Plume moisture enhancement observed during FireFlux

Micrometeorological measurements made during the FireFlux field campaign are used to diagnose the enhancement of water vapor in fire plumes due to the combustion of grass fuels. High-frequency measurements of water vapor concentration were made using two Li-Cor 7500 open-path infrared gas analyzers located at 10 and 28 m AGL and one CSI KH20 krypton hygrometer located at 2 m AGL. 3-D sonic anemometers were collocated with the hygrometers and used to compute vertical moisture fluxes from the fire. Water vapor mixing ratios were also measured using temperature/RH probes at 2, 10, 20 m AGL. Preliminary analyses indicate that increases of approximately 1.5-2 g/kg occurred during the fire front passage, but a gradual decrease in water vapor concentration occurred after the plume passage. It is hypothesized that this decrease in water vapor concentration is a result of either the downward entrainment of air from aloft, the removal of fuels at the surface or a combination of both. Future experiments are planned to measure plume humidity and temperature using a remote controlled model airplane platform.