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At least 361 records · Page 20

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NASA NTRS1990

Reconnection versus Kelvin-Helmholtz instability in magnetospheric energy transfer - ISEE observations

Examination of multiple magnetopause crossings observed with the magnetometers on ISEE 1 and 2 makes it possible to determine the amplitude of the oscillation of surface waves on the magnetopause with periods greater than about 2 min and its dependence on latitude, local time, and the direction of the IMF. The magnetopause is more oscillatory for southward IMF than for northward IMF. When the IMF is southward, the amplitude of the oscillation increases with increasing angle from the subsolar point, which suggests that reconnection-related phenomena can generate surface waves on the magnetopause. When the IMF is northward, the oscillation does not grow with distance from the subsolar point, which is contrary to the expected growth of the Kelvin-Helmholtz (K-H) instability. It is also found that solar-wind pressure fluctuations may cause all of the observed boundary oscillations for northward IMF.

Song, PU↗

NASA NTRS1990

Deformation effects of droplet fluctuations on dynamics in an Ising ferromagnetic state

Deformation effects of droplet fluctuations on the dynamics in an Ising ferromagnetic state in two dimensions are studied in the case of an order-parameter-nonconserving system by investigating an equation of motion for a domain boundary. Analytic and numerical studies show that the deformation effects on the survival probability of the droplets simply result in changing the time scale or renormalizing a kinetic coefficient.

Nakanishi, Hiizu↗

NASA NTRS1991

The 1983 tail-era series. Volume 1: ISEE 3 plasma

Observations from the ISEE 3 electron analyzer are presented in plots. Electrons were measured in 15 continuous energy levels between 8.5 and 1140 eV during individual 3-sec spacecraft spins. Times associated with each data point are the beginning time of the 3 sec data collection interval. Moments calculated from the measured distribution function are shown as density, temperature, velocity, and velocity azimuthal angle. Spacecraft ephemeris is shown at the bottom in GSE and GSM coordinates in units of Earth radii, with vertical ticks on the time axis corresponding to the printed positions.

Fairfield, D. H.↗

NASA NTRS1990

ISEE observations of low frequency waves and ion distribution function evolution in the plasma sheet boundary layer

This paper describes ISEE plasma and magnetic fluctuation observations during two crossings of the plasma sheet boundary layer (PSBL) in the earth's magnetotail. Distribution function observations show that the counterstreaming ion components undergo pitch-angle scattering and evolve into a shell distribution in velocity space. This evolution is correlated with the development of low frequency, low amplitude magnetic fluctuations. However, the measured wave amplitudes are insufficient to accomplish the observed degree of ion pitch-angle scatttering locally; the near-earth distributions may be the result of processes occurring much farther down the magnetotail. Results show a clear correlation between the ion component beta and the relative streaming speed of the two components, suggesting that electromagnetic ion/ion instabilities do play an important role in the scattering of PSBL ions.

Elphic, R. C.↗

NASA NTRS1990

Observations of the earth's continuum radiation in the distant magnetotail with ISEE 3

Observations of the earth's nonthermal continuum radiation made with the radio receiver on ISEE 3 are analyzed, emphasizing rapid crossings of the magnetopause in the distant magnetotail. The intensity and anisotropy of the radiation field are always found to be larger in the lobes than in the magnetosheath. The radiation is interpreted as arising from a source located at or near the plasmapause. It is suggested that the observed variations across the magnetopause of the intensity and anisotropy can be understood by taking into account the facts that the magnetotail is a plasma waveguide whose walls are sometimes rough and leaky and that there are density fluctuations in the magnetosheath. The efficiency with which the continuum power at 30 kHz is collected in the near-earth regions and ducted toward the distant tail is a strong, increasing function of the magnetosheath plasma frequency (MPF). The percentage of that power which travels in the magnetosheath decreases with increasing MPF.

Steinberg, J.-L.↗

NASA NTRS1991

ISEE 1 observations of electrostatic ion cyclotron waves in association with ion beams on auroral field lines from about 2.5 to 4.5 R(E)

Quasi-monochromatic waves at about the hydrogen cyclotron frequency were observed as the ISEE 1 satellite traversed auroral field lines at radial distances of about 2.5-4.5 R(E) near midnight on June 19, 1981. Waves and both lower and higher frequencies were observed at higher altitudes, and possible electrostatic helium cyclotron and oxygen cyclotron waves occurred at lower altitudes. Upflowing hydrogen and oxygen beams and field-aligned currents occurred simultaneously. The features of the waves are most consistent with the current-driven mode. In addition, numerical studies of the linear dispersion relation, using parameters based on the observations, show that both the parallel and oblique two-stream modes and the ion-beam-driven modes were stable while oblique current-driven modes were unstable. The O(+) and H(+) distributions provide evidence for interactions with local electrostatic ion cyclotron waves and for the H(+)-O(+) two-stream instability at altitudes below the satellite.

