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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

The use of the three dimensional coherency matrix in analyzing the polarization properties of plane waves

A technique for analyzing the polarization properties of plane waves is developed which offers a number of advantages over methods currently used in the analysis of both ground and satellite observations of waves. This technique reduces the computations required to find the wave normal vector, is less sensitive to common noise sources, and is amenable to analog implementation. This technique is applied specifically to the analysis of a proton whistler, but may also be used in most studies of ULF, ELF, and VLF magnetic wave phenomena.

Means, J. D.↗
NASA NTRS1972

Theory of discrete wave packets in the solar wind.

Discrete wave packets were observed by Ogo 5 and earlier satellites. These waves were believed to be in the whistler mode. Since their group velocities were found to be smaller than the solar-wind speed, these waves could not have been generated in the bow shock and could not have propagated upstream later. The present theory discusses a mechanism similar to that of the echo phenomenon in plasma physics discovered in recent years. The present theory enables us to explain (a) why the wave packets were associated with the bow shock, (b) why the wave packets were characterized by coherent oscillations, and (c) why the wave packets had group velocities smaller than the solar wind and yet could still occur in the solar wind. In short, our theory is able to interpret all the essential features deduced from the observational data.

Wu, C. S.↗
NASA NTRS1972

Magnetospheric plasma.

This paper reviews the principal features of the distribution of plasma in the magnetosphere as inferred from observations of particles with energies in the keV range and below. Low energy electrons are found within the equatorial region of the magnetotail, where they form the plasma sheet, and throughout the outer magnetosphere, where they envelop the earth with a complicated and as yet only partly explored structure. The sum of particle and magnetic pressures is roughly constant across the plasma sheet. The intense electron fluxes of the plasma sheet terminate at the so-called inner boundary of the plasma sheet, which is located at about 11 earth radii in the evening side of the magnetosphere and approaches the plasmapause near the midnight meridian. During substorms, the inner boundary moves closer to the earth, while deep in the magnetotail the plasma sheet first becomes thinner and then expands. Comparison between magnetotail electron densities and whistler measurements suggests that the observed plasma sheet particles may constitute the thermal particle population of the magnetotail.

Vasyliunas, V. M.↗
NASA NTRS1972

Particle-flux limits in the synchronous orbit.

Examination of measurements of 40- and 75-keV electrons and 60and 120-keV protons on the ATS 5 satellite in synchronous orbit in order to show that fluxes of such particles often approach but rarely exceed limiting values that agree within a factor of about 2 with the fluxes predicted by Kennel and Petschek (1966) from consideration of whistler-mode wave-particle interactions. A study is made of the proton and electron fluxes for evidence of the stably trapped flux limits in order to determine them, and to study the local-time dependences of their existence.

Mozer, F. S.↗
NASA NTRS1972

Inner-zone energetic-electron repopulation by radial diffusion.

Quantitative study of the intrusion of natural electrons into the inner radiation zone during and after the geomagnetic storm of Sept. 2, 1966. It is shown that the transport is consistent with a radial-diffusion mechanism in which the first two invariants are conserved. Except for the three-day period of the storm main phase when data were missing, the radial-diffusion coefficient is found to have a value which could be produced by a variation of a large-scale electric field across the magnetosphere having an amplitude of 0.28 mV/m and a period of 1600 sec. Electric fields having approximately these characteristics have been inferred from previous observations of the motion of whistler ducts within the plasmapause. If fields of this amplitude and period exist throughout the magnetosphere, the radial diffusion of all geomagnetically trapped particles except the high-energy inner-zone protons is strongly influenced by electric-field variations. A comprehensive review of previously reported radial-diffusion coefficients shows reasonable agreement for L less than about 3.0, but serious discrepancies among reported values exist for determinations made in the outer zone. These discrepancies cannot be explained by the simple theory of radial diffusion due to variation of large-scale electric or magnetic fields.

Tomassian, A. D.↗
NASA NTRS1972

Pitch-angle diffusion of radiation belt electrons within the plasmasphere.

