Stratospheric particles and solar radiation over northeast Australia after Mt Agung's eruptions in 1963

Mossop' s size distribution of stratospheric-volcanic particles, sampled over northeast Australia in May 1963, about 10 weeks after Mt Agung' s first eruption, is used for estimating the effect of these particles on solar radiation. The particles are idealised to be concentric spheres having a mineral core (Mossop's 'volcanic' particles) and an outer shell of concentrated sulphuric acid, and the Mie theory appropriate to concentric spheres (Kerker) is applied. Making the arbitrary assumption that the particles occupied a stratospheric air layer 10 km thick, we find that the total reduction in the direct solar flux could not have amounted to more than about 0.5 per cent; corrections applied to Mossop's reported particle-size distribution raise the latter figure to 1 per cent or to, at most, 2 per cent. Mossop's stratospheric particle samplings over the ocean area off Tasmania, to the south of Melbourne, lead to calculated reduction rates in solar radiation that are even lower than those computed for northeast Australia. In contrast, about that time over the Melbourne area, 1500 km south of Mossop's northeast Australian sampling line, the observed decrease in the direct flux time reached some 20 per cent (Dyer and Hicks). An examination is made of other factors whose neglect or underestimation may have led to the very low computed effects on solar radiation. The conclusions are negative with respect to all but one; that remaining factor is not thought to have had a protracted influence. We thus infer that, in all probability, the concentration of stratospheric-volcanic particles over northeast Australia must have been substantially lower than over the southeast. An inspection of upper air charts suggests that the upper air flowing over southeast Australia passed earlier close to the general area of Mt Agung, which is not the case for the air that crossed the northeast of 'the continent during the period of concern. This is the likely explanation for the inferred great disparity for the two regions of concern.