The Odd-Nitrogen Chemistry of the Near- and Post-Terminator Venus Ionosphere

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We investigate the odd nitrogen chemistry of the near- and post-terminator thermosphere of Venus by numerical modeling of the density profiles of N, NO, and NO+ (along with the 13 other ions, and 7 other neutral species) in our Venus thermosphere/ionosphere model. Odd nitrogen is produced on the dayside by N2 photo- and electron-impact dissociation, and ion-molecule reactions. Odd nitrogen species are interconverted rapidly. Atomic nitrogen (and atomic oxygen) are transported to the nightside from the dayside. In a 1-D model, we mimic the day-to-night transport of N by introducing a flux of N at the top of the model (as others have done, including Gerard et al., 2008). The VTGCM of S. Bougher (e.g., Stewart et al., 1980; Gerard et al., 1981) has also been used to model horizontal and downward transport of N and O atoms to produce the nitric oxide nightglow. Our model is constrained by the limb profiles of the nightglow emissions of the nitric oxide gamma and delta bands, as measured by the SPICAM on VEX, by the surface brightnesses of these emissions measured by the Pioneer Venus Orbiter Ultraviolet Spectrometer, and by comparison of the N density profile to those of the VTS3 and VIRA models. We find that we cannot reproduce a maximum in the density profiles of N without a finite value for the rate coefficient for the reaction N + CO2= NO + CO. Measurements to date have only yielded upper limits for this rate coefficient. We use our model calculations to estimate the value (or range) of the rate coefficient.


Presented at the 42nd Annual Meeting of the Division for Planetary Sciences of the American Astronomical Society, Pasadena, CA.

Presentation Number 10.01.

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