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Nagy, A. F.

Publications and source records attributed to Nagy, A. F..

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

The energetics of the ionosphere of Venus - A preliminary model based on Pioneer Venus observations

A model of the energy balance of the dayside ionosphere of Venus is presented. The coupled energy equations for electrons and ions are solved numerically and the calculated temperatures are compared with temperatures measured by instruments on the Pioneer Venus Orbiter. Neutral and ion density profiles consistent with those measured by various Pioneer Venus experiments are used in the model. It was found that using standard EUV sources and thermal conductivities the calculations produce temperatures that are much lower than the measured ones. Consequently, further calculations were performed in which (1) the thermal conductivities were inhibited by means of an almost horizontal magnetic field and/or (2) heat inflow into both the electron and ion gas at the top of the ionosphere was assumed due to the solar wind interaction. It was found that the calculated and measured temperatures were in reasonably good agreement if the thermal conductivities were inhibited by a near horizontal field of about 10 gammas and if the electron and ion heat fluxes were taken to be 4 x 10 to the 9th eV/sq cm/sec and 10 to the 7th eV/sq cm/sec, respectively.

Cravens, T. E.↗
NASA NTRS1979

On the configuration of the nightside Venus ionopause

Nightside measurements of electron and ion concentrations by instruments on the Pioneer Venus Orbiter have revealed an ionopause which is highly dynamic and whose global configuration is surprisingly complex. Inbound crossing which occur at high northern latitudes encounter the ionopause at an average altitude of 870 km in the late afternoon sector. The average ionopause altitude increases slightly near 100 deg solar zenith angle (SZA) followed by a nightside compression to well below 500 km. The outbound crossings of the ionopause occur at about 20 deg south of the equator. The ionospause at this latitude is found at an average altitude of 800 km in the afternoon-evening sector between 65 and 110 deg SZA, followed by a pronounced rise to altitudes as high as 3000 km in a pronounced bulge near 130 deg SZA.

Brace, L. H.↗
NASA NTRS1979

Plasma diffusion into the wake of Venus

A model of the diffusion of ionosheath plasma into the wake region of Venus is presented. It is shown that particle diffusion, which is assumed to be a consequence of the fluctuating magnetic field observed in the wake of Venus by Pioneer Venus and Veneras 9 and 10, can explain the plasma observations made in the wake by Veneras 9 and 10. The pressure due to these diffusing particles when balanced against the ionospheric pressure yield ionopause heights less than 1000 km for zenith angles less than about 135 deg. The model also predicts significant fluxes of low energy electrons and ions for zenith angles less than 135 deg, which are capable of producing the observed nightside ionosphere.

Gombosi, T.↗
NASA NTRS1979

Electron temperatures and densities in the Venus ionosphere - Pioneer Venus orbiter electron temperature probe results

The Pioneer Venus orbiter electron temperature probe was used to obtain altitude profiles of electron temperature and density in the ionosphere of Venus. Elevated temperatures at times of low solar wind flux might indicate support for a certain model. According to this model, less than 5% of the solar wind energy is deposited at the ionopause and is conducted downward through an unmagnetized ionosphere to the region below 200 km where electron cooling to the neutral atmosphere proceeds rapidly. The patterns of electron temperatures and densities at higher solar wind fluxes are considered, the variability of the ionopause height in the late afternoon is noted, and the role of an induced magnetic barrier in the neighborhood of the ionopause is discussed.

Brace, L. H.↗
NASA NTRS1978

Zodiacal light dynamics experiment: A wideband imaging Fabry-Perot interferometer

The Solar Probe will provide an ideal platform from which to study dynamics of dust particles near the sun by measuring the detailed character of the Fraunhofer structure of the zodiacal light. The suggested instrument is a wideband imaging Fabry-Perot interferometer with state of the art technology in both the optics and the detector. The instrument would function as a high-resolution imaging device providing wavelength resolution of 0.03 A over about a 20 A range. The wideband imaging capability would provide sky maps of the zodiacal light on a despun spacecraft without mechanical scanning. The Solar Probe mission would allow the velocity distribution of the dust to be mapped along most of the trajectory of the spacecraft.

