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NASA NTRS1972

The light-ion trough, the main trough, and the plasmapause.

Although the plasmapause has been detected as a global phenomenon by both VLF and ion composition measurements, the electron and ion density troughs have been identified primarily as nightside features. This problem, as well as the difficulty in explaining various inconsistencies in relating the position of the plasmapause and the ionization trough, is explained by a close examination of the ion composition, generally unavailable in previous trough studies. In particular, ion composition results from the polar-orbiting Ogo satellites identify the persistence of a pronounced light-ion trough (LIT) in H(+) and He(+), often identified by order-of-magnitude decreases in the light-ion concentrations, that occurs within a few degrees of latitude and reaches residual concentration levels of 100 to 1000 ions/cu cm near 60 deg dipole latitude. The LIT, observed both within the thermosphere and at high latitudes in the magnetosphere, has been correlated directly with the VLF whistler identification of the plasmapause.

Taylor, H. A., Jr.↗

NASA NTRS1972

Evidence for a common origin of the electrons responsible for the impulsive X-ray and type III radio bursts.

Observations of impulsive solar flare X-rays greater than or about equal to 10 keV made with the OGO-5 satellite are compared with ground-based measurements of type III solar radio bursts in 10- to 580-MHz range. It is shown that the times of maxima of these two emissions, when detectable, agree within about 18 sec. This maximum time difference is comparable to that between the maxima of the impulsive X-ray and impulsive microwave bursts. In view of the various observational uncertainties, it is argued that the observations are consistent with the impulsive X-ray, impulsive microwave, and type III radio bursts being essentially simultaneous. The observations are also consistent with 10- to 100-keV electron streams being reponsible for the type III emission. The observations indicate that the non-thermal electron groups responsible for the impulsive X-ray, impulsive microwave, and type III radio bursts are accelerated simultaneously in essentially the same region of the solar atmosphere.

Kane, S. R.↗

NASA NTRS1973

Proton scattering in the region near the earth's bow shock.

Lockheed spectrometer data from orbits 1 through 20 of Ogo 5 are used to study proton scattering near the bow shock. Correlative UCLA fluxgate magnetometer data from the satellite are used to complete motion studies of the bow shock when spectrometer data are missing. Thirty-eight analyzable sets of multiple shock crossings show 358 shock encounters ranging from 10 to 22 earth radii and spanning sun-earth-satellite angles from 30 to 90 deg. Gross features of the study show that the location and shape of the bow shock are in good agreement with the hydrodynamic model of the bow shock.

Ossakow, S. L.↗

NASA NTRS1973

Large ion concentration gradients below the equatorial F peak.

Very large vertical and longitudinal gradients in the ion concentrations are observed below the F peak near the magnetic equator with the retarding potential analyzer on Ogo 6. Ion concentration 'bite outs' of up to a factor of 1000 are observed above 400 km. They appear to be associated with the bottomside of the nighttime F layer. The ion composition in the minima may contain large fractions of ions heavier than O(+) (e.g., NO(+) and Fe(+)). It is suggested that convective electric fields associated with spread F steepen the bottomside of the F layer and also introduce longitudinal irregularities in the vertical ion concentration profiles.

Hanson, W. B.↗

NASA NTRS1973

Excitation of oxygen permitted line emissions in the tropical nightglow.

The ultraviolet oxygen emissions at 1304 and 1356 A in the tropical nightglow seen from Ogo 4 by Hicks and Chubb (1970) and Barth and Schaffner (1970) are accompanied by emission at 7774 and 4368 A, which have been studied from the ground by looking through the beam of an ionosonde operated under the Appleton anomaly ionization peaks. Simultaneous forbidden O I 6300-A measurements were also made. A theoretical value for the partial rate coefficient for 7774 emission by radiative recombination has been obtained, and from the ionospheric data and a model atmosphere the expected rates of radiative recombination and ion-ion recombination were calculated. The time variations and absolute intensity of the calculated and observed intensities agree reasonably well, when the uncertainties involved are considered. It is concluded that radiative recombination is the major source of the tropical oxygen permitted line emissions, accompanied by a small contribution from ion-ion recombination.

Tinsley, B. A.↗

NASA NTRS1973

Plasmaspheric hiss.

