A study of the arrival over the United Kingdom in April 2010 of the Eyjafjallajِkull ash cloud using ground-based lidar and numerical simulations

We make a qualitative and quantitative comparison of numerical simulations of the ash cloud generated by the eruption of Eyjafjallajökull in April 2010 with ground-based lidar measurements at Exeter and Cardington in southern England. The numerical simulations are performed using the Met Office’s dispersion model, NAME (Numerical Atmospheric-dispersion Modelling Environment). The results show that NAME captures many of the features of the observed ash cloud. The comparison enables us to estimate the fraction of material which survives the near-source fallout processes and enters into the distal plume. A number of simulations are performed which show that both the structure of the ash cloud over southern England and the concentration of ash within it are particularly sensitive to the height of the eruption column (and the consequent estimated mass emission rate), to the shape of the vertical source profile and the level of prescribed ‘turbulent diffusion’ (representing the mixing by the unresolved eddies) in the free troposphere with less sensitivity to the timing of the start of the eruption and the sedimentation of particulates in the distal plume.