On Plume Rise—The Role of Initial Plume Moisture on Subsequent Plume Growth as Simulated by Daysmoke

Combustion of forest litter releases copious quantities of water vapor within smoke plumes. [Recent measurements of moisture and temperature from smoldering “smokes” in the aftermath of prescribed burns suggest moisture excesses (plume moisture exceeding ambient moisture) ranging from 10 gm kg-1 to 30 gm kg-1 for these smokes.] As the plume temperature is hot just above the flaming zone, the plume relative humidity is low. However, as the plume cools rapidly by long wave radiation to just a few degrees above ambient temperature, plume relative humidity increases, possibly to saturation. Thus, for some Southern smoke plumes, what is viewed as hot, dry, particulate-filled plumes, may in fact be warm, dirty water clouds. Large, moist plumes with partially undiluted cores may ascend some distance before mixing with drier ambient air lowers plume relative humidity below 100 percent and moist processes cease. Moist processes can assist plume rise to heights much higher than can be expected with dry processes operating alone. Thus moist processes can impact predictions of plume rise based on plume rise models. Simulations with Daysmoke for two plumes in Georgia and North Carolina show that modeled plumes cannot attain heights observed apart from moist processes