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.