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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

On the causes of spectral enhancements in solar wind power spectra

Enhancements in power spectra of the solar-wind ion flux in the frequency neighborhood of 0.5 Hz had been noted by Unti et al. (1973). It was speculated that these were due to convected small-scale density irregularities. In this paper, 54 flux spectra calculated from OGO 5 data are examined. It is seen that the few prominent spectral peaks which occur were not generated by density irregularities, but were due to several different causes, including convected discontinuities and propagating transverse waves. A superposition of many spectra, however, reveals a moderate enhancement at a frequency corresponding to convected features with a correlation length of a proton gyroradius, consistent with the results of Neugebauer (1975).

Unti, T.↗
NASA NTRS1976

Apollo 16 far ultraviolet imagery of the polar auroras, tropical airglow belts, and general airglow

Far-ultraviolet imagery of the earth in the wavelength ranges from 1050 to 1600 A and from 1250 to 1600 A was obtained from the lunar surface during the Apollo 16 mission on Apr. 21, 1972. The images have an angular resolution of about 2 arcmin (230-km linear resolution) and have been quantitatively analyzed to obtain absolute intensities and spatial distributions of the polar auroras (both wavelength ranges), the day and night airglow, and tropical airglow belts (1250-A to 1600-A wavelength range). The observations are consistent with previous results obtained from the OGO-4 spacecraft, but they have also provided details on the spatial distributions of the various emissions over an entire hemisphere at a single time. A general night airglow, at least in the Northern Hemisphere, is indicated.

Carruthers, G. R.↗
NASA NTRS1976

High-latitude troughs and the polar cap boundary

OGO 6 observations of troughs in the thermal plasma densities in the topside ionosphere are discussed. Ion mass spectrometer measurements were correlated with energetic electron detector and electric field measurements. It is shown that the variation of ion composition at high latitudes is complex and frequently characterized by mid-latitude and high-latitude density depression. Prominent high-latitude troughs in the atomic ion (H, He, O) distributions were seen to lie frequently near the polar cap boundary. This indicates that these troughs are unrelated to the plasmapause which is found on closed magnetic field lines away from the trapping boundary. The production of the high-latitude troughs is shown to be related to enhancements in the soft electron flux and/or to the convection electric field.

Grebowsky, J. M.↗
NASA NTRS1976

Dependence of the latitude of the cleft on the interplanetary magnetic field and substorm activity

The latitudinal motion of the cleft (the polar cusp) associated with the southward interplanetary magnetic field (IMF) and substorm activity is examined. The cleft location is identified on the basis of the location of midday auroras and of electron precipitation by the OGO 4 and ISIS 1 satellites. It is found that the IMF and substorm activity control independently the latitude of the cleft and that they can shift the cleft location by 3 or 4 deg under average conditions.

Kamide, Y.↗
NASA NTRS1976

Diurnal and seasonal variations in atomic and molecular oxygen inferred from Atmosphere Explorer-C

Mass-spectrometer measurements of O and N2, obtained with the Atmosphere Explorer-C satellite during December 1974 and January 1975, are used to derive the O2 concentration near 250 km from several ionization reactions. In order to separate temperature effects from diffusion effects, the measured O and inferred O2 concentrations are employed to determine, under the assumption of diffusive equilibrium, the O/N2 and O2/N2 ratios at 120 km. It is found that the latitudinal and diurnal variations in the O concentration at 120 km are consistent with previous results obtained with OGO 6 and that the O2 concentration in the Northern (winter) Hemisphere is about twice as high as that in the Southern (summer) Hemisphere. The possible importance of photodissociation in the diurnal O2 variations is discussed.

Mayr, H. G.↗
NASA NTRS1976

Behavior of the sodium and hydroxyl nighttime emissions during a stratospheric warming

The behavior of the sodium and hydroxyl nighttime emissions during a stratospheric warming has been studied principally by use of data from the airglow photometers on the OGO 4 satellite. During the late stages of a major warming, both emissions increased appreciably, with the sodium emission returning to normal values prior to the decrease in the hydroxyl emission. The emission behaviors are attributed to temperature and density variations from 70 to 94 km, and a one-dimensional hydrostatic model for that altitude range is used to calculate the effects on the emissions and on the mesospheric ozone densities. These results support the existence of a warming in the upper part of the mesosphere that is correlated with a major stratospheric warming.

