HR: 0800h
AN: A21B-0727    [Abstracts]
TI: A Modeling Study of the Interaction Between Meteorological Background Conditions and the Dynamical Development of a Boreal Pyrocumulonimbus Cloud
AU: * Luderer, G
EM: gunnar@mpch-mainz.mpg.de
AF: Max-Planck-Instutue for Chemistry, Biogeochemistry Dept., P.O. Box 3060, Mainz, 55020 Germany
AU: Trentmann, J
EM: jtrent@atmos.washington.edu
AF: Department of Atmospheric Sciences, University of Washington, P.O. Box 351640, Seattle, WA 98195-1640 United States
AU: Winterrath, T
EM: tanja.winterrath@dwd.de
AF: Max-Planck-Instutue for Chemistry, Biogeochemistry Dept., P.O. Box 3060, Mainz, 55020 Germany
AU: Textor, C
EM: textor@lsce.saclay.cea.fr
AF: Laboratoire des Sciences du Climat et l'Environnement, CEA Saclay, L'Orme des Merisiers, Bat. 709, Gif-sur-Yvette, 91191 France
AU: Wernli, H
EM: wernli@mail.uni-mainz.de
AF: Institute for Atmospheric Physics, University of Mainz, PO Box, Mainz, 55099 Germany
AU: Andreae, M O
EM: andreae@mpch-mainz.mpg.de
AF: Max-Planck-Instutue for Chemistry, Biogeochemistry Dept., P.O. Box 3060, Mainz, 55020 Germany
AB: Large boreal forest fires emerge as an additional, previously under-appreciated direct source of smoke gases and aerosol particles in the upper troposphere and lower stratosphere (UT/LS). A well documented case of a fire induced convective blow-up with direct injection of smoke into the lower stratosphere is given presented by the Chisholm fire, that burned in Alberta, Canada and peaked on 28 May 28, 2001. There is observational evidence that convective blow-ups of boreal pyro-clouds with significant injection of smoke into the UT/LS region are triggered by the passage of synoptic scale cold fronts. This suggests that the advent of a cold front not only results in an intensification of the fire itself, but also in an intensification of the fire induced atmospheric convection. There are several possible mechanisms through which the convection dynamics can be influenced by the cold front. First, the fire- induced convection is very sensitive to the wind shear and the orientation of the fire front relative to the wind direction, both of which change as the cold front passes. Second, whereas the surface temperature has a sharp negative gradient, there is a maximum of specific humidity at the cold front. This gives rise to a maximum in convective available potential energy (CAPE). Third, large-scale convergence enhances the onset of convection. We have performed numerical simulations of the pyro-cloud convection of over the Chisholm fire using the non-hydrostatic cloud resolving plume model ATHAM (Active Tracer High Resolution Atmospheric Model). Our results show that the fluxes of sensible heat and water vapor are indeed strong enough to explain the penetration of the fire plume into the tropopause region. Different meteorological background conditions are adopted from ECMWF reanalysis data and used to investigate the sensitivity of the pyro-cloud convection to the variation of the wind field as well as the temperature and humidity profiles as during the cold front passage. Using a two-moment scheme, we also analyzed the sensitivity to interactions between the fire-smoke aerosols and cloud processes. Whereas we find a strong sensitivity to the meteorological background conditions, our results suggest that the sensitivity of the plume dynamics to the effects of microphysical interactions between fire aerosols and cloud processes is rather weak, at least with the currently implemented parameterization.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0341 Middle atmosphere--constituent transport and chemistry (3334)
DE: 0400 Biogeosciences
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting