New model for volcano ash light scattering
Suspended ash particles scatter and absorb the incoming solar radiation. How much of this radiation is reflected back to space, how much is absorbed to heat the atmosphere, and how much is transmitted to heat the surface depends on the optical properties of individual particles.
The optical properties of the particles depend on their amount, size, shape and composition. Knowledge of the optical properties is instrumental in the proper interpretation of remote sensing measurements of the atmosphere. Finnish Meteorological Institute, together with scientists from the Helsinki University and Instituto de Astrofísica de Andalucía, Spain, used measurements of collected volcano ash particles from various locations to investigate how to model their optical properties. Previously unpublished measurements from Eyjafjallajökull and Puyehue volcanoes were also introduced in this paper and released to be freely available in the Amsterdam – Granada Light Scattering Database (www.iaa.es/scattering/).
"Real particles have complex shapes, as seen from this electron microscope image of ash particles that originate from the Puyehue volcano."
A modeling scheme was found which reproduced the laboratory measured optical properties very well.The optical properties of volcanic ash particles were modeled by using ellipsoidal shapes, which proved to improve hugely on often used assumption of spherical particles. We also performed sensitivity studies on the point of view of the AATSR (Advanced Along Track Scanning Radiometer) instrument and concluded that the ensembles of ellipsoidal model shapes could be used to improve the data interpretation from instruments like such as this. The work will continue to incorporate the ellipsoidal model in the Finnish Meteorological Institutes AATSR data analysis procedures.
Volcanoes exist around the globe and thus also the potential hazards they create are potentially of global nature.
Further information:
Research scientist Sini Merikallio, tel. +358 50 409 7566, sini.merikallio@fmi.fiSenior researcher Timo Nousiainen, puh +358 50 441 5451, timo.nousiainen@fmi.fi