Abstract

Volcanic ash can interact with the earth system on many temporal and spatial scales and is a significant hazard to aircraft. In the event of a volcanic eruption, fast and robust decisions need to be made by aviation authorities about which routes are safe to operate. Such decisions take into account forecasts of ash location issued by Volcanic Ash Advisory Centers (VAACs) which are informed by simulations from Volcanic Ash Transport and Dispersion (VATD) models. The estimation of the time-evolving vertical distribution of ash emissions for use in VATD simulations in real time is difficult which can lead to large uncertainty in these forecasts. This study presents a method for constraining the ash emission estimates by combining an inversion modeling technique with an ensemble of meteorological forecasts, resulting in an ensemble of ash emission estimates. These estimates of ash emissions can be used to produce a robust ash forecast consistent with observations. This new ensemble approach is applied to the 2011 eruption of the Icelandic volcano Grímsvötn. The resulting emission profiles each have a similar temporal evolution but there are differences in the magnitude of ash emitted at different heights. For this eruption, the impact of precipitation uncertainty (and the associated wet deposition of ash) on the estimate of the total amount of ash emitted is larger than the impact of the uncertainty in the wind fields. Despite the differences that are dominated by wet deposition uncertainty, the ensemble inversion provides confidence that the reduction of the unconstrained emissions (a priori), particularly above 4 km, is robust across all members. In this case, the use of posterior emission profiles greatly reduces the magnitude and extent of the forecast ash cloud. The ensemble of posterior emission profiles gives a range of ash column loadings much closer in agreement with a set of independent satellite retrievals in comparison to the a priori emissions. Furthermore, airspace containing volcanic ash concentrations deemed to be associated with the highest risk (likelihood of exceeding a high concentration threshold) to aviation are reduced by over 85%. Such improvements could have large implications in emergency response situations. Future research will focus on quantifying the impact of uncertainty in precipitation forecasts on wet deposition in other eruptions and developing an inversion system that makes use of the state-of-the-art meteorological ensembles which has the potential to be used in an operational setting.

Highlights

  • Volcanic ash, released into the atmosphere when a volcano explosively erupts, provides a significant hazard to aircraft as it can cause engines to malfunction and visibility can be reduced by external corrosion

  • The aim of this paper is to present a method that optimally combines satellite retrievals and ensemble numerical weather prediction simulations to produce improved ash forecasts that can be used by the aviation industry during future volcanic eruptions

  • Inversion Technique for Emission Modeling (InTEM) using a single member of the Ensemble Prediction System (EPS) ensemble and the emission rates have a temporal resolution of 3 h and a vertical resolution of 4 km

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Summary

Introduction

Volcanic ash, released into the atmosphere when a volcano explosively erupts, provides a significant hazard to aircraft as it can cause engines to malfunction and visibility can be reduced by external corrosion. It can cause permanent engine damage which leads to high maintenance costs [1]. The ash forecasts show the maximum expected extent of the ash cloud within 3 flight level ranges but contain no quantitative information about ash concentration These forecasts aid the aviation community in making decisions to minimize the risk of encountering ash during their flight operations. Before the 2010 Eyjafjallajökull eruption, the International Civil Aviation Organization (ICAO) guidelines were to avoid all ash [3]

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