On dust in the tropical and midlatitude stratosphere from recent twilight measurements

Abstract

The variation of stratospheric turbidity in recent years in midlatitudes and in the tropics as indicated by the amplitude of the λ715/477 or λ810/500 color ratio of twilight radiance at 20° elevation is investigated. Since late 1963, the stratospheric turbidity in northern mid-latitudes has been much higher than it was before the explosion of the Agung volcano in March 1963; a considerable latitude effect is indicated. In the tropics, the stratospheric dust layer was even stronger (and at a greater altitude) in 1969, and very likely was also stronger during the preceding years. There is not much direct evidence that the apparently persistent, yet abnormal, tropical reservoir of stratospheric aerosol was replenished by more recent volcanic activity.