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At least 109 records · Page 6
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NASA NTRS1980

Gamma-ray burst observations from the UCB/LASL experiment of ISEE-3

The University of California at Berkeley (UCB)/Los Alamos Scientific Laboratory (LASL) gamma-ray burst experiment on board ISEE-3 is described and initial results of the experiment are presented. The instrument consists of an X-ray spectrometer originally designed to monitor solar emission continuously over the energy range 4.8-1264 keV with additional electronics to record data from the intense, short-lived gamma ray bursts at a very high rate and with good timing accuracy. Since the launch of ISEE-3 into a heliocentric orbit at the inner Lagrangian point in August, 1978, the UCB/LASL experiment has detected and recorded 12 gamma-ray bursts, including the unusually intense burst of November 4, 1978, which exhibited most of the classical gamma-ray burst characteristics, the intense burst of November 19, 1978, with an atypical time history and an unusually hard spectrum, and the extended burst of March 7, 1979. The spectral and temporal data demonstrate the diverse nature of the gamma-ray burst phenomenon, and are currently being combined with those of the Pioneer Venus Orbiter and Venera 11 and 12 to obtain accurate burst locations.

Evans, W. D.↗
NASA NTRS1981

Bi-directional streaming of solar wind electrons greater than 80 eV - ISEE evidence for a closed-field structure within the driver gas of an interplanetary shock

In near time coincidence with the arrival of helium enriched plasma driving the shock wave disturbance of November 12-13, 1978, strong bi-directional streaming of solar wind electrons greater than about 80 eV was observed with Los Alamos instrumentation on ISEE 3. The streaming persisted for many hours simultaneously parallel and anti-parallel to the interplanetary magnetic field which was directed roughly perpendicular to the sun-satellite line. This example of bidirectional streaming cannot be explained by field line connection to the earth's bow shock or the outward propagating interplanetary shock which passed ISEE 3 approximately 16 hours earlier. The event is explained if the local interplanetary field was a part of a magnetic bottle rooted at the sun or a disconnected loop propagating outward.

Bame, S. J.↗
NASA NTRS1981

Energetic ion and electron observations of the geomagnetic plasma sheet boundary layer - Three-dimensional results from ISEE 1

A description of energetic ion and electron behavior in the geomagnetic plasma sheet boundary layer is presented based on observations made by the medium-energy particle experiment on board ISEE 1. Three-dimensional observations of ions of energies 24-2081 keV and electrons of energies 22.5-1200 keV were obtained by the NOAA/WAPS instrument near the center of the magnetotail at a distance of approximately 15 earth radii. Large-scale motions of plasma sheet energetic particles are observed as an apparent result of a series of magnetospheric disturbances (substorms), which are characterized by substantial contractions and expansions. Ion flow velocity in a distinct boundary layer in energetic ions has been found to be in the earthward direction in each of the five ISEE 1 boundary crossings. Boundary layer motion during one of these crossings is interpreted as large-amplitude boundary waves with periodicities of a few minutes superimposed on the general plasma sheet behavior associated with the substorm process.

Spjeldvik, W. N.↗
NASA NTRS1981

Nonducted coherent VLF waves and associated triggered emissions observed on the ISEE-1 satellite

A description is given of new observations of nonducted coherent VLF waves from ground-based transmitters and associated VLF emissions in the magnetosphere. The data reported were acquired by the Stanford University VLF Wave Injection Experiment on the ISEE-1 satellite. The experiment has four main components, including a broadband (1-32 kHz) VLF receiver on ISEE-1 connected to a long electric antenna, a broadband (1-20 kHz) controllable VLF transmitter located at Siple Station in the Antarctic, various VLF navigation and communications transmitters, and ground stations in the Antarctic and Canada. The main goal of the experiment is to acquire understanding of interactions between coherent VLF waves and energetic particles in the magnetosphere, in particular the whistler mode instability through which both natural and stimulated VLF emissions are produced.

