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At least 721 records · Page 40

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NASA NTRS1978

Rocket observations of electron-density irregularities in the equatorial ionosphere below 200 km

Nike Apache rockets carring instrumentation to measure electron density and its fine structure in the equatorial ionosphere were launched from Chilca, Peru in May and June 1975. The fine structure experiment and the data reduction system are described. Results obtained from this system are presented and compared with those obtained by VHF radar and from other rocket studies. A description of the equatorial ionosphere and its features is also presented.

Klaus, D. E.↗

NASA NTRS1979

Changes in the terrestrial atmosphere-ionosphere-magnetosphere system due to ion propulsion for solar power satellite placement

Preliminary estimates of the effects massive Ar(+) injections on the ionosphere-plasmasphere system with specific emphasis on potential communications disruptions are given. The effects stem from direct Ar(+) precipitation into the atmosphere and from Ar(+) beam induced precipitation of MeV radiation belt protons. These injections result from the construction of Solar Power Satellites using earth-based materials in which sections of a satellite must be lifted from low earth to geosynchronous orbit by means of ion propulsion based on the relatively abundant terrestrial atmospheric component, Ar. The total amount of Ar(+) injected in transporting the components for each Solar Power Satellite is comparable to the total ion content of the ionosphere-plasmasphere system while the total energy injected is larger than that of this system. It is suggested that such effects may be largely eliminated by using lunar-based rather than earth-based satellite construction materials.

Curtis, S. A.↗

NASA NTRS1978

Operational physical models of the ionosphere

Global models of the neutral constituents are considered relevant to ion density models and improved knowledge of the ion chemistry. Information provided on the pressure gradients that control the wind system and the electric field systems due to balloon, satellite, and incoherent scatter measurements is discussed along with the implication of these results to the development of global ionospheric models. The current state of knowledge of the factors controlling the large day to day variations in the ionosphere and possible approaches for operational models are reviewed.

Nisbet, J. S.↗

NASA NTRS1978

Investigation of electrical currents in the auroral ionosphere

Two papers are presented on the investigation of electrical currents in the auroral ionosphere: (1) The Relationship Between Field-Aligned Current Carried by Suprathermal Electrons, and the Auroral Arc; and (2) Ionospheric Electrical Currents in the Late Evening Plasma Flow Reversal. In the first paper (1), data from four auroral sounding rockets, which directly measured field-aligned currents with partical detectors, are presented. In the second paper (2), data are presented for an instrumented sounding rocket that was launched from Andoya, Norway in January 1977, in the late evening auroral oval.

Arnoldy, R. L.↗

NASA NTRS1979

Electric generators in the magnetosphere-ionosphere system

The nature and cause of electric fields in the coupled magnetosphere-ionosphere system and their effects in the middle atmosphere are discussed. Electric fields induced by the solar wind are reported. The equivalence between forces and electric currents and also between current closure and stress balance is described. The motions of the magnetospheric and ionospheric fluids and the electric fields of interest were determined by the balance of these forces, or equivalently by the closure of the currents. The physical nature of stresses and currents was examined.

Akinson, G.↗

NASA NTRS1979

Rocket radio measurement of electron density in the nighttime ionosphere

One experimental technique based on the Faraday rotation effect of radio waves is presented for measuring electron density in the nighttime ionosphere at midlatitudes. High frequency linearly-polarized radio signals were transmitted to a linearly-polarized receiving system located in a spinning rocket moving through the ionosphere. Faraday rotation was observed in the reference plane of the rocket as a change in frequency of the detected receiver output. The frequency change was measured and the information was used to obtain electron density data. System performance was evaluated and some sources of error were identified. The data obtained was useful in calibrating a Langmuir probe experiment for electron density values of 100/cu cm and greater. Data from two rocket flights are presented to illustrate the experiment.

Gilchrist, B. E.↗

NASA NTRS1979

Ionospheric research

Projects currently in progress on ionospheric research are described. General topics discussed include: planetary atmospheres, the ionosphere and its region, and mass spectroscopy.

