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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Solar corona electron density distribution

The paper discusses the three and one-half months of single-frequency time delay data which were acquired from the Helios 2 spacecraft around the time of its solar occultation. The excess time delay due to integrated effect of free electrons along the signal's ray path could be separated and modeled following the determination of the spacecraft trajectory. An average solar corona and equatorial electron density profile during solar minimum were deduced from the time delay measurements acquired within 5-60 solar radii of the sun. As a point of reference at 10 solar radii from the sun, an average electron density was 4500 el/cu cm. However, an asymmetry was found in the electron density as the ray path moved from the west to east solar limb. This may be related to the fact that during entry into occultation the heliographic latitude of the ray path was about 6 deg, while during exit it was 7 deg. The Helios density model is compared with similar models deduced from different experimental techniques.

Esposito, P. B.↗
NASA NTRS1984

Ionospheric electron density irregularities observed by satellite-to-satellite, dual-frequency, low-low Doppler tracking link

A low-low, satellite-to-satellite, dual-frequency, Doppler tracking experiment was performed. The data are analyzed here for irregularities in electron density at the altitude of 212 km. The differential Doppler data with the relative motion term removed are integrated to obtain a representation of the electron density variation along the satellite path. Well-known large-scale features such as the equatorial geomagnetic anomaly and day/night ionization level differences are clearly observed in the integrated data. The larger crest of the morning geomagnetic anomaly is seen to occur in the southern (winter) hemisphere in agreement with previous observations. In addition, a sharp peak in the electron density at the day-to-night transition point is observed in two consecutive revolutions. This effect may be due to the previously postulated atmospheric shock wave generated by supersonic motion of the terminator.

Estes, R. D.↗
NASA NTRS1984

The electron density in the galactic center as derived from the S III 18.71/33.47 micron line ratio

High signal-to-noise ratio measurements of the S III lines 18.71 and 33.47 microns from the galactic center, Sgr A West, are reported. The average electron density is calculated for the S III-emitting region and is found to be 1800 + or - 500 per cu cm. This value is much less than the rms electron density of the clumps as derived from radio observations. The implications for various models are discussed. The S III result is consistent with the electron density previously derived from low signal-to-noise ratio measurements of the O III lines at 88 and 52 microns, if newer values are used for the O III atomic constants.

Herter, T.↗
NASA NTRS2005

Electron Density Images of the Middle and High Latitude Magnetosphere in Response to the Solar Wind

Electron density images and plasma dynamics in the middle and high latitude dayside magnetosphere are studied with the IMAGE/RPI remote measurements of the electron densities along magnetic field lines, measured before and during a magnetic storm when the solar wind and interplanetary magnetic field (IMF) impinging on the magnetopause varied considerably. Several regions of different density distribution characteristics, including plasmasphere, plasma trough, sub-auroral/auroral density depletion, density enhancements in the aurora/cusp, and polar cap, are identified in 'two dimensional images', i.e., along the satellite orbit and field lines. The plasma dynamics, such as the plasma refilling in the outer plasmasphere and the plasma acceleration in the aurora/cusp region are inferred from density gradients along the field lines. It is shown that the densities and locations of the plasma regions vary in accordance with the solar wind, particularly with the IMF variations for the case examined. The changes in these regions reflect the way the magnetosphere reconfigures in response to changes in the solar wind.

Tu, Jiannan↗
NASA NTRS1983

Saturn's ionosphere: Inferred electron densities

During the two Voyager encounters with Saturn, radio bursts were detected which appear to have originated from atmospheric lightning storms. Although these bursts generally extended over frequencies from as low as 100 kHz to the upper detection limit of the instrument, 40 MHz, they often exhibited a sharp but variable low frequency cutoff below which bursts were not detected. We interpret the variable low-frequency extent of these bursts to be due to the reflection of the radio waves as they propagate through an ionosphere which varies with local time. We obtain estimates of electron densities at a variety of latitude and local time locations. These compare well with the dawn and dusk densitis measured by the Pioneer 11 Voyager Radio Science investigations, and with model predictions for dayside densities. However, we infer a two-order-of-magnitude diurnal variation of electron density, which had not been anticipated by theoretical models of Saturn's ionosphere, and an equally dramatic extinction of ionospheric electron density by Saturn's rings.

