Abstract
It has been 10 years since the ash cloud from the eruption of Eyjafjallajökull caused unprecedented disruption to air traffic across Europe. During this event, the London Volcanic Ash Advisory Centre (VAAC) provided advice and guidance on the expected location of volcanic ash in the atmosphere using observations and the atmospheric dispersion model NAME (Numerical Atmospheric-Dispersion Modelling Environment). Rapid changes in regulatory response and procedures during the eruption introduced the requirement to also provide forecasts of ash concentrations, representing a step-change in the level of interrogation of the dispersion model output. Although disruptive, the longevity of the event afforded the scientific community the opportunity to observe and extensively study the transport and dispersion of a volcanic ash cloud. We present the development of the NAME atmospheric dispersion model and modifications to its application in the London VAAC forecasting system since 2010, based on the lessons learned. Our ability to represent both the vertical and horizontal transport of ash in the atmosphere and its removal have been improved through the introduction of new schemes to represent the sedimentation and wet deposition of volcanic ash, and updated schemes to represent deep moist atmospheric convection and parametrizations for plume spread due to unresolved mesoscale motions. A good simulation of the transport and dispersion of a volcanic ash cloud requires an accurate representation of the source and we have introduced more sophisticated approaches to representing the eruption source parameters, and their uncertainties, used to initialize NAME. Finally, upper air wind field data used by the dispersion model is now more accurate than it was in 2010. These developments have resulted in a more robust modelling system at the London VAAC, ready to provide forecasts and guidance during the next volcanic ash event.
Highlights
Volcanic ash clouds can cause widespread disruption to aviation operations due to the serious detrimental effect ash has on jet engines [1,2,3]
We present the evolution of the operational volcanic ash transport and dispersion modelling setup used at the London Volcanic Ash Advisory Centre (VAAC) (Met Office), following their response to the ash clouds from the eruptions of Eyjafjallajökull in 2010 and Grímsvötn in 2011
To reduce temporal resolution errors associated with its offline application, the London VAAC performs a linear interpolation in time to the meteorological fields, and it should be noted that data assimilation in the Numerical Weather Prediction (NWP) necessarily incorporates the impact of the volcanic ash on future weather predictions, which are updated every 6 h
Summary
Volcanic ash clouds can cause widespread disruption to aviation operations due to the serious detrimental effect ash has on jet engines [1,2,3]. On the 20th April 2010, new procedures were introduced in Europe based on ash concentration thresholds defined by engine manufacturers, replacing the zero-ash tolerance approach This saw the introduction of supplementary forecast ash concentration charts, produced by the Met Office and Météo-France (the homes of London and Toulouse VAACs, respectively), alongside the VAACs VAA and VAG, representing a step-change in the level of interrogation of the dispersion model output. We present the evolution of the operational volcanic ash transport and dispersion modelling setup used at the London VAAC (Met Office), following their response to the ash clouds from the eruptions of Eyjafjallajökull in 2010 and Grímsvötn in 2011.
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