Walker, J. D.↗
NASA NTRS1975

On the quiet-time increases of low energy cosmic ray electrons

With a detector on board the OGO-5 satellite, the flux and energy spectrum of electrons in the 10-30 MeV range has been continuously monitored from 1968 to 1972. Sudden increases by factors of up to 300 percent have been observed during solar quiet periods. These 'Quiet-Time Increases' abruptly die out above 30 MeV and correlate well with identical increases reported at lower energies leading to a flat relative energy spectrum. A large fraction of these electrons is most likely of Jovian origin.

Lheureux, J.↗
NASA NTRS1976

Satellite measurements of ion composition and temperatures in the topside ionosphere during medium solar activity

Information on both ion density and temperature is obtained from analysis of Retarding Potential Analyzer data from the OGO-4 and Explorer-31 satellites. Results obtained from data in the altitude range of 700-2000 km during medium solar activity are presented. An attempt is made to describe the major altitude variations of ion densities and temperatures at middle and low latitudes. The transition heights, where the heavier and lighter ions are equal, are found to be about 1600 and 1300 km at middle and low latitudes, respectively, for daytime and 700 km at night for middle latitudes. Based on the observed data and using diffusive equilibrium as a first-order approximation, topside ionospheric composition models are given for medium solar activity.

Goel, M. K.↗
NASA NTRS1976

The interpretations of ultraviolet observations of comets

The paper summarizes recent cometary UV observations, most of which were made in Ly-alpha light with instruments aboard earth-orbiting satellites. These include OAO-2 observations of comets Bennett and Tago-Sato-Kosaka, OGO-5 observations of comets Bennett and Encke, and numerous observations of comet Kohoutek. Models for the production of cometary hydrogen atoms are described, including the fountain, syndyname, and parent-daughter models. Calculations of emission line profiles and multiple-scattering effects are also discussed. Results of observations and interpretations are reviewed for each cited comet, far-UV observations in other emission lines are noted, and the use of comets as solar-wind probes is considered. It is concluded that the results of the present cometary Ly-alpha observations strongly support the concept of an icy conglomerate solid cometary nucleus and suggest water to be one of the most abundant molecules in comets.

Keller, H. U.↗
NASA NTRS1976

Net field-aligned currents observed by Triad

The existence of a net current flowing into or away from the ionosphere in the current layer is inferred from the Triad-satellite magnetometer observation of a steplike level shift in the east-west component of the magnetic field at 800 km altitude. The current direction is toward the ionosphere on the morning side and away from it on the afternoon side. The current layer is identified as the same layer that was observed by the Ogo 5 satellite at much higher altitudes. Thus, the field-aligned currents observed by Triad must be considered to be an important element in the electrodynamical coupling between the distant magnetosphere and the ionosphere.

Sugiura, M.↗
NASA NTRS1976

ELF hiss associated with plasma density enhancements in the outer magnetosphere

The low-frequency narrow hiss bands associated with plasma-density enhancements in the magnetosphere near and beyond L = 4 have been studied with the search coil magnetometer and ion mass spectrometer data from OGO 5. ELF hiss is found to accompany most of the detached plasmas in the outer magnetosphere and to be sharply limited by the steep ion-density gradient at their boundary. The observations indicate that the hiss originates in and is ducted by the plasma-density enhancements. In a particularly favorable case after an interval of low AE and Dst indices, a series of enhanced plasma-density peaks was observed between L = 4 and L = 6 in the afternoon local-time sector. In this case, it was possible to develop an empirical relation among hiss amplitude, plasma density, and L by using in situ simultaneous measurements.

Chan, K.-W.↗
NASA NTRS1976

Field-aligned precipitation of greater than 30-keV electrons

A search through 2-3 months of data from Ogo 6 has revealed about 10 cases of field-aligned precipitation of electrons at energies greater than 30 keV. Brief descriptions are given of the four most spectacular of these events, in which the ratio between precipitated and trapped fluxes reached about 100 in one case. Preliminary indications are that such events occur mainly in the evening and midnight sectors and at high geomagnetic latitudes (usually at or above the trapping boundary for electrons with energies greater than 30 keV).

