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Full-Text Articles in Physical Sciences and Mathematics
Variation Of The Martian Ionospheric Electron Density From Mars Express Radar Soundings, D. D. Morgan, D. A. Gurnett, D. L. Kirchner, Jane L. Fox, E. Nielsen, J. J. Plaut
Variation Of The Martian Ionospheric Electron Density From Mars Express Radar Soundings, D. D. Morgan, D. A. Gurnett, D. L. Kirchner, Jane L. Fox, E. Nielsen, J. J. Plaut
Physics Faculty Publications
The Mars Advanced Radar for Subsurface and Ionospheric Sounding aboard Mars Express has been in operation for over 2 years. Between 14 August 2005 and 31 July 2007, we obtain 34,492 ionospheric traces, of which 14,060 yield electron density profiles and 12,291 yield acceptable fits to the Chapman ionospheric model. These results are used to study the Martian ionosphere under changing conditions: the presence or absence of solar energetic particles, solar EUV flux, season, solar zenith angle, and latitude. The 2-year average subsolar maximum electron density n 0 is 1.62 × 105 cm−3, the average subsolar electron …
Near-Terminator Venus Ionosphere: How Chapman-Esque?, Jane L. Fox
Near-Terminator Venus Ionosphere: How Chapman-Esque?, Jane L. Fox
Physics Faculty Publications
We have modeled the near-terminator ionosphere of Venus for solar zenith angles χ 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 …
Near-Terminator Venus Ionosphere: Evidence For A Dawn/Dusk Asymmetry In The Thermosphere, Jane L. Fox, W. T. Kasprzak
Near-Terminator Venus Ionosphere: Evidence For A Dawn/Dusk Asymmetry In The Thermosphere, Jane L. Fox, W. T. Kasprzak
Physics Faculty Publications
Recent models of the near-terminator ionosphere of Venus constructed using neutral density profiles from the VTS3 model of Hedin et al. (1983) have shown that altitudes of the electron density peaks are in agreement with those measured by Pioneer Venus (PV) Orbiter Radio Occultation (ORO) and other radio occultation profiles in the solar zenith angle (SZA) range 60 to 70°, where they are near 140 km (Fox, 2007). The model peaks in the 75–85° range, however, do not decrease in altitude to near 135 km, as do the PV ORO electron density peaks shown in the study of Cravens et …
Ion Cyclotron Waves In The Saturnian Magnetosphere Associated With Cassini's Engine Exhaust, C. T. Russell, J. S. Leisner, K. K. Khurana, M. K. Dougherty, X. Blanco-Cano, Jane L. Fox
Ion Cyclotron Waves In The Saturnian Magnetosphere Associated With Cassini's Engine Exhaust, C. T. Russell, J. S. Leisner, K. K. Khurana, M. K. Dougherty, X. Blanco-Cano, Jane L. Fox
Physics Faculty Publications
Five hours after the orbit insertion maneuver that placed Cassini into orbit about Saturn, a long (90 minute) burst of ion cyclotron waves were seen, very different than any waves on the inbound leg of the orbit or on succeeding orbits. The ion cyclotron waves were left-hand elliptically polarized and propagating at a moderately large angle to the local magnetic field. The waves had a noticeable compressional component consistent with their off angle propagation. The frequency band of the signals was moderately broad and consistent with the singly ionized components of the engine exhaust gases: CO2, N2 …
Solar Cycle Variability Of Hot Oxygen Atoms At Mars, Jhoon Kim, Andrew F. Nagy, Jane L. Fox, Thomas E. Cravens
Solar Cycle Variability Of Hot Oxygen Atoms At Mars, Jhoon Kim, Andrew F. Nagy, Jane L. Fox, Thomas E. Cravens
Physics Faculty Publications
The population of hot oxygen atoms in the Martian exosphere is reexamined using newly calculated hot O production rates for both low and high solar cycle conditions. The hot oxygen production rates are assumed to result from the dissociative recombination of O2+ ions. These calculations take into account the calculated vibrational distribution of O2+ and the new measured branching ratios. Furthermore, these calculations also consider the variation of the dissociative recombination cross section with the relative speed of the participating ions and electrons, the rotational energy of the O2+ ions, and the spread of …
