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 parameterise 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
parametrisation 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 parametrisation 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 parametrisation as the submodel SPACENOX in ECHAM5/MESSy1
and discuss the results from test simulations. The NOx enhancements are shown to be in
good agreement with independent measurements. Ap index data is available for almost one century,
thus the parametrisation 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., 9, 2729-2740, doi:10.5194/acp-9-2729-2009, 2009.