Lidar in Italy, Germany, Japan, and the USA detected the arrival of new stratospheric aerosols between 29 September and 5 November (figure 32), but their source remains uncertain. The 24 September eruption of Mt. Etna produced substantial tephra falls, but ground observers estimated that the eruption column reached a maximum altitude of only 10-13 km. No other strong explosive eruptions have been reported in recent months.

Figure 32. Lidar data from various locations, showing altitudes of aerosol layers. Note that some layers have multiple peaks. Backscattering ratios from Fukouka, Japan, are for the Nd-YAG wavelength of 1.06 µm; from Oshkosh, Wisconsin, for the Nd-YAG wavelength of 0.53 µm; all others 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.

From Fukuoka, Japan, a sharp new peak in the lidar profile at 19.9 km altitude, accompanied by a general background increase in stratospheric aerosols, was first detected 29 September. The new peak was less distinct during the next observation, on 2 October, but the increase in total backscatter was substantial, especially at altitudes below the peak. On 6 October, a secondary peak was detected at 23 km, associated with a substantial increase in backscattering at 22-26 km. No observations were made 7-29 October, but data 30 October and 1-2 November continued to show substantially enhanced total backscatter.

Lidar in Garmisch-Partenkirchen, Germany showed a peak on 24 October from an apparently fresh layer that was probably not thicker than 500-1000 m. During initial observations (1807-1821 local time; = GMT + 1 hour), the peak was seen at 19.2 km altitude; later (1822-1845) at 19.8 km. Scattering ratios of the individual peaks were about 1.6.

At Firenze, Italy, lidar measurements resumed on 5 November, when a distinct new aerosol layer was observed from 15.5 to at least 18 km altitude. Data were noisy above 20 km, but a second peak was noted at 20.2 km and possible enhancement continued to 23 km.

At Hampton, VA, a new layer at 18.5-22 km was first seen on 16 October, 1 month after the previous observation. The layer remained evident on 20 October, but by the 28th had merged with remnants of the November 1985 Ruiz aerosols. Data collected at Oshkosh, Wisconsin (44°N, 88.5°W) on 11 October did not appear to show new aerosols. Data from Mauna Loa, Hawaii seemed to show an increase in total backscatter, but no fresh aerosol layers were evident.

Particle sampling data from balloons launched near Laramie, WY showed a new layer of condensation nuclei (CN), too small to be detected by lidar, on 5 September. CN concentrations were about 100 x normal background values in a zone about 0.75 km thick. By 1 October, the layer had broadened to 2 km (22-24 km altitude) but concentrations had decreased to about 5 x background. In early September, particle sizes were an order of magnitude smaller than normal for that altitude, but were somewhat larger by the beginning of October. Balloon launches from Laramie will resume in December.

Information Contacts: Motowo Fujiwara, Physics Department, Kyushu University, Fukuoka 812, Japan; Leopoldo Stefanutti, Istituto di Ricerca sulle onde Elettromagnetiche, CNR, Via Panciatichi 64, 50127 Firenze, Italy; H. Jäger, Fraunhofer-Institut für Atmosphärische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, West Germany; William Fuller, NASA Langley Research Center, Hampton, VA 23665 USA; Thomas DeFoor, Mauna Loa Observatory, P.O. Box 275, Hilo, HI 96720 USA; James Rosen, Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 USA.