The sizes of the stratospheric volcanic particles over south-east Australia after Mt. Agung's eruption in 1963
✍ Scribed by J. Neumann
- Publisher
- John Wiley and Sons
- Year
- 1974
- Tongue
- English
- Weight
- 326 KB
- Volume
- 100
- Category
- Article
- ISSN
- 0035-9009
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✦ Synopsis
Abstract
Assuming an air layer of geometric thickness L, a particle number density N, particles of uniform radius a and density ϱ, the optical depth of the particle layer is τ = π__a__^2^ QNL, Q being the extinction efficiency factor. The total mass M of the particles in a vertical air column of unit cross‐section is M = (4/3)π__a__^3^ρ__NL__. The ratio of the two quantities is M/τ = 4__a__ϱ/3__Q__.
The above ratio is applied to data of τ for the observed 20% reduction in direct solar radiation over south‐east Australia about mid‐1963, reported by Dyer and Hicks. For M, an estimate given by Deirmendjian is used. It is inferred from the above ratio that a particle radius of a few tenths of one micron leads to a Q value such that the values for the radius and for Q are mutually consistent with the Mie scattering theory. If we assume much smaller radii, we run into contradiction with the latter. We thus conclude that most of the extinction must have been effected by particles of radii of about the same magnitude as the wavelengths where the bulk of the solar radiation energy resides. We estimate that the particle concentration may have been about 5 cm^−3^ and that absorption by the particles was probably very small.