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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Hot plasmas in the earth's magnetosphere

Several recent findings from observational researches of various facets of magnetospheric plasmas are summarized. These new results encompass entry of solar wind plasmas into the dayside magnetosphere, the acceleration of plasmas both at great distances from the earth in the magnetotail and at low altitudes over auroral luminosities, and the substantial contributions of the upper ionosphere to the plasma compositions of the distant magnetosphere.

Frank, L. A.↗
NASA NTRS1979

Satellite observations of the spatial extent and structure of Pc 3, 4, 5 pulsations near the magnetospheric equator

Simultaneous observations of Pc 3, 4, 5 pulsations by five satellites in the pre-noon local time sector at and near synchronous orbit are examined. The periods of these simultaneous pulsations are not the same at the different observation points. This difference is attributed to site dependent resonant conditions. The spatial properties of the temporal phenomenon are demonstrated with observations by ISEE-1 and -2 as they pass through oscillations in a spatially limited region. Fundamental and second harmonic standing Alfven waves are observed simultaneously on the same field line. The periods are consistent with model predictions when the measured plasma composition, which by mass consists mainly of singly ionized oxygen, is taken into account.

Singer, H. J.↗
NASA NTRS1981

Transversely accelerated ions in auroral arcs

Ionospheric ions apparently accelerated transversely to the geomagnetic field in the topside ionosphere are regularly detected by the soft particle spectrometers on the ISIS satellites. Such gyro-accelerated ions are observed in association with precipitating auroral electrons. A detailed study of their relationship with such electrons and with field-aligned currents, together with simultaneous measurements of the local plasma composition and density, reveals the specific conditions present in the topside ionosphere during the generation of such transversely accelerated ions (TAI). A proposed mechanism for generation of TAI involving acceleration by electrostatic ion cyclotron waves is consistent with the present observations.

Klumpar, D. M.↗
NASA NTRS1983

Low-energy (less than 100 eV) ion pitch angle distributions in the magnetosphere by ISEE 1

Attention is given to isotropic distribution, bidirectional field alignment distribution, unidirectional field alignment distribution, and low flux, in a statistical examination of low energy ion data from the ISEE 1 plasma composition experiment whose aim was the study of pitch angle distributions in all local times of the magnetosphere. The isotropic distribution consisting of less than 10 eV ions is a persistent inner region feature, while the bidirectional field-aligned distribution consisting of warm ions is a persistent feature of the outer dayside and is seen just outside the isotropic distribution region of the nightside. On the outer nightside, the unidirectional field-aligned distribution consisting of warm ions is the dominant signature. The 'sources' of ions in various regions are discussed in view of the present and other results.

Johnson, J. F. E.↗
NASA NTRS1984

Anomalously high potentials observed on ISEE

Data from the two electric field experiments and from the plasma composition experiment on ISEE-1 show that the spacecraft charged to close to -70 V in sunlight at about 0700 UT on March 17, 1978. Data from the electron spectrometer experiment show that there was a potential barrier of some -10 to -20 V about the spacecraft during this event. The potential barrier was effective in turning back emitted photoelectrons to the spacecraft. Potential barriers can be formed because of differential charging on the spacecraft or because of the presence of space charge. The stringent electrostatic cleanliness specifications imposed on ISEE make the presence of differential charging unlikely, if these precautions were effective. Modeling of this event is required to determine if the barrier was produced by the presence of space charge.

Whipple, E. C.↗
NASA NTRS1983

Determination of solar wind elemental abundances from M/Q observations during three periods in 1980

Mass spectra in the M/Q range from 2 to 3, provided by a high-resolution mode of the ISEE-3 Plasma Composition Experiment, were evaluated for three selected periods during early 1980. The observed Ne/O ratios are compatible with estimated solar abundance ratios. In two of the three periods, the He/Ne-ratios agree with the Apollo foil results. Freezing-in temperatures for oxygen are similar to those obtained by other groups. Possible reasons for an unexpectedly high flux at M/Q = 2.4 are discussed.

Kunz, S.↗
NASA NTRS1985

Anomalously high potentials observed on ISEE

Data from two electric field experiments and from the plasma composition experiment on ISEE-1 are used to show that the spacecraft charged to close to -70 V in sunlight at 0700 UT on March 17, 1978. Data from the electron spectrometer experiment show that there was a potential barrier of -10 to -20 V about the spacecraft during this event. The potential barrier was effective in turning back emitted photoelectrons to the spacecraft. The stringent electrostatic cleanliness specifications imposed on ISEE make the presence of differential charging unlikely. Modeling of this event is required to determine if the barrier was produced by the presence of space charge.

