Volcanic material from Mount St Helens in the stratosphere over Europe

Abstract

The two most recent balloon flights devoted to studying the stratospheric aerosol vertical structure by comparison with winds, temperature and ozone vertical structures took place on 7 May and on 5 June 1980. At 15.23 h GMT on 18 May Mount St Helens volcano (46 °N, 122 °W) erupted with a tremendous explosion, projecting ash into the stratosphere. An explosion of this size occurs only about once a decade¹. This sudden introduction of material into the atmosphere offers the opportunity to study air motions both horizontally and vertically. The last such large-scale opportunity was offered by the Mount Fuego eruption which took place in 1974. In this latter case, the enhancement of stratospheric aerosols was observed by means of ground-based lidars and of balloon-borne particle counters. The time development of the aerosol event in 1974 and 1975 has been described elsewhere^2–4. Mount St Helens material can now also be traced by various satellite-borne instruments. This new stratospheric aerosol event appears to be spectacular. As shown by the photographs discussed here, it leads in its early stage of development to an increase by a factor of three of the Earth limb reflectivity at 15-km altitude after a period of several years of low stratospheric aerosol content.