The Ceiling Height of Wildland Fire Plumes in Quasi‐Steady Stratified and Sheared Boundary Layers

Abstract

Radar observations from a prescribed fire experiment reveal a large‐scale, billow‐like vorticity structure associated with the plume head near the onset of plume bending. This bending limits the vertical extent of the plume and defines the characteristic plume ceiling height. This study investigates plume bending under idealized sheared‐crossflow and quasi‐steady stratified atmospheric boundary layer conditions. Large‐eddy simulations using the Cloud Model 1 are conducted under idealized boundary‐layer configurations to qualitatively reproduce the observed plume morphology and to examine plume‐head evolution under varying fire‐generated surface heat‐flux, background shear, and stratification. Building on the classic theory, this study presents a scaling framework for estimating the characteristic plume ceiling height based on a modified Byram's convective number that accounts for sheared crossflow. The proposed scaling successfully reproduces the behavior of the idealized large‐eddy simulations and highlights the roles of shear and stratification in controlling the characteristic plume ceiling height.