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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Speed-dependent collision effects on radar back-scattering from the ionosphere

A computer code to accurately compute the fluctuation spectrum for linearly speed dependent collision frequencies was developed. The effect of ignoring the speed dependence on the estimates of ionospheric parameters was determined. It is shown that disagreements between the rocket and the incoherent scatter estimates could be partially resolved if the correct speed dependence of the i-n collision frequency is not ignored. This problem is also relevant to the study of ionospheric irregularities in the auroral E-region and their effects on the radio communication with satellites.

Theimer, O.↗
NASA NTRS1980

Microwave heating of the lower ionosphere

Changes in the properties of the lower ionosphere due to ohmic heating of the plasma by the solar power satellite (SPS) microwave power beam are considered. The development of a predictive model of the underdense interaction of an electromagnetic beam and the lower ionosphere is described. The extent to which the Platteville and Arecibo experiments simulate SPS conditions is considered.

Meltz, G.↗
NASA NTRS1981

On the maintenance of the Venus nightside ionosphere - Electron precipitation and plasma transport

The relative contributions of electron precipitation and transport of dayside plasma to the maintenance of the Venus nightside ionosphere during the long Venusian night are investigated based on simultaneous Pioneer Venus Orbiter Retarding Potential Analyzer measurements of suprathermal electron fluxes and plasma densities. In about 20 orbits, the nightside integral electron flux of electrons with energies between 5 and 45 eV is observed to be relatively constant in time and altitude, while plasma density is observed to vary by a factor of 10 or more with no correlation with the electron flux. Ionization rates and ion density height profiles are computed for O(+) and O2(+) as a function of magnetic dip angle based on a typical electron spectrum, or a downward flux of O(+) ions. Comparison of the computed profiles with the measured median O(+) and O2(+) density profiles reveals that the measured profiles can only be reproduced by a downward flux of O(+) equal to about 10 to the 8th/sq cm per sec; suprathermal electron energy distributions produce O2(+) and O(+) levels only about half and one tenth those usually observed, respectively. It is thus concluded that transport of O(+) ions from the dayside Venus ionosphere is responsible for approximately 75% of the typical nightside ionization, with variations in O(+) transport mechanism responsible for most of the observed nightside density variations. The remaining ionization is attributed to suprathermal electrons, which contribute principally to the O2(+) peak.

Spenner, K.↗
NASA NTRS1981

Ionospheric remote sensing of medium-scale gravity waves and tornadic storms

Gravity waves associated with severe storms are investigated on the basis of ionospheric sounding using a ground-based Doppler system. Reverse-group ray tracing computations are used to determine the origin of over 20 gravity waves detected within 800 km of Huntsville, Alabama in association with a group of tornadoes, isolated tornadoes in the presence of a squall line, and isolated tornadoes in the absence of a squall line. Gravity waves associated with tornadoes are found either to be generated by thunderstorms with enhanced convection embedded in a squall line, or in an isolated cloud with enhanced convection. The computed wave sources are observed in all cases to be located near the points where the tornadoes touched down more than an hour after wave excitation. Results show that gravity waves play an important role in troposphere-ionosphere coupling during times of intense convection associated with tornadic storm activity.

Hung, R. J.↗
NASA NTRS1981

The ionospheric peak on the Venus dayside

The behavior of the ionospheric peak on the dayside of Venus is described and interpreted by combining radio occultation measurements with theoretical calculations. The theoretical models are shown to be able to reproduce the measured electron densities very accurately when careful consideration is given to such parameters as the level of solar activity, the electron temperature, and the neutral density. What is more, the models are able to provide a check on the accuracy of neutral atmospheric models in the vicinity of 140 km. Chemical equilibrium is assumed for the calculation of ion and electron densities. A table giving Pioneer Venus radio occultation measurements of the Venus dayside ionosphere is included.

Cravens, T. E.↗
NASA NTRS1981

Energization of ionospheric ions by electrostatic hydrogen cyclotron waves

Interactions between ionospheric ions and electrostatic hydrogen cyclotron waves are studied numerically in an investigation of a possible mechanism for the energization of the low-energy ionospheric ions flowing along geomagnetic field lines to high altitudes. Ion equations of motion are solved numerically for a given number of O(+), He(+) and He(2+) ions initially in a Maxwellian distribution. All the ions considered are found capable of undergoing stochastic acceleration by a coherent electrostatic hydrogen cyclotron wave with parameters typical of the auroral plasma above 1 earth radius. The fraction of the initial ion population undergoing heating depends strongly on the mass, charge and initial temperature of the ion species, with O(+) ions only heated when their initial temperature is approximately greater than the hydrogen temperature and the lighter ions able to be heated even when cold, due to cyclotron resonant stochastic heating.

