Dry deposition modelling in a Lagrangian dispersion model

Webster, Helen; Thomson, David J.

doi:10.1504/ijep.2011.047322

Cited by 28 publications

(28 citation statements)

References 2 publications

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“…NAME is a Lagrangian atmospheric dispersion model, in which model particles are advected by 3D meteorological fields and dispersed using a random walk scheme which includes parameterizations for sub–grid‐scale atmospheric turbulence and mesoscale motions (Thomson et al ., ; Webster et al ., ). NAME also includes parameterizations for wet and dry deposition, with sedimentation schemes for both spherical and non‐spherical particles (Webster and Thomson, ; Beckett et al ., ).…”

Section: Methodsmentioning

confidence: 99%

The importance of grain size and shape in controlling the dispersion of the Vedde cryptotephra

Saxby

Rust

Cashman

et al. 2019

J Quaternary Science

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Volcanic ash is dispersed in the atmosphere according to meteorology and particle properties, including size and shape. However, the multiple definitions of size and shape for non-spherical particles affect our ability to use physical particle properties to understand tephra transport. Moreover, although particles >100 m μ are often excluded from operational ash dispersion model setups, ash in tephra deposits > 1000 km from source can exceed 100 m μ . Here we measure the shape and size of samples of Vedde ash from Iceland, an exceptionally widespread tephra layer in Europe, collected in Iceland and Norway. Using X-ray computed tomography and optical microscopy, we show that distal ash is more anisotropic than proximate ash, suggesting that shape exerts an important control on tephra dispersion. Shape also impacts particle size measurements. Particle long axis, a parameter often reported by tephrochronologists, is on average 2.4× greater than geometric size, used by dispersion modellers. By using geometric size and quantifying shape, we can explain the transport of Vedde ash particles 190 m ≤ μ more than 1200 km from source. We define a set of best practices for measuring the size and shape of cryptotephra shards and discuss the benefits and limitations of using physical particle properties to understand cryptotephra transport. Figure 3. Balloon-borne radiosonde data for the weather stations at (a) Keflavík, Iceland, (b) Tórshavn, Faroe Islands, and (c) Ørland, Norway. Station codes correspond to locations in Fig. 2. Coloured lines show monthly mean speed at each height for the period 1973 -2018. Dashed lines show individual records for days with extremely high winds, with the day and time chosen based on the highest (height-averaged mean) wind velocities. [Color figure can be viewed at wileyonlinelibrary.com].

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Section: Methodsmentioning

confidence: 99%

The importance of grain size and shape in controlling the dispersion of the Vedde cryptotephra

Saxby

Rust

Cashman

et al. 2019

J Quaternary Science

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“…The sedimentation uses a fall velocity calculated using the Reynolds number dependent drag coefficient given by Maryon et al [1999] with the Cunningham correction applied for small particle sizes. The dry deposition parametrization uses a deposition velocity calculated by the resistance analogy and is combined with the sedimentation as described by Webster and Thomson [2008]. Wet deposition uses scavenging coefficients and accounts for rain out and wash out by precipitation as described by Maryon et al [1999].…”

Section: Name Simulationsmentioning

confidence: 99%

Evaluating the structure and magnitude of the ash plume during the initial phase of the 2010 Eyjafjallajökull eruption using lidar observations and NAME simulations

