Small-scale mixing processes enhancing troposphere-to-stratosphere transport by pyro-cumulonimbus storms

G. Luderer (1) , J. Trentmann (2) , K. Hungershöfer (3) , M. Herzog (4) , M. Fromm (5) , M. O. Andreae (1)

1 MPIC - Max Planck Institute for Chemistry
2 IPA - Institute for Atmospheric Physics [Mainz]
3 LIM - Leipziger Institut für Meteorologie
4 GFDL - NOAA Geophysical Fluid Dynamics Laboratory
5 NRL - Naval Research Laboratory

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 enhance the stratospheric penetration of the smoke by up to 30 K and thus are of major significance for irreversible transport of forest fire smoke into the lower stratosphere.

Domaines: Océan, Atmosphère

G. Luderer, J. Trentmann, K. Hungershöfer, M. Herzog, M. Fromm, et al.. Small-scale mixing processes enhancing troposphere-to-stratosphere transport by pyro-cumulonimbus storms. Atmospheric Chemistry and Physics Discussions, 2007, 7 (4), pp.10371-10403. ⟨hal-00328216⟩