The effect of a crossflow on isolated buoyant plumes arising from intense heat sources based on or near the surface is examined via numerical simulations of a compressible, nonhydrostatic model. In particular, the generation and evolution of vortical structures associated with the interaction of the plume with the crossflow are investigated for a range of the controlling parameters [i.e., intensity of heat source (internal Rayleigh number), and magnitude of the shear of the crossflow]. Two types of plume are considered: (i) initially two-dimensional plumes associated with linear heat sources; and (ii) three-dimensional plumes associated with axisymmetric heat sources.

Plumes due to linear heat sources in the presence of a crossflow are shown to be unstable to transverse perturbations, such that a periodic array of vortices of alternating sign forms in the along-line direction. This instability apparently leads to a transition of the plume from its initial two-dimensional structure to a three-dimensional structure, particularly in the region far from the heat source. Plumes due to axisymmetric heat sources are dominated by an embedded counter-rotating vortex pair, which typically results in the bifurcation of the plume above the heat source into two separate cores. The development of these vortical features in the two types of plumes is examined through the numerical simulations, as is the dependence of this development on the internal Rayleigh number and crossflow shear. The relevance of the results of these simulations to buoyant plumes arising from intense heat sources such as wildland fires is discussed.