Smoke transport and dispersion from prescribed burns:

Plume-rise models for smoke from prescribed fires are more accurately simulating how land managers spread fire over the landscape and therefore how heat columns organize to disperse smoke through the atmosphere. For small burns, smoke is dispersed within the planetary boundary layer (mixing layer). For larger burns, particularly those ignited by stripping or aerial ignition, heat released from combustion can loft some smoke into the free atmosphere above the boundary layer. Given tiny terminal velocities of fine particulate matter, this smoke could remain aloft indefinitely for long distances until taken up as condensation nuclei and precipitated out.

There are instances when smoke transported long distances within the free atmosphere is injected back into the mixing layer and mixed to the ground in high concentration. One of a number of explanations for plume collapse holds that the top of the boundary layer (mixing height) is higher where plume collapse occurs.

We ran the MM5 meso-meteorological weather model for the southern Appalachian Mountains near the Tennessee/North Carolina border for 18 March 2006. On this day a smoke plume from a prescribed burn in eastern Tennessee collapsed over North Carolina causing hazardous air quality over Asheville about 50 km away. We mapped the mixing height for each hour during the burn. We found complex mixing height patterns formed from local heating and advection. The mountains impact the height of the boundary layer not only over high terrain but also over lowlands downwind. These results could change land management practices near mountainous terrain.