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At least 91 records · Page 5

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NASA NTRS1985

AMPTE/CCE observations of the plasma composition below 17 keV during the September 4, 1984 magnetic storm

Observations from the Hot Plasma Composition Experiment on the AMPTE/CCE spacecraft during the magnetic storm of 4-5 September 1984 reveal that significant injection of ions of terrestrial origin accompanied the storm development. The compression of the magnetosphere at storm sudden commencement carried the magnetopause inside the CCE orbit clearly revealing the shocked solar wind plasma. A build up of suprathermal ions is observed near the plasmapause during the storm main phase and recovery phase. Pitch angle distributions in the ring current during the main phase show differences between H(+) and O(+) that suggest mass dependent injection, transport and/or loss processes.

Shelley, E. G.↗

NASA NTRS1986

Designing Delta-DOR acquisition strategies to determine highly elliptical earth orbits

Delta-DOR acquisition strategies are designed for use in determining highly elliptical earth orbits. The requirements for a possible flight demonstration are evaluated for the Charged Composition Explorer spacecraft of the Active Magnetospheric Particle Tracer Explorers. The best-performing strategy uses data spanning the view periods of two orthogonal baselines near the same orbit periapse. The rapidly changing viewing geometry yields both angular position and velocity information, but each observation may require a different reference quasar. The Delta-DOR data noise is highly dependent on acquisition geometry, varying several orders of magnitude across the baseline view periods. Strategies are selected to minimize the measurement noise predicted by a theoretical model. Although the CCE transponder is limited by S-band and a small bandwidth, the addition of Delta-DOR to coherent Doppler and range improves the one-sigma apogee position accuracy by more than an order of magnitude. Additional Delta-DOR accuracy improvements possible using dual-frequency (S/X) calibration, increased spanned bandwidth, and water-vapor radiometry are presented for comparison. With these benefits, the residual Delta-DOR data noise is primarily due to quasar position uncertainties.

Frauenholz, R. B.↗

NASA NTRS1986

Solar wind carbon, nitrogen and oxygen abundances measured in the earth's magnetosheath with AMPTE/CCE

The solar wind number density ratios of C(6+) + C(5+) and N(7+) + N(6+) + N(5+) relative to O(8+) + O(7+) + O(6+) have been measured for the first time using data from the Charge-Energy-Mass Spectrometer on the AMPTE/CCE spacecraft during four solar active periods from Sept. 19 to Nov. 1, 1984 when CCE traversed the subsolar magnetosheath of the compressed magnetosphere. It is found that the average values of the density ratios of C/O and N/O to be 0.43 + or - 0.03 and 0.15 + or - 0.06, respectively. These ratios, as well as the average He(2+)/O ratio of 43 + or - 5 for these same time periods, are in excellent agreement with Solar Energetic Particles (SEP) abundance ratios as well as SEP-derived coronal abundances of these elements. The solar wind C/O ratio is substantially below the generally accepted photospheric value of 0.60.

Gloeckler, G.↗

NASA NTRS1987

Simultaneous observation of Pc 3-4 pulsations in the solar wind and in the earth's magnetosphere

The equatorially orbiting Active Magnetospheric Particle Tracer Explorers CCE and IRM satellites have made numerous observations of Pc 3-4 magnetic field pulsations (10-s to 100-s period) simultaneously at locations upstream of the earth's bow shock and inside the magnetosphere. These observations show solar wind/IMF control of two categories of dayside magnetospheric pulsations. Harmonically structured, azimuthally polarized pulsations are commonly observed from L = 4 to 9 in association with upstream waves. More monochromatic compressional pulsations are clearly evident on occasion, with periods identical to those observed simultaneously in the solar wind. The observations reported here are consistent with a high-latitude (cusp) entry mechanism for wave energy related to harmonically structured pulsations.