Catell, C. A.↗

NASA NTRS1991

Wave mode identification of electrostatic noise observed with ISEE 3 in the deep tail boundary layer

The characteristics of the VLF electrostatic noise observed with ISEE 3 in the low-latitude boundary layer of distant geomagnetic tail are examined using a display format for the wave dynamic spectra different from that used by Scarf et al. (1984). It is shown that the observed noise is composed of impulsive bursts. The results of the detailed analysis of the noise parameters are used to develop a model of plasma wave behavior in the plasma rest frame. A hypothesis is proposed that the wide frequency extent of the noise spectra is composed of Doppler effects of waves propagating nearly omnidirectionally within the plasma rest frame, which is moving with the electron bulk speed. On the basis of this hypothesis, the wavelength of the observed waves were determined from the width of the frequency extent and the measured electron bulk speed. It is shown that the wavelength ranges from 2 to 8 times the plasma Debye length.

Tsutsui, M.↗

NASA NTRS1991

Weak, quasiparallel profiles of earth's bow shock - A comparison between numerical simulations and ISEE 3 observations on the far flank

Over 200 crossings of the distant downwind flanks of earth's magnetosonic bow shock by ISEE 3 included many cases of weak, or low Mach number, quasi-parallel shocks. A consistent feature of the magnetic field profiles was the presence of large amplitude, near periodic to irregular transverse oscillations downstream from even the weakest Q-parallel shocks. Large downstream perturbations with whistler-like features similar to those of the observations appear in 1D simulations when the Alfven Mach number M(A) is greater than 2.5 but not when M(A) = 2.1. The observed cases with downstream waves also occurred when M(A) is greater than about 2.5, suggesting the importance of the Alfven as opposed to magnetosonic Mach number in determining the signature of weak, Q-parallel shocks.

Greenstadt, E. W.↗

NASA NTRS1992

On the structure of the distant magnetotail - ISEE 3

The relative frequency of observation of the magnetosheath and magnetotail in the region where a nominal magnetotail is expected is determined on the basis of ISEE-3 magnetic field and electron plasma data. These observations are compared with how frequently a tail of a given radius would be expected to be seen, assuming typical variations in the direction of the solar wind flow relative to the radial. Observations match expectations if the average radius consistent with an open magnetotail where field lines are lost both through the magnetopause and also by closing along the equatorial current sheet. This relatively small radius is consistent with an open magnetotail where field lines are lost both through the magnetopause and also by closing across the equatorial current sheet. The average solar magnetospheric Bz component of the field in the distant plasma sheet is 0.6 nT during quiet times but zero during disturbed times, which suggests that when the polar cap becomes smaller during quiet times, many of the field lines that previously formed the distant tail lobes are converted into closed field lines that cross the equatorial plane earthward of 240 RE.

Fairfield, D. H.↗

NASA NTRS1992

He(2+) in field-aligned beams - ISEE results

He(2+) concentrations are determined for 14 field-aligned proton-beam events observed in the ion-foreshock region upstream from the earth's bow shock by the ISEE spacecraft. For all 14 events, most under normal solar-wind conditions, the He(2+) concentrations were a factor of 10 or more below the H(+) concentrations in the field-aligned beams when normalized by the solar wind He(2+) to H(+) density ratio. These results indicate that field-aligned beams do not provide the principal He(2+) seed population for ion acceleration in the ion-foreshock region.

Fuselier, Stephen A.↗

NASA NTRS1992

Electromagnetic ion cyclotron waves observed near the oxygen cyclotron frequency by ISEE 1 and 2

The first results of observations of ion cyclotron waves by the elliptically orbiting ISEE 1 and 2 pair of spacecraft are reported. The most intense waves (8 nT) were observed in the outer plasmasphere where convection drift velocities were largest and the Alfven velocity was a minimum. Wave polarization is predominantly left-handed with propagation almost parallel to the ambient magnetic field, and the spectral slot and polarization reversal predicted by cold plasma propagation theory are identified in the wave data. Computations of the experimental wave spectra during the passage through the plasmapause show that the spectral slots relate to the local plasma parameters, possibly suggesting an ion cyclotron wave growth source near the spacecraft. A regular wave packet structure seen over the first 30 min of the event is attributed to the modulation of this energy source by the Pc 5 waves seen at the same time.

Fraser, B. J.↗

NASA NTRS1992

Multi-satellite observations of plasmoids - IMP 8 and ISEE 3

An examination of IMP 8 and ISEE 3 magnetotail data during the 1983 Geotail Mission yielded one plasmoid event which was observed by both satellites and two other possible cases. These are the first multisatellite observations of plasoids. These observations provide a unique opportunity to examine how plasmoid characteristics change as plasmoids propagate downtail and they show that plasmoids are very stable structures.

Moldwin, Mark B.↗

NASA NTRS1992

A scenario for solar wind penetration of earth's magnetic tail based on ion composition data from the ISEE 1 spacecraft

Based on He(2+) and H(-) ion composition data from the Plasma Composition Experiment on ISEE 1, a scenario is proposed for the solar wind penetration of the earth's magnetic tail, which does not require that the solar wind plasma be magnetized. While this study does not take issue with the notion that earth's magnetic field merges with the solar wind magnetic field on a regular basis, it focuses on certain aspects of interaction between the solar wind particles and the earth's field, e.g, the fact that the geomagnetic tail always has a plasma sheet, even during times when the physical signs of magnetic merging are weak or absent. It is argued that the solar plasma enters along slots between the tail lobes and the plasma sheet, even quite close to earth, convected inward along the plasma sheet boundary layer or adjacent to it, by the electric fringe field of the ever present low-latitude magnetopause boundary layer (LLBL). The required E x B drifts are produced by closing LLBL equipotential surfaces through the plasma sheet.

