Lidar continued to detect remnants of the aerosol cloud produced by the March-April 1982 explosions from El Chichón, México. Peak backscattering ratios decreased at Fukuoka, Japan, where 2 layers were evident. Altitudes and peak backscattering ratios of the main layers at Hampton, Virginia were similar in April and May. However, measurements made in an Arctic airmass 16 May yielded a total backscatter nearly twice as large as it had been a week earlier in tropical air. Aerosols were relatively dense down to the tropopause, at 11 km altitude on the 9th and 9.6 km on the 16th. On 24 May, many small layers were present, the tropopause was much higher (13.5 km), and total backscatter had decreased to late April levels. Little structure was evident in the aerosol material 4 June. Values from Garmisch-Partenkirchen, Germany showed minor variation between January and April, but were generally slightly lower than in late 1983. Lidar measurements resumed 30 May at Mauna Loa Observatory. Peak and total backscattering had decreased slightly since late March.

From Jeddah, Saudi Arabia, dawns and dusks observed by Edward Brooks varied in intensity. Moderately strong colors observed from 16-21 April persisted through dawn on the 23rd, but were only intermittently present through the end of the month. Weak dawns and twilights from 30 April through the dawn of 6 May suggested that little or no aerosol material was present. Moderate colors returned late 6 May and dusk on the 9th was long and strongly illuminated, indicating the presence of high-altitude aerosols. Dawns and twilights were colorful through 14 May, and faint N-S bands of high-altitude aerosols were visible at dawn on the 11th. Morning and evening colors were again absent 15-18 May, then clouds prevented observations through the 22nd. Moderate colors were present 23-24 May but were weak the following 2 days.

Information Contacts: R. Reiter, Garmisch-Partenkirchen, W Germany; W. Fuller, NASA; M. Fujiwara and M. Hirono, Kyushu Univ., Japan; T. DeFoor, MLO; E. Brooks, Saudi Arabia.