Toyotaro Yamauchi and Hidehiro Shimura report that atmospheric turbidity over Japan (figure 5) reached a maximum between late autumn 1982 and spring 1983. Atmospheric turbidity has decreased gradually since then, but was still considerably higher than normal during the winter of 1983-84. At noon on clear days in December 1982, direct solar radiation (I) and global solar radiation (G) showed decreases of 0.17 kW/m² (20%) and 0.02 kW/m² (3%), and diffuse solar radiation (D) a 0.07 kW/m² (74%) increase at Tsukuba, Japan (36.17°N, 141.09°E) as compared to a normal year. In December 1983, I was 0.05 kW/m² (6%) lower and D was 0.02 kW/m² (26%) higher than a normal year at Tsukuba, while G was approximately normal (figure 6).

Figure 5. Three measures of aerosol content of the atmosphere; (top) variation in atmospheric turbidity (t0), (center) transmissivity (A), and (bottom) direct solar radiation (I), for all stations in Japan, 1950-1983. The largest changes followed the eruptions of Agung in 1963 and El Chichón in 1982. Courtesy of T. Yamauchi and H. Shimura.

Figure 6. Monthly means of direct, diffuse, and global solar radiation observed at noon on clear days at Tsukuba, Japan. [Note that the decline in direct solar radiation after the 1982 El Chichón eruption is mirrored by an increase in diffuse radiation as the aerosol cloud scatters sunlight.] Courtesy of Minoru Obata, Aerological Observatory.

Lidar at Mauna Loa, Hawaii continued to detect stratospheric aerosols from the March-April 1982 eruption of El Chichón. Altitude and peak backscatter of the main layer remained similar through June. A small peak in the upper troposphere or lower stratosphere was also observed throughout the month. Particularly pronounced on 14 June, it was distinctly weaker although still evident on the 29th. There was no obvious single source for this layer, although moderate explosions had occurred at low latitudes at several volcanoes in previous weeks, including Pagan (Mariana Islands), Soputan (Indonesia), and Manam (Papua New Guinea). A similar layer was present over Hampton, Virginia in late May, but a distinct lower layer was not reported from there in June. Altitude and backscattering of the main layer were relatively uniform through the month, but a lower tropopause on the 25th (10.5 km) was accompanied by an increase in total backscatter.

Information Contacts: T. Yamauchi and H. Shimura, JMA; T. DeFoor, MLO; W. Fuller, NASA.