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Operational Modelling of Umbrella Cloud Growth in a Lagrangian Volcanic Ash Transport and Dispersion Model

1
Met Office, FitzRoy Road, Exeter EX1 3PB, UK
2
College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, UK
3
U.S. Geological Survey, Cascades Volcano Observatory, Vancouver, WA 98683, USA
*
Author to whom correspondence should be addressed.
Atmosphere 2020, 11(2), 200; https://doi.org/10.3390/atmos11020200
Received: 22 November 2019 / Revised: 9 January 2020 / Accepted: 20 January 2020 / Published: 13 February 2020
(This article belongs to the Special Issue Forecasting the Transport of Volcanic Ash in the Atmosphere)
Large explosive eruptions can result in the formation of an umbrella cloud which rapidly expands, spreading ash out radially from the volcano. The lateral spread by the intrusive gravity current dominates the transport of the ash cloud. Hence, to accurately forecast the transport of ash from large eruptions, lateral spread of umbrella clouds needs to be represented within volcanic ash transport and dispersion models. Here, we describe an umbrella cloud parameterisation which has been implemented into an operational Lagrangian model and consider how it may be used during an eruption when information concerning the eruption is limited and model runtime is key. We examine different relations for the volume flow rate into the umbrella, and the rate of spreading within the cloud. The scheme is validated against historic eruptions of differing scales (Pinatubo 1991, Kelud 2014, Calbuco 2015 and Eyjafjallajökull 2010) by comparing model predictions with satellite observations. Reasonable predictions of umbrella cloud spread are achieved using an estimated volume flow rate from the empirical equation by Bursik et al. and the observed eruption height. We show how model predictions can be refined during an ongoing eruption as further information and observations become available. View Full-Text
Keywords: umbrella cloud; volcanic ash transport and dispersion model; lateral spread; satellite observations; operational forecasting umbrella cloud; volcanic ash transport and dispersion model; lateral spread; satellite observations; operational forecasting
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Webster, H.N.; Devenish, B.J.; Mastin, L.G.; Thomson, D.J.; Van Eaton, A.R. Operational Modelling of Umbrella Cloud Growth in a Lagrangian Volcanic Ash Transport and Dispersion Model. Atmosphere 2020, 11, 200.

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