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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 667 records · Page 37
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NASA NTRS1975

Plasma in the Jovian magnetosphere

It is shown that the plasma in Jupiter's ionosphere is collisionless above a certain level. In the outer magnetosphere, where the rotational force dominates the gravitational force, the collisionless plasma has a beam-like distribution and gives rise to a two-stream instability. This leads to trapping of plasma in the centrifugally dominated region of the magnetosphere. Plasma is lost by recombination. Equilibrium-trapped particle densities are calculated by requiring a balance between trapping by wave-particle interaction and loss by recombination. The results are compared with recent observations from Pioneer 10. It is suggested that the observations require an unexplained ion-heating mechanism. Some consequences of the model are discussed.

Goertz, C. K.↗
NASA NTRS1975

Preliminary model studies of the magnetosphere of Jupiter: Pioneer 10

Observations of the Jovian magnetic field and its interaction with the solar wind plasma were made while the Pioneer 10 spacecraft was within about 100 R sub j of the planet. The magnetosphere was found to be severely stretched due to the presence of an intense current sheet, which was particularly evident during the outbound passage of Pioneer 10 near the dawn terminator. Plots of the angle between the orientation of the outbound field and the radius vector from the planet to the spacecraft showed a strong tendency for the field to become radial at large distances from the planet. A similar trend has also been seen in both the inbound and outbound Pioneer 11 data. Preliminary work on a mathematical model of the magnetosphere of Jupiter is given, based upon the Pioneer 10 outbound data. Some of the implications of the radial field configuration inferred from the Pioneer 10 and 11 data are also discussed.

Jones, D. E.↗
NASA NTRS1975

Cyclotron side band emissions from magnetospheric electrons

Very low frequency emissions with subharmonic cyclotron frequency from magnetospheric electrons were detected by the S(3)-A satellite (Explorer 45) whose orbit is close to the magnetic equatorial plane where the wave-particle interaction is most efficient. These emissions were observed during the main phase of a geomagnetic storm in the nightside of the magnetosphere outside of the plasmasphere. During the event of these side-band emissions, the pitch angle distributions of high energy electrons (greater than 50 keV) and of energetic protons (greater than 100 keV) showed remarkable changes with time, whereas those of low energy electrons and protons remained approximately isotropic. In this type of event, emissions consist essentially of two bands, the one below the equatorial electron gyrofrequency, and the other above. The emissions below are whistler mode, and the emissions above are electrostatic mode.

Maeda, K.↗
NASA NTRS1975

The source of the electric field in the nightside magnetosphere

In the open magnetosphere model magnetic field lines from the polar caps connect to the interplanetary magnetic field and conduct an electric field from interplanetary space to the polar ionosphere. By examining the magnetic flux involved it is concluded that only slightly more than half of the magnetic flux in the polar caps belongs to open field lines and that such field lines enter or leave the magnetosphere through narrow elongated windows stretching the tail. These window regions are identified with the tail's boundary region and shift their position with changes in the interplanetary magnetic field, in particular when a change of interplanetary magnetic sector occurs. The circuit providing electric current in the magnetopause and the plasma sheet is extended across those windows; thus energy is drained from the interplanetary electric field and an electric potential drop is produced across the plasma sheet. The polar cap receives its electric field from interplanetary space on the day side from open magnetic field lines and on the night side from closed field lines leading to the plasma sheet. The theory described provides improved understanding of magnetic flux bookkeeping, of the origin of Birkeland currents, and of the boundary layer of the geomagnetic tail.

Stern, D. P.↗
NASA NTRS1975

Observations of magnetospheric ionization enhancements using upper-hybrid resonance noise band data from the RAE-1 satellite

Noise bands associated with the upper-hybrid resonance were used to provide direct evidence for the existence of regions of enhanced density in the equatorial magnetosphere near L = 2. Density enhancements ranging from several percent to as high as 45 percent are observed with radial dimensions of several hundred kilometers. The enhancement characteristics strongly suggest their identification as magnetospheric whistler ducts.

Mosier, S. R.↗
NASA NTRS1974

Centrifugal instability of the Jovian magnetosphere and its interaction with the solar wind

The outer regions (r greater than 2.3 Jupiter radii) of the magnetosphere of Jupiter will systematically accumulate plasma. If sufficient plasma accumulates, the field lines must open to allow the plasma to escape. Available energy sources appear able to supply plasma at a high enough rate to keep the field lines constantly open beyond about 60 Jupiter radii. It is suggested that the solar wind interaction with Jupiter may be essentially different from that with the earth, with the Jovian magnetosphere opening up to form a planetary wind.