Lennartsson, W.↗

NASA NTRS1992

A determination of twisting of the Earth's magnetotail at distances 115-220 RE - ISEE 3

Observations from magnetic field and plasma experiments on ISEE 3 are used to identify and to analyze 16 crossings of the distant magnetotail neutral sheet. Four methods of analyses have been employed to measure the extent of the magnetotail twisting, which is found to be much greater than what was previously observed or, the theoretically inferred twist. A twist of more than 90 deg has frequently been observed on both open and closed magnetic field lines. In addition, the location of the magnetic neutral line of the magnetotail has been found to move over the distance interval of 115 to 220 Earth radii. Some features of these results suggest that a modification of the present solar wind-geomagnetic field interaction model may be needed.

Macwan, Snehavadan E.↗

NASA NTRS1993

Energetic (greater than 0.2 MeV) electron bursts observed by ISEE 3 in the deep (less than 240 R(E)) geomagnetic tail

The study reports the detection by the Goddard Space Flight Center medium energy cosmic ray experiment of bursts of 0.2-2.0-MeV electrons with durations of less than 1 hr during the ISEE 3 geotail mission in October 1982 to November 1983. Bursts are observed in all tail regions, with the majority (about 60 percent) associated with encounters with the plasma sheet, about 20 percent occurring in the tail lobes and a similar number in the magnetosheath. The electron burst intensity and occurrence rate fall abruptly by around an order of magnitude at about 80-90 R(E) downtail. The majority (about 64 percent) of plasma sheet electron bursts are associated with northward B(z). Plasma sheet electron bursts associated with southward B(z) are rare (6 percent of all plasma sheet events). It is suggested that temporal variations in the electron intensity associated with substorms may be present, in addition to spatial variations reflecting the average quiet-time tail configuration.

Richardson, I. G.↗

NASA NTRS1991

Measurements of the spatial structure and directivity of 100 KeV photon sources in solar flares using PVO and ISEE-3 spacecraft

The objective of this grant was to measure the spatial structure and directivity of the hard X-ray and low energy gamma-ray (100 keV-2 MeV) continuum sources in solar flares using stereoscopic observations made with spectrometers aboard the Pioneer Venus Orbiter (PVO) and Third International Sun Earth Explorer (ISEE-3) spacecraft. Since the hard X-ray emission is produced by energetic electrons through the bremsstrahlung process, the observed directivity can be directly related to the 'beaming' of electrons accelerated during the flare as they propagate from the acceleration region in the corona to the chromosphere/transition region. Some models (e.g., the thick-target model) predict that most of the impulsive hard X-ray/low energy gamma-ray source is located in the chromosphere, the effective height of the X-ray source above the photosphere increasing with the decrease in the photon energy. This can be verified by determining the height-dependence of the photon source through stereoscopic observations of those flares which are partially occulted from the view of one of the two spacecraft. Thus predictions about beaming of electrons as well as their spatial distributions could be tested through the analysis proposed under this grant.

Anderson, Kinsey A.↗

NASA NTRS1994

Analysis of data from the plasma composition experiment on the International Sun-Earth Explorer (ISEE 1)

The Lockheed plasma composition experiment on the ISEE 1 spacecraft has provided one of the largest and most varied sets of data on earth's energetic plasma environment, covering both the solar wind, well beyond the bow shock, and the near equatorial magnetosphere to a distance of almost 23 earth radii. This report is an overview of the last four years of data analysis and archiving. The archiving for NSSDC includes most data obtained during the initial 28-months of instrument operation, from early November 1977 through the end of February 1980. The data products are a combination of spectra (mass and energy angle) and velocity moments. A copy of the data user's guide and examples of the data products are attached as appendix A. The data analysis covers three major areas: solar wind ions upstream and downstream of the day side bowshock, especially He(++) ions; terrestrial ions flowing upward from the auroral regions, especially H(+), O(+), and He(+) ions; and ions of both solar and terrestrial origins in the tail plasma sheet and lobe regions. Copies of publications are attached.

Lennartsson, O. W.↗

NASA NTRS1993

ISEE 3 observations of traveling compression regions in the earth's magnetotail

A comprehensive study is conducted of traveling compression regions (TCRs) in the distant magnetotail; a total of 116 TCRs were studied from ISEE 3 observations. Strong support is obtained for the interpretation of TCRs as large-scale compressions of the lobes that are caused by the rapid downtail motion of plasmoids. TCRs furnish information on the 3D shape and volume of the plasmoid bulge. The close association noted between the substorm expansion phase onset and the TCRs provides strong support for the plasmoid model of magnetotail dynamics.

Slavin, J. A.↗