Upper Limits To The Outflow Of Ions At Mars: Implications For Atmospheric Evolution, Jane L. Fox
Upper Limits To The Outflow Of Ions At Mars: Implications For Atmospheric Evolution, Jane L. Fox
Physics Faculty Publications
Escape of ions is potentially important for the evolution of volatiles on Mars, but the mechanisms and rates of ion escape processes are not fully understood. Instruments on the Russian Phobos 2 orbiter have, however, measured fluxes of heavy ions apparently of ionospheric origin in the optical shadow of Mars. These ions are assumed to arise from escape processes induced by the interaction of the solar wind with the ionosphere. We determine here upper limits to the ion loss rates by imposing upward flux boundary conditions on models of the low and high solar activity Mars ionosphere. The maximum fluxes …
Hydrocarbon Ions In The Ionosphere Of Titan, Jane L. Fox, Roger V. Yelle
Hydrocarbon Ions In The Ionosphere Of Titan, Jane L. Fox, Roger V. Yelle
Physics Faculty Publications
We have constructed a new model of the ionosphere of Titan that includes 67 species and 626 reactions. Although N2+ is the major ion produced over most of the ionosphere, the ionization flows to ions whose parent neutrals have lower ionization potentials and to ions formed from species with large proton affinities. In contrast to other models, which have predicted that HCNH+ should be the major ion, our calculations suggest that the major ions at and below the ion peak are hydrocarbon ions, and H, C, and N-containing ions. Our predicted peak electron density for a solar …
A Theoretical Study Concerning The Solar Cycle Dependence Of The Nightside Ionosphere Of Venus, Zoltan Dobe, Andrew F. Nagy, Jane L. Fox
A Theoretical Study Concerning The Solar Cycle Dependence Of The Nightside Ionosphere Of Venus, Zoltan Dobe, Andrew F. Nagy, Jane L. Fox
Physics Faculty Publications
We modeled the chemical and physical processes taking place in the nightside ionosphere of Venus by solving the one dimensional coupled continuity and momentum equations for 12 ion species [CO2+, O2+, O+, H+, NO+, CO+, N2+, N+, He+, C+, O+ (²D) and O+ (²P)]. We investigated the relative importance of the two major processes responsible for maintaining the nightside plasma densities: atomic ion transport from the dayside and impact ionization due to energetic electron precipitation. …
Rate Coefficient For The Reaction N + No, Jane L. Fox
Rate Coefficient For The Reaction N + No, Jane L. Fox
Physics Faculty Publications
Evidence has been advanced that the rate coefficient for the reaction N + NO → N2; + O has a small positive temperature dependence at the high temperatures (900-1500 K) that prevail in the terrestrial middle and upper thermosphere by Siskind and Rusch (1992), and at the low temperatures (100-200 K) of the Martian lower thermosphere by Fox (1993). Assuming that the rate coefficient recommended by the Jet Propulsion Laboratory evaluation (DeMore et al., 1992) is accurate at 300 K, we derive here the low temperature value of the activation energy for this reaction and thus the rate …
Evidence For Day-To-Night Ion Transport At Low Solar Activity In The Venus Pre-Dawn Ionosphere, J. F. Brannon, Jane L. Fox, H. S. Porter
Evidence For Day-To-Night Ion Transport At Low Solar Activity In The Venus Pre-Dawn Ionosphere, J. F. Brannon, Jane L. Fox, H. S. Porter
Physics Faculty Publications
Periapsis of the Pioneer Venus spacecraft dropped below 180 km on August 28, 1992 near midnight, and 42 orbits of low altitude data at moderately low solar activity in the pre-dawn sector were obtained before contact was lost to the spacecraft in October, 1992. Through a combination of analysis of data from the PV orbiter ion mass spectrometer (OIMS) and modeling, we consider here what can be learned about the relative importance of plasma transport from the dayside and electron precipitation in maintaining the nightside ionosphere during the re-entry period. In particular, we examine here the atomic ion density profiles. …