Michel, F. C.↗
NASA NTRS1974

Periodic escape of relativistic electrons from the Jovian magnetosphere

We adopt a model in which the Jovian magnetospheric tail is forced open by plasma that is accelerated out of the ionosphere by the centrifugal force of corotation. Any longitudinal asymmetry that exists in the ionospheric plasma source and/or the planetary magnetic field will cause a diurnal variation in the radial extent of the trapping region for energetic electrons. This diurnal variation in the extent of the particle trapping region can result in a time-dependent loss of relativistic electrons from the Jovian magnetosphere, modulated at the planetary rotation period. The diurnal trapping process may be relevant to the observation of electron pulses in interplanetary space during the Pioneer 10 approach to Jupiter.

Hill, T. W.↗
NASA NTRS1975

Substorm-associated reconfiguration of the dusk side equatorial magnetosphere - A possible source mechanism for isolated plasma regions

A rapid reconfiguration of the dusk side magnetosphere was observed near the magnetic equator by particle and field experiments aboard Explorer 45 at 1715 UT on June 17, 1972. Following the onset of an 800-gamma negative bay in the auroral zone, Explorer 45, inbound at 1700 MLT and L about 5, observed a sharp dropout of outer zone electrons. Simultaneously, the plasma density dropped from a level typical of the plasmasphere to one typical of the ion trough, and plasma sheet proton fluxes increased, producing a 100-gamma depression in B, in a shift to a taillike configuration. Outer zone electrons with pitch angles near 45 deg returned with delay times consistent with injection near midnight at the time of dropout and eastward drift to the dusk meridian. Approximately 45 min after the reconfiguration, the satellite reentered the plasmasphere, and the electron fluxes returned to previous levels. In the next orbit, approximately 6 hours later, a region of isolated plasma was detected near apogee at 1400 MLT. There is therefore circumstantial evidence that the type of magnetospheric reconfiguration observed here is responsible for the detachment of regions of cold plasma from the plasmasphere.

Barfield, J. N.↗
NASA NTRS1975

A quantitative magnetospheric model derived from spacecraft magnetometer data

The model is derived by making least squares fits to magnetic field measurements from four Imp satellites. It includes four sets of coefficients, representing different degrees of magnetic disturbance as determined by the range of Kp values. The data are fit to a power series expansion in the solar magnetic coordinates and the solar wind-dipole tilt angle, and thus the effects of seasonal north-south asymmetries are contained. The expansion is divergence-free, but unlike the usual scalar potential expansion, the model contains a nonzero curl representing currents distributed within the magnetosphere. The latitude at the earth separating open polar cap field lines from field lines closing on the day side is about 5 deg lower than that determined by previous theoretically derived models. At times of high Kp, additional high-latitude field lines extend back into the tail. Near solstice, the separation latitude can be as low as 75 deg in the winter hemisphere. The average northward component of the external field is much smaller than that predicted by theoretical models; this finding indicates the important effects of distributed currents in the magnetosphere.

Mead, G. D.↗
NASA NTRS1975

Magnetospheric mapping with a quantitative geomagnetic field model

Mapping the magnetosphere on a dipole geomagnetic field model by projecting field and particle observations onto the model is described. High-latitude field lines are traced between the earth's surface and their intersection with either the equatorial plane or a cross section of the geomagnetic tail, and data from low-altitude orbiting satellites are projected along field lines to the outer magnetosphere. This procedure is analyzed, and the resultant mappings are illustrated. Extension of field lines into the geomagnetic tail and low-altitude determination of the polar cap and cusp are presented. It is noted that while there is good agreement among the various data, more particle measurements are necessary to clear up statistical uncertainties and to facilitate comparison of statistical models.

Fairfield, D. H.↗
NASA NTRS1975

Pioneer 11 observations of energetic particles in the Jovian magnetosphere

A preliminary report is presented of energetic electrons and protons observed with the University of Iowa instrument on Pioneer 11. A graph shows absolute, spin-averaged unidirectional intensities of electrons and protons as a function of time during traversal of the central magnetosphere. Another graph shows the effects of the Jovian satellites Io and Amalthea on particle intensities. It is pointed out that a full analysis of satellite effects is the most promising technique for understanding the physical dynamics of the magnetosphere of Jupiter.

