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The atmospheric chemistry general circulation model ECHAM5/MESSy1 has been extended byprocesses that parameterise particle precipitation. Several types of particle precipitation thatdirectly affect NOy and HOx concentrations in the middle atmosphere are accountedfor and discussed in a series of papers. In the companion paper, the ECHAM5/MESSy1 solar proton eventparametrisation is discussed, while in the current paper we focus on low energy electrons (LEE) thatproduce NOx in the upper atmosphere. For the flux of LEE NOx into the top of themodel domain a novel technique which can be applied to most atmospheric chemistry general circulationmodels has been developed and is presented here. The technique is particularly useful for modelswith an upper boundary between the stratopause and mesopause and therefore cannot directly incorporateupper atmospheric NOx production. The additional NOx source parametrisation is basedon a measure of geomagnetic activity, the Ap index, which has been shown to be a good proxy forLEE NOx interannual variations.HALOE measurements of LEE NOx that has been transported into the stratosphere are used todevelop 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/MESSy1and discuss the results from test simulations. The NOx enhancements are shown to be ingood agreement with independent measurements. Ap index data is available for almost one century,thus the parametrisation is suitable for simulations of the recent climate

atmospheric chemistry and physics

Energetic particle precipitation in ECHAM5/MESSy1 – Part 1: Downward transport of upper atmospheric NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; produced by low energy electrons