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At least 685 records · Page 38

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NASA NTRS1975

The lower ionosphere of Mars

Recently reported (Savich et al. 1975) results of dual frequency (0.94 and 3.75 GHz) radio occultation experiments indicated the existence of a nocturnal ionospheric layer between the Martian surface and 80 km altitude. It is suggested that the observed ionosphere is due to ionization by galactic cosmic rays. The observed nocturnal electron density profile is compared with that of the negative ion model assumed by Whitten et al. (1971). The profiles are similar below 50 km if the negative ion concentration is reduced by a factor of 10.

Whitten, R. C.↗

NASA NTRS1976

Electron content of the ionosphere and the plasma sphere on the basis of ATS-6-Data, NNSS-data, and ionograms

The reported investigation takes into account data obtained with the aid of the geostationary satellite ATS-6, the satellites of the U.S. navy navigation system (NNSS) at an altitude between 900 and 1200 km, and the satellites ISIS 1 and ISIS 2. The altitude range between ground and ATS-6 is divided into two regions, including the 'ionosphere', involving the region with an upper limit of 2000 km, and the 'plasma sphere', involving the region above an altitude of 2000 km. Data concerning the electron content obtained from different sources are compared, taking into account discrepancies between ionogram-derived values and values computed on the basis of satellite measurements. Attention is also given to the vertical electron content of the ionosphere on the basis of a combination of data obtained with the aid of the ATS-6 and the NNSS.

Leitinger, R.↗

NASA NTRS1976

Io's atmosphere and ionosphere - New limits on surface pressure from plasma models

The paper studies charge particle impact as a mechanism for the production of Io's ionosphere. Pioneer 10 thermal plasma measurements and magnetospheric plasma models which explain the observed spatial distribution of neutral hydrogen and sodium atoms in the vicinity of Jupiter's satellite Io imply electron fluxes of about 10 to the 10th/sq cm/s. The fluxes and the temperature (about 100 eV) of this plasma suggest that electron impact ionization is the dominant process in forming the ionosphere of Io. It is found that the surface number density of the neutral species required to match the observed electron density profiles is about 10 to the 9th/cu cm or less. This value is two orders of magnitude lower than previous estimates.

Johnson, T. V.↗

NASA NTRS1976

The day-to-day variability in ionospheric electric fields and currents

The daily variations in ionospheric drift velocities are examined from incoherent scatter measurements at Millstone Hill. The data with summed Kp greater than 24 behave differently from those with low magnetic activity and basically follow the convection pattern but have large day-to-day variations. The influence of the magnetic conjugate point is discussed, and solar cycle variations are examined in conjunction with geomagnetic variations. Ionospheric currents calculated by using a semidiurnal neutral wind model are in good agreement with ground-based magnetograms for low magnetic activity, but the E region neutral wind model appears to be applicable only to this case.

Kirchhoff, V. W. J. H.↗

NASA NTRS1976

The topside ionosphere - A region of dynamic transition

The review article concentrates on dynamic processes at work in the topside ionosphere (between the F2 peak and about 3000 km) where the H ion dominates and ionic reactions can be neglected. The history of ionosphere and plasmasphere research using radio waves is reviewed. Low-speed and high-speed multispecies plasma ion flow is studied with various models (13-moment approximation, 5-moment approximation, kinetic models of the polar wind). Experimental observations of the plasmapause, results of vertical soundings of the topside, and global pole-to-pole distributions of ion composition, plasma temperature, and electron density are reviewed.

Banks, P. M.↗

NASA NTRS1976

Mercury and Mars - The role of ionospheric conductivity in the acceleration of magnetospheric particles

Although Mercury and Mars appear to have magnetospheres of comparable size, Mercury's magnetosphere accelerates charged particles, whereas Mars' magnetosphere apparently does not. We propose that this difference results from the fact that rapid steady-state convection, and the associated particle acceleration, cannot occur in a Martian magnetosphere because of its connection to a highly conducting ionosphere. Mercury, which has no conducting ionosphere and probably an insufficiently conducting surface, can exhibit rapid solar-wind-induced convection and hence particle acceleration in its magnetospheric tail.

Hill, T. W.↗

NASA NTRS1977

Chemical depletion of the ionosphere

A theoretical study of the chemical and gas dynamical processes resulting from the release of reactive gases into the daytime ionosphere is discussed. Only point releases, such as from an explosion or a pulsed jet, are considered. Some scientific uses of the artificial reduction of the ionospheric plasma are considered.