Bell, T. F.↗
NASA NTRS1981

Energetic ion beams at the edge of the plasma sheet - ISEE 1 observations plus a simple explanatory model

It has been found that energetic ions with energies in the range from 10 keV to 2 MeV are an important part of the geomagnetic tail particle population. A description is presented of energetic ion, three-dimensional distribution observations from ISEE 1 during 0400-2000 UT, May 3, 1978, a time when several encounters with the geomagnetic tail plasma sheet occurred. Pronounced energetic ion streaming is observed at each entry to and exit from the plasma sheet. Azimuthal gradients observed during these times indicate that this streaming occurs within two gyroradii of the plasma sheet edge. Streaming characteristics show both narrow and broad angular flows at arbitrary angles to B. These flows are observed simultaneously and individually. The time, energy, and pitch angle evolution of the ion fluxes show that ISEE 1 is encountering a dynamic and not a static equilibrium situation at the edge of the plasma sheet.

Williams, D. J.↗
NASA NTRS1982

Plasma electron signature of magnetic connection to the earth's bow shock - ISEE 3

New observations of bowshock modified electron velocity distribution for upstreams are investigated using the Los Alamos ISEE 3 electron analyzer. Examples of two-dimensional electron distributions observed when ISEE 3 magnetically connected to the bowshock are presented, and the velocity moments are determined. The origin of the enhanced backstreaming electron fluxes and their likely effects on the upstream microturbulence spectrum are interpreted. A nearly isotropic component of back-streaming shock-heated electrons is found with energies at least as high as 1 keV. Phase-space density of the low energy parts of distributions measures well within the boundaries of accessibility and is observed to be depressed. Such distributions are likely to result from the direct sampling of electrons originating within the forward edge of the earth's bowshock, and may be unstable to whistler waves.

Feldman, W. C.↗
NASA NTRS1982

ISEE-3/IMP-8 observations of simultaneous upstream proton events

Upstream 50-200 keV proton events were observed simultaneously by the low energy proton detectors on ISEE-3 and IMP-8, and the gradient from the spin averaged fluxes at the two spacecraft was calculated. The dependence of that gradient upon the angular distributions at IMP-8 was investigated as well as the distance from IMP-8 to the bow shock. The pitch angle distributions are narrow at ISEE-3 and wide and often pancake-shaped at IMP-8 with a peak near 90 degrees. This implies the existence of a weak scattering region about 5-15 earth radii upstream of the earth's bow shock.

Sanderson, T. R.↗
NASA NTRS1982

Conical pitch angle distributions of very low-energy ion fluxes observed by ISEE 1

Observations are presented of conical distributions of low-energy ion fluxes from throughout the magnetosphere. The data were provided by the plasma composition experiment (PCE) on ISEE 1. ISEE 1 was launched in October 1977 into a highly elliptical orbit with a 30 deg inclination to the equator and 22.5 earth radii apogee. Particular attention is given to data taken when the instrument was in its thermal plasma mode, sampling ions in the energy per charge range 0-100 eV/e. Attention is given to examples of conical distributions in 0- to 100-eV/e ions, the occurrence of conical distributions of 0- to 100-eV ions in local time-geocentric distance and latitude-geocentric distance coordinates, the cone angles in 0- to 100-eV ion conics, Kp distributions of 0- to 100-eV ion conics, and some compositional aspects of 0- to 100-eV ion conics.

Horwitz, J. L.↗
NASA NTRS1982

Standing hydromagnetic waves observed by ISEE 1 and 2 - Radial extent and harmonic

Direct measurements of the spatial extent of the resonant hydromagnetic waves associated with Pc 4 and 5 magnetic pulsations made by the closely spaced ISEE 1 and 2 satellites are presented together with ISEE 1 determinations of the harmonic of the resonant waves. The use of two satellites in similar orbits, which makes it possible to distinguish between spatial and temporal features, has shown the resonant region widths to extend over about 0.2 to 1.6 L shells for three events detected on the dayside between L = 4 and L = 7. The two events for which plasma density data was available occurred at plasma density gradients in the vicinity of the plasmapause. The standing wave harmonic was determined by the combination of two techniques: the comparison of the observed wave period with that predicted by standing wave theory, and the comparison of the phases of the observed wave electric and magnetic field. The two events analyzed are found to be second harmonic oscillations, suggesting internal generation in the magnetosphere by a bounce resonant mechanism.

