Energetic particle precipitation in ECHAM5/MESSy1 – Part 1: Downward transport of upper atmospheric NO<sub>x</sub> produced by low energy electrons
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 NO<sub>y</sub> and HO<sub>x</sub> concentrations in the middle atmosphere ar...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2009-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/9/2729/2009/acp-9-2729-2009.pdf |
| Summary: | 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 NO<sub>y</sub> and HO<sub>x</sub> 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 NO<sub>x</sub> in the upper atmosphere. For the flux of LEE NO<sub>x</sub> 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 NO<sub>x</sub> production. The additional NO<sub>x</sub> source parametrisation is based on a measure of geomagnetic activity, the <i>A<sub>p</sub></i> index, which has been shown to be a good proxy for LEE NO<sub>x</sub> interannual variations. HALOE measurements of LEE NO<sub>x</sub> that has been transported into the stratosphere are used to develop a scaling function which yields a flux of NO<sub>x</sub> 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 NO<sub>x</sub> enhancements are shown to be in good agreement with independent measurements. <i>A<sub>p</sub></i> index data is available for almost one century, thus the parametrisation is suitable for simulations of the recent climate. |
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| ISSN: | 1680-7316 1680-7324 |