Bernhardt, P. A.↗

NASA NTRS1976

Line-of-sight electron density gradients as deduced from an empirical ionospheric model

A topside ionospheric model (Bent Ionospheric Model) was developed for an accurate prediction of integrated total electron content (TEC), from a global data acquired for the years 1962 to 1969. In this paper the effects of line-of-sight electron density gradients on ground to satellite measurements are discussed. The results of analyses show that in the presence of increasing density gradients, deduced values of vertical electron content or slab thicknesses will be too large, while for decreasing gradients these values will be smaller than they should be.

Nesterczuk, G.↗

NASA NTRS1977

The influence of convection electric fields on thermal proton outflow from the ionosphere

The continuity, momentum and energy hydrodynamic equations for an O(+)-H(+) ionosphere have been solved self-consistently for steady state conditions when a perpendicular (convection) electric field is present. Comparison of the H(+) temperature profiles obtained with and without the electric field show that the effect of the electric field is to enhance the H(+) temperature at high altitudes from about 3600 to 6400 K. Due to ion heating by the electric field, there is a net reduction of O(+) in the F2-region as compared with the case of a nonconvecting ionosphere. When the reduction of O(+) is neglected, the electric field acts to increase the H(+) outward flux. However, when the reduction of O(+) is included, there is a net reduction in the outward H(+) flux. Nevertheless, the convection electric field still results in an increase in the rate of depletion of the F-region ionization due to H(+) outflow, by a factor of 2.2 for a 100 mV/m electric field.

Raitt, W. J.↗

NASA NTRS1977

Determination of thermospheric quantities from simple ionospheric observations using numerical simulation

Measured ionospheric electron content and peak electron concentration data are introduced into a numerical simulation of the ionosphere to yield values of induced plasma drifts and exospheric neutral temperatures consistent with the observations. Data collected on 23-24 March 1970 on the East Coast of the U.S.A. are analyzed and the results are in agreement with incoherent radar measurements at Millstone Hill, Massachusetts. Neutral winds and meridional exospheric temperature gradients that give rise to the computed plasma drifts are calculated through the use of a dynamic model of the thermosphere.

Antoniadis, D. A.↗

NASA NTRS1977

The upper ionosphere of Titan

Photoionization of the upper atmosphere of Titan by sunlight is expected to produce a substantial ionospheric layer. One-dimensional forms of the mass, momentum, and energy conservation equations for ions and electrons have been solved along with electron number densities of about 1000/cu cm, using various model atmospheres. The significant ions in a CH4-H2 atmosphere are H(+), H3(+), CH5(+), CH3(+), and C2H5(+). Electron temperatures may be as high as 1000 K, depending on the abundance of hydrogen in the high atmosphere. Interaction of the solar wind with the ionosphere is also discussed.

Whitten, R. C.↗

NASA NTRS1977

The large-scale ionospheric electric field - Its variation with magnetic activity and relation to terrestrial kilometric radiation

Four days of simultaneous auroral zone electric field measurements on balloons flown from six sites spanning 180 deg of magnetic longitude have been analyzed. The average electric field behavior during this magnetically quiet epoch is consistent with earlier single-point measurements, although the average auroral zone electric field was more affected by corotation effects than it was during more disturbed times. When these data, which primarily reflect the large-scale (several hundred kilometer) ionospheric electric field, are mapped to the equator, a steady dawn to dusk component is apparent only on the average, while instantaneously the field is quite variable. The ionospheric electric field during isolated substorms is shown to have differing signatures east and west of 2200 LT. A worldwide positive correlation is shown to exist between the auroral zone electric field strength and the intensity of terrestrial kilometric radiation.

Holzworth, R. H.↗

NASA NTRS1977

The ionospheres of Saturn, Uranus, and Neptune

Models of the ionospheres of Saturn, Uranus, and Neptune are presented. It is postulated that galactic cosmic-ray ionization is an important component of these ionospheres. For example, in the case of Neptune, the level of ionization caused by cosmic rays is comparable with that due to solar extreme-ultraviolet (EUV) radiation. The existence of cosmic-ray, as well as solar EUV-produced ionization, could be a valuable diagnostic tool for investigating the atmospheric thermal structure of those planets.

