Intense heating of air in the vicinity of a bushfire leads to deep ascent. If this ascent is deep enough to lift air above the lifting condensation level, cumulus or cumulonimbus clouds form in a process known as pyro-convection. There is abundant anecdotal evidence to suggest that pyro-convection may have a significant impact on fire behaviour by (i) amplifying burn and spread rates; (ii) enhancing spotting through plume intensification; and (iii) igniting new fires via pyrocumulonimbus lightning. Pyro-convection is also responsible for the transport of smoke and other aerosol into the stratosphere. Therefore, knowledge of the processes that lead to the generation of pyro-convection is an important component of being able to understand and predict fire behaviour, as well as the potential climatic influences of large fires.

Here we present idealised simulations of bushfire plumes using a cloud-resolving model, the UK Met Office Large-Eddy Model (LEM). The model is initialised with idealised temperature and moisture profiles representative of that associated with high fire-danger conditions. A bushfire plume is then generated by imposing a localised heat flux at the model surface. We explore the conditions under which the bushfire plume leads to pyro-convection and the sensitivity of that pyro-convection to variations in the environmental conditions and the heat and moisture flux. The implications of the observed changes in the pyro-convection are discussed in terms of their impact on fire behaviour, primarily through the potential to affect near-surface conditions in the vicinity of the fire and spotting potential via plume intensification.