Singer, H. J.↗
NASA NTRS1982

Use of the thin sheath approximation for obtaining ion temperatures from the ISEE 1 limited aperture RPA

A procedure for analyzing low-energy (less than approximately 100 eV) ion data from the plasma composition experiment on ISEE 1 is set forth. The method is based on a derived analytic expression for particle flux to a limited aperture retarding potential analyzer (RPA) in the thin sheath approximation, which makes allowance for some effects of a charged spacecraft on plasma particle trajectories. Calculations using simulated data are employed in testing the efficacy and accuracy of the technique. On the basis of an analysis of these calculation results and the mathematical model, the method is seen as being able to provide accurate ion temperatures from all good plasmaspheric RPA data. It is noted that corresponding densities and spacecraft potentials should be accurate when spacecraft potentials are negative but that they are subject to error for positive spacecraft potentials, particularly when ion Mach numbers are much less than 1. An analysis of data from a representative ISEE 1 pass produces a plasmasphere temperature profile that is consistent in overall structure with previous observations.

Comfort, R. H.↗
NASA NTRS1982

ISEE-1 and -2 observations of laminar bow shocks - Velocity and thickness

The ISEE-1 and -2 spacecraft have provided the opportunity for studying the thickness and velocity of the bow shock on a regular basis. There are two models for the thickness of quasi-perpendicular laminar shocks. Galeev (1976) has calculated the thickness of the nearly perpendicular laminar bow shock by means of a weak ion sound turbulence (WIST) approach. Morse and Greenstadt (1976), on the other hand, assume that the shock thickness adjust itself to stay close to the drift velocity for marginal stability of current driven electrostatic waves. The present investigation is concerned with an evaluation of the competing theories, taking into account ISEE-1 and -2 observations of laminar bow shocks. It is found that the formula used by Morse and Greenstadt does not predict the observed thicknesses as well as the formula given by Galeev.

Russell, C. T.↗
NASA NTRS1982

ISEE work on collisionless shocks - CDAW-3, the meeting and the results July 23-26, 1979

At CDAW(Coordinated Data Analysis Workshop)-3, data from ISEE-1 and -2 were used, and 17 data sets were incorporated into a total of 44 megabytes of disk storage. The presence of ISEE-1 and -2 at variable separation distances has made it possible to settle the question of shock motion and to obtain shock thicknesses. A full range of wave instrumentation was available to study upstream waves and turbulence, and energetic particle investigations made it possible to obtain good observations of shock-induced particle acceleration. It is concluded that these improved observations have resulted in a revival of interest in the study of the collisionless shock, both as an experimental and theoretical research problem. It is expected that these investigations will lead to a better understanding of how to use the earth's bow shock to provide well-defined and theoretically useful examples for study.

Ogilvie, K. W.↗
NASA NTRS1983

Observations of upstream ions and low-frequency waves on ISEE 3

Three examples are presented of observations of upstream ions and low-frequency waves made at ISEE 3 at distances of up to 200 earth radii upstream from the earth's bow shock. The observations demonstrate that even at 200 earth radii, weak scattering plays an important role in the transport of upstream ions. At ISEE 3, during long-lasting events, a correlation is observed between the growth of the waves and the intensity of the upstream ions. An increase in the number of pitch-angle-scattered ions, frequently with a moderate amount of ions having pitch angles greater than 90 deg, is observed, and this is correlated with the growth of the waves. It is concluded that during long-lasting events an equilibrium is reached where the region between the spacecraft and the bow shock contains a significant amount of low-frequency wave activity, together with significant pitch angle scattering.

