced by lidar operating at wavelengths N1 and N2. The value of x varies with the aerosol size distribution at a given time. Using techniques described in McCormick et al., (1984), McCormick and Swissler calculated values of x for a typical background aerosol size distribution (no significant volcanic contribution) from Russell et al. (1981) and for the aerosols measured by Hofmann using a 6-channel dustsonde on 24 August and 21 December, 1983 (about 17 and 21 months after the March-April 1982 eruption of El Chichón). After calculating x, equation (1) can be simplified to:
(2) (R1-1) = k(R2-1)
By substituting k values into equation (2) from the appropriate model in table 1, lidar data of different frequencies can be made approximately comparable.
|Aerosol model||x||k(r,y)||k(g,y)||k (g,r)|
|Hirono (SEAN 07:05)||1.85||0.40||0.23||0.56|
|Russell et al. 1981||1.60||0.36||0.19||0.53|
|Hofmann 24 Aug and 21 Dec 1983||0.90||0.27||0.12||0.44|
From Millville, New Jersey, Fred Schaaf continued to observe unusual twilight colors. From mid-July through mid-September, weak to moderate primary glows were usually present, and purple and crimson colors were often observed for somewhat longer after sunset. Timing of the disappearance of later colors suggested that aerosols were present to at least 8-13 km. Strong crepuscular rays were observed during the evenings of 20 August and 11 September. On a few evenings, little or no glow was evident. In late September and early October, weak secondary illumination was visible, and the timing of primary colors suggested that aerosols were present to 13-19 km altitude on 26 September. From about 38°N, 75.5°W (Maryland-Virginia border), Schaaf saw moderate colors and many crepuscular rays on 28 October. In arctic air over New Jersey 7-8 November, colors were relatively weak and faded quickly.
References. Russell, P. B., Swissler, T.J., McCormick, M. P., Chu, W. P., Livingston, J. M., and Pepin, T. J., 1981, Satellite and correlative measurements of the stratospheric aerosol. I: An optical model for data conversions: Journal of Atmospheric Sciences, v. 38, no. 6, p. 1279-1294.
McCormick, M. P., Swissler, T. J., Fuller, W. H., Hunt, W. H., and Osborn, M. T., 1984, Airborne and ground-based Lidar measurements of the El Chichón stratospheric aerosol from 90°N to 56°S: Geofísica Internacional, v. 23, no. 2, p. 187-221.
Information Contacts: L. Stefanutti, Isto. di Ricerca Sulle Onde Electromagnetiche, Italy; R. Reiter, Garmischen-Partenkirchen, W. Germany; P. McCormick, T. Swissler, W. Fuller, and M. Osborn, NASA; T. DeFoor, MLO; M. Fujiwara and M. Hirono, Kyushu Univ. Japan; F. Schaaf, Millville, NJ.