The ash concentration of co-PDC clouds: implications for operational modelling and the aviation hazard

Pyroclastic density currents (PDCs) can generate co-PDC plumes, which segregate and buoyantly rise from the underlying gravity current. Using the atmospheric-dispersion model NAME we perform a series of co-PDC simulations that vary the particle release height and mass eruption rate for eight different weather patterns that characterise the UK and the surrounding European area. We examine the ash cloud concentration as a function of vertical elevation (flight level) within the atmosphere. We find that the ash clouds are compact in shape and often contain high (above 10 mg m −3 ) ash concentrations in the first few hours after particle release. Our results are discussed in terms of the hazard to aviation and operational modelling by volcanic ash advisory centres.