Study of the formation of the quiet-time electron slot, which divides the radiation belt electrons into an inner and an outer zone. The pitch-angle diffusion of radiation belt electrons resulting from resonant interactions with the observed plasmaspheric whistler-mode wave band is quantitatively investigated. The effects of wave propagation obliquely to the geomagnetic field direction with the resulting diffusion at all cyclotron-harmonic resonances and the Landau resonance are evaluated along with the effects of interactions occuring at all geomagnetic latitudes. The results obtained account for the long-term stability of the inner radiation zone, the location of its outer edge as a function of electron energy, and the removal of electrons to levels near zero throughout the slot. Computed pitch-angle distributions and precipitation decay rates are in good agreement with slot-region observations.

Lyons, L. R.↗
NASA NTRS1972

Electric dipole radiation at VLF in a uniform warm magneto-plasma.

Use of a linear full electromagnetic wave theory to calculate the input impedance of an electric antenna embedded in a uniform, lossless, unbounded warm magnetoplasma, which is assumed to consist of warm electrons and cold ions. In calculating the dipole radiation resistance for the thermal modes and the thermally modified whistler mode the analysis includes the finite temperature only for the electrons. In deriving the formal solution of the warm plasma dipole input impedance a full-wave analysis is used and two antenna orientations are considered, parallel and perpendicular to the static magnetic field. A general dispersion equation governing the modes of propagation is derived and a detailed analysis is made of the propagation characteristics of these modes.

Wang, T. N. C.↗
NASA NTRS1972

Storm time instabilities of the ring current.

Demonstration that the resonant cyclotron instability between radiation belt protons and ion-cyclotron waves can account for many observed features of the magnetospheric ring current. Analogous results apply to the electron-whistler interaction although the former are not considered to be important for ring current energetics. Particles with energy exceeding 100 keV are readily destabilized throughout the entire magnetosphere and their fluxes are consequently limited to the stably trapped levels described by Kennel and Petschek (1966). However, at the dominant ring current energies between 10 and 100 keV, a broad zone of stability exists in the region just outside the plasmapause. Particles injected into this outer zone during substorms may remain trapped for many drift orbits allowing an intense ring current to develop. In direct contrast, this stable ring current zone is bounded by regions of rapid precipitational loss within the plasmasphere and at large radial distance in the auroral zone.

Thorne, R. M.↗
NASA NTRS1972

Plasma wave observations near the plasmapause with the S3-A satellite

The electric field noise phenomena is described which was observed by the S3-A spacecraft near the plasmapause during the magnetic storm of 16 to 17 December, 1971. The occurrence is noted of a region of intense, low frequency (20 Hz to 500 Hz) electrostatic noise bursts just outside the plasmapause boundary. These noise bursts occurred concurrent with the rapid decrease in 24.3 or = E or = 35.1 keV ring current protons mirroring near the equator during this storm and may be responsible for the pitch angle diffusion and loss of these particles. The characteristics of other phenomena, such as whistlers, ELF hiss, and banded chorus, observed near the plasmapause during this period are also discussed.

Anderson, R. R.↗
NASA NTRS1971

ELF propagation in the plasmasphere based on satellite observations of discrete and continuous forms

The propagation of electromagnetic waves in a nonhomogeneous anisotropic medium is examined from the point of view of geometrical optics. In particular, the propagation of ELF waves in the magnetosphere is described in terms of the electron and ion densities and the intensity and inclination of the earth's magnetic field. The analysis of the variations of wave normal angle along the ray path is extended to include the effects of ions. A comparison of the relative importance of each of the above parameters in controlling the orientation of the wave normals is made in the region of the magnetosphere where most of the ion whistlers have been detected.