On The Escape Of Oxygen And Hydrogen From Mars, Jane L. Fox
On The Escape Of Oxygen And Hydrogen From Mars, Jane L. Fox
Physics Faculty Publications
Escape rates of oxygen atoms from dissociative recombination of O2+ above the Martian exobase are computed in light of new information from ab initio calculations of the dissociative recombination process, and our recently revised understanding of the Martian dayside ionosphere. Only about 60% of the dissociative recombinations occur in channels in which the O atoms are released with energies in excess of the escape velocity. Futhermore, we find that the computed escape fluxes for O depend greatly on the nature of the ion loss process that has been found necessary to reproduce the topside ion density profiles measured …
Upper Limits To The Nightside Ionosphere Of Mars, Jane L. Fox
Upper Limits To The Nightside Ionosphere Of Mars, Jane L. Fox
Physics Faculty Publications
The nightside ionosphere of Mars could be produced by electron precipitation or by plasma transport from the dayside, by analogy to the Venus, but few measurements are available. We report here model calculations of upper limits to the nightside ion densities on Mars that would be produced by both mechanisms. For the auroral model, we have adopted the downward traveling portions of the electron spectra measured by the HARP instrument on the Soviet Phobos spacecraft in the Martian plasma sheet and in the magnetotail lobes. For the plasma transport case, we have imposed on a model of the nightside thermosphere, …
The Production And Escape Of Nitrogen Atoms On Mars, Jane L. Fox
The Production And Escape Of Nitrogen Atoms On Mars, Jane L. Fox
Physics Faculty Publications
We have computed the production rates and densities of odd nitrogen species in the Martian atmosphere using updated rate coefficients and a revised ionosphere-thermosphere model. We find that the computed densities of NO are somewhat smaller than those measured by Viking 1, but reasonable agreement can be obtained by assuming that the rate coefficient for loss of odd nitrogen in the reaction of N with NO is smaller at temperatures that prevail in the lower Martian thermosphere (about 130–160 K) than the standard value, which applies to temperatures of 200–400 K. We have also modeled the escape fluxes of N …
O++ In The Venusian Ionosphere, Jane L. Fox, G. A. Victor
O++ In The Venusian Ionosphere, Jane L. Fox, G. A. Victor
Physics Faculty Publications
It is shown that the revised photochemical theory for O++ in the earth's ionopshere, where double photoionization of O is the dominant source, is consistent with recent O++ measurements on Venus. A rate coefficient of 1.5 × 10−10 cm³ s−1 for O++ + O is obtained, and the possible importance of O++ chemistry on minor atomic ions and airglow emissions is explored.
Ionization, Luminosity, And Heating Of The Upper Atmosphere Of Mars, Jane L. Fox, Alexander Dalgarno
Ionization, Luminosity, And Heating Of The Upper Atmosphere Of Mars, Jane L. Fox, Alexander Dalgarno
Physics Faculty Publications
A model based upon Viking data is constructed of the Martian atmosphere, and a comprehensive quantitative discussion is given of the measurements of the ultraviolet dayglow. A detailed assessment is made of the heating of the neutral and ionized components of the atmosphere arising from the absorption of ultraviolet solar radiation.
The Nitrogen Dayglow On Mars, Jane L. Fox, Alexander Dalgarno, E. R. Constantinides, G. A. Victor
The Nitrogen Dayglow On Mars, Jane L. Fox, Alexander Dalgarno, E. R. Constantinides, G. A. Victor
Physics Faculty Publications
The ultraviolet dayglow spectrum arising from emission of N2 in the Mars atmosphere is predicted. The intensities are such that a high-resolution spectrum should readily reveal the presence of N2 at the abundances suggested by the Viking experiments.