Singh, N.↗
NASA NTRS1981

Evidence for the acceleration of ionospheric O/+/ in the magnetosheath of Venus

Plasma spectra from 12 orbits of the Pioneer-Venus Orbiter are reported which suggest the presence of ionospheric material in the magnetosheath plasma near and sunward of the terminator plane. Each spectrum shows a high E/q peak, consistent with O(+) moving at a speed lower than or comparable to that of the ambient magnetosheath plasma. It is pointed out that even though the data set is limited, the most intense heavy-ion fluxes clearly occur at altitudes less than a few thousand km. With the identification of the energetic component at O(+), the data reveal a trend for the speed of O(+) near the planet to be lower than the local magnetosheath speed, whereas the two speeds are comparable at altitudes above a few thousand km. These data, in combination with related observations that indicate O(+) moving at ambient speed in the distant wake, suggest that ionospheric material is swept up by the magnetosheath, accelerated to ambient speed within a few thousand km, and carried back through the wake region.

Mihalov, J. D.↗
NASA NTRS1981

High-latitude ionospheric model - First step towards a predictive capability

In order to study the plasma density features associated with both weak and strong convection in the winter high-latitude F-region, a simple plasma convection model was combined with an ionospheric-atmospheric composition model. In a model calculation, a field tube of plasma is followed as it moves along a convection trajectory through a moving, neutral atmosphere. The altitude profiles of the ion densities are obtained by solving the appropriate continuity, momentum and energy equations, including many high-latitude processes. The result of following many such plasma field tubes is a time-dependent, three-dimensional ion density distribution for the ions NO(+), O2(+), O(+), N(+), and He(+). The high-latitude ionosphere is covered over one complete day above 42 deg N magnetic latitude, at altitudes of 160-800 km.

Schunk, R. W.↗
NASA NTRS1982

Optical signature of an ionospheric hole

Simultaneous radio and optical diagnostics of a large, artificially-induced ionospheric modification were conducted during the June 1981 launch of a weather satellite. Intensified imaging and photometer observations at 6300 A, along the same ray path as VHF polarimeter measurements of the ionosphere's total electron content (TEC), were made while the rocket plume caused disturbances. A rapid TEC chemical depletion, on the order of -16.8 x 10 to the 12th el/sq cm, caused a burst of 6300 A radiation which expanded over 60 deg of the sky, with a peak intensity of almost 9 k R. Atmospheric diffusion and O(1D) quenching rate theoretical estimates were then tested, using the event as an active space plasma experiment.

Mendillo, M.↗
NASA NTRS1981

The atmosphere and ionosphere of Jupiter

The thermal structure of the upper atmosphere of Jupiter, the composition of the atmosphere and the strength of mechanical mixing, and sources and sinks of ionization in the Jupiter ionosphere are described from Voyager UV spectrometer, radio, IR, and imaging data. A topside ionospheric temperature of 1300 K was observed, along with an energy equilibrium between the plasma and neutral gas in the upper atmosphere. A composite thermal structure is provided, noting a close similarity to earth conditions at upper levels, and enhanced thermal behavior has been detected between the times of solar minimum and maximum activity. Ammonia photochemistry is examined, and measured concentrations of H2, CH4, C2H6, and C2H2 as a function of height are outlined. Eddy diffusion coefficient calculations are carried out, yielding a highest Ly-alpha intensity of 100 million sq cm/sec. The increased exospheric temperature between 1973 and 1980 is stressed to have no known satisfactory explanation.

Atreya, S. K.↗
NASA NTRS1981

On plasma instabilities in the high-latitude ionospheric E region

The use of the Farley-Buneman instability in the high-latitude E region of the earth's ionosphere as a diagnostic tool for ionospheric and solar wind electric fields, and the effect of Farley-Buneman waves on cosmic radio noise events observed on riometers, are discussed. Data are analyzed and presented in support of the hypothesis, suggested by Olesen (1972), that the Slant E condition in polar cap ionograms is a manifestation of the Farley-Buneman instability in the E region. Detailed descriptions are given of the experimental apparatus employed in these investigations.

Dangelo, N.↗
NASA NTRS1982

Spatial irregularities in Jupiter's upper ionosphere observed by Voyager radio occultations

Radio scintillations (at 3.6 and 13 cm) produced by scattering from ionospheric irregularities during the Voyager occultations are interpreted using a weak-scattering theory. Least squares solutions for ionospheric parameters derived from the observed fluctuation spectra yield estimates of (1) the axial ratio, (2) angular orientation of the anisotropic irregularities, (3) the power law exponent of the spatial spectrum of irregularities, and (4) the magnitude of the spatial variations in electron density. It is shown that the measured angular orientation of the anisotropic irregularities indicates magnetic field direction and may provide a basis for refining Jovian magnetic field models.

