Satellite retrievals and inverse modeling of volcanic SO2 clouds: Implications for accurate transport modelling of volcanic emissions

An analytical inverse modeling method has been developed to estimate the vertical emission profile of SO2 resulting from volcanic eruptions using satellite-observed total SO2 columns and an atmospheric transport model (FLEXPART). It utilizes the fact that winds normally change with altitude and, thus, the plume position and shape depend on the altitude of the emissions. The method finds the vertical emission distribution with which the model can optimally reproduce the shape and horizontal position of the observed SO2 plume. We have applied it to two eruptions (Jebel at Tair in September 2007 and Kasatochi in August 2008) for which a comprehensive observational data set from various satellite instruments (AIRS, OMI, SEVIRI, CALIPSO) could be compiled. Using satellite data from the first 24 hours after the eruption for the inversion, we could estimate emission maxima. The overall plume dispersion over the following week as observed by OMI could be simulated very well. Also, the altitude of the simulated plume is in agreement with CALIPSO observations of stratospheric aerosol. The inversion result was rather robust. Even when using only SEVIRI data from the first 15 hours after the eruption, the emission profile was reasonably accurate. Using our method, the emission altitudes of volcanic eruptions can be estimated with great accuracy. Therefore the method is suitable for real time predictions of the threat posed by volcanic ash for commercial air traffic.