Figure 1

Maps of modelled air mass trajectories, calculated with the NAME Lagrangian dispersion model (Witham et al.2007). The plots are forward trajectory simulations using the Met Office Global Unified Model on a 25 km grid. The different paths are produced by releasing particles from different elevations within a 1 km vertical range. Vertical velocities are taken from the weather model. The purpose of the maps is to give a general impression of wind trajectories from different release heights and they do not include particle settling or other parameters used in dispersion modelling of tephra. The release time, 00:00 on 22 May 2011 is 5 hours after the onset of the eruption, and when the plume was well-established. (a) Release from 3–4 km. (b) Release from 8–9 km. Only particles from the lower part of the eruption column were initially transported towards the UK.