Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
doi:10.5194/gmd-2016-200
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Development and technical paper
15 Sep 2016
Review status
A revision of this discussion paper was accepted for the journal Geoscientific Model Development (GMD) and is expected to appear here in due course.
Variational assimilation of IASI SO2 plume height and total-column retrievals in the 2010 eruption of Eyjafjallajökull using the SILAM v5.3 chemistry transport model
Julius Vira1, Elisa Carboni2, Roy G. Grainger3, and Mikhail Sofiev1 1Finnish Meteorological Institute, Erik Palménin aukio 1, FI-00560 Helsinki, Finland
2COMET, Atmospheric, Oceanic and Planetary Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UK
3National Centre for Earth Observation, Atmospheric, Oceanic and Planetary Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK
Abstract. This study focuses on two new aspects on inverse modelling of volcanic emissions. First, we derive an observation operator for satellite retrievals of plume height, and second, we solve the inverse problem using the 4D-Var method. The approach is demonstrated by assimilating IASI SO2 plume height and total column retrievals in a source term inversion for the 2010 eruption of Eyjafjallajökull. The inversion resulted in temporal and vertical reconstruction of the SO2 emissions during the 1–20 May, 2010 with formal vertical and temporal resolutions of 500 m and 12 hours.

The plume height observation operator is based on simultaneous assimilation of the plume height and total column retrievals. The plume height is taken to represent the vertical centre of mass, which is transformed into the first moment of mass. This makes the observation operator linear and simple to implement. The necessary modifications to the observation error covariance matrix are derived.

Regularisation by truncated iteration is investigated as a simple and efficient regularisation method for the 4D-Var based inversion. In an experiment with synthetic observations, the truncated iteration was found to perform similarly to the commonly used Tikhonov regularisation. However, the truncated iteration allows the amount of regularisation to be varied a posteriori, without repeating the inversion. For inverting the Eyjafjallajökull SO2 emission at the temporal and vertical resolution used in this study, the 4D-Var method required about 70 % less computational effort than commonly used methods based on performing a separate model simulation for each degree of freedom in the estimated source term.

Compared to the inversion using only total column retrievals, assimilating the plume height resulted in a vertical emission profile more closely matching the ash plume heights observed by radar. The a posteriori source term gave an estimate of 0.29 Tg erupted SO2 of which 95 % was injected below 11 km.


Citation: Vira, J., Carboni, E., Grainger, R. G., and Sofiev, M.: Variational assimilation of IASI SO2 plume height and total-column retrievals in the 2010 eruption of Eyjafjallajökull using the SILAM v5.3 chemistry transport model, Geosci. Model Dev. Discuss., doi:10.5194/gmd-2016-200, in review, 2016.
Julius Vira et al.
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
 
RC1: 'Review', Anonymous Referee #1, 02 Nov 2016 Printer-friendly Version 
 
RC2: 'Assimilation method may be flawed', Anonymous Referee #2, 04 Dec 2016 Printer-friendly Version Supplement 
AC1: 'Assimilation method explained', Julius Vira, 13 Dec 2016 Printer-friendly Version Supplement 
Julius Vira et al.
Julius Vira et al.

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Short summary
This study reconstructed the vertical and temporal distribution of sulphur dioxide emissions during the 2010 eruption of Eyjafjallajökull by combining data from the IASI satellite instrument with a dispersion model. Contrary to previous studies, both column density (the total amount above a given point) and the plume height were derived from the satellite data. This noticeably improved the agreement between the estimated vertical emission profile and radar observations of the plume.
This study reconstructed the vertical and temporal distribution of sulphur dioxide emissions...
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