The Venus ionosphere

Bauer, S. J.; Brace, L. M.; Taylor, H. A.; Бреус, Т. К.; Kliore, A. J.; Knudsen, W. C.; Nagy, Andrew F.; Russell, C. T.; Savich, N. A.

doi:10.1016/0273-1177(85)90203-0

Cited by 42 publications

(17 citation statements)

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“…The results of the simulations suggest that several mechanisms can explain the observed intensity of the green-line in the nightside of Venus, namely the Barth, and the controversial Frederick/Kopp mechanisms. In this latter case, the variations of the O + 2 density (Bauer et al 1985;Miller & Whitten 1991) could also explain the observed intensity fluctuations. Coordinated measurements from orbiting spacecraft, and Earthbased observatories, of both O + 2 density and green-line intensity, on the nightside ionosphere of Venus, are however necessary to confirm this hypothesis.…”

Section: Discussionmentioning

confidence: 92%

Modelling the Venusian airglow

Gronoff¹,

Lilensten²,

Simon

et al. 2008

A&A

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Context. Modelling of the Venusian ionosphere fluorescence is required, to analyse data being collected by the SPICAV instrument onboard Venus Express. Aims. We present the modelling of the production of excited states of O, CO and N 2 , which enables the computation of nightglow emissions. In the dayside, we compute several emissions, taking advantage of the small influence of resonant scattering for forbidden transitions. Methods. We compute photoionisation and photodissociation mechanisms, and the photoelectron production. We compute electron impact excitation and ionisation, through a multi-stream stationary kinetic transport code. Finally, we compute the ion recombination using a stationary chemical model. Results. We predict altitude density profiles for O( 1 S) and O( 1 D) states, and emissions corresponding to their different transitions. They are found to agree with observations. In the nightside, we discuss the different O( 1 S) excitation mechanisms as a source of green line emission. We calculate production intensities of the O( 3 S) and O( 5 S) states. For CO, we compute the Cameron bands and the Fourth Positive bands emissions. For N 2 , we compute the LBH, first and Second Positive bands. All values are compared successfully to experiments when data are available. Conclusions. For the first time, a comprehensive model is proposed to compute dayglow and nightglow emissions of the Venusian upper atmosphere. It relies on previous works with noticeable improvements, both on the transport side and on the chemical side. In the near future, a radiative-transfer model will be used to compute optically-thick lines in the dayglow, and a fluid model will be added to compute ion densities.

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Section: Discussionmentioning

confidence: 92%

Modelling the Venusian airglow

Gronoff¹,

Lilensten²,

Simon

et al. 2008

A&A

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“…Such small values of T e are difficult to reconcile, however, with the nearly SZA invariant median values of T e measured by the PV Langmuir probe near 147.5 km of ∼940 K presented by Theis et al [1984; see also Theis et al , 1980], or that from the PV RPA data, [ Miller et al , 1980], which showed a sharp increase in the altitude profile of the median values of T e near periapsis that was largely SZA invariant. The average electron temperatures at 150 km in the 80–90 and 90–100° SZA ranges are 800 and 1000 K, respectively, according the Venus International Reference Ionosphere [ Bauer et al , 1985].…”

Section: Resultsmentioning

confidence: 99%

“…There are only a few studies of T e as a function of SZA. In fact it appears that the median altitude profiles of T e are nearly SZA invariant [ Miller et al , 1980; Theis et al , 1980, 1984; Bauer et al , 1985].…”

Section: Discussionmentioning

confidence: 99%

Near‐terminator Venus ionosphere: How Chapman‐esque?

Fox

2007

J. Geophys. Res.

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[1] We have modeled the near-terminator ionosphere of Venus for solar zenith angles c between 60 and 85°in 5°increments, and from 86 to 90°in 1°increments. The most important neutral densities of the background thermospheres have been adopted from the VTS3 model of Hedin et al. (1983), which is based on densities from the Pioneer Venus (PV) Orbiter Neutral Mass Spectrometer (e.g., Niemann et al., 1980) that are normalized to the PV Orbiter Atmospheric Drag data (e.g., Keating et al., 1980). We compare the ion density profiles to those of a Chapman layer and to those obtained from radio occultation data. We determine the best fit values of n max,0 i and k in the Chapman expression n max,ck for each solar zenith angle interval; using a linear least squares regression for log n max,c i as a function of log cos(c) we also derive the best fit values for the group of ten models for solar zenith angles from 60 to 89°. For a theoretical Chapman layer with plane parallel geometry, k = 0.5, and n max,0 i is the peak electron density at the subsolar point. In the near-terminator region, the production rates and densities must be computed using spherical geometry, and this alone will cause the derived value of k to be reduced below the theoretical factor of 0.5. For the solar zenith angle models in the range 60-85°, we find that the magnitudes of the both the main (F 1 ) and lower (E) peaks decrease as the solar zenith angle increases in a somewhat Chapman-like manner, but the altitudes of the F 1 and E peaks increase only slowly from 140 to 144 km and from 125 to 129.5 km, respectively. The nearly constant altitude of the F 1 peaks has been attributed to the collapse of the thermosphere as it merges into the nighttime cryosphere (Cravens et al., 1981). This behavior is quite different from that of Mars, where the electron density peak altitudes have been observed to rise monotonically as the solar zenith angle increases. The predicted behavior for the Venus ionosphere is in general agreement with radio occultation data, but some differences also are observed. We discuss the differences between the modeled and observed peak altitudes and we attribute the differences partly to deficiencies in the VTS3 models and partly to uncertainties in the electron temperatures. There also may be some errors introduced into the radio occultation profiles in the very near-terminator region due to deviations from spherical symmetry. In addition, differences exist between the measured and model peak magnitudes at solar zenith angles near 60°that we ascribe partly to the use of the S2K v2.22 solar flux model of Tobiska (2004), for which the EUV and soft X-ray photon fluxes are significantly smaller than those of the S2K v1.24 or the Hinteregger solar flux models.

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“…For SZAs near and beyond about 145°, T i increases significantly and exceeds T e at high altitudes due to the formation of a shock as the nightward flowing ions become supersonic and their kinetic energy is transformed into thermal energy (e.g., Knudsen et al, 1981;Knudsen, 1992;Nagy et al, 1991). For an SZA of 145°, we adopt the values of T i from the VIRA model (Bauer et al, 1985). The T e and T i profiles were obtained for the 155°and 165°SZA models by adding at each altitude the difference between the neutral temperature and that for the 145°SZA model to the value of T i for the 145°model.…”

Section: Modelsmentioning

confidence: 99%

“…The electron temperatures in the Venus nightside ionosphere at high solar activity have been measured by the Pioneer Venus (PV) Orbiter Langmuir Probe (OETP) and by the retarding potential analyzer (ORPA), and have been found not to vary much over the nightside (e.g., Miller et al, 1980). At low altitudes we expect the values of T e to be thermalized with the neutral temperatures, but they may reach values of up to about 3000 K at 250 km, and about 5000 K near 800 km (e.g., Bauer et al, 1985).…”

Section: Introductionmentioning

confidence: 98%

The ionospheric source of the red and green lines of atomic oxygen in the Venus nightglow

Fox

2012

Icarus

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The Venus ionosphere

Cited by 42 publications

References 0 publications

Modelling the Venusian airglow

Modelling the Venusian airglow

Near‐terminator Venus ionosphere: How Chapman‐esque?

The ionospheric source of the red and green lines of atomic oxygen in the Venus nightglow

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