Isolating and Investigating Updrafts Induced by Wildland Fires Using an Airborne Doppler Lidar During FIREX‐AQ

Abstract

Understanding the complex dynamical interactions that occur during the evolution of a wildland fire still remains a challenge within the research community. Processes such as entrainment, the incident wind field, the interaction between neighboring updrafts, among other processes, motivates the need for more intensive measurement campaigns to determine the mechanisms responsible for the processes observed as wildland fire updrafts evolve. A recent opportunity to examine processes associated with wildland fires was made possible with a Doppler lidar (DL) mounted on a Twin Otter aircraft to measure horizontal and vertical winds during the 2019 Fire Influence on Regional‐to‐Global Environments and Air Quality campaign. Using the data collected, a technique was developed to isolate updrafts over designated hotspots with the intention of statistically analyzing the updraft samples as well as assessing specific cases that underscore the complex dynamical interactions generated by wildland fire behavior. Strong evidence in support of statistically derived relationships between the updraft characteristics and downdraft extrema at the flanks of updrafts are shown using methods developed herein. In addition to the influence of entrainment/detrainment on the updraft structure are features such as updraft displacement and interacting updrafts that could only be resolved by a high along‐ and cross‐beam resolution DL. Lastly, it was found that a high degree of symmetry between profiles to the left and right of core updrafts was preserved for most of the cases, which validates some of the assumptions typically used in idealized updraft formulations.

An Air Quality and Boundary Layer Dynamics Analysis of the Los Angeles Basin Area During the Southwest Urban NOx and VOCs Experiment (SUNVEx)

“…These velocities are quite a bit higher compared to the slope of 0.03 m s −1 derived by applying a linear fit to BL height in Figure 10c. However, acknowledging that turbulent eddies inherently have vortical motion and therefore rotate air, and BL growth involves upward motion driven by convection and downward motion as the residual layer gets mixed into the growing BL, we decided to normalize the slopes from Figure 10b by 2π to account for full eddy rotations, noting that the velocity scales are too small to be resolved explicitly by the DL (Schroeder et al, 2020;Strobach et al, 2023). Adopting the 2π normalization factor and noting constant velocities derived from the slopes leads to agreement with dz BL /dt during BL growth phase such that…”

A Case Study Featuring the Time Evolution of a Fire‐Induced Plume Jet Over the Rum Creek Fire: Mechanisms, Processes, and Dynamical Interplay

“…(2020) used data collected from a King Air aircraft to map out the vertical dynamics of a pyroCb as well as flight level dynamics to infer residual buoyancy at cruising altitude. In 2019, the Fire Influence on Regional to Global Environments and Air Quality (FIREX‐AQ) campaign was conducted with a component of the effort focused on flights over active burn areas to target the evolution of fire‐induced updrafts at a high spatial resolution using a Doppler lidar (DL) aboard the NOAA Twin Otter (TO) aircraft (Strobach et al., 2023, i.e., S23).…”