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Abstract The western U.S. wildfire smoke plumes observed by the upward-pointing Wyoming Cloud Lidar (WCL) during the Biomass Burning Fluxes of Trace Gases and Aerosols (BB-FLUX) project are investigated in a two-part paper. Part II here presents the reconstructed vertical structures of seven plumes from airborne WCL measurements. The vertical structures evident in the fire plume cross sections, supported by in situ measurements, showed that the fire plumes had distinct macrophysical and microphysical properties, which are closely related to the plume transport, fire emission intensity, and thermodynamic structure in the boundary layer. All plumes had an injection layer between 2.8 and 4.0 km above mean sea level, which is generally below the identified boundary layer top height. Plumes that transported upward out of the boundary layer, such as the Rabbit Foot and Pole Creek fires, formed a higher plume at around 5.5 km. The largest and highest Pole Creek fire plume was transported farthest and was sampled by University of Wyoming King Air aircraft at 170 km, or 2.3 h, downwind. It was associated with the warmest, driest, deepest boundary layer and the highest wind speed and turbulence. The Watson Creek fire plume intensified in the afternoon with stronger CO emission and larger smoke plume height than in the morning, indicating a fire diurnal cycle, but some fire plumes did not intensify in the afternoon. There were pockets of relatively large irregular aerosol particles at the tops of plumes from active fires. In less-active fire plumes, the WCL depolarization ratio and passive cavity aerosol spectrometer probe mass mean diameter maximized at a height that was low in the plume.
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Plume Dynamics Drive Extreme Long‐Range Spotting During California's Dixie Fire
Abstract Observations reveal extreme long‐range fire spotting occurred during California's Dixie Fire. Specifically, we describe the occurrence of remarkable 9, 12, and 16 km spotting events on 16 August 2021. Radar data reveal these spot fires are linked to bent‐over but deep convective plumes with plume tops reaching 10–12 km MSL. These plumes have characteristic lofting regions in the fire‐generated updrafts and pyrometeor fall out locations in the downwind subsiding portion of the plume. Infrared data indicate spot fires occur along the plume's central axis. The cross winds impacting the plume rise and pyrometeor transport were ∼15 m s−1, and the inferred transit time firebrands causing the longest‐range spot fire is ∼18 min. We also provide photographic evidence for large, partially burned pyrometeors at a range of ∼20 km from the fire and link these data to Ka‐band radar observations showing pyrometeor pulses and fall out over the observing site. The results of the study suggest that operational and research radars may be able to isolate periods conducive to long range spotting in near real‐time.
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- Award ID(s):
- 2114251
- PAR ID:
- 10593994
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 130
- Issue:
- 9
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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