Convective Transport of Biomass Burning Emissions: The Passive and Active Cases (Invited Presentation)

Deep convection can transport pollution to high altitudes. In the tropics, this was first seen anecdotally in aircraft CO profiles showing a localized maxima over the Inter-tropical Convergence Zone. The CO was associated with biomass burning emissions in South America entrained into nearby deep convection and lofted to high altitudes. This phenomenon can now be seen more generally from space; measurements from MOPITT and TES have shown, for example, that persistent CO features through the troposphere depend on horizontal transport of biomass burning in dry regions into convectively active regions. MLS retrievals have shown that CO can persist in the upper troposphere given a strong enough emissions source and strong enough nearby convection.  We have examined the pathways through which the NASA GISS ModelE coupled composition-climate model distributes biomass burning emissions at the surface through the depth of the troposphere, and shown that these pathways are dependent on how the subgrid physics are configured. This hints at how trace gas measurements can provide a complementary observational constraint for model evaluation.

In the most extreme ‘pyro-convective’ cases, explosive fires can inject smoke directly into the upper troposphere over a matter of hours. In certain cases, pyro-convective smoke plumes enter the lower stratosphere, persist for months, and look like small volcanic plumes. Capturing such acute emissions pulses to high altitudes represents an additional modeling challenge, particularly as we try to understand their radiative and chemical effects. Our current work suggests, for example, that the evolution of the plume depends strongly on heating of UV absorbing material in the plume and consequent diabatic ‘self-lofting’.