Hinson, D. P.↗
NASA NTRS1983

Nonstationary coupling between the magnetosphere and ionosphere

Resonant coupling of large scale MHD waves to small scale kinetic Alfven waves is described. The small-scale waves drive field-aligned currents tens of micro A/sqm into the ionosphere with accelerated electrons of energies a few keV. Bounce resonant interaction with standing kinetic Alfven waves may precipitate higher energy electrons. East-west aligned arcs should be thinnest and move polewards relative to the plasma at the poleward edge. Downward travelling wave packets trap electrons between the wave front and the ionosphere whose energy is below the peak energy and whose phase-space density should be independent of the peak energy.

Goertz, C. K.↗
NASA NTRS1982

The chemistry of metastable species in the Venusian ionosphere

Reactions of metastable species are important in determining the densities of minor ions in the Venusian ionosphere. Calculations are carried out in which the coupled continuity and momentum equations are solved for twelve ions and four neutral species in the dayside ionosphere, including O(+)(2D), O(2P), N(2D), and N(2P). Altitude profiles of these metastable species are presented. Their reactions are shown to be a significant source of several minor ions, especially N2(+), CO(+), and N(+). The discrepancies which existed between model and measured densities of these ions are resolved.

Fox, J. L.↗
NASA NTRS1982

The dynamics of the Venus ionosphere. II - The effects of the time scale of the solar wind dynamic pressure variations

The effects on the upper dayside Venus ionosphere of a slow increase in solar wind dynamic pressure are simulated numerically with a one-dimensional (spherically symmetric) Lagrangian hydrodynamical code. The simulation is started with an extended ionosphere in pressure equilibrium with the solar wind at the ionopause. The pressure at the ionopause is gradually increased to five times the initial pressure with rise times of 5, 15, and 30 min. It is found that, for rise times greater than about 10 min, the compression of the ionopause is nearly adiabatic, with the ionopause moving downward at velocities of approximately 1-2 km/sec until it reaches a maximally compressed state, at which time the motion reverses. For short rise times the compression produces a shock wave similar to that occurring in the case of a sudden increase in pressure. The global implications of these processes are discussed within the context of Pioneer Venus observations and future theoretical work on this problem is outlined.

Stein, R. F.↗
NASA NTRS1983

The interaction of flowing plasmas with planetary ionospheres - A Titan-Venus comparison

Voyager I data from the moon Titan's wake are employed to model the external flow direction and, in comparison with magnetotail observations of Venus, show that the magnetic field may change in response to the presence of flux tubes. The Titan magnetic field was measured at distances as close as 2.7 Titan radii, showing final, unperturbed fields directly southward, while a northern lobe was observed which pointed away from Titan. The central portion of the pattern was displaced radially toward Saturn relative to the direction of corotation. Pioneer Venus orbiter data have shown that Venus, like Titan, is a nonmagnetic body, and both objects have displayed a two-lobe wake field with oppositely oriented fields separated by a neutral sheet and lowered field magnitudes on flux tubes near the dayside ionospheres. It is suggested that the asymmetries in the wake structure are due to coupling of different regions of the wakes with the dayside or nightside ionosphere.

Kivelson, M. G.↗
NASA NTRS1983

Particle and wave observations of low-altitude ionospheric ion acceleration events

Two sounding rockets were launched into the expansive phases of two auroral substorms and passed through source regions of transversely accelerated ionospheric ions. Energetic ion and electron, wave, and ambient plasma observations were made. The events were observed in the 400-600 km range and resulted in the ion energization of hundreds of electron volts. In the acceleration region the ionospheric ion velocity distribution function in the direction perpendicular to the local magnetic field showed a non-Maxwellian, high-energy tail. Plasma density was lower than theoretical quiescent values. Strong thermal ion drift was observed only in the perpendicular direction. Large-amplitude, low-frequency fluctuations in plasma density were present along with a number of different wave modes. The characteristics of the ion energy spectra agreed with a model of ion cyclotron acceleration and energy loss due to ion-neutral collisions.

Yau, A. W.↗
NASA NTRS1982

HF produced ionospheric electron density irregularities diagnosed by UHF radio star scintillations

Three observations of radio star intensity fluctuations at UHF are reported for HF ionospheric modification experiments carried out at the Arecibo Observatory. Two observations at 430 MHz and one at 1400 MHz suggest that the the thin phase screen theory is a good approximation to the observed power spectra. It is noted, however, that the theory has to be extended to include antenna filtering. This type of filtering is important for UHF radio star scintillations since the antenna usually has a narrow beamwidth. HF power densities of less than 37 microwatts/sq m incident on the ionosphere give rise to electron density irregularities larger than 13% of the ambient density (at 260 km) having scale sizes of approximately 510 m perpendicular to the geomagnetic field. The irregularities are found to form within 20-25 s after the HF power is turned on. The drift velocities of the irregularities can be estimated from the observed power spectra.

Frey, A.↗