Small-scale mixing processes enhancing troposphere-to-stratosphere transport by pyro-cumulonimbus storms G. Luderer1,*, J. Trentmann2, K. Hungershöfer3,**, M. Herzog4,***, M. Fromm5, and M. O. Andreae1 1Max Planck Institute for Chemistry, Dept. Biogeochemistry, Mainz, Germany 2Institute for Atmospheric Physics, Johannes Gutenberg University Mainz, Mainz, Germany 3Institute for Meteorology, University of Leipzig, Leipzig, Germany 4NOAA GFDL, Princeton, New Jersey, USA 5Naval Research Laboratory, Washington DC, USA, *now at: Potsdam Institute for Climate Impact Research, Potsdam, Germany **now at: LISA, CNRS/Univ. Paris 7&12, Crétail, France ***now at: Department of Geography, University of Cambridge, Cambridge, UK
Abstract. Deep convection induced by large forest fires is an efficient
mechanism for transport of aerosol particles and trace gases into the upper
troposphere and lower stratosphere (UT/LS). For many pyro-cumulonimbus clouds
(pyroCbs) as well as other cases of severe convection without
fire forcing, radiometric observations of cloud tops in the thermal infrared (IR) reveal
characteristic structures, featuring a region of relatively high brightness
temperatures (warm center) surrounded by a U-shaped
region of low brightness temperatures.
We performed a numerical simulation of a specific case study of
pyroCb using a
non-hydrostatic cloud resolving model with a two-moment cloud
microphysics parameterization and a prognostic turbulence scheme. The model is
able to reproduce the thermal IR
structure as observed from satellite radiometry. Our findings establish a
close link between the observed temperature
pattern and small-scale mixing processes atop and downwind
of the overshooting dome of the pyroCb. Such small-scale mixing processes are
strongly enhanced by the formation and breaking of a stationary gravity wave
induced by the overshoot. They are found to increase the stratospheric
penetration of the smoke by up to almost 30 K and thus are of major significance for
irreversible transport of forest fire smoke into the lower stratosphere.
Citation: Luderer, G., Trentmann, J., Hungershöfer, K., Herzog, M., Fromm, M., and Andreae, M. O.: Small-scale mixing processes enhancing troposphere-to-stratosphere transport by pyro-cumulonimbus storms, Atmos. Chem. Phys., 7, 5945-5957, doi:10.5194/acp-7-5945-2007, 2007.