Balloon data - Wyoming. Particle counters on a balloon flight from Laramie, Wyoming 14 December detected a layer of tiny condensation nuclei (CN), centered at about 30 km altitude. Particle concentrations reached about 200/cm³, compared to background values of about 10/19cm³ at that altitude. Temperatures at 30 km altitude had warmed to -30 to -35°C on 10-11 December. David Hofmann noted that particle concentrations observed on the 14th were consistent with values that would be expected in a CN cloud produced a few days earlier.

Data on larger particles were collected during a balloon flight 21 December. The base of the aerosol layer was just above the tropopause (at about 8 km altitude, indicating an arctic air mass). Maximum particle concentrations of about 10/19cm³ (larger than 0.15 µm) were detected at about 12.5 km, declining gradually to about half that value at 18 km and 10% of the peak at 23 km. No distinct sublayers were observed.

Lidar data. In December, lidar at Mauna Loa, Hawaii detected slightly less stratospheric aerosol, as measured by total integrated backscattering, than in October and November. On 7 December, major backscattering peaks, marking the strongest aerosol layers, were separated by only small decreases in values; the 23.2 km layer was the strongest among several sharp peaks. The 2 major layers were well-defined on 14 December. On the 28th, each had a broad, smooth shape and backscattering values dropped sharply between them. At Hampton, Virginia peak backscattering remained somewhat enhanced over lowest summer values. The aerosol profile was considerably more irregular on 3 January than during the previous reading 7 December. The 12 January data at Fukuoka, Japan showed a broad monolayer that included most aerosols below 21 km.

Unusual sunrises and sunsets. From Jeddah, Saudi Arabia, Edward Brooks reported that dawn and twilight colors diminished in late November. Dawns showed no evidence of the presence of a volcanic aerosol layer over nearby Saudi Arabia 28 November - 6 December. Colored but rather subdued dawns indicated that aerosols returned during the second week in December. On 18 December, only the late dawn had significant color, indicating that the aerosol layer was at relatively low altitude. Separate early and late dawn illumination 24 December showed the presence of 2 scattering layers, at high and low altitudes respectively.

Information Contacts: D. Hofmann, Univ. of Wyoming; T. DeFoor, MLO; W. Fuller and M. Osborn, NASA; M. Fujiwara and M. Hirono, Kyushu Univ., Japan; E. Brooks, Saudi Arabia.