et al. 2011

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[1] The Eyjafjallajökull volcano in Iceland erupted explosively on 14 April 2010, emitting a plume of ash into the atmosphere. The ash was transported from Iceland toward Europe where mostly cloud-free skies allowed ground-based lidars at Chilbolton in England and Leipzig in Germany to estimate the mass concentration in the ash cloud as it passed overhead. The UK Met Office's Numerical Atmospheric-dispersion Modeling Environment (NAME) has been used to simulate the evolution of the ash cloud from the Eyjafjallajökull volcano during the initial phase of the ash emissions, 14-16 April 2010. NAME captures the timing and sloped structure of the ash layer observed over Leipzig, close to the central axis of the ash cloud. Relatively small errors in the ash cloud position, probably caused by the cumulative effect of errors in the driving meteorology en route, result in a timing error at distances far from the central axis of the ash cloud. Taking the timing error into account, NAME is able to capture the sloped ash layer over the UK. Comparison of the lidar observations and NAME simulations has allowed an estimation of the plume height time series to be made. It is necessary to include in the model input the large variations in plume height in order to accurately predict the ash cloud structure at long range. Quantitative comparison with the mass concentrations at Leipzig and Chilbolton suggest that around 3% of the total emitted mass is transported as far as these sites by small (<100 mm diameter) ash particles. , et al. (2011), Evaluating the structure and magnitude of the ash plume during the initial phase of the 2010 Eyjafjallajökull eruption using lidar observations and NAME simulations,

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“…where R a is the aerodynamic resistance, R b is the laminar sublayer resistance and R c is the surface resistance (taken to be zero for particulates such as ash) (Webster and Thomson, 2011). The aerodynamic resistance, R a , is used to specify the efficiency with which the ash is transported to the ground by turbulence.…”

Section: Dry Depositionmentioning

confidence: 99%

“…This velocity is calculated using the particle diameter (D), particle density (ρ p ) and ambient meteorological variables at the particle location (see Maryon, 1997;Webster and Thomson, 2011). In this study, w sed is not perturbed as it is assumed that changes in PSD and particle density cover the range of plausible sedimentation velocities.…”

Section: Sedimentationmentioning

confidence: 99%

Multi-level emulation of a volcanic ash transport and dispersion model to quantify sensitivity to uncertain parameters

Harvey

Huntley

Dacre

et al. 2018

Nat. Hazards Earth Syst. Sci.

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Abstract. Following the disruption to European airspace caused by the eruption of Eyjafjallajökull in 2010 there has been a move towards producing quantitative predictions of volcanic ash concentration using volcanic ash transport and dispersion simulators. However, there is no formal framework for determining the uncertainties of these predictions and performing many simulations using these complex models is computationally expensive. In this paper a Bayesian linear emulation approach is applied to the Numerical Atmospheric-dispersion Modelling Environment (NAME) to better understand the influence of source and internal model parameters on the simulator output. Emulation is a statistical method for predicting the output of a computer simulator at new parameter choices without actually running the simulator. A multi-level emulation approach is applied using two configurations of NAME with different numbers of model particles. Information from many evaluations of the computationally faster configuration is combined with results from relatively few evaluations of the slower, more accurate, configuration. This approach is effective when it is not possible to run the accurate simulator many times and when there is also little prior knowledge about the influence of parameters. The approach is applied to the mean ash column loading in 75 geographical regions on 14 May 2010. Through this analysis it has been found that the parameters that contribute the most to the output uncertainty are initial plume rise height, mass eruption rate, free tropospheric turbulence levels and precipitation threshold for wet deposition. This information can be used to inform future model development and observational campaigns and routine monitoring. The analysis presented here suggests the need for further observational and theoretical research into parameterisation of atmospheric turbulence. Furthermore it can also be used to inform the most important parameter perturbations for a small operational ensemble of simulations. The use of an emulator also identifies the input and internal parameters that do not contribute significantly to simulator uncertainty. Finally, the analysis highlights that the faster, less accurate, configuration of NAME can, on its own, provide useful information for the problem of predicting average column load over large areas.

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Dry deposition modelling in a Lagrangian dispersion model

Cited by 28 publications

References 2 publications

The importance of grain size and shape in controlling the dispersion of the Vedde cryptotephra

The importance of grain size and shape in controlling the dispersion of the Vedde cryptotephra

Evaluating the structure and magnitude of the ash plume during the initial phase of the 2010 Eyjafjallajökull eruption using lidar observations and NAME simulations

Multi-level emulation of a volcanic ash transport and dispersion model to quantify sensitivity to uncertain parameters

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