Engebretson, M. J.↗

NASA NTRS1988

The Environment for Application Software Integration and Execution (EASIE), version 1.0. Volume 3: Program execution guide

The Environment for Application Software Integration and Execution, EASIE, provides a methodology and a set of software utility programs to ease the task of coordinating engineering design and analysis codes. EASIE was designed to meet the needs of conceptual design engineers that face the task of integrating the results of many stand-alone engineering analysis programs. EASIE provides access to these programs via a quick, uniform, user-friendly interface. In addition, EASIE provides utilities which aid in the execution of the following tasks: selection of application programs, modification and review of program data, automatic definition and coordination of data files during program execution and a logging of steps executed throughout a design study. Volume 3, the Program Execution Guide, describes the executive capabilities provided by EASIE and defines the command language and menus available under Version 1.0. EASIE provides users with two basic modes of operation. One is the Application-Derived Executive (ADE) which provides users with sufficient guidance to quickly review data, select menu action items, and execute application programs. The second is the Complete Control Executive (CCE), which provides a full executive interface allowing users in-depth control of the design process.

Schwing, James L.↗

NASA NTRS1987

An eastward propagating compressional Pc 5 wave observed by AMPTE/CCE in the postmidnight sector

This paper presents a detailed analysis of a compressional Pc 5 wave observed in the postmidnight sector on July 21, 1986, using data from the magnetometer, the charge-energy-mass spectrometer, and the medium-energy particle analyzer aboard the AMPTE/Charge Composition Explorer (CCE) spacecraft. The Pc 5 wave exhibited harmonically related transverse and compressional magnetic oscillations, modulation of the flux of medium energy protons, and a large azimuthal wave number, i.e., properties that are similar to those of compressional Pc5 waves observed previously at geostationary orbit. The unique observations recorded by the AMPTE/CCE included the occurrence of the wave in the postmidnight sector, its sunward propagation with respect to the spacecraft, and the left-handed polarization of the perturbed magnetic field. In spite of the morphological uniqueness observed, the excitation of the July 21 event is considered to be due to the same type of instability as operates at geostationary orbit.

Takahashi, K.↗

NASA NTRS1988

A case study of magnetotail current sheet disruption and diversion

On June 1, 1985 the AMPTE/CCE spacecraft (at a geocentric distance of about 8.8 earth radii at the midnight neutral sheet region) observed a dispersionless energetic particle injection and an increase in magnetic field magnitude, which are features commonly attributed to disruption of the near-earth cross-tail current sheet during substorm expansion onsets. An analysis based on high time-resolution measurements from the magnetometer and the energetic particle detector indicates that the current sheet disruption region exhibited localized (less than 1 earth radius) and transient (less than 1 min) particle intensity enhancements, accompanied by complex magnetic field changes with occasional development of a southward magnetic field component. Similar features are seen in other current disruption/diversion events observed by the CCE. The present analysis suggests that the current disruption region is quite turbulent, similar to laboratory experiments on current sheet disruption, with signatures unlike those expected from an X-type neutral line configuration. No clear indication of periodicity in any magnetic field parameter is discernible for this current disruption event.

Lui, A. T. Y.↗

NASA NTRS1988

Birkeland currents and charged particles in the high-latitude prenoon region - A new interpretation

The relationship between Birkeland currents and charged particles in the ionosphere was investigated for the period between the late morning through early afternoon, using data on simultaneous conjugate measurements of magnetic fields and charged particles at low altitude in the high-latitude prenoon sector, acquired on November 1, 1984 by four spacecraft, IMP 8, AMPTE CCE, DMSP F7, and HILAT. The results of these observations indicate that, for both northward and southward IMF, the traditional 'cusp Birkeland currents' lie poleward of the most intense sheathlike particle precipitation, and it is likely that these currents map to the plasma mantle and are associated with divergent flow of ionospheric plasma near noon. It is suggested that the traditional 'cusp' current system might be more appropriately named the 'mantle' Birkeland current system.

