Reinhold Reiter provided the following summary of the results of lidar measurements from Garmisch-Partenkirchen, West Germany, January 1982-April 1983. A more detailed analysis [appears in Reiter and others, 1983].

"The stratospheric dust veil from the early 1982 "Mystery Cloud" caused from January on (before the El Chichón eruption) a clearly increased background level of particle backscattering at 10-20 km altitude, but not at higher levels. We observed the arrival of the dust veil from El Chichón on 3 May 1982 at 10-20 km altitude (peak at 15 km). In this height interval the aerosol backscatter intensity rose until March 1983, with fluctuations of a factor of 5 (weakened by preloading from the "Mystery Cloud"). We noted the strongest increase, by about a factor of 40, in January 1983 in the height interval 20-30 km. Since August 1982, a clearly increased aerosol backscatter from the El Chichón dust veil can also be seen at levels higher than 30 km. In contrast to the other dust veils that we traced in the stratosphere (St. Helens and Alaid), the aerosol backscatter intensity increased, as figure 4 shows, up to the recent past, i.e. over many months. Only in the 20-30 km range can a slight decrease be recognized from January 1983 on; at this level sedimentation of particles seems now to prevail over their influx. The time history of the stratospheric aerosol loading can be explained by El Chichón's position near the equator. There was only a slow meridional transport and a poleward homogenization of the stratospheric material in the northern hemisphere. Surely, part of the material also entered the stratosphere in the southern hemisphere.

"Important for an assessment of possible global climate affects is the change in the optical thickness. Before the eruption of St. Helens, its value was about 0.002, before the eruption of El Chichón, 0.022, and presently it is about 0.18. This means a considerable increase which, according to known models, suggests most probably a cooling of the earth's surface by some tenths of a degree within the next 1-2 years. In the stratosphere, however, warming is to be expected."

The following is from M. P. McCormick. "A dedicated El Chichón survey mission was flown on the NASA CV990 aircraft 8-20 May, 1983, from 71°N to 56°S (California - Alaska - S of New Zealand, and return to California). Previous missions were conducted on the NASA Electra aircraft in July and October-November 1982, and January-February 1983 and on the CV990 in December 1982. These flights were coordinated with measurements by satellites or balloons, or with in situ measurements aboard other aircraft.

"During the May 1983 flight, lidar profiles were obtained over the full latitude range, showing a definite peak in integrated stratospheric backscattering (related to optical depth or mass of stratospheric aerosols) at about 50-55°N. This agreed with lidar data collected during the January-February 1983 arctic mission. The May lidar profiles showed a well-defined southern boundary of the dense stratospheric aerosols between 40° and 50°N, with a minimum near 20°N, a small maximum near the equator, and a definite falloff to even lower values near 10°S. These data are preliminary at this time and are being processed for future publication. In addition to the airborne lidar measurements, other experiments conducted during the May 1983 flight included measurements of optical depth at visible and infrared wavelengths, radiation flux, and total SO₂ and O₃ column content."

Ground-based lidar in Hawaii and Virginia showed a continuing gradual (although somewhat irregular) decrease in total integrated backscatter. Peak backscattering remained similar.

Edward Brooks reported that bands of aerosols and brilliant dawns and twilights were visible on some days through mid-June from Jeddah, Saudi Arabia. Aerosol bands were seen early 22-24 and 26 May and impressive sunrises and sunsets were frequent during this period, some showing 2 distinct stages caused by illumination of unusually high layers. Optical effects declined 16-20 June, but weather conditions made observations difficult. From Millville, New Jersey, Fred Schaaf reported that only occasional observations were possible because of cloudy weather. Aerosols at moderate altitudes were illuminated 10 May and early sunset color was slightly enhanced 11 and 13 May. Jos‚ Caburian noted that fiery red sunrises and sunsets, seen in the Philippines for the previous several months, were not evident at the end of May and early June.

