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Report on Atmospheric Effects (1980-1989) — June 1986

Scientific Event Alert Network Bulletin, vol. 11, no. 6 (June 1986)
Managing Editor: Lindsay McClelland.

Atmospheric Effects (1980-1989) Ruiz aerosols persist; 1985-86 lidar data summarized

Please cite this report as:

Global Volcanism Program, 1986. Report on Atmospheric Effects (1980-1989) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 11:6. Smithsonian Institution.

Atmospheric Effects (1980-1989)

All times are local (unless otherwise noted)

Lidar profiles at Mauna Loa, Hawaii varied substantially in June (figure 27). No trends were obvious but the increased integrated stratospheric backscattering coefficient observed since May persisted, apparently due to increased aerosols above about 21 km.

Figure with caption Figure 27. Lidar data from Hawaii and Virginia, showing altitudes of aerosol layers. Note that some layers have multiple peaks. Backscattering ratios are for the ruby wavelength of 0.69 µm. Integrated values show total backscatter, expressed in steradians-1, integrated over 300-m intervals from 16-33 km at Mauna Loa and from the tropopause to 30 km at Hampton. Altitudes of maximum backscattering ratios and coefficients are shown for each layer at Mauna Loa. The 9 June data from Hampton replace previously published preliminary values.

Thomas DeFoor reports that "Figure 28 shows the trend in integrated non-Rayleigh backscattering coefficient between January 1985 and June 1986. Integrated aerosol scattering reached its lowest value since before the "Mystery Cloud" (20 January 1982 = 0.6 x 10-4 sr-1) on 23 May 1985 (1.0 x 10-4) as the remnant of the El Chichón aerosol continued to decline toward the 'non-volcanic' background of 0.4 x 10-4 sr-1. However, this trend was abruptly interrupted with an increase beginning 30 May 1985. This increase and the subsequent declining trend through 22 November 1985 is judged to have been the result of an unknown 1985 eruption. Evidence strongly suggests that this injection was at least several months old at first detection and probably had a Southern Hemisphere source, as it was apparently not detected by other Northern Hemisphere lidar stations. The increased backscatter first observed 26 November 1985 was probably the result of the 13 November Ruiz eruption. The variable backscatter values that followed for the next few months are not surprising. However, the apparent increasing trend between February and June 1986 is peculiar, especially since there is no obvious evidence of post-Ruiz aerosol sources in any of the Mauna Loa lidar profiles to date."

Figure with caption Figure 28. Integrated non-Rayleigh backscatter coefficient between 16 and 33 km at Mauna Loa, Hawaii, 15 January 1985-24 June 1986. The decline of El Chichón aerosols toward background January-May 1985 was interrupted by the 30 May arrival of aerosols from an unknown source, perhaps originating in the Southern Hemisphere several months earlier. Aerosols from Ruiz appeared in late November 1985 and a gradual increase again from an unknown source, was detected February-June, 1986. Courtesy or Thomas DeFoor.

At Hampton, VA, peak backscattering ratios have declined slightly since late April but integrated backscattering has generally increased. An unusually high tropopause on 9 June depressed integrated values but the remaining profile was similar in shape to others during the month. Lidar data from Firenze, Italy (43.78°N, 11.25°E) indicated a very small aerosol layer at about 20 km, with a scattering ratio (at 0.53 µm wavelength) of about 1.2-1.3.

Richard Keen observed the 24 April lunar eclipse from Auckland, New Zealand. Visual magnitude of the moon at mid-eclipse was -2.0, very close to the theoretical brightness for this eclipse, yielding a derived volcanic aerosol optical thickness of 0.00 ± 0.02. Because the moon passed through the southern part of the earth's shadow, this value is representative of the Southern Hemisphere stratosphere. The 28 October 1985 Southern Hemisphere lunar eclipse also yielded an unmeasureable volcanic aerosol optical thickness, suggesting that there had been no significant recent injections of stratospheric aerosols from Southern Hemisphere volcanoes. Stratospheric aerosols from an early 1985 Southern Hemisphere eruption suggested above by DeFoor were below the eclipse detection threshold.

Information Contacts: Thomas DeFoor, Mauna Loa Observatory, P.O. Box 275, Hilo, HI 96720 USA; William Fuller, NASA Langley Research Center, Hampton, VA 23665 USA; Leopoldo Stefanutti, Istituto di Ricerca sulle Onde Elettromagnetiche, CNR, Via Panciatichi 64, 50127 Firenze, Italy; Richard Keen, CIRES, Campus Box 449, University of Colorado, Boulder, CO 80309 USA.