Wildfire Smoke Observations in the Western US from the Airborne Wyoming Cloud Lidars during the 2018 Fire and Smoke Projects
The wildfire in the Western US has a strong annual cycle, which maximizes around May-September, as the prolonged drought and extreme heat wave in the summer tend to trigger more frequent and intensive wildfire activity. According to the wildfire statistics of National Interagency Coordination Center, the number of annual wildfires has decreased slightly over the last 5 years, but the number of acres impacted generally has increased, which indicates that the wildfire, on average, becomes larger. The buoyant wildfire smoke columns generate plumes that break through the atmospheric boundary layer (BL) and are transported hundreds to thousands of kilometers downwind. The smoke plumes remaining within the BL often become well-mixed in regions near the fire. The wildfire smoke is a complex mixture of pollutants that can undergo physical and chemical transformation processes during transport and can have major impacts on air quality and public health over vast geophysical areas. During the summer of 2018, the Wyoming Cloud Lidars (WCLs) were deployed onboard the University of Wyoming King Air (UWKA) and NSF/NCAR C-130 research aircrafts for the Biomass Burning Flux Measurements of Trace Gases and Aerosols (BB-FLUX) airborne field campaign and Western Wildfire Experiments for Cloud Chemistry, Aerosol absorption and Nitrogen (WE-CAN) field campaign, respectively. During BB-FLUX, the UWKA sampled smoke plumes from more than 20 wildfires during 35 flights over the western United States. 70% of flight time was spent below 3 km above ground level (agl) altitude, although the UWKA ascended up to 6 km agl to sample the top of some deep smoke plumes. The upward-pointing WCL observed a nearly equal amount of thin and dense aerosol below 2 km and above 5 km due to targeted fires. Between 2-5 km, where most of the wildfire smoke resided, the WCL observed slightly more thin smoke than dense smoke due to smoke spreading. Extinction coefficients in dense smoke were 2-10 times stronger, and dense smoke tended to have larger depolarization ratio, associated with irregular aerosol particles. The reconstructed vertical structures of 7 smoke plumes from consecutive WCL transects shows the evident and variant vertical structures in the fire plumes, supported by in situ measurements at different heights (such as the Pole Creek Fire on Sep. 15 2018 in Figure 1). The fire plumes had distinct macrophysical and microphysical properties, which closely related to the plume transport, fire intensity and thermodynamic structure in the boundary layer. All 7 fire plumes had an injection layer between 2.8 and 4.0 km. Plumes that transported upward out of the boundary layer formed a higher plume level at around 5.5 km. During WE-CAN, the both upward and download WCLs were deployed on the NSF/NCAR C-130. The smoke plumes were sampled in a pseudo-Lagrangian fashion. The vertical cross sections of the smoke plume from at different locations along the wind provide an opportunity to investigate the smoke transportation and the aerosol evolution in the same fire plume. The smoke plume vertical structures from both BB-FLUX and WE-CAN will be compared and combined to provide both spatial and temporal variations for the smoke plumes from the Western U.S. wildfires.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021