Recently erupted volcanic material from an unknown source was collected at 18-19 km altitude over the western US during a series of flights by a NASA U-2 aircraft 22-29 April. Samples from a 22 April mission flown at 37°N from near San Francisco (about 37.7°N, 122.5°W) to Topeka, Kansas (39.02°N, 95.68°W) included particles ranging from less than 0.1 µm to 20-30 µm in diameter: fragments of magnesian olivine, Cl-rich agglomerates, and H₂SO4 droplets, plus a few glass shards, fragments of SiO₂, and particles of copper and zinc oxide. The copper oxide-zinc oxide particles were similar to those found in previous aircraft samples of volcanic debris, with a characteristic 2:1 Cu to Zn ratio. During a flight from Topeka southward to Palestine, Texas 28 April, concentrations of volcanic material were less than on 22 April but remained above background levels. However, flying northward from Topeka to the U.S.-Canada border (49°N) the next day, particle concentrations were substantially higher, and the debris included many large fragments.

The source of the volcanic material remains uncertain. The samples were not similar to ejecta collected from the El Chichón aerosol cloud, and Raymond Chuan added that the large size of some of the particles suggests that the eruption probably occurred no more than about 2 months before the late April flights. Some large particles had been found in July 1982 samples from the El Chichón stratospheric cloud but none were recovered during flights in November 1982. Chuan also noted that a mid to high northern latitude source for the April 1983 material is suggested by the higher concentration of volcanic debris on more northern flight paths. No observations of early 1983 eruption clouds large enough to penetrate the stratosphere have been reported to SEAN. However, the largest clouds from the 8 April eruption of Asama (Japan, 36.40°N, 138.53°E) were produced before dawn and were not observed. Ashfall from this eruption extended more than 250 km ENE, reaching the coast of Honshu. Large plumes from Etna (Italy, 37.73°N, 15.00°E) have been observed from the ground and on satellite imagery during the eruption that began 28 March.

Lidar data from Mauna Loa, Hawaii showed an aerosol layer straddling the tropopause on 11 May that had not been present during the previous measurement on 4 May. This layer was narrow and well-defined, extending from 15.2-16.4 km altitude on 11 May and from 15.6-16.4 km on 28 May. Lidar data on 25 May seemed to show some mixing between the new layer and the base of the El Chichón material. Lesser amounts of aerosol were detected by lidar at 13-15.6 km on 8 June and 11.4-15.2 km on 29 June, but no upper tropospheric material was present 22 June. Clouds that were probably at too high an altitude to be cirrus persisted over Hawaii for several weeks and a corona and brilliant white aureole sometimes surrounded the sun. A relatively weak layer peaking at 13.5 km altitude was detected by lidar at Hampton, Virginia on 23 June but none was present at that level 22, 26, 27, or 30 June. Lidar data were not collected at Hampton between 22 March and 22 June. The relationship between these lidar observations and the fresh volcanic material collected during the NASA flight on 22 April is uncertain.

References. Labitzke, K., Naujokat, B., and McCormick, M. P., 1983, Temperature effects on the stratosphere of the April 4, 1982 eruption of El Chichón, Mexíco, in Pollack, J.B., Toon, O.B., Danielsen, E.F., Hofmann, D., et al., eds., 1983, The El Chichón volcanic cloud: An introduction: Geophysical Research Letters, v. 10, no. 11.

Reiter, R., et al, 1983, The El Chichón cloud over central Europe observed by Lidar at Garmisch-Partenkirchen during 1982: Geophysical Research Letters, v. 10, no. 11.

Information Contacts: R. Reiter, Garmisch-Partenkirchen, W. Germany; P. McCormick, D. Woods, and W. Fuller, NASA; T. DeFoor, MLO; E. Brooks, Saudi Arabia; F. Schaaf, Millville, NJ; J. Caburian, Manila, Philippines; R. Chuan, Brunswick Corp.