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Volcanic ash infrared signature: porous non-spherical ash particle shapes compared to homogeneous spherical ash particles

A. Kylling ; Michael Kahnert (Institutionen för rymd- och geovetenskap, Global miljömätteknik och modellering) ; H. Lindqvist ; T. Nousiainen
Atmospheric Measurement Techniques (1867-1381). Vol. 7 (2014), 4, p. 919-929.
[Artikel, refereegranskad vetenskaplig]

The reverse absorption technique is often used to detect volcanic ash clouds from thermal infrared satellite measurements. From these measurements effective particle radius and mass loading may be estimated using radiative transfer modelling. The radiative transfer modelling usually assumes that the ash particles are spherical. We calculated thermal infrared optical properties of highly irregular and porous ash particles and compared these with mass-and volume-equivalent spherical models. Furthermore, brightness temperatures pertinent to satellite observing geometry were calculated for the different ash particle shapes. Non-spherical shapes and volume-equivalent spheres were found to produce a detectable ash signal for larger particle sizes than mass-equivalent spheres. The assumption of mass-equivalent spheres for ash mass loading estimates was found to underestimate mass loading compared to morphologically complex inhomogeneous ash particles. The underestimate increases with the mass loading. For an ash cloud recorded during the Eyjafjallajokull 2010 eruption, the mass-equivalent spheres underestimate the total mass of the ash cloud by approximately 30% compared to the morphologically complex inhomogeneous particles.

Nyckelord: RADIATIVE-TRANSFER CALCULATIONS, DISCRETE-DIPOLE APPROXIMATION, LIGHT-SCATTERING, EXTINCTION SPECTRA, CLOUDS, RETRIEVAL, AEROSOLS, GLASSES, SPACE, LLACK JB, 1973, ICARUS, V19, P372, AMNES K, 1988, APPLIED OPTICS, V27, P2502, ATA AJ, 1989, GEOPHYSICAL RESEARCH LETTERS, V16, P1293



Denna post skapades 2014-06-23. Senast ändrad 2014-08-19.
CPL Pubid: 199482

 

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