A new look at the role of fire-released moisture on the dynamics of atmospheric pyro-convection

We investigate the contribution of the moisture released by wildland fires to the water budget and the convection dynamics of pyro-clouds forming atop fires. Using an approach based on stoichiometric principles and parcel theory of convection, we assess the relative contribution of sensible heat and latent heat to the convection energy. We find that moisture release is of much lesser importance for the fire convection than the release of sensible heat from the combustion. We conclude from theoretical considerations that it is highly unlikely that the decrease of the cloud base of pyro-cumulus compared with that of ambient free convection is due to the fire-released moisture alone, in contrast to what has been suggested previously. In addition to the analytical results, numerical simulations of a specific case study are presented. They show that the fire-released moisture accounts only for a small portion of the total water in the pyro-cumulus cloud. Also, the effect of the fire-released moisture on the convection dynamics and the height of injection is found to be small compared with the effect of the sensible heat release from the fire.