Observations from inside a Wildfire-Driven Thunderstorm:The 2019 FIREX-AQ Field Experiment

Abstract:

Intense heating by wildfires can generate deep, smoke-infused thunderstorms, known as pyrocumulonimbus (pyroCb), which can release a large quantity of smoke into the upper troposphere and lower stratosphere (UTLS). Recent work has shown that an extreme pyroCb event can significantly influence the lower-stratosphere in a manner similar to a moderate volcanic eruption. While sampling the Williams Flats fire in Washington State, the 2019 FIREX-AQ field experiment obtained the first comprehensive dataset of an active pyroCb event, including fresh pyroCb smoke outflow at high altitudes, the upper portion of an active pyroCb updraft, and the fire characteristics contributing to pyroCb development. Analysis of this unique dataset is targeted at several key unknowns in the pyroCb research community. Results show that three regions of the fire front (updraft zones) contributed to four total pyroCb anvil “pulses” over a three-hour period. All three contributing updrafts were linked to an expansive flaming region, large sensible heat flux, and dense fuels. Ice crystal habit, structure, and size in the pyroCb anvil region is examined relative to traditional convective clouds. Variation in aerosol and gas phase chemistry is examined in the active updraft regions and downwind pyroCb smoke exhaust relative to traditional low altitude smoke plumes from the same fire. This analysis is essential for understanding the role of pyroCb activity in the global climate system.