Sanderson, T. R.↗
NASA NTRS1982

Search for time variations in 511 keV flux by ISEE-3 gamma-ray spectrometer

Upper limits to the variation of galactic 511 keV flux as observed by the ISEE-3 gamma-ray spectrometer for 500 days of nearly continuous observation are reported. It is pointed out that if sources similar to the galactic center source were distributed uniformly throughout the Galaxy, a source within 2-3 kpc could have been detected by the ISEE-3 spectrometer. The lack of detection is evidence that the galactic center source is unique within the Galaxy. The galactic center observations made with the HEAO-3 gamma-ray spectrometer are seen as supporting the contention that a time-varying source is 511 keV emission lies near the galactic center.

Norris, J. P.↗
NASA NTRS1983

An ISEE 3 high time resolution study of interplanetary parameter correlations with magnetospheric activity

The coupling between the solar wind and the geomagnetic disturbances was examined using data from the ISEE-3 spacecraft at an earth-sun libration point and ground-based data. One minute data were used to avoid aliasing in determining the internal magnetospheric response to solar wind conditions. Attention was given to the cross-correlations between the geomagnetic index (AE), the total energy dissipation rate (UT), and the solar wind parameters, as well as the spatial and temporal scales on which the magnetosphere reacts to the solar wind conditions. It was considered necessary to characterize the physics of the solar wind-magnetosphere coupling in order to define the requirements for a spacecraft like the ISEE-3 that could be used as a real time monitoring system for predicting storms and substorms. The correlations among all but one parameter were lower during disturbance intervals; UT was highly correlated with all parameters during the disturbed times. An intrinsic 25-40 min delay was detected between interplanetary activity and magnetospheric response in quite times, diminishing to no more than 15 min during disturbed times.

Baker, D. N.↗
NASA NTRS1983

Average configuration of the distant (less than 220-earth-radii) magnetotail - Initial ISEE-3 magnetic field results

Magnetic field measurements from the first two passes of the ISEE-3 GEOTAIL Mission have been used to study the structure of the trans-lunar tail. Good agreement was found between the ISEE-3 magnetopause crossings and the Explorer 33, 35 model of Howe and Binsack (1972). Neutral sheet location was well ordered by the hinged current sheet models based upon near earth measurements. Between X = -20 and -120 earth radii the radius of the tail increases by about 30 percent while the lobe field strength decreases by approximately 60 percent. Beyond X = -100 to -1200 earth radii the tail diameter and lobe field magnitude become nearly constant at terminal values of approximately 60 earth radii and 9 nT, respectively. The distance at which the tail was observed to cease flaring, 100-120 earth radii, is in close agreement with the predictions of the analytic tail model of Coroniti and Kennel (1972). Overall, the findings of this study suggest that the magnetotail retains much of its near earth structure out to X = -220 earth radii.

Slavin, J. A.↗
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

Multiple spacecraft observations of interplanetary shocks ISEE three-dimensional plasma measurements

ISEE 1 and ISEE 3 three-dimensional solar wind plasma measurements are used together with magnetic field measurements across five previously studied interplanetary shocks to test the accuracy of the mixed-mode shock-normal determination technique and to test whether the shock properties are best approximated with a ratio of specific heats of 5/3 or 2. In the shocks examined, the assumption that the velocity jump was along the normal provided an estimate of the shock normal within 15 deg of the best fit normal 50 percent of the time and within 50 deg, 90 percent of the time. The mixed-mode normals lay within 12 deg of the best fit normal 50 percent of the time and within 36 deg, 90 percent of the time. Part of this deviation may be due to differences in the orientation of the local normal from that of the average normal. Finally, the jump in plasma and field across the shock is better predicted from the Rankine-Hugoniot equations using a ratio of specific heats of 5/3 rather than 2.

Russell, C. T.↗