Wind to plume driven wildfire cycles caused by topographically forced wildfire – atmosphere coupling, Southeast Queensland, Australia.

Mountains create their own weather through topographic modification of the prevailing synoptic meteorology. As a result, wildfires in mountainous terrain may exhibit erratic and extreme behaviour as ridges and valleys modify the prevailing winds. Here we present a case study analysis of a wildfire that occurred in mountainous terrain in subtropical eastern Australia. The wildfire was observed to transition between a wind-driven and plume-driven wildfire on at least three occasions with a periodicity of around 60 minutes. The Weather Research and Forecasting (WRF) model was used to investigate the surface windfield and vertical thermodynamic properties of the atmosphere. Results from the WRF simulations aligned with observational data indicating that topographic lifting caused by only moderate changes in terrain may have contributed to the coupling of the wildfire plume to an elevated layer of humidity leading to rapid pyrocumulus (pyroCu) development. Strong horizontal wind shear caused the pyroCu to detach from the wildfire on at least three occasions with a subsequent return to wind-driven wildfire behaviour. Our results highlight the importance of understanding the influence of what may be perceived as only subtle to moderate changes in terrain on local meteorological conditions and wildfire behaviour.