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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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doi:10.5194/amt-2016-92
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
04 May 2016
Review status
A revision of this discussion paper for further review has not been submitted.
Inferring the size distribution of volcanic ash from IASI measurements and optimal estimation
Luke M. Western1, Peter N. Francis2, I. Matthew Watson1, and Shona Mackie3 1COMET, School of Earth Sciences, University of Bristol, Bristol, UK
2Met Office, Exeter, UK
3School of Earth Sciences, University of Bristol, Bristol, UK
Abstract. This study demonstrates a method of retrieving the mass column loading and cloud-top pressure of a volcanic ash cloud, together with the effective radius and spread of the ash particle size distribution, as well as the cloud top pressure of any underlying water cloud, using an optimal estimation technique applied to Infrared Atmospheric Sounding Interferometer data. Two shapes of particle size distribution are considered, a log-normal and a gamma distribution. Results show that it is viable to retrieve a measure of the size distribution spread, namely the geometric standard deviation, when a log-normal distribution is assumed, whereas this is not the case for an assumed gamma distribution in terms of its effective variance. The volcanic conditions under which the method works well are discussed, as are its shortcomings. The method is applied to two volcanic eruptions: Eyjafjallajökull, Iceland using data from 6th May 2010 and Kasatochi, Alaska using data from 8th August 2008. The results show that the retrieved geometric standard deviation of these ash clouds is spatially variable, and is generally similar to what is assumed in many passive infrared remote sensing techniques. An abrupt change in the retrieved geometric standard deviation has been observed for the Eyjafjallajökull eruption along the trajectory of the ash cloud, and possible explanations for this are discussed.

Citation: Western, L. M., Francis, P. N., Watson, I. M., and Mackie, S.: Inferring the size distribution of volcanic ash from IASI measurements and optimal estimation, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-92, in review, 2016.
Luke M. Western et al.
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RC1: 'Review', Anonymous Referee #1, 29 May 2016 Printer-friendly Version 
 
RC2: 'Review of “Inferring the size distribution of volcanic ash from IASI measurements and optimal estimation” by Luke M. Western et al.', Anonymous Referee #3, 08 Jul 2016 Printer-friendly Version 
Luke M. Western et al.
Luke M. Western et al.

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Short summary
This work aims to infer the size distribution of airborne volcanic ash using satellite measurements. The size distribution of volcanic ash is typically described using two parameters, of which one is normally assumed and one can be measured using satellites. This work shows that it is possible, using a satellite with high spectral resolution, to retrieve both parameters. This work has been done to reduce uncertainty in mass calculations for airspace management during volcanic unrest.
This work aims to infer the size distribution of airborne volcanic ash using satellite...
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