Torr, D. G.↗
NASA NTRS1978

Electron temperatures in the F region of the ionosphere - Theory and observations

The theory and observations relating to electron temperatures in the F region of the ionosphere are reviewed. The review is divided into three basic parts. In the first part the theory concerning electron heating, cooling, and energy transport processes is reviewed, and all the relevant expressions are updated. In the second part the behavior of F region electron temperatures, as measured by satellites, rockets, and incoherent scatter radars, is discussed. This portion covers electron temperature variations with altitude, latitude, local time, season, geomagnetic activity, and solar cycle. The third part is primarily devoted to a discussion of the various attempts to compare measured and calculated F region electron temperatures.

Schunk, R. W.↗
NASA NTRS1978

The Martian ionosphere in light of the Viking observations

A theoretical model has been constructed in which the ion density and the ion and electron temperature distributions are calculated by solving the coupled continuity-momentum equations and the coupled energy equations. The latest experimental results from the Viking 1 and 2 landers are used to vary some of the parameters in the model in order to obtain agreement between the theoretical and experimental results. It is found that solar EUV radiation alone is not able to maintain the observed high ion temperatures. It was also established that the energy coupling between the electron and ion gas is insufficient to account for the measured ion temperatures even in the presence of very large electron temperatures. Direct heat input to the ion gas, probably due to solar wind-ionosphere interactions, can result in ion temperature values in reasonable agreement with the observations. The ion densities calculated with the present model agree well with the Viking observations in the chemically controlled region, but at higher altitudes, dynamic transport processes need to be invoked to achieve consistency among the observed and calculated temperature and density values.

Chen, R. H.↗
NASA NTRS1978

The ionosphere and airglow of Venus - Prospects for Pioneer Venus

The paper presents model calculations for the Cytherean nighttime and daytime ionosphere. It is shown how some of the proposed mechanisms can be tested with the aid of the Pioneer Venus observations scheduled for December 1978. Theoretical calculations of the energetics of the Cytherean ionosphere are performed, and it is concluded that the Project Venus measurements will find elevated ion and electron temperatures, resulting primarily from energy fluxes associated in some manner with the solar wind. According to this model, the energy flux will act directly on the ion gas. Ultraviolet dayglow intensities were calculated, and it is anticipated that hundreds of kR's of CO2-related emission features such as the CO Cameron bands will be observed. Nightside ionosphere calculations were made assuming the precipitation of energetic electrons as an ionization source, and the intensities of some of the resulting emission features are calculated.

Cravens, T. E.↗
NASA NTRS1978

A comprehensive model of the Venus ionosphere

Coupled time-dependent continuity-momentum and energy balance equations for the Venus ionosphere were simultaneously solved for CO2(+), O2(+), O(+), He(+), and H(+) densities and electron and ion temperatures for an altitude range of 120-500 km. Values of the solar zenith angle varied from 0 deg (subsolar point) to 90 deg (terminator). The calculations include the horizontal bulk transport of ions by neutral winds but not the horizontal diffusion. The two-stream photoelectron transport method was used to find the heating rates for the ambient electrons. Different boundary conditions were considered, and a nightside ionosphere was calculated. The results of these model calculations are in good agreement with measurements in the region of maximum electron density. Characteristics of topside and nightside densities and temperatures are discussed.

Chen, R. H.↗
NASA NTRS1978

Effect of diffusion-thermal processes on the high-latitude topside ionosphere

The extent to which diffusion-thermal heat flow affects H(+) temperatures in the high-latitude topside ionosphere is studied. Such a heat flow occurs whenever there are H(+)-O(+) relative drifts. From our study we have found that at high-latitudes, where H(+) flows up and out of the topside ionosphere, diffusion-thermal heat flow acts to reduce H(+) temperatures by 500-600 K at altitudes above about 900 km.

Schunk, R. W.↗
NASA NTRS1977

Comparison between calculated and measured photoelectron fluxes from Atmosphere Explorer C and E

The two-stream method has been used to calculate photoelectron fluxes. These results have been compared to those obtained by the photoelectron spectrometer on Atmosphere Explorers C and E. At both low altitudes, and higher altitudes (where transport effects are significant) the calculated and measured photoelectron fluxes yield good agreement. It is suggested that (1) better photoionization and scattering cross-section data will yield improved flux calculations, and (2) measurements of the pitch angle distribution are necessary for better high-altitude comparisons.

