Atmos. Chem. Phys. Discuss., 8, 21201-21228, 2008
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Energetic particle precipitation in ECHAM5/MESSy1 – Part 1: Downward transport of upper atmospheric NOx produced by low energy electrons
A. J. G. Baumgaertner, P. Jöckel, and C. Brühl
Max Planck Institute for Chemistry, Mainz, Germany

Abstract. The atmospheric chemistry general circulation model ECHAM5/MESSy1 has been extended by processes that parameterize particle precipitation. Several types of particle precipitation that directly affect NOy and HOx concentrations in the middle atmosphere are accounted for and discussed in a series of papers. In the companion paper, the ECHAM5/MESSy1 solar proton event parameterization is discussed, while in the current paper we focus on low energy electrons (LEE) that produce NOx in the upper atmosphere. For the flux of LEE NOx into the top of the model domain a novel technique which can be applied to most atmospheric chemistry general circulation models has been developed and is presented here. The technique is particularly useful for models with an upper boundary between the stratopause and mesopause and therefore cannot directly incorporate upper atmospheric NOx production. The additional NOx source parametrization is based on a measure of geomagnetic activity, the Ap index, which has been shown to be a good proxy for LEE NOx interannual variations. HALOE measurements of LEE NOx that has been transported into the stratosphere are used to develop a scaling function which yields a flux of NOx that is applied to the model top. We describe the implementation of the parameterization as the submodel SPACENOX in ECHAM5/MESSy1 and discuss the results from test simulations. The NOx enhancements and associated effects on ozone are shown to be in good agreement with independent measurements. Ap index data is available for almost one century, thus the parameterization is suitable for simulations of the recent climate.

Citation: Baumgaertner, A. J. G., Jöckel, P., and Brühl, C.: Energetic particle precipitation in ECHAM5/MESSy1 – Part 1: Downward transport of upper atmospheric NOx produced by low energy electrons, Atmos. Chem. Phys. Discuss., 8, 21201-21228, doi:10.5194/acpd-8-21201-2008, 2008.
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