Volcanic Contributions to the Stratospheric Sulfate Layer

Abstract

Abstract We have detected the transport of volcanic sulfate through the tropical tropopause. This is particularly noteworthy because the source volcanic eruption was only of modest intensity and, therefore, not normally thought to be of stratospheric importance. Using lidar, the veil was detected on two days during January 1977. Although the bulk of the material was in the troposphere, there was evidence of transport through the tropopause on both days. Trajectory calculations suggested that the source was Nyiragongo volcano in central Africa (1.5°S, 29.2°E). The presence of an adiabatic temperature profile through the dust layer suggests that the volcanic layer was being convected by means of radiative absorption. This mechanism may provide sulfate for the maintenance of a background level of stratospheric sulfate. During the six years of lidar observations in Hawaii (19.5°N), we have rarely observed such layers. Visual, lidar and other observations of the volcanic cloud are presented.