Numerical simulation of tropospheric injection of biomass burning products by pyro-thermal plumes

Abstract

The thermal plume model, a mass-flux scheme originally developed to represent the vertical transport by convective structures within the boundary layer, is adapted to the representation of plumes generated by fires, with the aim of estimating the height at which fire emissions are actually injected in the atmosphere. The parameterization, which takes into account the excess of near surface temperature induced by fires and the mixing between convective plumes and environmental air, is first evaluated on two well-documented fires. Simulations over Southern Africa performed with the general circulation model LMDZ over one month show that the CO₂ can be injected far above the boundary layer height, leading to a daily excess of CO₂ in the mid-troposphere of an order of 2 ppmv. These results agree with satellite retrievals of a diurnal cycle of CO₂ in the free troposphere over regions affected by biomass burning in the Tropics.