Van Allen, J. A.↗
NASA NTRS1975

Magnetospheric and auroral plasmas - A short survey of progress

Important milestones in our researches of auroral and magnetospheric plasmas for the past quadrennium 1971-1975 are reviewed. Many exciting findings, including those of the polar cusp, the polar wind, the explosive disruptions of the magnetotail, the interactions of hot plasmas with the plasmapause, the auroral field-aligned currents, and the striking inverted V electron precipitation events, were reported during this period. Solutions to major questions concerning the origins and acceleration of these plasmas appear possible in the near future. A comprehensive bibliography of current research is appended to this brief survey of auroral and magnetospheric plasmas.

Frank, L. A.↗
NASA NTRS1975

Magnetospheric chorus - Amplitude and growth rate

A new study of the amplitude of magnetospheric chorus with 1966-1967 data from the Stanford University/Stanford Research Institute VLF receivers on Ogo 1 and Ogo 3 has confirmed the band-limited character of magnetospheric chorus in general and the double-banding of near-equatorial chorus. Chorus amplitude tended to be inversely correlated with frequency, implying lower intensities at lower L values. Individual chorus emissions often showed a characteristic amplitude variation, with rise times of 10 to 300 ms, a short duration at peak amplitude, and decay times of 100 to 3000 msec. Growth was often approximately exponential, with rates from 200 to nearly 2000 dB/sec. Rate of change of frequency was found in many cases to be independent of emission amplitude, in agreement with the cyclotron feedback theory of chorus (Helliwell, 1967, 1970).

Burtis, W. J.↗
NASA NTRS1975

Pioneer 10 - Observations of energetic electrons in the Jovian magnetosphere

Data obtained by Pioneer 10 on the properties of energetic electrons in the Jovian magnetosphere are analyzed. The basic detectors (seven miniature Geiger-Mueller tubes) are described together with the signal processor and sampling techniques. The model of Jupiter used in the data analysis is a centered dipole with a tilt of 9.5 deg toward 230 deg System III longitude. The energetic-electron observations within the inner magnetosphere are found to indicate that radial as well as pitch-angle diffusion of energetic electrons must take place very rapidly. Outbound observations within the magnetodisk (the region beyond 20 Jupiter radii) are found to indicate a spiraling of the apparent location of the longitude of the dipole tilt, while inbound data indicate a constant value for the apparent longitude of the dipole tilt out to 70 Jupiter radii.

Randall, B. A.↗
NASA NTRS1975

Approximations for the study of drift boundaries in the magnetosphere

An approximate relation between energy and equatorial radial distance for a particle of given equatorial pitch angle moving adiabatically in a dipole magnetic field is used to describe the Alfven layer for particles of arbitrary pitch angle. The convection electric field is assumed to be uniform in the equatorial plane of the magnetosphere, and magnetic field lines are taken to be equipotentials in the region traversed by the magnetospheric particles being studied. Approximate solutions in the high- and low-energy limits are given in a form directly applicable to the interpretation of measurements at fixed particle energy and pitch angle. These results are particularly useful for electrons, since the approximations provide lower bounds to the exact solutions. The results are used to interpret recent Explorer 45 electron measurements of Williams et al. (1974).

Kivelson, M. G.↗
NASA NTRS1975

On the detection of magnetospheric radio bursts from Uranus and Neptune

Earth, Jupiter, and Saturn are sources of intense but sporadic bursts of electromagnetic radiation or magnetospheric radio bursts (MRB). The similarity of the differential power flux spectra of the MRB from all three planets is examined. The intensity of the MRB is scaled for the solar wind power input into a planetary magnetosphere. The possibility of detecting MRB from Uranus and Neptune is considered.

Kennel, C. F.↗
NASA NTRS1976

Energetic particles of the outer regions of planetary magnetospheres

High energy particles, with energies above those attainable by adiabatic or steady-state electric field acceleration, have been observed in and around the outer regions of planetary magnetospheres. Acceleration by large amplitude sporadic cross-tail electric fields over an order of magnitude greater than steady-state convection fields is proposed as a source of these particles. It is suggested that such explosive electric fields will occur intermittently in the vicinity of the tail neutral line in the expansive phase of substorms. Laboratory and satellite evidence are used to estimate this electric potential for substorms at earth; values of 500 kilovolts to 2 megavolts are calculated, in agreement with particle observations. It is further suggested that these particles, which have been accelerated in the night side magnetosphere, drift to the dayside on closed field lines, and under certain interplanetary conditions can escape to regions upstream of the bow shock.

Tsurutani, B. T.↗