Kaiser, M. L.↗
NASA NTRS1984

Saturn's ionosphere - Inferred electron densities

During the two Voyager encounters with Saturn, radio bursts were detected which appear to have originated from atmospheric lightning storms. Although these bursts generally extended over frequencies from as low as 100 kHz to the upper detection limit of the instrument, 40 MHz, they often exhibited a sharp but variable low frequency cutoff below which bursts were not detected. We interpret the variable low-frequency extent of these bursts to be due to the reflection of the radio waves as they propagate through an ionosphere which varies with local time. We obtain estimates of electron densities at a variety of latitude and local time locations. These compare well with the dawn and dusk densities measured by the Pioneer 11 Voyager Radio Science investigations, and with model predictions for dayside densities. However, we infer a two-order-of-magnitude diurnal variation of electron density, which had not been anticipated by theoretical models of Saturn's ionosphere, and an equally dramatic extinction of ionospheric electron density by Saturn's rings. Previously announced in STAR as N84-17102

Kaiser, M. L.↗
NASA NTRS1981

Electron densities for 10 planetary nebulae derived from the semiforbidden C III lambda 1907/1909 ratio. II

Electron densities for IC 351, IC 2165, J900, IC 3568, NGC 6644, NGC 6891, IC 4997, NGC 7009, Hu 1-2, and IC 5217 are derived from high-dispersion semiforbidden C III spectrograms. For seven of these nebulae, the derived electron density is larger than the values derived from either surface brightness measurements or forbidden line ratios. Only one object, Hu 1-2, shows pronounced splitting of the semiforbidden C III emission lines due to a large expansion velocity.

Feibelman, W. A.↗
NASA NTRS1976

Equilibrium and nonequilibrium electron density measurements in transient shock-heated hydrogen-helium plasmas

In the NASA planetary program, atmospheric entry probe missions to Jupiter, Saturn, and Uranus are potential programs now being planned for the 1980's. The work reported in this paper is concerned with predicting the electron density, and resulting radiative emission from the shock layer which must be accommodated by the entry probe heatshield. Within the hydrogen-helium plasma surrounding the forward heatshield, there are regions of near thermochemical equilibrium whose properties are predictable - however, there are uncertainties in these electron density calculations necessitating further measurements by H-beta line broadening and holographic interferometer fringe shift as reported here. There is good agreement between the results obtained from the holographic measurements and the spectroscopic measurements which lends confidence to each of the two completely independent diagnostic techniques. The equilibrium electron density determined from the experimental measurements is somewhat higher than that predicted.

Livingston, F. R.↗
NASA NTRS1977

A model of F2 peak electron densities in the main trough region of the ionosphere

An empirical model of the peak electron densities in the region of the northerly main trough in the ionospheric F region is presented. The model was derived from measurements made by the satellites Alouette I and II and is in the form of a multiplicative modification factor to the CCIR peak electron density model. The model is a computer program which, when provided with the location, universal time, day number, sunspot number, and Kp index, provides the modification factor, the CCIR model prediction of Nm F2, and the new prediction including the effect of the trough. The model is expected to be of considerable use for propagation calculations in the affected region.

Halcrow, B. W.↗
NASA NTRS1974

The evolution of electron density and temperature distributions in the topside ionosphere during magnetic storms

The latitudinal distributions of electron density and temperature during geomagnetic storms in the mid-latitude topside ionosphere are observed to change in a manner than can be related to the evolution of ring current particle populations. The region of auroral precipitation is characterized by correlated increases in electron temperature and density. Equatorwards of this region, there is a broad belt of elevated electron temperatures and depressed electron densities which is usually much broader than any stable auroral red arc distinguishable from the ground, but which is nevertheless the same basic physical phenomenon. The changes of position of this belt can be related to prior bursts of geomagnetic activity and injection of ring current particles into the magnetosphere.

Cole, K. D.↗
NASA NTRS1984

Partial Reflection D-region Electron Densities

The differential absorption technique of measuring electron densities as a function of height in the D region is discussed. In the basic experiment, pulses of medium or high frequency, usually at a fixed frequency (2 to MHz), are radiated upwards with known wave polarizatin (usually linear or circular) from a transmitter at ground level. Partial reflections, from ionospheric scatterers at heights below the E region, are received at the ground, and are resolved into two characteristic components, the ordinary (0) and extraordinary (E) modes whose amplitude ration A(x)/A(o) is then measured as a function of height, h. The heights of these are determined by delay times, the group retardation being minimal in the undisturbed D-region. The electronic system can be very simple. Power splitters and quadrature networks to separate the A(x) and A(o) components are commercially available at low prices and an A-D converter, height-gate system, and microcomputer allows the real-time calculation of mean amplitudes. The ratio of the coefficients of reflection of the two modes, as they originate at each reflection height is then calculable.

Manson, A. H.↗