Influence of fire-induced heat and moisture release on pyro-convective cloud dynamics during the Australian New Year's Event: A study using convection-resolving simulations and satellite data

Abstract

Understanding pyro-convective clouds is essential. These clouds transport significant quantities of aerosols and gases into the upper atmosphere and therefore influence atmospheric composition, weather, and climate on a global scale. This study investigates the dynamics of pyro-convective clouds during the Australian New Years Event 2019/2020 using convection-resolving simulations that incorporate the effects of sensible heat and moisture released by fires. These effects are modeled through parameterizations using retrievals from the Global Fire Assimilation System (GFAS). The results show that the plume top height remains unchanged when accounting for fire-induced heat and moisture release in regions where convective cells form independently of the fire. In areas with the most intense fires, the sensible heat and moisture release from the fire provide the necessary buoyancy for enabling the formation of pyro-convective clouds. Pyro-convective clouds lift aerosol masses up to altitudes of 12.0 km. During their formation, the plume top height more than doubles, compared with a reference simulation in which such clouds do not develop. Additionally, the plume height increase is, on average, just 0.87 km by fire-induced heat and moisture in cloud-free areas. We demonstrated that sensible heat release is the primary contributor to pyro-convective cloud formation. However, the release of moisture enhances the formation process and increases the lifetime of the pyro-convective cloud. Comparisons with observational data show that the plume's distribution and height are underestimated. However, the simulations align well with observations after a 5-6 h delay, indicating that pyro-convective cells are accurately modeled but occur later in the model than are actually observed.