Whipple, E. C.↗
NASA NTRS1984

Drift wave instabilities in a high beta multispecies plasma

The dispersion relation for drift-Alfven waves in two-component (cold and hot), high beta inhomogeneous multispecies plasma containing protons, oxygen, and sulfur ions is solved numerically. The magnetic field is assumed to have a gradient in simple slab geometry configuration. The plasma ion composition consists of H, O, S, SO2, and Na ions. The effect of heavy ions and multiple charge states on the growth rates has been numerically estimated for assumed ion compositions. The numerical calculations of growth rates also have been performed by using ion composition and plasma parameters based on Voyager spacecraft in the magnetospheres of Jupiter and Saturn.

Patel, V. L.↗
NASA NTRS1987

High spacecraft potentials on ISEE-1 in sunlight

Data from two electric field experiments and from the plasma composition experiment on ISEE-1 show that the spacecraft charged to close to -70 V in sunlight at about 0700 UT on March 17, 1978. Data from the electron spectrometer experiment show that there was a potential barrier of some -10 to -20 V about the spacecraft during this event. The potential barrier was effective in turning back emitted photoelectrons to the spacecraft. Potential barriers can be formed by differential charging on the spacecraft or by the presence of space charge. The stringent electrostatic cleanliness specifications imposed on ISEE made the presence of differential charging seem unlikely, if these precautions were effective. Modeling of the event to determine if the barrier was produced by the presence of space charge suggested that this could not explain the observed barrier. The angular shape of the distribution could be successfully modeled as a product of differential charging on the solar arrays. This implies that the conductive coating was not completely effective in preventing differential charging, and that differential charging did occur.

Whipple, E. C., Jr.↗
NASA NTRS1976

Electrostatic shocks as nonlinear ion acoustic waves

A cold fluid approach is presented which yields exact double-layer solutions that can be used to model electrostatic S-type shocks. Solutions derived from the two-temperature electron model are presented in order to show the range of amplitudes and scale lengths possible for this plasma model and to examine how shock properties depend on orientation of the shock. The dependence of various double-layer quantities on plasma composition is then considered for the cold electron beam model. Double-layer solutions pertinent to describing electrostatic shocks are pointed out.

Witt, E.↗
NASA NTRS1986

Plasmasphere thermal structure as measured by ISEE-1 and DE-1

Characteristics of plasmaspheric ion thermal structure are presented from a statistical survey of low-energy of ion measurements made by the retarding ion mass spectrometer (RIMS) on the DE-1 satellite. Morning and evening results are compared to illustrate diurnal trends. Typical day side temperature range from about 4000 K in the inner plasmasphere to over 10,000 K in the outer plasmasphere, while corresponding evening side temperatures range from near 2000 K to over 10,000 K. Magnetic activity is found to affect the morning and evening sides somewhat differently. Temperatures are found to remain constant or increase with altitude along magnetic field lines, depending on local time and L shell. Thermal equilibrium between H(+) and He(+) prevails to a high degree throughout the plasmasphere. Ion temperatures from the Plasma Composition Experiment (PCE) on ISEE-1 are generally consistent with those from DE-1/RIMS, but are lower and tend to indicate more large scale structure on the day side.

Comfort, R. H.↗
NASA NTRS1989

High-speed flows of H(+) and He(2+) ions at the magnetosphere

Observations of high-speed flows of H(+) and He(2+) ions obtained by the hot plasma composition experiment on AMPTE/CCE provide direct support for the single-particle approach to acceleration in current layers. These high-speed flows are attributed to single-fluid momentum balance across a magnetopause with a normal magnetic field and a tangential electric field. The flow speeds of the two ion species are found to be approximately equal.

Paschmann, G.↗
NASA NTRS1991

On the origins of energetic ions in the earth's dayside magnetosheath

Energetic ion events in the earth's dayside subsolar magnetosheath (0900 - 1300 Local Time) are surveyed using data from the AMPTE/CCE Hot Plasma Composition Experiment. Ion species carrying the signature of their origin O(+) and energetic He(2+) are used to distinguish between magnetospheric and solar wind origins for the energetic ion events. The results of this survey indicate that the majority of energetic (10-17 keV/e) H(+) and He(2+) ions observed in the dayside magnetosheath are accelerated from the solar wind population. The energetic He(2+) to H(+) density ratio in the magnetosheath is consistent with that predicted from first-order Fermi acceleration of solar wind ions in the turbulent regions upstream and downstream from the earth's quasi-parallel bow shock. The simultaneous occurrence of both energetic He(2+) and magnetospheric O(+) indicates that, on occasion, both Fermi acceleration of solar wind ions and leakage of magnetospheric ions occurs in the dayside magnetosheath.

