The ultraviolet dayglow at solar maximum: 3. Photoelectron‐excited emissions of N<sub>2</sub> and O

Meier, R. R.; Conway, Robert R.; Anderson, Donald E.; Feldman, P. D.; Eastes, R.; Gentieu, E. P.; Christensen, A. B.

doi:10.1029/ja090ia07p06608

Cited by 50 publications

(22 citation statements)

References 41 publications

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“…Their model calculations reproduced the measurements if the O densities from the BNMS model were reduced by about 40~o, but their analysis was based on cross sections for electron impact production of emission at 1304 and 1356 ~_ reported by Stone and Zipf (1974) that were later reduced by a factor of 2.8 (Zipf and Erdman, 1985;Zipf, 1986). A model of the terrestrial dayglow oxygen emissions (Meier et al, 1985) suggested that the Stone and Zipf cross sections should be scaled down by 40~o. A reanalysis of the Pioneer Venus data using the renormalized cross sections showed good agreement between the O densities necessary to explain the measured emission and the BNMS model densities (Paxton and Meier, 1986).…”

Section: Species Sourcementioning

confidence: 78%

Structure, luminosity, and dynamics of the Venus thermosphere

Fox

Bougher

1991

Space Sci Rev

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We review here observations and models related to the chemical and thermal structures, airglow and auroral emissions and dynamics of the Venus thermosphere, and compare empirical models of the neutral densities based in large part on in situ measurements obtained by the Pioneer Venus spacecraft.Observations of the intensities of emissions are important as a diagnostic tool for understanding the chemical and physical processes taking place in the Venus thermosphere. Measurements, ground-based and from rockets, satellites, and spacecraft, and model predictions of atomic, molecular and ionic emissions, are presented and the most important sources are elucidated. Coronas of hot hydrogen and hot oxygen have been observed to surround the terrestrial planets. We discuss the observations of and production mechanisms for the extended exospheres and models for the escape of lighter species from the atmosphere. Over the last decade and a half, models have attempted to explain the unexpectedly cold temperatures in the Venus thermosphere; recently considerable progress has been made, although some controversies remain. We review the history of these models and discuss the heating and cooling mechanisms that are presently considered to be the most important in determining the thermal structure. Finally, we discuss major aspects of the circulation and dynamics of the thermosphere: the sub-solar to anti-solar circulation, superrotation, and turbulent processes.

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Section: Species Sourcementioning

confidence: 78%

Structure, luminosity, and dynamics of the Venus thermosphere

Fox

Bougher

1991

Space Sci Rev

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“…Low-energy electrons play a strong role in auroral and dayglow activity [Cartwright, 1978;Doering et al, 1975]. A recent analysis of the N2 LBH system in dayglow and auroral observations by Meier et al [1985] suggest that threshold effects may play a role in understanding the processes, but it is apparent that other unexplained complications are present [Meier et al, 1985]. Figure 11…”

Section: Calibrationmentioning

confidence: 99%

“…The results obtained here should be particularly useful for model calculations of atmospheric phenomena in nitrogen systems. We have determined that the N2 LBH system, which apparently is an important component in the understanding of energy deposition and atmospheric physical chemistry [Meier et al, 1985], has a particularly simple excitation function. An accurate analytic fit to the cross section allows direct calculation of excitation effects over all energies above threshold.…”

Section: Calibrationmentioning

confidence: 99%

A reexamination of important N₂ cross sections by electron impact with application to the dayglow: The Lyman‐Birge‐Hopfield Band System and N I (119.99 nm)

Ajello¹,

Shemansky²

1985

J. Geophys. Res.

144

140

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The far ultraviolet emission spectrum (120 to 210 nm) of electron‐excited N2 has been obtained in a crossed‐beam laboratory experiment. The cross section of the Lyman‐Birge‐Hopfield (LBH) band system (a¹Πg → X¹Σg+) has been remeasured using experimental techniques we have previously developed for this metastable transition. The improved laboratory data set for the a¹Πg state allows a determination of the excitation, emission, and predissociation cross section from threshold to 200 eV for use in planetary atmosphere models of the dayglow and aurora. An analytic fit to the experimental cross section allows accurate estimates to arbitrarily high excitation energy. The close agreement in both energy dependence and absolute cross section values between the emission measurements, presented here, and published electron scattering results shows cascade is small (<5%). The total excitation cross section for the N2 a¹Πg state is estimated to be 6.22 ± 1.37×10−18 cm² at 100 eV. The absence of emission bands for υ′ ≥ 7 suggests the predissociation yield is unity. The excitation function of each vibrational level is found to have the same shape to within 5%. In the low‐energy region, ε < 20 eV, differences in excitation threshold lead to a significant departure of the relative vibrational cross sections from the Franck‐Condon distribution. Thus the relative LBH vibrational population distribution in a planetary dayglow or aurora is affected by the energy distribution of the electron flux; and we show that atmospheric models need to include this threshold effect. The N I (119.99 nm) cross section has also been remeasured and found to be 3.48 ± 0.77×10−18 cm² at 200 eV on the basis of a comparison with Lyman α emission from dissociative excitation of H2.