Bythrow, P. F.↗

NASA NTRS1988

Protons and alpha particles in field-aligned beams upstream of the bow shock

Measurements of H(+) and He(2+) ions in field-aligned beams (about 10 keV/nuc) made with the AMPTE-CCE spacecraft are reported. The proton beam population has a density of less than about 1 percent of the solar wind density and a significant thermal anisotropy, in agreement with previous observations. The observed beam velocities are in reasonable agreement with the 'direct reflection' model, in which a portion of the solar wind is reflected and energized at the earth's bow shock, but are consistently larger than expected from magnetosheath leakage models. The He(2+) ions in the beams have approximately the same velocity as the H(+) ions, but the He(2+) to H(+) density ratio is dramatically smaller than that measured simultaneously in the solar wind. The present beam observations were obtained during several of the time intervals previously analyzed by other workers, using data from the same spacecraft, who attributed the streaming upstream ions to magnetospheric rather than bow shock origin.

Ipavich, F. M.↗

NASA NTRS1988

Counter-streaming electrons at the geomagnetic equator near 9 earth radii

AMPTE/CEE observations are used to study short-lived, highly anisotropic electron distributions in the region of the equatorial magnetosphere bewtween 6.6 earth radii and the CCE apogee at 8.8 earth radii. Intense bursts of highly collimated counterstreaming electrons were observed at keV energies with durations of a few tens of seconds to a few minutes near the geomagnetic equator on L-shells that intersect the high-latitude ionosphere in the region normally associated with the auroral zone. It is found that the counterstreaming electrons at energies below the peak energy are accompanied by simultaneous deep depressions of the locally mirroring fluxes. It is suggested that these equatorial electrons may result from the release of auroral electrons trapped beneath the auroral accelerating potentials at lower altitudes along the same magnetic flux tubes.

Klumpar, D. M.↗

NASA NTRS1988

AMPTE/CCE observations of shell-like He(2+) and O(6+) distributions in the magnetosheath

Simultaneous observations of solar wind He(2+) and O(6+) shell-like distributions in the magnetosheath were obtained by the AMPTE CCE on November 1, 1984. It is found that the present distributions are centered on the downstream H(+) bulk velocity and have radii proportional to the mass/charge ratio. The results support an electrostatic cross-shock potential model.

Fuselier, S. A.↗

NASA NTRS1988

Observations of intense ULF pulsation activity near the geomagnetic equator during quiet times

This paper analyzes observations, made by particle and field instruments on the AMPTE CCE satellite, of intense ULF pulsations in the earth's magnetosphere near the geomagnetic equator. These pulsations were observed during magnetically quiet periods in regions characterized by intense fluxes of warm strongly trapped light ions, predominantly H(+), and often with streaming low-energy plasma. The strong latitudinal localization of these pulsations is interpreted to be due to equatorial mass loading or to partial reflection of Alfven wave energy by latitudinal gradients in plasma density. Possible sources of wave energy for these events are discussed.

Engebretson, M. J.↗

NASA NTRS1989

Transport of ions injected by AMPTE magnetotail releases

The BA and Li ions released in the magnetotail by the AMPTE IRM satellite were not observed in the inner magnetosphere with the AMPTE CCE satellite. In an effort to understand these results, Cladis and Francis (1988) modeled the expansion and ionization of the released atoms and computed several hundred guiding-center trajectories of the ions to sample the motion of each ion cloud. Here, the transport calculations are improved, principally by computing the full gyration motion of the ions in a more realistic model of the geomagnetic tail. The results indicate that the Ba(+) ions were convected inward along a narrow corridor, which was at least 2 earth radii away from the satellite in the case of the first Ba release and at least 3 earth radii away in the case of the second Ba release. Even if the ions had reached the satellite, their energies would have been too low to be detected. The Li(+) ions from both releases drifted inward over broad regions which overlapped the satellite in space and time. However, their fluxes at the satellite were somewhat too low to be detected.

Cladis, J. B.↗

NASA NTRS1990

The energetic ion substorm injection boundary

In this paper, 167 dispersionless energetic ion injections which were observed by AMPTE CCE are identified. The radial and local time distribution of the events as a function of kp is qualitatively similar to that envisioned in the injection boundary model of Mauk and McIlwain (1974). It is argued that particles observed during dispersionless injections are locally energized during the disruption of the cross-tail current sheet. Therefore, the injection boundary is identified as derived from the spatial distribution of dispersionless injections, with the earthward edge of the region of the magnetotail which undergoes current sheet disruption during the substorm expansion phase. It is shown that this qualitative model for the generation of the injection boundary can provide an explanation for the dispersionless nature, the double spiral shape, and the Kp dependence of the boundary.

