Modeling the Effect of Plumerise on the Transport of Carbon Monoxide over Africa and Its Exports with NCAR CAM
H. Guan1,2, R. B. Chatfield2, S. R. Freitas3, R. W. Bergstrom1, and K. M. Longo3
1Bay Area Environmental Research Institute, Sonoma, USA
2NASA Ames Research Center, Moffett Field, USA
3Center for Weather Forecasting and Climate Studies (CPTEC), INPE, Cachoeira Paulista, Brazil
ABSTRACT We investigated the effects of fire induced plumerise on the predicted export of carbon monoxide (CO) over Africa during SAFARI 2000 using the NCAR Community Atmosphere Model (CAM) with a CO tracer and plumerise parameterization scheme. The plumrise parameterization scheme simulates the consequences of strong bouyancy of hot gases emitted from biomass burning including both dry and cloud associated (pyrocumulus) lofting. The scheme was first adapted from a regional model. The current implementation of the plumerise parameterization scheme into the global model provides an opportunity to examine the effect of plumerise on long range transport. The CAM simulation with the plumerise parameterization scheme shows a substantial improvement of the agreements between the modemed and aircraft measured vertical distribution of CO over southern Africa biomass burning area. The plumerise mechanism plays a crucial role in lofting biomass burning pollutants to the middle troposphere. In the presence of deep convection we found that the plumeris mechanism results in a decrease of CO concentration in the upper troposphere. The plume rise depletes the boundary layer, and thus leaves lower concentrations of CO to be lofted by the deep convection process. The effect of the plumerise on free troposhere CO concentration is more important for the source area (short distance transport) than for remote areas (long distance transport). The plumerise scheme also increases the CO export fluxes from Africa to the Atlantic and Indian Oceans. These results further confirm and extend previous findings in a regional model study. Effective lofting of large concentration of CO by the plumerise mechanism also has implication for local air quality forecast in areas affected by other fire related pollutants.