Nagy, A. F.↗
NASA NTRS1977

Measurement of the nitric oxide altitude distribution in the mid-latitude mesosphere

A simple rocket-borne system has been developed for deriving nitric oxide concentration in the mesosphere from measurements of resonantly scattered solar ultraviolet radiation in the NO gamma band near 2150 A. The NO signal is extracted from a background of Rayleigh-scattered light by a direct measurement of this scattered light by use of an NO absorption cell. This system was utilized to measure the NO concentration above White Sands, New Mexico, in the altitude range from 69 to 101 km. The derived NO profile shows a concentration of about 30 million per cu cm at 67 and 100 km with a deep valley (more than an order of magnitude less) at about 84 km. Comparison with model calculations indicates that the time constant for NO chemistry is smaller than or comparable with that for transport.

Baker, K. D.↗
NASA NTRS1977

The Venus ionosphere and solar wind interaction

The current state of knowledge of the chemistry, dynamics and energetics of the upper atmosphere and ionosphere of Venus is reviewed together with the nature of the solar wind-Venus interaction. Because of the weak, though perhaps not negligible, intrinsic magnetic field of Venus, the mutual effects between these regions are probably strong and unique in the solar system. The ability of the Pioneer Venus Bus and Orbiter experiments to provide the required data to answer the questions outstanding is discussed in detail.

Bauer, S. J.↗
NASA NTRS1976

Vibrationally-excited hydroxyl molecules in the lower atmosphere

The vibrational energy distributions of hydroxyl molecules in the lower atmosphere were calculated. As expected, the distributions are found to be highly nonequilibrated. Attention is drawn to the role that vibrationally-excited molecules may play in modifying the chemistry of the lower atmosphere. The most likely role for the OH molecule in the stratosphere is via reactions that may not otherwise be energetically viable.

Nagy, A. F.↗
NASA NTRS1976

Electron temperatures in the Jovian ionosphere

The daytime electron temperature profile of the Jovian ionosphere was calculated, taking into account the effects of thermal conduction and heat inflow from the plasmasphere. The photoelectron fluxes and electron heating rates were determined by using the two-stream approach of Banks and Nagy (1970) and Nagy and Banks (1970). The calculated electron temperatures were found to follow the neutral temperature up to an altitude slightly above the electron density peak, while at higher altitudes they were significantly enhanced above the assumed neutral temperature value.

Nagy, A. F.↗
NASA NTRS1975

A model of the Venus ionosphere

Results of model calculations of the Venus ionosphere from 120 to 300 km are presented. The chemical scheme and reaction rates used are the same as given by Kumar and Hunten (1974) except that the electron temperature dependence of the dissociative recombination rates is taken into account. Calculations are made for low and high atomic oxygen models in which the O/CO2 ratios are 0.4% and 4% respectively at 140 km, and the results agree well in shape and magnitude with the Mariner 5 and 10 occultation results in the chemically controlled region. Reasonable agreement is obtained at higher altitudes if diffusive equilibrium and high vertical flow velocities (10 km/s) are assumed as upper boundaries for the Mariner 5 and 10 conditions respectively, although solar wind-ionosphere interactions are considered to be the controlling mechanism for the Mariner 10 results.

Nagy, A. F.↗
NASA NTRS1975

Ionospheric direct measurement techniques

The most important physical parameters of the ionosphere which have been studied extensively over the years are: (1) the temperature, density, chemical composition, and directed motion (wind) of the ionized and neutral gas particles; and (2) the electric and magnetic fields. This review will discuss direct in situ techniques used on sounding rockets and satellites to measure these physical parameters. The techniques reviewed are restricted to those which are applicable to altitudes above about 100 km, where the mean free path is greater than the characteristic dimension of the instruments. Direct in situ instrumentation is defined as an experiment which measures the parameters in the immediate vicinity of the vehicle carrying the instrument; remote sensing techniques will not be discussed here.

Bauer, S. J.↗