Fuselier, S. A.↗
NASA NTRS1993

Mass density and pressure changes across the dayside magnetopause

Plasma composition measurements at about 2-min time resolution from 27 magnetopause crossings are used to determine if mass density rho, modified by the anisotropic pressure term (1-alpha), is constant across the magnetopause. Pressure and mass density in the magnetosheath and low-latitude boundary layer were found to be dominated by H(+) except on one occasion when O(+) was the dominant contributor to the total mass density in the low-latitude boundary layer. Using these measurements, it is found that rho(1-alpha) is not constant for almost all magnetopause crossings even when there is independent evidence for magnetic reconnection and an open magnetopause. These results indicate that the reason why rho(1-alpha) is not constant across the magnetopause is that the H(+) density decrease from the magnetosheath to the low-latitude boundary layer is not compensated for by either a change in the pressure anisotropy or a change in the total mass density and suggest that the magnetopause can never be described as a time-stationary 1D rotational discontinuity.

Fuselier, S. A.↗
NASA NTRS1994

Origins of energetic ions in the Earth's magnetosheath

This final report describes activities under NASA contract NAS5-31213 to Lockheed Missiles and Space Company. The report covers the entire contract period from 8 May 1991 to 7 Jun. 1994. This is a contract under the NASA Guest Investigator Program for the analysis and interpretation of the combined scientific data from the Hot Plasma Composition Experiment (HPCE) and the Charge Energy Mass (CHEM) spectrometer on the AMPTE/Charge Composition Explorer (CCE) spacecraft. These combined data sets have been used to survey the energetic ion environment in the earth's magnetosheath to determine the origins and relative strengths of the energetic ion populations found there.

Source record↗
NASA NTRS1994

Response of thermal ions to electromagnetic ion cyclotron waves

Electromagnetic ion cyclotron waves generated by 10 - 50 keV protons in the Earth's equatorial magnetosphere will interact with the ambient low-energy ions also found in this region. We examine H(+) and He(+) distribution functions from approx. equals 1 to 160 eV using the Hot Plasma Composition Experiment instrument on AMPTE/CCE to investigate the thermal ion response to the waves. A total of 48 intervals were chosen on the basis of electromagnetic ion cyclotron (EMIC) wave activity: 24 with prevalent EMIC waves and 24 with no EMIC waves observed on the orbit. There is a close correlation between EMIC waves and perpendicular heated ion distributions. For protons the perpendicular temperature increase is modest, about 5 eV, and is always observed at 90 deg pitch angles. This is consistent with a nonresonant interaction near the equator. By contrast, He(+) temperatures during EMIC wave events averaged 35 eV and sometimes exceeded 100 eV, indicating stronger interaction with the waves. Furthermore, heated He(+) ions have X-type distributions with maximum fluxes occurring at pitch angles intermediate between field-aligned and perpendicular directions. The X-type He(+) distributions are consistent with a gyroresonant interaction off the equator. The concentration of He(+) relative to H(+) is found to correlate with EMIC wave activity, but it is suggested that the preferential heating of He(+) accounts for the apparent increase in relative He(+) concentration by increasing the proportion of He(+) detected by the ion instrument.

Anderson, B. J.↗
NASA NTRS1994

Magnetospheric filter effect for Pc 3 Alfven mode waves

We present a ray-tracing study of the propagation of Pc 3 Alfven mode waves originating at the dayside magnetopause. This study reveals interesting features of a magnetospheric filter effect for these waves. Pc 3 Alfven mode waves cannot penetrate to low Earth altitudes unless the wave frequency is below approximately 30 mHz. Configurations of the dispersion curves and the refractive index show that the gyroresonance and pseudo-cutoff introduced by the heavy ion O(+) block the waves. When the O(+) concentration is removed from the plasma composition, the barriers caused by the O(+) no longer exist, and waves with much higher frequencies than 30 mHz can penetrate to low altitudes. The result that the 30 mHz or lower frequency Alfven waves can be guided to low altitudes agrees with ground-based power spectrum observations at high latitudes.

Zhang, X.↗
NASA NTRS1995

Magnetospheric filter effect for Pc 3 Alfven mode waves

We present a ray-tracing study of the propagation of Pc 3 Alfven mode waves originating at the dayside magnetopause. This study reveals interesting features of magnetospheric filter effect for these waves. Pc 3 Alfven mode waves cannot penetrate to low Earth altitudes unless the wave frequency is below approximately 30 mHz. Configurations of the dispersion curves and the refractive index show that the gyroresonance and pseudo-cutoff introduced by the heavy ion O(+) block the waves. When the O(+) concentration is removed from the plasma composition, the barriers caused by the O(+) no longer exist, and waves with much higher frequencies than 30 mHz can penetrate to low altitudes. The result that the 30 mHz or lower frequency Alfven waves can be guided to low altitudes agrees with ground-based power spectrum observation at high altitudes.

Zhang, X.↗