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“…Extinction due to absorption by O 2 molecules in the Schumann-Runge continuum is important between 100 and 150 km altitude where O 2 is the predominant species (Meier, 1991). Contamination by the N 2 (a 1 g -X 1 + g ) LBH (3,0) band at 135.4 nm may also occur, especially in the bottom-side of the atmosphere, as explained in Meier et al (1985) and reaches 8 to 20 % of the overall emission at 200 km altitude depending on solar and atmospheric conditions. O + -O − neutralization may also play a role (around 5 % of the total emission), especially in the mid-latitude ionosphere (Meier, 1991;Dymond et al, 2000) and at low altitudes.…”

Section: Ionospheric Response: Modelling the Optical Emissionsmentioning

confidence: 99%

Polar cap arcs from the magnetosphere to the ionosphere: kinetic modelling and observations by Cluster and TIMED

et al. 2012

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Abstract. On 1 April 2004 the GUVI imager onboard the TIMED spacecraft spots an isolated and elongated polar cap arc. About 20 min later, the Cluster satellites detect an isolated upflowing ion beam above the polar cap. Cluster observations show that the ions are accelerated upward by a quasistationary electric field. The field-aligned potential drop is estimated to about 700 V and the upflowing ions are accompanied by a tenuous population of isotropic protons with a temperature of about 500 eV.The magnetic footpoints of the ion outflows observed by Cluster are situated in the prolongation of the polar cap arc observed by TIMED GUVI. The upflowing ion beam and the polar cap arc may be different signatures of the same phenomenon, as suggested by a recent statistical study of polar cap ion beams using Cluster data.We use Cluster observations at high altitude as input to a quasi-stationary magnetosphere-ionosphere (MI) coupling model. Using a Knight-type current-voltage relationship and the current continuity at the topside ionosphere, the model computes the energy spectrum of precipitating electrons at the top of the ionosphere corresponding to the generator electric field observed by Cluster. The MI coupling model provides a field-aligned potential drop in agreement with Cluster observations of upflowing ions and a spatial scale of the polar cap arc consistent with the optical observations by TIMED. The computed energy spectrum of the precipitating electrons is used as input to the Trans4 ionospheric transport code. This 1-D model, based on Boltzmann's kinetic formalism, takes into account ionospheric processes such as photoionization and electron/proton precipitation, and computes the optical and UV emissions due to precipitating electrons. The emission rates provided by the Trans4 code are compared to the optical observations by TIMED. They are similar in size and intensity. Data and modelling results are consistent with the scenario of quasi-static acceleration of electrons that generate a polar cap arc as they precipitate in the ionosphere. The detailed observations of the acceleration region by Cluster and the large scale image of the polar cap arc provided by TIMED are two different features of the same phenomenon. Combined together, they bring new light on the configuration of the high-latitude magnetosphere during prolonged periods of Northward IMF. Possible implications of the modelling results for optical observations of polar cap arcs are also discussed.

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The ultraviolet dayglow at solar maximum: 3. Photoelectron‐excited emissions of N₂ and O

Cited by 50 publications

References 41 publications

Structure, luminosity, and dynamics of the Venus thermosphere

Structure, luminosity, and dynamics of the Venus thermosphere

A reexamination of important N₂ cross sections by electron impact with application to the dayglow: The Lyman‐Birge‐Hopfield Band System and N I (119.99 nm)

Polar cap arcs from the magnetosphere to the ionosphere: kinetic modelling and observations by Cluster and TIMED

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The ultraviolet dayglow at solar maximum: 3. Photoelectron‐excited emissions of N2 and O

Cited by 50 publications

References 41 publications

Structure, luminosity, and dynamics of the Venus thermosphere

Structure, luminosity, and dynamics of the Venus thermosphere

A reexamination of important N2 cross sections by electron impact with application to the dayglow: The Lyman‐Birge‐Hopfield Band System and N I (119.99 nm)

Polar cap arcs from the magnetosphere to the ionosphere: kinetic modelling and observations by Cluster and TIMED

Contact Info

Product

Resources

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The ultraviolet dayglow at solar maximum: 3. Photoelectron‐excited emissions of N₂ and O

A reexamination of important N₂ cross sections by electron impact with application to the dayglow: The Lyman‐Birge‐Hopfield Band System and N I (119.99 nm)