A relatively steady band of ELF hiss has been detected by the OGO 5 search coil magnetometer on almost every passage through the plasmasphere; except for an anomalous region of the dayside at high geomagnetic latitudes, the emissions terminate abruptly at the plasmapause and are therefore referred to as 'plasmaspheric hiss.' A preliminary statistical study of the properties of the observed whistler mode turbulence has yielded the following characteristics: the waves are band limited with a sharp lower-frequency cutoff and a more diffuse upper-frequency cutoff; power spectra show a well-defined maximum near a few hundred hertz, the peak intensities generally ranging between 10 to the minus 7th power and 0.00001 gamma squared/Hz; the wave energy is spread over a bandwidth of a few hundred hertz, and corresponding wideband amplitudes are 5 to 50 milligamma; the waves are highly turbulent in nature and show little tendency toward definite polarization.

Thorne, R. M.↗

NASA NTRS1973

An association of magnetospheric whistler dispersion characteristics with changes in local plasma density.

We use OGO 5 measurements made within the plasmapause on May 15, 1969, to investigate the possible association between changes in lightning whistler dispersion characteristics and local density fluctuations. It is shown that groups of whistlers with relatively constant dispersions tended to be detected in regions where the local ion concentration was significantly enhanced. It is assumed that these local density fluctuations represent characteristics of large-scale field-aligned variations. The results are then compared with ray refraction estimates appropriate for low-frequency whistler mode propagation (wave components with frequencies comparable to the local lower hybrid frequency) in a nonuniform medium.

Scarf, F. L.↗

NASA NTRS1973

Distributions and characteristics of high-latitude field-aligned electron precipitation.

Satellite measurements of field-aligned auroral electron precipitation have been analyzed using 16 months of data from the OGO 4 auroral particles experiment. As can be seen from the moving satellite, the anisotropies are of short duration and are most likely to occur when particle fluxes are high. Field-aligned 2.3-keV electron precipitation is found in an oval-shaped region primarily in the nighttime hours; maximum probability is at about 70 deg invariant latitude near midnight, congruent to and poleward of the auroral optical emissions in these hours. This precipitation is found to be associated with the high-latitude boundary of auroral electron precipitation during substorm expansion and is characterized by a slightly harder and considerably more intense energy spectrum than typical isotropic precipitation.-

Berko, F. W.↗

NASA NTRS1973

Magnetic control of the near equatorial neutral thermosphere.

Neutral density data between 400 and 500 km obtained with the Ogo 6 neutral mass spectrometer indicate that at all longitudes the daytime N2 and O densities have latitudinal minimums at the magnetic equator that are about 20 and 10%, respectively, below maximums observed between plus and minus 20 deg magnetic latitude. Our calculations suggest that this anomaly could result from latitudinal variations in ion drag associated with the 'equatorial anomaly' in F region ionization. At latitudes of enhanced electron density the energy flow from the dayside to the nightside of the earth is damped, and thus the amplitude of the temperature and density variations is enhanced, and the time of maximum is shifted to later local times.

Hedin, A. E.↗

NASA NTRS1973

A neutral-atmosphere composition experiment for the Atmosphere Explorer-C, -D, and -E.

The neutral-atmosphere composition experiment instrumentation is designed to obtain in-situ measurements of neutral thermosphere composition from Atmosphere Explorer-C, -D, and -E. The system is based on previously flown OGO-6 and San Marco-3 composition instruments. The mass-spectrometer sensor includes a gold-plated thermalizing chamber and ion source, a hyperbolic rod quadrupole analyzer, and an off-axis electron multiplier. Automatic ion-source sensitivity control and pulse-counting techniques provide density measurement capability from approximately 125 to 1000 km altitude. The normal operating mode includes measurement at all masses in the range of 1 to 44 amu, with emphasis on hydrogen, helium, oxygen, nitrogen, and argon.

Pelz, D. T.↗

NASA NTRS1973

Observation of a current-driven plasma instability at the outer zone-plasma sheet boundary.

Several spacecraft experimenters have reported on the detection of large temporal variations in trapped electron fluxes near L = 5 to 6 at midlatitudes in the night hemisphere. In this report we describe in detail the particle, wave, and field changes measured when Ogo 5 traversed an outer-zone trapping boundary of this type on September 7, 1968. It is shown that thermal proton concentrations and E greater than 50-keV electron fluxes abruptly decreased when electrons with (1-4) keV mean energy were detected. It is also shown that currents flowed along the average geomagnetic field direction near the plasma boundaries and that these were accompanied by intense VLF electrostatic waves. It is proposed that turbulent resistivity produced by current-driven plasma instabilities allows parallel dc electric fields to develop along this boundary.

