Preprints
https://doi.org/10.5194/acp-2021-858
https://doi.org/10.5194/acp-2021-858

  09 Nov 2021

09 Nov 2021

Review status: this preprint is currently under review for the journal ACP.

Refining an ensemble of volcanic ash forecasts using satellite retrievals: Raikoke 2019

Antonio Capponi1, Natalie J. Harvey2, Helen F. Dacre2, Keith Beven1, Cameron Saint3, Cathie A. Wells2, and Mike R. James1 Antonio Capponi et al.
  • 1Lancaster Environment Centre, LEC Building, Lancaster, LA1 4AQ, UK
  • 2Department of Meteorology, University of Reading, Earley Gate, Reading, RG6 6ET, UK
  • 3Met Office, Fitzroy Road, Exeter EX1 3PB, UK

Abstract. Volcanic ash advisories are produced by specialised forecasters who combine several sources of observational data and volcanic ash dispersion model outputs based on their subjective expertise. These advisories are used by the aviation industry to make decisions about where it is safe to fly. However, both observations and dispersion model simulations are subject to various sources of uncertainties that are not represented in operational forecasts. Quantification and communication of these uncertainties are fundamental for making more informed decisions. Here, we develop a data assimilation technique which combines satellite retrievals and volcanic ash transport and dispersion model (VATDM) output, considering uncertainties in both data sources. The methodology is applied to a case study of the 2019 Raikoke eruption. To represent uncertainty in the VATDM output, 1000 simulations are performed by simultaneously perturbing the eruption source parameters, meteorology and internal model parameters (known as the prior ensemble). The ensemble members are filtered, based on their level of agreement with Himawari satellite retrievals of ash column loading, to produce a posterior ensemble that is constrained by the satellite data and its uncertainty. For the Raikoke eruption, filtering the ensemble skews the values of mass eruption rate towards the lower values within the wider parameters ranges initially used in the prior ensemble (mean reduces from 1 Tg h−1 to 0.1 Tg h−1). Furthermore, including satellite observations from subsequent times increasingly constrains the posterior ensemble. These results suggest that the prior ensemble leads to an overestimate of both the magnitude and uncertainty in ash column loadings. Based on the prior ensemble, flight operations would have been severely disrupted over the Pacific Ocean. Using the constrained posterior ensemble, the regions where the risk is overestimated are reduced potentially resulting in fewer flight disruptions. The data assimilation methodology developed in this paper is easily generalisable to other short duration eruptions and to other VATDMs and retrievals of ash from other satellites.

Antonio Capponi et al.

Status: open (until 23 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Antonio Capponi et al.

Antonio Capponi et al.

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Short summary
Forecasts of the dispersal of volcanic ash in the atmosphere are hampered by uncertainties in parameters associated with the eruption plume. Uncertainty quantification is vital for making robust flight-planning decisions. We present a method aiming to use satellite data to refine a series of simulations of volcanic ash dispersion and quantify these uncertainties. We show how we can improve forecasts accuracy and potentially reduce the regions of high risk of volcanic ash relevant to aviation.
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