92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Wednesday, 25 January 2012: 10:30 AM
Modelling the Resuspension of Ash Deposited During the Eruption of Eyjafjallajökull in April/May 2010
Room 357 (New Orleans Convention Center )
Susan J. Leadbetter, Met Office, Exeter, Devon, United Kingdom; and M. Hort, S. von Löwis, K. Weber, and C. Witham

Eyjafjallajökull, a volcano in southern Iceland erupted explosively in April and May 2010 depositing ash over a region of more than 3000km2 to the west and southwest of the volcano. This deposited ash has been frequently remobilised by the wind causing health issues for the Icelanders living in the region. On occasion the ash has also been blown as far as Reykjavík and Keflavík airports causing concern for aviation. An investigation was carried out to determine whether it would be possible to produce forecasts of days when high airborne ash concentrations were likely to occur.

Many complex dust models exist but they rely on information about the spatially varying surface characteristics. This information is not available for new dust sources such as the ash deposited by a volcano so an alternative approach is required. In the modelling approach adopted here ash is released from the surface at a rate proportional to the cube of the friction velocity only when the local friction velocity exceeds a threshold. The ash is then advected by three-dimensional model winds and dispersed using random walk techniques.

Modelling is carried out in the UK Met Office's Lagrangian dispersion model NAME (Numerical Atmospheric-dispersion Modelling Environment). Information about the source region is provided by the Institute of Earth Sciences at the University of Iceland and the Icelandic Meteorological Office. Modelled ash concentrations are then compared to observed concentrations from two periods. First, the model predictions were compared with PM10 observations both within the source region and in Reykjavík collected between the end of the eruption on 23 May and the 2 July 2010. Second, the model predictions were compared to airborne particle counts carried out at Drangshlidardalur between the 21 September 2010 and 16 February 2011.

Generally the timing of the resuspension episodes is captured well by the model, although some of the larger events appear slightly truncated in duration, in the model. The relative magnitudes of the episodes in June and July are also reasonably well captured by the model although those the relative magnitudes of the events between October and February is less well captured. This study has concentrated on predicting the resuspension of ash using only wind and precipitation information. However, there are number of other factors which will influence the likelihood of ash resuspension including consolidation of the surface, covering of the surface and (in some places) a depletion of the supply of volcanic ash. The impact of these factors on the resuspension of ash is likely to increase with time.

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