Lidar data showed a continuing gradual decline in backscattering ratios from El Chichón aerosols. However, lidar in Hampton, Virginia and Fukuoka, Japan detected layers near the local tropopause that may have been from another eruption. A weak layer peaking at 13.5 km altitude was present over Hampton 23 June and aerosols were also observed at 9-14 km on 7 July and 11-13.5 km on 26 July. In July, this material was associated with a "double tropopause", a condition in which 2 temperature inversions were found instead of the single one that typically marks the boundary between the troposphere (where temperature decreases with altitude) and the lower stratosphere (where temperature increases with altitude). No aerosols were detected below the El Chichón material 12 and 27 July. From Fukuoka, new thin layers were observed 1-5 August between 12 and 16 km altitudes, at or below the local tropopause. The layers had fine structures of 100 m and were much more stable than the often-observed cirrus clouds in that altitude range, indicating the possibility that they were volcanic ejecta. Their peak scattering ratios were about 3-30 using YAG lidar. Aerosol layers were observed below the El Chichón material at Mauna Loa, Hawaii on some nights in May and June, but none were detected in July and early August. The source of this material and its relationship to the recently-erupted volcanic material collected in late April by a NASA aircraft over the central United States remain uncertain. Although the eruption of Una Una, Indonesia (0.17°S, 120.61°E) that began 18 July probably injected tephra into the stratosphere, meteorologists anticipated little northward migration of this material until autumn.

From Norwich, England, H. H. Lamb observed little change in optical phenomena. Skies in the direction of the sun continued to be whitish with much diffuse radiation; broken clouds seen against this background appeared an unusually pale gray. Clear twilight skies still produced abnormal colors, often bronze or sepia near the horizon, and whitish shades sometimes with a magenta or purplish patch above, in the direction of the sun. Before sunset, a fan-shaped area of brilliant bluish-white glow above the sun was common. On 30 June between 2245 and 2315 GMT (and probably for some time before and after) noctilucent clouds, structured like dense cirrus, were seen glowing strongly with a soft bluish-white light against the background of the brightest part of the twilight sky, between the horizon and about 9° elevation. The implied altitude of the clouds was about 80 km. Noctilucent clouds are rare at England's latitude and are seen only within about 2-3 weeks of the summer solstice. Lamb last observed noctilucent clouds a year or 2 after the 1963 Agung eruption, which injected large quantities of aerosols into the stratosphere.

Richard Keen reported that enhanced twilights returned to Boulder, Colorado on 14 June, after an absence of 5 months. Unusual twilights were observed 14 and 17 June, and 2-5, 13-14, 17, 22, and 24 July. The twilights were salmon-colored, with brightest and most pronounced coloring at solar depression angle (SDA) of 4°, disappearing on the horizon at SDA 5-6°. In addition, the 3, 13, and 17 July twilights included fainter purplish color that continued to an SDA of about 11°. None of the twilights were as bright as those seen in January, and they ended at somewhat smaller SDA's, suggesting that they were produced by aerosols at somewhat lower altitudes. Cloudy weather February-May made observations difficult but no unusual twilights were observed on clear evenings. Raymond Chuan began to see similar salmon-colored twilights about 10 July from Costa Mesa, California (33.65°N, 117.93°W) and these continued through the week of 18 July, but no enhanced colors were present in early August.

From Millville, New Jersey, Fred Schaaf observed twilight glows in June, July, and early August that were the strongest since January. Skies were whitened by volcanic aerosols 9 June and a 20° Bishop's Ring was seen the next evening. Purple light after sunset indicated aerosols to more than 8 km altitude 13-14 June. Faint but very late color 22 June was followed by a 2-stage twilight the next evening suggesting the presence of both lower-altitude material and aerosols extending to 24 km. Colors caused by high-altitude material were not evident 24-25 June but returned on the 26th, from aerosols at 24-27 km. Sunsets showed no evidence of high-altitude material for the rest of June, but Bishop's Ring was seen on the 30th. Poor weather prevented additional observations until 10 July, when a 2-stage twilight again indicated aerosols at low and high altitudes; if aerosols were being directly illuminated, continued color at 2200 suggests material extended to 40-48 km. Twilight was spectacular the next evening. Shortly after sunset, an intense narrow red band was observed, indicating strong low-altitude aerosols, but late color was also the strongest since January; if caused by direct illumination, aerosols reached more than 50 km altitude. Twilights were similar 12-13 July. Poor weather limited observations during the next 2 weeks. Moderately-colored 2-stage twilights were observed 22 and 26 July, with a mid-level layer at 13-19 km altitude. This layer was still present 27 July, but higher material seemed absent. Dawn observations 1, 2, and 5 August continued to show mid-level aerosols but no high-altitude material was observed.

Late June observations by Edward Brooks of dawns and twilights from Jeddah, Saudi Arabia were hampered by haze, sand, and occasional clouds. However, very early dawns, although often nearly colorless, suggested the presence of high-altitude aerosols. Brilliant dusk colors were observed 3 July and and faint bands of volcanic aerosols were observed with a very early dawn the next day.

Information Contacts: T. DeFoor, MLO; W. Fuller, NASA; M. Hirono, Kyushu Univ., Japan; R. Reiter, Garmisch-Partenkirchen, W. Germany; H. Lamb, Univ. of East Anglia, England; F. Schaaf, Millville, NJ; R. Keen, Univ. of Colorado; E. Brooks, Saudi Arabia; R. Chuan, Brunswick Corp.