A Case Study Featuring The Time Evolution of A Fire-induced Plume Jet Over The Rum Creek Fire: Mechanisms, Processes, and Dynamical Interplay

Abstract

Results are presented from the Rum Creek fire during the California Fire Dynamics Experiment (CalFiDE). An instrumented payload aboard the NOAA Twin Otter (TO) aircraft, which included a scanning micro-pulsed Doppler lidar (DL) and in situ chemistry packages, was used to address the evolution of a buoyant plume jet (BPJ) and transport dynamics over the southwest corner of the fire between 09/01/2022 and 09/02/2022. An approach previously developed to isolate updrafts was modified to account for the Gaussian core structure when addressing the evolution of the updraft, plume-top entrainment, lateral entrainment, and the role of fire-atmosphere interactions on the characteristics of the BPJ during four overpasses. A persistent cross-valley flow leading up to the BPJ was observed for all four overpasses, with flow enhancement during the second overpass that coincided with changes in the BPJ structure and turbulence characteristics surrounding the BPJ. Length scales and entrainment rates were estimated at the lateral edges and the top of the plume. In the case of the latter, an analytical form of the BPJ profile above the vertical velocity maximum of the updraft was derived using a simplified form of the vertical momentum equation following a partial budget analysis that accounted for plume-top entrainment and the boundary layer (BL) inversion. Velocity core strength and characteristics were analyzed away from the updraft with similar relationships between depth-to-widths of velocity cores found in a forthcoming study focused on wildfire plumes. Key Points Airborne Doppler lidars are capable of resolving small scale dynamics over short distances spanning the width of the fireline Complex interactions between fire-induced updrafts and the surrounding atmosphere can lead to non-ideal representation of the updraft profile Terrain and fire-modified winds are important for updraft evolution and transport dynamics Plain Language Summary The goal of the California Fire Dynamics Experiment (CalFiDE) during the fall of 2022 was to survey wildfire dynamics and impacts on air quality over areas historically affected by wildfires. The Rum Creek fire, which occurred west of Medford, Oregon, was one of several fires observed using data collected aboard the NOAA Twin Otter (TO) aircraft. In this study, we focused on a smoke plume at the southwest corner of the fire that featured strong upward motion. Multiple flyovers of this plume led to an analysis of how the plume changed with time, and how the conditions surrounding the plume supported its development. The work presented details the internal structure of the plume and the influence of background winds on the evolution of the plume, which has implications for understanding the transport of smoke away from the fire.