SAGE-II OBSERVATIONS OF A PREVIOUSLY UNREPORTED STRATOSPHERIC VOLCANIC AEROSOL CLOUD IN THE NORTHERN POLAR SUMMER OF 1990

Analysis of aerosol extinction profiles obtained by the spaceborne SAG E II sensor reveals that there was an anomalous increase of aerosol ex tinction below 18.5 km at latitudes poleward of 50-degrees-N from July 28 to September 9, 1990. This widespread increase of aerosol extincti on in the lower stratosphere was apparently due to a remote high-latit ude volcanic eruption that has not been reported to date. The increase in stratospheric optical depth in the northern polar region was about 50% in August and had diminished by October 1990. This eruption cause d an increase in stratospheric aerosol mass of about 0.33 x 10(5) tons , assuming the aerosol was composed of sulfuric acid and water.