Muzzio, J. L. R.↗
NASA NTRS1972

Two substorm studies of relations between westward electric fields in the outer plasmasphere, auroral activity, and geomagnetic perturbations

Temporal variations of the westward component of the magnetospheric convection electric field in the outer plasmasphere were compared to auroral activity near L = 7, and to variations in the geomagnetic field at middle and high latitudes. The substorms occurred on July 29, 1965 near 0530 UT and on August 20, 1965 near 0730 UT. The results on westward electric field E(w) were obtained by the whistler method using data from Eights, Antarctica (L is approximately 4). All sky camera records were obtained from Byrd, Antarctica, (L is approximately 7), located within about 1 hour of Eights in magnetic local time. It was found that E(w) within the outer plasmasphere increased rapidly to substorm levels about the time of auroral expansion at nearby longitudes. This behavior is shown to differ from results on E(w) from balloons, which show E(w) reaching enhanced levels prior to the expansion. A close temporal relation was found between the rapid, substorm associated increases in E(w) and a well known type of nightside geomagnetic perturbation. Particularly well defined was the correlation of E(w) rise and a large deviation of the D component at middle latitudes.

Carpenter, D. L.↗
NASA NTRS1972

Approximations to the plasma dispersion function

Linear wave propagation in hot collisionless plasmas is described by the linearized Vlasov and Maxwell equations. In uniform media, the utilization of spatial and temporal transforms of those equations leads to the consideration of integrals of the Hilbert transform type. Analysis and comparison of two simple approximations are provided based on the utilization of resonance velocity distributions. Application is then made to the Landau and whistler waves, along with a discussion of the results, and commentary on possible improvements.

Brinca, A. L.↗
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 NTRS1973

A theoretical and experimental study of non-ducted VLF waves after propagation through the magnetosphere.

The nonducted propagation of artificial VLF waves through the magnetosphere has been studied by means of data obtained by the FR-1 satellite experiment, in which fixed frequency (16.8 kHz) waves radiated by a transmitter at the ground (at L equals 2.1) are received by the satellite, at 750 km altitude, both in the zone close to the transmitter and in the conjugate zone. From the wave-normal directions and Doppler shifts measured in the conjugate zone, it has been possible to identify waves that have been propagated from the Northern to the Southern Hemisphere in both ducted and nonducted modes. In this paper, the main features of the nonducted wave have been interpreted by ray tracing in models of the magnetosphere. The results improve our understanding as to why very few whistlers are observed on the ground at low latitudes.

Cerisier, J. C.↗
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

Plasma wave observations near the plasmapause with the S3-A satellite.

Description of the electric field noise phenomena observed by the S3-A spacecraft near the plasmapause during the magnetic storm of Dec. 16, 17, 1971. The most striking and unusual feature of these storm time electric field observations is the occurrence of a region of intense low-frequency (20 to 500 Hz) electrostatic noise bursts just outside the plasmapause boundary. These noise bursts occurred concurrently with the rapid decrease in low-energy (E ranging from 20 to 50 keV) ring current protons mirroring near the equator during this storm and may be responsible for the loss of these particles. The characteristics of other phenomena, such as whistlers, ELF hiss, and banded chorus, observed near the plasmapause during this period are also discussed.

Anderson, R. R.↗
NASA NTRS1973

Electron concentrations calculated from the lower hybrid resonance noise band observed by Ogo 3.

A noise band at the lower hybrid resonance (LHR) is often detected by the VLF and ELF receivers on Ogo 3, using the electric antenna. In some cases the noise band is at the geometric mean gyrofrequency as measured by the Goddard Space Flight Center (GSFC) magnetometer, and local LHR in a dense H(+) plasma is indicated; in such cases, electron concentration can be calculated, if it is assumed that heavy ions are negligible. Observations at midlatitudes and altitudes of a few earth radii show local concentrations as low as 1.4 electrons/cu cm. In one case the concentrations obtained from the LHR noise band agree with those measured simultaneously by the GSFC ion mass spectrometer within a factor of 2. In another case the concentration is observed to fall by a factor of 2 in 150 km and then to decrease roughly as R to the minus fourth power, in agreement with whistler measurements outside the plasmapause.

Burtis, W. J.↗