Volcanic material from Mount St Helens in the stratosphere over Europe

Observations of aerosols in the stratosphere prior to and following the eruption of Mount St. Helens volcano on May 18, 1980 are reported. Photographic observations of the earth limb in the azimuthal direction of the sun at low solar elevations were obtained at balloon altitudes over Europe on October 10, 1979 and May 7 and June 5, 1980. Analysis of the limb pictures acquired reveals an abrupt increase in earth limb radiance between 15 and 16 km altitude on June 5 relative to the earlier dates, at which radiance varied smoothly with altitude. The increased radiance is attributed to aerosols from the volcanic event, and possible mechanisms for the decrease of the amount of solar radiation reaching the ground due to the stratospheric aerosols are indicated.