Scarf, F. L.↗

NASA NTRS1973

Magnetic storm characteristics of the thermosphere.

Energy and diffusive mass transport associated with the thermospheric circulation are considered in a self-consistent, though mathematically relatively simple, form to describe in a three-dimensional two-constituent model magnetic storm characteristics in composition (N2, O, and He), temperature, and mass-density. It is shown that during disturbed conditions the latitudinal variations of composition and gas temperature reflect the local nature of the magnetic storm heat input assumed to be primarily confined to the auroral zones. Thereby gas temperature and N2 increase, He decreases, and O remains constant through the auroral zones at exospheric heights (due to the superposition of temperature and diffusion effects) in agreement with Ogo 6 mass spectrometer measurements. In contrast, the magnetic storm response in the total mass density is characterized by a strong worldwide component and a relatively insignificant increase toward the poles.

Mayr, H. G.↗

NASA NTRS1972

Satellite and ground-based observations of a red arc.

Simultaneous observations carried out during the red-arc period of Aug. 8-9, 1970 at Richland, Washington and by the Ogo 6 satellite are examined in the light of the present-day theoretical knowledge. The observed formation of the arc at the electron temperature peak and density trough supports the thermal-conduction theory of red-arc formation. The lack of dc electric fields in the red-arc region rules out these fields as an excitation mechanism. Particle precipitation as a direct source of red-line emission can also be ruled out by the observations presented. The formation of the arc in the plasmapause region and the detection of low-frequency ac fields are consistent with a theory that predicts wave-particle interaction at the plasmapause as a mechanism for supplying thermal energy to the plasmasphere electrons.

Nagy, A. F.↗

NASA NTRS1973

The altitude of the scattering layer near the mesopause over the summer poles.

The time and latitude variation in the radiance and altitude of the dense scattering layers observed over the summer poles is reported using OGO 6 airglow photometer data. The average altitude was 84.3 km with a tendency for higher values on the night side than on the day side of the polar cap. The average radiance increased by a factor of 5 between day 163 and day 180 (1969), but decreased thereafter.

Donahue, T. M.↗

NASA NTRS1973

Equatorial phenomena in neutral thermospheric composition.

Several interesting phenomena relating to the equatorial ionosphere have been observed in the data from the OGO-6 mass spectrometer. The diurnal variations during equinox at an altitude of 450 km show the N2 and O densities peaking near 1500 hr while He peaks near 1000 hr. The latitudinal variation in N2 during the day is very similar to the F-region electron density exhibiting the well known features of the ionospheric anomaly. During periods of intense geomagnetic disturbance (e.g. the large storm of 8 March 1970), the low latitude thermospheric temperature increases on the order of 50-150 K, while at mid latitudes, increases of more than 1000 K are observed.

Reber, C. A.↗

NASA NTRS1973

The POGO data.

During intervals in 1967-1970, the OGO-4 and 6 spacecraft made over 2000 traversals over the equatorial electrojet in the altitude range 400-800 km when local times were between 9 and 15 hr. These spacecraft carried total field magnetometers making measurements to an accuracy of 2 gammas with a sample rate greater than once a second. Delta-F values, the deviations of these observations from an internal reference model, were plotted for a 30 deg band about the Equator, and the characteristics of the electrojet effect in the data were investigated. This effect was characterized by a sharp negative V-signature of some 16-19 deg in width and a variable amplitude.

Cain, J. C.↗

NASA NTRS1973

Solar wind density model from km-wave type III bursts.

The analysis of type III bursts observed from the OGO-5 satellite between 3.5 MHz and 50 kHz gives an empirical expression for the frequency drift rate as a function of frequency that is valid from 75 kHz to 550 MHz. Using this expression and some simplifying assumptions we obtain indirectly an empirical formula for the electron density distribution of the solar wind to 1 AU which is consistent with published values of electron density and with observed type III burst drift rates.

Alvarez, H.↗

NASA NTRS1973

Electron precipitation patterns and substorm morphology.

Statistical analysis of data from the auroral particles experiment aboard OGO 4, performed in a statistical framework interpretable in terms of magnetospheric substorm morphology, both spatial and temporal. Patterns of low-energy electron precipitation observed by polar satellites are examined as functions of substorm phase. The implications of the precipitation boundaries identifiable at the low-latitude edge of polar cusp electron precipitation and at the poleward edge of precipitation in the premidnight sector are discussed.

Hoffman, R. A.↗