Capone, L. A.↗

NASA NTRS1977

Simultaneous in situ magnetospheric and ionospheric detection of detached plasmas

On January 19, 1972, in situ measurements by Explorer 45, orbiting in the magnetosphere near the equatorial plane, and ISIS 2, in a circular polar orbit at 1400 km, simultaneously detected patches of enhanced ionization outside the main body of the plasmasphere. The magnetospheric plasma region extended between (geomagnetic latitude) L values 3.4-4.8 and the ionospheric electron density enhancement extended between L values 3.6-4.4. The two plasma features were detected near 22 hours magnetic local time (MLT). Based on a number of observations, it is inferred that the plasma density enhancement persisted for more than 5 hours and extended over at least 2 hours in MLT near L = 5. These results provide experimental evidence that some detached magnetospheric plasma regions are signatures of a flux tube containing enhanced ionization throughout a volume extending from the topside ionosphere out to the equator.

Miller, N. J.↗

NASA NTRS1977

Ionospheric and magnetospheric plasmapauses'

During August 1972, Explorer 45 orbiting near the equatorial plane with an apogee of about 5.2 R sub e traversed magnetic field lines in close proximity to those simultaneously traversed by the topside ionospheric satellite ISIS 2 near dusk in the L range 2-5.4. The locations of the Explorer 45 plasmapause crossings during this month were compared to the latitudinal decreases of the H(+) density observed on ISIS 2 near the same magnetic field lines. The equatorially determined plasmapause field lines typically passed through or poleward of the minimum of the ionospheric light ion trough, with coincident satellite passes occurring for which the L separation between the plasmapause and trough field lines was between 1 and 2. Vertical flows of the H(+) ions in the light ion trough as detected by the magnetic ion mass spectrometer on ISIS were directed upward with velocities between 1 and 2 kilometers/sec near dusk on these passes. These velocities decreased to lower values on the low latitude side of the H(+) trough but did not show any noticeable change across the field lines corresponding to the magnetospheric plasmapause.

Grebowsky, J. M.↗

NASA NTRS1977

Nighttime thermospheric winds at low latitudes deduced from AE-C ionospheric measurements

The paper describes a method for determining the height of the F2 peak and of neutral wind velocities in the tropical nighttime ionosphere from measurements of ionospheric plasma parameters. The ratio of the O I 6300-A column density, observed above the AE-C satellite, to its volume emission rate, at the satellite, was shown to be dependent on the satellite height, the exospheric temperature, and the height of the F2 peak. The analysis of simultaneous nighttime measurements of the electron density, the O2(plus) density, and the 6300-A vertical column intensity has led to the values of the height of the F2 peak. The sum of the neutral wind velocities in the magnetic meridian at magnetically conjugate points has been inferred from the height difference in the F2 peak at the conjugate points.

Bittencourt, J. A.↗

NASA NTRS1977

Stimulated plasma waves in the ionosphere

The reported discussion is concerned with longitudinal waves associated with electron motions. These waves are easily stimulated in the ionosphere by rocket- and satellite-borne RF sounders. Most of the observations of stimulated plasma waves in the ionosphere are based on ionograms obtained from the sounders carried on board five satellites, including Explorer 20, Alouette 1 and 2, and ISIS 1 and 2. The majority of the observations can be explained by considering the propagation of the sounder-stimulated plasma waves. Attention is given to aspects of plasma wave dispersion, linear phenomena, plasma wave instabilities and nonlinear phenomena, unexplained phenomena, diagnostic applications, geophysical and astrophysical applications, and a number of experiments planned for the future.

Benson, R. F.↗

NASA NTRS1978

On a method computing transient wave propagation in ionospheric regions

A consequence of an exoatmospheric nuclear burst is an electromagnetic pulse (EMP) radiated from it. In a region far enough away from the burst, where nonlinear effects can be ignored, the EMP can be represented by a large-amplitude narrow-time-width plane-wave pulse. If the ionosphere intervenes the origin and destination of the EMP, frequency dispersion can cause significant changes in the original pulse upon reception. A method of computing these dispersive effects of transient wave propagation is summarized. The method described is different from the standard transform techniques and provides physical insight into the transient wave process. The method, although exact, can be used in approximating the early-time transient response of an ionospheric region by a simple integration with only explicit knowledge of the electron density, electron collision frequency, and electron gyrofrequency required. As an illustration of the method, it is applied to a simple example and contrasted with the corresponding transform solution.

Gray, K. G.↗