Data from Hawaii and Wyoming suggest that aerosol material, perhaps from the 13 November eruption of Ruiz volcano, Colombia, has recently been injected into the stratosphere. Through 22 November, lidar measurements at Mauna Loa, Hawaii continued to show only remnants of the 1982 El Chichón aerosol cloud. On 26 and 27 November, a distinct new layer centered at 25-25.5 km appeared on Mauna Loa lidar profiles (figure 12), accompanied by a substantial increase in total backscatter. This layer was absent over Mauna Loa on 3 December, but new layers centered at 15, 16.8, and 18.6 km altitude (tropopause altitude was 16.5 km) were detected and total backscatter remained elevated. Preliminary data 7 and 10 December showed some apparent new material, but less distinctly than on the 3rd. No new material was evident 10 December over Hampton, Virginia.

Figure 12. Arrival of Ruiz aerosols at different altitudes, shown by preliminary lidar profiles from Mauna Loa, Hawaii, 26 November-30 December 1985. Backscattering ratios are on the x axis, altitudes above sea level on the y axis. In the six dated graphs, the solid line records the data collected that night, the dotted line represents the average December profile. The final graph compares the average December profile (solid line) containing the new Ruiz aerosols with the average November profile (dotted line), primarily aerosols remaining from the 1982 eruption of El Chichón. Courtesy of Thomas DeFoor.

While flying from Honolulu to Los Angeles on 27 November at approximately 22°N, 140°W, David Hofmann saw a cloud of particles above the aircraft at an estimated elevation of 12 km. The gray haze and large ring around the sun were very similar towhat Hofmann observed shortly after the eruption of Fuego volcano, Guatemala in October 1974, suggesting that this cloud was also of volcanic origin.

On 5 December, balloon-borne particle counters detected a 10-fold increase in condensation nuclei (CN, H₂SO₄ droplets with diameters much less than 0.1 µm) between 15 and 17 km altitude over Laramie, Wyoming. Particle counts were 400 per cm³ compared to background values of 40 particles per cm³ at that altitude [see 10:12]. This CN event is distinguishable from El Chichón aerosols by both its altitude (El Chichón aerosols are found at 17-19 km) and particle size (El Chichón particles are now larger than 0.1 µm). A subsequent balloon flight on 11 December showed only background CN concentrations at these elevations.

Information Contacts: D. Hofmann and J. Rosen, Univ. of Wyoming; T. DeFoor, MLO; R. Reiter, Garmisch-Partenkirchen, W Germany; W. Fuller, NASA.