HR: 0800h
AN: A21B-0743    [Abstracts]
TI: A New 2D-Advection-Diffusion Model Simulating Trace Gas Distributions in the Lowermost Stratosphere
AU: * Hegglin, M I
EM: michaela.hegglin@env.ethz.ch
AF: Institute for Atmospheric and Climate Science IACETH,, Swiss Federal Institute of Technology, Zurich, 8093 Switzerland
AU: Brunner, D
EM: dominik.brunner@env.ethz.ch
AF: Institute for Atmospheric and Climate Science IACETH,, Swiss Federal Institute of Technology, Zurich, 8093 Switzerland
AU: Peter, T
EM: thomas.peter@env.ethz.ch
AF: Institute for Atmospheric and Climate Science IACETH,, Swiss Federal Institute of Technology, Zurich, 8093 Switzerland
AU: Wirth, V
EM: vwirth@mail.uni-mainz.de
AF: Institute for Atmospheric Physics, Johannes-Gutenberg University, Mainz, 55099 Germany
AU: Fischer, H
EM: hofi@mpch-mainz.mpg.de
AF: Max-Planck Institute for Chemistry, Mainz, Mainz, 55128 Germany
AU: Hoor, P
EM: hoor@mpch-mainz.mpg.de
AF: Max-Planck Institute for Chemistry, Mainz, Mainz, 55128 Germany
AB: Tracer distributions in the lowermost stratosphere are affected by both, transport (advective and non-advective) and in situ sources and sinks. They influence ozone photochemistry, radiative forcing, and heating budgets. In-situ measurements of long-lived species during eight measurement campaigns revealed relatively simple behavior of the tracers in the lowermost stratosphere when represented in an equivalent-latitude versus potential temperature framework. We here present a new 2D-advection-diffusion model that simulates the main transport pathways influencing the tracer distributions in the lowermost stratosphere. The model includes slow diabatic descent of aged stratospheric air and vertical and/or horizontal diffusion across the tropopause and within the lowermost stratosphere. The diffusion coefficients used in the model represent the combined effects of different processes with the potential of mixing tropospheric air into the lowermost stratosphere such as breaking Rossby and gravity waves, deep convection penetrating the tropopause, turbulent diffusion, radiatively driven upwelling etc. They were specified by matching model simulations to observed distributions of long-lived trace gases such as CO and N2O obtained during the project SPURT. The seasonally conducted campaigns allow us to study the seasonal dependency of the diffusion coefficients. Despite its simplicity the model yields a surprisingly good description of the small scale features of the measurements and in particular of the observed tracer gradients at the tropopause. The correlation coefficients between modeled and measured trace gas distributions were up to 0.95. Moreover, mixing across isentropes appears to be more important than mixing across surfaces of constant equivalent latitude (or PV). With the aid of the model, the distribution of the fraction of tropospheric air in the lowermost stratosphere can be determined.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting