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Mcentire, R. W.

Publications and source records attributed to Mcentire, R. W..

51 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

A statistical study of ion pitch-angle distributions

Preliminary results of a statistical study of energetic (34-50 keV) ion pitch-angle distributions (PADs) within 9 Re of earth provide evidence for an orderly pattern consistent with both drift-shell splitting and magnetopause shadowing. Normal ion PADs dominate the dayside and inner magnetosphere. Butterfly PADs typically occur in a narrow belt stretching from dusk to dawn through midnight, where they approach within 6 Re of earth. While those ion butterfly PADs that typically occur on closed drift paths are mainly caused by drift-shell splitting, there is also evidence for magnetopause shadowing in observations of more frequent butterfly PAD occurrence in the outer magnetosphere near dawn than dusk. Isotropic and gradient boundary PADs terminate the tailward extent of the butterfly ion PAD belt.

Sibeck, D. G.↗
NASA NTRS1986

Magnetospheric particle injection and the upstream ion event of September 5, 1984

Energetic particle data from the AMPTE Charge Composition Explorer (CCE) spacecraft in the outer dayside magnetosphere are examined during the period of an upstream ion event observed by the AMPTE Ion Release Module (IRM) spacecraft on September 5, 1984. The CCE data reveal the following: (1) an ion enhancement was observed at about 0040 UT in near coincidence with a substorm onset at about 0035 UT, approximately 15 minutes prior to the onset of the event upstream of the shock; (b) ions of both solar-wind - H(2+) Fe-group - and ionospheric O(+) - origin over a broad energy range (about 20 keV to greater than 1350 keV) were injected at substorm onset; (3) the time evolution of the H(+), He(2+), and O(+) pitch angle distributions markedly differed, with O(+) exhibiting mostly enhancements at off-90-deg angles for the first hour after injection; (4) an enhancement in the Fe-group ions inside the magnetosphere at L = about 6.4 occurred simultaneously with the appearance of an O(+) burst upstream of the shock. The CCE observations, taken together with the simultaneously observed IRM ion event, suggest that a plausible explanation for the appearance of upstream ions is leakage from the magnetosphere into the upstream region, rather than the alternative explanation which requires in situ acceleration of solar wind ions via the Fermi Mechanims.

Krimigis, S. M.↗
NASA NTRS1986

AMPTE lithium tracer releases in the solar wind - Observations inside the magnetosphere

The transfer of mass from the solar wind to the magnetosphere and its transport and energization within the magnetosphere are investigated. Lithium atoms released on September 11 and 20, 1984 are utilized as the tracers in this study. The components and capabilities of the Charge Composition Explorer, which are to measure magnetospheric ion composition, are described. The data collected is analyzed and it is observed that Li ions did not enter the magnetosphere in sufficient quantities to be distinguished from the background particles. The modeling of solar wind and magnetosheath transport of Li ions is examined; more than 20 percent of the Li released on September 11, and 50 percent of the Li released on September 20 are mapped to the area around the stagnation point of the magnetopause.

Krimigis, S. M.↗
NASA NTRS1986

The response of energetic particles to nightside magnetic pulsations as seen by AMPTE/CCE

This paper reports the response of energetic ions during two types of magnetic oscillations: an azimuthal fluctuation and a radial fluctuation, both with periods in the Pc4-Pc5 range. The azimuthal oscillations occur on April 30, 1985 from 0950 to 1210 UT at 8.7 to 7.0 R(E) and from 1.5 to 2.8 MLT. The radial oscillations occur on April 26, 1985 from 1200 to 1400 UT at 8.7 to 7.5 R(E) and from 2.2 to 3.0 MLT. In this case the particles show in phase periodic flux variations in sectors with radial gradients in the flux. These particle fluctuations represent two distinct modulations, each associated with a basic mode of magnetic oscillation in the near-earth magnetotail.

Lopez, R. E.↗
NASA NTRS1986

Acceleration of energetic oxygen (E greater than 137 keV) in the storm-time ring current

Measurements obtained with the medium-energy particle analyzer of the equatorial-orbit AMPTE/CCE satellite during a geomagnetic storm on September 4-7, 1984 are reported and analyzed, with a focus on the high-energy populations (H, He, and CNO-group ions with E greater than 56, 72, and 137 keV, respectively). During the main phase of the storm, ring-current-region increases in O(+) intensity by factors up to 2000 are observed at L = 2.5-7.0, and the component at L = 3.5-5.5 is attributed to a 1.5-earth-radius inward displacement of the prestorm energetic-oxygen population followed by betatron acceleration. Alternative oxygen sources and/or acceleration mechanisms to account for the component at L = 6.5-8 and pitch angle 90 deg are discussed.

