Modeling of biomass smoke injection into the lower stratosphere by a large forest fire (Part I): reference simulation J. Trentmann1, G. Luderer2, T. Winterrath2, M. D. Fromm3, R. Servranckx4, C. Textor5, M. Herzog6, H.-F. Graf7, and M. O. Andreae2 1Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, Germany 2Max Planck Institute for Chemistry, Dept. Biogeochemistry, Mainz, Germany 3Naval Research Laboratory, Washington, D.C., USA 4Meteorological Service of Canada, Montreal, Canada 5Service d'Aéronomie, CNRS, Paris, France 6NOAA GFDL, Princeton, NJ, USA 7Department of Geography, Centre of Atmospheric Science, University of Cambridge, Cambridge, UK
Abstract. Wildland fires in boreal regions have the potential to initiate deep
convection, so-called pyro-convection, due to their release of sensible heat.
Under favorable atmospheric conditions, large fires can result in
pyro-convection that transports the emissions into the upper troposphere and
the lower stratosphere. Here, we present three-dimensional model simulations of
the injection of fire emissions into the lower stratosphere by pyro-convection.
These model simulations are constrained and evaluated with observations
obtained from the Chisholm fire in Alberta, Canada, in 2001. The active tracer
high resolution atmospheric model (ATHAM) is initialized with observations
obtained by radiosonde. Information on the fire forcing is obtained from
ground-based observations of the mass and moisture of the burned fuel.
Based on radar observations, the pyro-convection reached an altitude of about
13 km, well above the tropopause, which was located at about 11.2 km.
The model simulation yields a similarly strong convection with an overshoot of
the convection above the tropopause. The main outflow from the
pyro-convection occurs at about 10.6 km, but a significant fraction (about
8%) of the emitted mass of the smoke aerosol is transported above the
tropopause. In contrast to regular convection, the region with maximum
updraft velocity in the pyro-convection is located close to the surface above
the fire. This results in high updraft velocities >10 m s−1 at cloud
base. The temperature anomaly in the plume decreases rapidly with height from
values above 50 K at the fire to about 5 K at about 3000 m above the fire.
While the sensible heat released from the fire is responsible for the
initiation of convection in the model, the release of latent heat from
condensation and freezing dominates the overall energy budget. Emissions of
water vapor from the fire do not significantly contribute to the energy
budget of the convection.
Citation: Trentmann, J., Luderer, G., Winterrath, T., Fromm, M. D., Servranckx, R., Textor, C., Herzog, M., Graf, H.-F., and Andreae, M. O.: Modeling of biomass smoke injection into the lower stratosphere by a large forest fire (Part I): reference simulation, Atmos. Chem. Phys., 6, 5247-5260, doi:10.5194/acp-6-5247-2006, 2006.