Measurements and interactive modeling of the 1960s stratospheric aerosol layer

In contrast to the near-quiescent decades of the 1920s-1950s, the 1960s stratospheric aerosol layer had continued volcanic enhancement, with the major eruption of 1963 Agung and the subsequent VEI4 eruptions of 1965 Taal, 1966 Awu and 1968 Fernandina.

The first in-situ measurements of a volcanic enhancement to the stratosphere aerosol layer were made from high-altitude balloon in 1963 and 1964, from Minneapolis. A continuing program of these dust-sondes were launched approximately quarterly from Minneapolis, and a short series of launches from Panama in September 1966 (Rosen, 1968) measured strong volcanic enhancement just weeks after the Aug 1966 Awu eruption.

A different series of balloon measurements were made from Minneapolis in 1965-1968, and within coincident soundings in Panama in Sep 1966. This instrument was a rotating 4-telescope sun photometer designed to measure the vertical profile of solar extinction at 4 wavelengths and provided the foundations for the SAGE and SAM satellite instruments launched in 1979.  A 2021 MRes project at Leeds University has recovered the vertical profile datasets of the 910nm channel of these 22 balloon solar extinction soundings from Figures within the University of Wyoming PhD thesis of Ted Pepin. 

This poster presentation will present the 1965-1968 solar extinction measurements, analysed within an 2024/25 undergraduate dissertation project, comparing to CMIP stratospheric aerosol forcing datasets and showing the clear signal of volcanic enhancement apparent during NH winter 1966/67.  We are preparing the dataset for inclusion in the archive of the Network for Detection of Atmospheric Composition and Change (NDACC), alongside the 1963-1967 dust-sonde measurements provided in 2017 to the NDACC archive by the instrument PI (James Rosen (University of Wyoming).

We will analyse 1963-67 simulations with the UM-UKCA interactive stratospheric aerosol model, from continuing from runs already validated for the Agung period (Dhomse et al. 2020). The Minneapolis balloon measurements will be used to assess potential SO₂ emissions from 1965 Taal (September) and 1966 Awu (August), the 3D model shown to represent well variations in the transport to mid-latitudes of volcanic aerosol from similar tropical eruptions.