The effect of phase changes of water on the development of volcanic plumes

A complex thermodynamic–microphysical package has been formulated that is able to deal with the microphysical processes of condensed water vapour in a volcanic plume. The microphysics follows a prognostic bulk approach for cloud water, cloud ice, rain and graupel and the interaction between them. In a standard experiment, this module, applied within a new nonhydrostatic volcano plume model, Active Tracer High Resolution Atmospheric Model (ATHAM), produces reasonable concentrations of different types of hydrometeors. Under tropical conditions, the plume gains three times as much water from the environment through entrainment as from the volcanic source. The formed hydrometeors are dominated by the ice phase. Thermodynamic effects of phase changes contribute about 13% to the plumeʹs total thermal energy and therefore have a considerable effect on the vertical development of the plume.