Source record↗

NASA NTRS1978

Effect of anomalous transport coefficients on the thermal structure of the storm time auroral ionosphere

By analyzing an observed storm time auroral electron temperature profile it is shown that anomalous transport effects strongly influence the thermal structure of the disturbed auroral ionosphere. Such anomalous transport effects are a consequence of plasma turbulence, the existence of which has been established by a large number of observations in the auroral ionosphere. The electron and composite ion energy equations are solved with anomalous electron thermal conductivity and parallel electrical resistivity coefficients. The solutions are parameterized with respect to a phenomenological altitude-dependent anomaly coefficient A and are compared with an observed storm time electron temperature profile above Chatanika. The calculated temperature profile for the classical case (A = 1) disagrees considerably with the measured profile over most of the altitude range up to 450 km. It is shown that an anomaly coefficient with a sharp peak of the order of 10,000 centered around the F2 peak is consistent with observations.

Fontheim, E. G.↗

NASA NTRS1978

A case study of the aurora, high-latitude ionosphere, and particle precipitation during near-steady state conditions

An Isis 2 pass studied in related experiments was singled out for a detailed examination of the particle fluxes, optical emissions, and ionospheric parameters observed during a quiescent period (late recovery) between two substorms. Since both long-duration measurements (aircraft) and transient snapshot (spacecraft) data are available, space and time effects can, on a macroscopic level, be separated. The latitudinal morphology observed by the satellite is found to be basically spatial in nature. It is suggested that the observed particle fluxes can be explained in terms of precipitation from the quiet time plasma sheet without intervening acceleration. The agreement of the observed optical emissions and ionospheric parameters with the electron fluxes is discussed.

Winningham, J. D.↗

NASA NTRS1979

Ionosphere of Venus - First observations of the effects of dynamics on the dayside ion composition

Data obtained by Bennett radio-frequency ion mass spectrometers indicate that the ionosphere envelope, dominated above 200 km by O(+), responds dramatically to variations in the solar wind pressure. The pressure compresses the thermal ion distributions from heights as great as 1800 km inward to 280 km. At the thermal ion boundary, or ionopause, the ambient ions are swept away by the solar wind, while at higher altitudes energetic ion currents are detected. Within the ionosphere, ion convection stimulated by the solar wind interaction causes pass-to-pass differences in the ion scale heights.

Taylor, H. A., Jr.↗

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 NTRS1979

Localized deposition and sputtering of Jovian ionospheric sodium on Io

Because of relative motion between the innermost Galilean satellite Io and Jupiter's ionosphere, a current is drawn from the ionosphere that can be a source of both deposition on, and sputtering from, the surface of Io. It is shown that the ions in this current strike Io in a localized region in the quadrant bounded by a line connecting Io and Jupiter and a tangent line extended in the direction of Io's orbital motion. If these ions are the principal source of sodium that is sputtered from Io, then this current provides a simple explanation of the observation of a localized area from which sodium ions escape from Io. The geometry of this current may also affect the optical surface of Io. Several experimental tests are suggested that can determine the compatibility of this hypothesis with the directly observable properties of Io's surface.

Hill, T. W.↗

NASA NTRS1979

Energetic particle precipitation into the high-latitude ionosphere and the auroral electrojets. I - Definition of electrojet boundaries using energetic electron spectra and ground-based magnetometer data

Magnetometric data are used to define the poleward and equatorward borders of the eastward electrojet in the evening sector. The relationship between central plasma sheet (cps) and boundary plasma sheet (bps) and the auroral electrojet region is explored. This relationship is used to infer the electric field configuration in the cps and bps regions. It is shown that in the evening sector the cps is threaded by field lines carrying current flowing into the ionosphere, while the bps is threaded by field lines carrying current flowing out of the ionosphere.

