Atmospheric Dispersion Modelling at the London VAAC: A Review of Developments since the 2010 Eyjafjallajökull Volcano Ash Cloud

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.

The fate of volcanic ash: premature or delayed sedimentation?

“…We performed a series of simulations which considered the transport of different particles and aggregates of varying size, density and shape. We considered sizes <1500 μm which guarantees a particle relaxation time on the order of a few seconds, appropriate for consideration in NAME 24 , 26 , and consistent with operational forecasting of the long-range transport of ash clouds 27 . For the two most relevant size bins (phi = 3 and phi = 2), we considered the median of the equivalent diameters as representative of the entire size range, with the equivalent diameter defined as d eq = ( L ∙ I ∙ S ) 1/3 .…”

“…5 are specific to one eruption; more investigations on the effect of increase of drag due to both particle aggregation and particle shape should be carried out for a larger dataset of eruptions and particle characteristics (shape, density) to better characterize the increase in travel distance due to these two aspects. In addition, travel distances of larger core particles (>500 μm) should also be investigated; here we only explored the range of travel distances of particles typically considered in operational modeling using NAME 26 , 27 (i.e. particles with Stokes number <1).…”

The global impacts of COVID-19 lockdowns on urban air pollution

“…The ability of CTMs to correctly simulate atmospheric composition is traditionally verified through comparisons of model and observational outputs. Extreme events, such as volcanic eruptions Wilkins et al, 2016;Beckett et al, 2020), wildfires (Liu et al, 2010), and heatwaves (Churkina et al, 2017;Zhao et al, 2019), play a particularly important role in this regard, as such events can expose model biases or missing processes.…”

A Lagrangian Stochastic Model of a Volcanic Eruption Column

“…While simple one‐dimensional (1D) integral models of volcanic plumes (see, e.g., Costa et al., 2016, and references therein; Devenish, 2013; Glaze et al., 1997; Mastin, 2007; Woods, 1988, 1993) can provide the variation with height of bulk properties of the plume including the mass concentration, this latter quantity has the undesirable property that it tends to infinity at the top of the plume. The vertical profile of mass concentration produced by an integral model is then not suitable for initializing an atmospheric dispersion model such as the UK Met Office’s operational dispersion model NAME (Numerical Atmospheric‐dispersion Modeling Environment) that is regularly used for modeling the dispersion of volcanic ash downwind of an eruption (e.g., Beckett et al., 2020). One motivation for this article is to present a model that can provide a more realistic vertical profile of the mass concentration.…”