Williams, D. J.↗
NASA NTRS1976

Diurnal variation of thermal plasma in the plasmasphere

All of the OGO-5 light ion density measurements were used to determine the average global topology of the equatorial plasmasphere density distribution. The variation of the light ion equatorial density at L less than or equal to 3.2 with local time was deduced by determining the average density observed within one hour of a specific local time and within 0.1 of a given L coordinate. The average H(+) density showed a semidiurnal variation with peaks near noon and midnight. The He(+) observations also revealed multiple peaks throughout the day but with smaller amplitudes than those of H(+). At L above 3.2 plasma trough conditions increase the scatter of densities. The average variation of the H(+) density with L within the plasmasphere is found to be steepest near midnight and can be least-squares fitted equally well to either an exponential variation or to a power law.

Chen, A. J.↗
NASA NTRS1976

Critical electron pitch angle anisotropy necessary for chorus generation

Simultaneous wave, resonant-particle, and ambient-plasma data from OGO 5 for chorus emissions on August 15, 1968, were found consistent with the theoretical critical pitch-angle-anisotropy condition for whistler-mode instability by Doppler-shifted electron cyclotron resonance. Local generation, as determined by wave normal measurements, occurred only when the pitch-angle anisotropy of resonant electrons required for instability substantially exceeded the critical anisotropy defined by Kennel and Petschek (1966).

Burton, R. K.↗
NASA NTRS1976

Structure of a quasi-parallel, quasi-laminar bow shock

A thick, quasi-parallel bow shock structure was observed with field and particle detectors of both HEOS 1 and OGO 5. The typical magnetic pulsation structure was at least 1 to 2 earth radii thick radially and was accompanied by irregular but distinct plasma distributions characteristic of neither the solar wind nor the magnetosheath. Waves constituting the large pulsations were polarized principally in the plane of the nominal shock, therefore also in the plane perpendicular to the average interplanetary field. A separate interpulsation regime detected between bursts of large amplitude oscillations was similar to the upstream wave region magnetically, but was characterized by disturbed plasma flux and enhanced noise around the ion plasma frequency. The shock structure appeared to be largely of an oblique, whistler type, probably complicated by counterstreaming high energy protons. Evidence for firehose instability-based structure was weak at best and probably negative.

Greenstadt, E. W.↗
NASA NTRS1977

Thermospheric temperature, density, and composition: New models

The models essentially consist of two parts: the basic static models, which give temperature and density profiles for the relevant atmospheric constituents for any specified exospheric temperature, and a set of formulae to compute the exospheric temperature and the expected deviations from the static models as a result of all the recognized types of thermospheric variation. For the basic static models, tables are given for heights from 90 to 2,500 km and for exospheric temperatures from 500 to 2600 K. In the formulae for the variations, an attempt has been made to represent the changes in composition observed by mass spectrometers on the OGO 6 and ESRO 4 satellites.

Jacchia, L. G.↗
NASA NTRS1977

Atomic oxygen between 80 and 120 km: Evidence for a rapid spatial variation in vertical transport near the ionosphere

Analysis of OGO-6 OI green line photometer results was carried out for 8 cases when the alignment of the spacecraft was such that local emission rates could be determined below the altitude of maximum emission and down to about 80 km. Results show a variation on a scale of 6 deg to 8 deg in latitude between regions where the emission rate increases rapidly between 90 and 95 km and regions where it increases slowly from 80 km to 95 km. Latitude-altitude maps of iso-emissivity contours and iso-density contours for oxygen concentration are presented. The latter are computed under 3 assumptions concerning excitation mechanisms. Comparisons of the spatial variations of oxygen density with the results of a time dependent theory suggest the regions of strong downward transport alternate on a scale of about 1000 km with regions of weak transport near 90 km. In the first case conversion of O to O3 at night appears to be overwhelmed by downward transport of O.

Donahue, T. M.↗
NASA NTRS1976

Quiet-time increases of low-energy electrons - The Jovian origin

With a detector on board the OGO-5 satellite, the flux and energy spectrum of electrons in the 10-200-MeV range has been continuously measured from 1968 to 1971. Sudden increases in intensity by factors of up to 300% have been observed during solar quiet times. It is shown that these increases are nearly independent of energy up to about 25 MeV and disappear rapidly above that energy. The frequency of the increases peaks every 13 months at a time following the crossing by earth of the interplanetary magnetic-field line which passes the vicinity of the planet Jupiter. Most of the increases occur in a period of 3 to 5 months following this crossing and often appear to be 27 days apart. A Jovian origin for these electrons and their mode of transport to the inner solar system are discussed.

Lheureux, J.↗