PARTIAL PENETRATION OF AN ELEVATED INVERSION LAYER BY CHIMNEY PLUMES

Laboratory results and a theoretical model are described with quantify the apportionment of buoyant chimney plume material between that trapped and that which penetrates a sharp elevated atmospheric inversion layer under conditions of otherwise neutral lapse rate and uniform cross-wind. Some penetration should occur if P [penetration parameter] is > 0.08, and when corrected for the effects of momentum overshoot of the plume and re-entrainment back into the plume of material already trapped in the inversion, the model predicts that the fraction trapped is related to the penetration parameter which is a function of the buoyancy efflux of the chimney. The crosswind speed above chimney top and the jump in buoyancy across the sharp inversion which is at a given height above chimney top are discussed. The model is a little conservative in estimating the fraction-trapped and predicts that the amount of plume material trapped per unit distance in the inversion layer is approximately independent of windspeed, provided only that partial penetration occurs. This is also supported by experiment. [This study is relevant to air pollution.].