Winningham, J. D.↗

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

Radio science with Voyager 1 at Jupiter - Preliminary profiles of the atmosphere and ionosphere

A preliminary profile of the atmosphere of Jupiter in the South Equatorial Belt shows (1) the tropopause occurring at a pressure level of 100 millibars and temperature of about 113 K, (2) a higher warm inversion layer at about the 35-millibar level, and (3) a lower-altitude constant lapse rate matching the adiabatic value of about 2 K/km, with the temperature reaching 150 K at the 600-millibar level. Preliminary afternoon and predawn ionospheric profiles at 12 deg and near the equator, respectively, have topside plasma scale heights of 590 km changing to 960 km above an altitude of 3500 km for the dayside, and about 960 km at all measured heights above the peak for the nightside. The higher value of scale height corresponds to a plasma temperature of 1100 K under the assumption of a plasma of protons and electrons in ambipolar diffusive equilibrium. The peak electron concentration in the upper ionosphere is approximately 200,000/cu cm for the dayside and about a factor of 10 less for the nightside. These peaks occur at altitudes of 1600 and 2300 km, respectively. Continuing analyses are expected to extend and refine these results, and to be used to investigate other regions and phenomena.

Eshleman, V. R.↗

NASA NTRS1979

Thermal structure and energy influx to the day- and nightside Venus ionosphere

The thermal structure of and energy influx to the dayside and nightside Venus ionosphere are discussed, based on data obtained by the Pioneer Venus spacecraft. Where the dayside ionosphere appears relatively constant in total ion concentration, ion and electron temperatures and ion composition below the ionopause, retarding potential analyzer measurements confirm the presence of strong spatial and temporal variations in nightside ion concentration. Ion temperatures on the nightside above 225 km are found to be larger by a factor of two or more than on the dayside, and comparable to electron temperatures on the day and night sides. Models of dayside and nightside ion temperatures consistent with observations require the heat input of 0.003 erg/sq cm sec and 0.005 erg/sq cm sec, respectively, to the ion gas to raise the ion temperature above that of the neutral gas, presumably by means of Joule heating.

Knudsen, W. C.↗

NASA NTRS1979

Transversely accelerated ions - An ionospheric source of hot magnetospheric ions

The paper considers observational data on transversely accelerated ion (TAI) events observed from the Isis 1 and 2 satellites. A source of hot magnetospheric ions was discovered in the auroral topside ionosphere, and a part of the cold ionospheric ion distribution is transversely accelerated within a source region as low as 1000 km. Subsequent to transverse acceleration, the ions are driven upward into the magnetosphere by the gradient B mirror force; they are observed by the soft particle spectrometers on the Isis 1 and 2 satellites, with sharply defined pitch angle distributions centered between 90 and 120 deg, and with energy distributions up to several hundred electron volts. Observations at 1400 km indicate that the transversely accelerated ion (TAI) events are predominantly a winter nightside auroral zone phenomenon, but in the summertime TAI events were observed at altitudes above 2750 km on the day-side within the cleft. Typical intensities exceeding 10 to the 8th power ions/sq cm s sr during TAI events suggest that they may be a significant source of hot ions for the magnetosphere.

Klumpar, D. M.↗

NASA NTRS1979

The auroral ionosphere - Comparison of a time-dependent model with composition measurements

A time-dependent model of the auroral ionosphere including the odd nitrogen species, NO, N(D-2), and N(S-4), is used for comparison with data from a coordinated rocket-satellite measurement of an auroral event. The chemical scheme and the adopted rate coefficients have been shown to be compatible with daytime mid-latitude ionospheric chemistry. The electron flux and neutral atmospheric parameters measured on the satellite are used to compute the appropriate ionization and dissociation rates. The calculated NO(plus), O2(plus), O(plus), Ne, and NO densities agree well with the rocket measurements. The calculated N2(plus) densities are larger than the measured densities by a factor of 3 at most altitudes. The calculations show that the nitric oxide content of the aurora (about 1.2 times 10 to the 9th NO molecules/cu cm at 105 km) is below the saturation value.

Gerard, J.-C.↗