Results from Daysmoke for weak smoke plumes

Although the eye is attracted to violent convective smoke plumes and associated pyrocumulus, smaller and weaker smoke plumes may account for locally higher concentrations of fine particulate matter. That is because strong plumes may inject particulate matter high above the mixing layer whereas weak plumes may release particulate matter near the ground short distances from the sources. Daysmoke, an empirical/stochastic smoke plume model, was used to simulate weak smoke plumes from prescribed burns conducted at Fort Benning, GA, during April 2008. The burns were conducted on lands with low fuel loadings.

Results show plume structures were strongly dependent on the number of updraft cores that characterize the burn. For a single-core updraft plume, the plume rose to near the top of the mixing layer and the bulk of the smoke was mixed down by large eddy circulations thus giving to the plume a “stalactite” appearance. For multiple-core updraft plumes, weak updrafts were intercepted by large eddy circulations on ascent. The plume broke into deep turrets or pillars of smoke some of which extended through the depth of the mixing layer.

Results from Daysmoke will be presented along with confirming radar and lidar observations and time series of PM2.5 concentrations from several locations beneath the plumes.