Lopez, R. E.↗

NASA NTRS1990

Observation and theory of Pc 5 waves with harmonically related transverse and compressional components

The properties of 23 magnetic pulsation events observed by the AMPTE CCE spacecraft are studied. These events are selected on the basis of the field magnitude which oscillated at the second harmonic of a simultaneously present transverse oscillation. The events have a second harmonic period of 80-600 s (roughly the Pc 5 range), are observed in cluster in the dawn (0300-0800 magnetic local time, MLT) and dusk (1600-2100 MLT) sectors, and are localized near the magnetic equator. Although the azimuthal wave number estimated from an ion finite Larmor radius effect, is generally large (about 50), there is a marked difference between the events observed in the dawn and dusk sectors. In the dawn sector the waves have low frequencies (1-5 mHz), indicate left-hand polarization with respect to the ambient magnetic field, and propagate eastward with respect to the spacecraft. In the dusk sector the waves have high frequencies (5-15 mHz), indicate right-hand polarization, and propagate westward. It is suggested that the waves are all westward propagating in the plasma rest frame and that local-time-dependent Doppler shift is the reason for the local time dependence of the wave properties.

Takahashi, K.↗

NASA NTRS1990

Ion flux oscillations associated with a radially polarized transverse Pc 5 magnetic pulsation

The AMPTE CCE spacecraft observed a transverse Pc 5 magnetic pulsation (period of about 200 s) at 2155-2310 UT on November 20, 1985, at a radial distance of 5.7 - 7.0 earth radii, at a magnetic latitude of 1.2 - 19 deg, and near 1300 magnetic local time. The magnetic pulsation exhibits properties consistent with a standing Alfven wave with a second-harmonic standing structure along the ambient magnetic field. The amplitude and the phase of the flux pulsation are found to be a function of the particle detector look direction and the particle energy. The observed energy dependence of the shift is interpreted as the result of a drift-bounce resonance of the ions with the wave. From this interpretation it follows that the wave propagated westward with an azimuthal wave number of approximately 100. Thus the study demonstrates that particle data can be useful for determining the spatial structure of some types of ULF waves.

Takahashi, K.↗

NASA NTRS1990

A multisatellite case study of the expansion of a substorm current wedge in the near-earth magnetotail

Results are presented on observations from four satellites (GOES 5, GOES 6, AMPTE CCE, and AMPTE IRM) and two ground stations (San Juan and Tucson) on a substorm that occurred on April 19, 1985 at about 0830 UT. The four spacecraft were arrayed in a configuration that made it possible to separate the effects arising from the longitudinal versus the radial expansion of the substorm current wedge and thus to examine its spatial evolution. The sequence of events that was observed suggests that, during this substorm, the disruption of the cross-tail current sheet, the formation of the substorm current wedge, and the expansion of the plasma sheet began in the near-earth region, and subsequently spread tailward as well as longitudinally.

Lopez, R. E.↗

NASA NTRS1990

A possible case of radially antisunward propagating substorm onset in the near-earth magnetotail

It is generally thought that the local effects associated with substorm onset in the near-earth magnetotail (R less than about 10 earth radii) have a component of propagation which is radially earthward. This study presents a case during which it is possible that the local effects of substorm onset propagated radially antisunward, examining energetic-ion and magnetic-field data from AMPTE/CCE and energetic-particle data from the GEO satellite 1982-019 during a period of weak substorm activity on June 11, 1985. Although the effects of this event on the ground were very weak, the substorm had a dramatic effect on at least one portion of the near-earth magnetotail. During the period the spacecraft were in an unusually close radial alignment. The data show that phenomena associated with the local effects of substorm onset began at or near GEO before they were observed at CCE. This event is best explained by a near-earth disruption of the cross-tail current sheet and the consequent formation of a substorm current wedge, with a component of expansion antisunward down the tail.

Lopez, R. E.↗