Lui, A. T. Y.↗
NASA NTRS1985

The Medium-energy particle analyzer (MEPA) on the AMPTE CCE spacecraft

A major objective in the design of the Charge Composition Explorer (CCE) is related to the measurement of small fluxes of ions (lithium and barium) injected in the solar wind and the deep magnetotail. A second important objective is concerned with the comprehensive measurement of the composition and dynamics of the natural-particle population. The medium-energy particle analyzer (MEPA) in the CCE is designed to cover an energy range which is normally covered by electrostatic analyzers. In order to prevent saturation by the large magnetospheric fluxes of low-energy protons, the MEPA sensor was designed to have a low efficiency for protons, but a high efficiency for the rarer heavier nuclei. The considered aims could be achieved by developing a technology, new to space flight, for measuring energetic ion composition. Particle mass is determined on the basis of the measurement of particle time of flight and total energy.

Mcentire, R. W.↗
NASA NTRS1985

AMPTE/CCE energetic particle composition measurements during the September 4, 1984 magnetic storm

The results of measurements for the magnetic-storm period of September 4-7, 1984 from the medium-energy particle analyzer (MEPA) on the CCE spacecraft are presented. It is shown that within L-shells of about 2.5 to 5 in the dusk sector near the equatorial plane, the enhancement factor in the fluxes for the CNO group is greater than that of helium, which is greater than that of protons. The flux ratios of helium and CNO over all ions at the same total energy show considerable increases in the same L-shell ranges. For the particle population measured by MEPA, a local current-density enhancement of about 0.5 nA/sq m is found over the L range of 3.5 to 6 during the magnetic storm. It is found that the total current density is dominated by the pressure-gradient current of the protons.

Mcentire, R. W.↗
NASA NTRS1985

Magnetic storm of September 4, 1984 - A synthesis of ring current spectra and energy densities measured with AMPTE/CCE

Compositional studies of the equatorial distributions of ring current ions during the September 4, 1984 magnetic storm have been made possible by comprehensive energy, charge state, and mass coverage data from the Charge Composition Explorer satellite. An examination of ion spectra at an L value of about 4 on September 5, in the local evening sector, shows that energy density was dominated by protons, with O ions contributing about 27 percent at the peak of about 150 keV, while He ions contributed less than about 2 percent. September 6 ion spectra, taken during the recovery phase of the storm, indicate that ion densities at more than 20 keV had decreased markedly, and that the ring current energy density was primarily provided by protons.

Krimigis, S. M.↗
NASA NTRS1983

The Active Magnetospheric Particle Tracer Explorers program

In order to study the access of solar wind ions to the magnetosphere, together with the processes that transport and accelerate magnetospheric particles, the Active Magnetospheric Particle Tracer Explorers (AMPTE) mission will release and monitor lithium and barium tracer ions in both the solar wind and the magnetosphere. A single, massive release of barium in the dawn magnetosheath will in addition create a visible artificial comet in the flowing solar wind plasma, within which studies of a range of different plasma effects will be undertaken. The AMPTE will obtain comprehensive measurements of natural magnetospheric particle populations' elemental composition and dynamics. AMPTE comprises three spacecraft: the Ion Release Module, the Charge Composition Explorer, and the United Kingdom Subsatellite.

Krimigis, S. M.↗
NASA NTRS1977

Low-energy particle observations in the quiet dayside cusp from AE-C and AE-D

AE-C and AE-D observations at low altitudes in the high-latitude region near magnetic local noon have revealed properties of low energy electrons and protons that are similar to those determined from earlier particle and field-aligned current observations. The principal feature determined in the present study is a well-defined boundary (less than a few km or 0.01 deg in invariant latitude) which appears only in the postnoon high-latitude region. Energy spectra of low energy electrons and protons show a distinctive softening at latitudes above this boundary. The region of soft particle precipitation above this boundary (located near 78 deg invariant latitude during moderately disturbed to quiet geomagnetic conditions) is identified as the dayside cusp.

Potemra, T. A.↗
NASA NTRS1977

Conjugate photoelectron fluxes observed on Atmosphere Explorer C

The results are presented of a number of observations made with the aid of the Atmosphere Explorer C spacecraft under conditions which provided an unambiguous opportunity to study photoelectrons entering the atmosphere after flowing along the geomagnetic field from the magnetic conjugate point. A graph is presented with energy spectra of electrons observed precipitating into the atmosphere when the magnetic conjugate point was illuminated. Another graph shows the average energy spectra of electrons observed at 263 km for a range of solar zenith angles when the zenith angles at the magnetic conjugate point varied from 100 to 81 deg.

Peterson, W. K.↗
NASA NTRS1977

Observations of 10-eV to 25-keV electrons in steady diffuse aurora from Atmosphere Explorer C and D

Electron energy spectra from 10 eV to 25 keV have been obtained from steady diffuse auroral forms at altitudes above 150 km by the Atmosphere Explorer C and D spacecraft. Overlapping coverage of the energy range was provided by the photoelectron spectrometer experiment (10-500 eV) and the low-energy electron experiment (0.2-25 keV). The spectral shape between 10 and 20 eV is independent of altitude between 150 and 270 km, has variable energy dependence between about 20 and 150 eV, and above approximately 150 eV has energy dependence determined primarily by the details of the energy spectrum of electrons incident on the atmosphere. The observed results are in satisfactory agreement with two recently published model calculations.

Peterson, W. K.↗