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At least 793 records · Page 44
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NASA NTRS1984

Interplanetary radio storms. II - Emission levels and solar wind speed in the range 0.05-0.8 AU

Storms of interplanetary type III radio bursts (IP storms) are commonly observed in the interplanetary medium by the ISEE-3 radio instrument. This instrument has the capability of accurately determining the arrival direction of the radio emission. At each observing frequency, the storm radio sources are tracked as they cross the line-of-sight to the sun. Using a simple model, the emission levels are determined at a number of radio frequencies for four separate storms. The IP storm radiation is found to occur in regions of enhanced density at levels of 0.05 to 0.8 AU. The density in these enhancements falls off faster than R(-2). The solar wind speed in the storm region is also measured. The analysis is consistent with steady conditions in the storm region during a few days around the III storm burst radio emission at the harmonic of the local plasma frequency.

Bougeret, J.-L.↗
NASA NTRS1984

Type III bursts in interplanetary space - Fundamental or harmonic?

ISEE-3 spacecraft observation of 120 relatively simple, isolated bursts in the 30-1980 kHz range are the basis of the present study of Type III bursts in the solar wind. Several characteristics are identified for many of these bursts which imply that the mode of emission changes from predominantly fundamental plasma radiation during the rise phase to predominantly second harmonic during decay. The fundamental emission begins in time coincidence with the start of Langmuir waves, confirming the conventional belief in these waves' causation of Type III bursts. Attention is given to the characteristics of fundamental components, by comparison to harmonics, at km-wavelengths.

Dulk, G. A.↗
NASA NTRS1985

Acceleration of greater than 47 keV ions and greater than 2 keV electrons by interplanetary shocks at 1 AU

It is pointed out that collisionless shocks may be responsible for much of the particle acceleration which occurs in the interplanetary medium. The present investigation is concerned with the conditions for acceleration of particles by interplanetary shocks near 1 AU. Interplanetary shocks near 1 AU have large scale sizes, radii of curvature on the order of 1 AU, or about 1000 times the size of the earth's bow shock. At the considered heliocentric distance the shocks are primarily associated with solar flares and/or solar coronal transients. Observations of magnetic fields, solar wind plasma, and energetic ions and electrons from the ISEE 3 spacecraft are used to study the interplanetary shocks occurring in the period from launch in August 1978 through November 1979. Attention is given to the method of analysis, the determination of the normal to the shock, and energetic particle results.

Tsurutani, B. T.↗
NASA NTRS1985

A simple model for the formation of 'reflected', 'intermediate', and 'diffuse' ion distributions upstream of earth's bow shock

Detailed energetic ion and low-frequency wave experiments on ISEE 1, 2, and 3, have established correlations between the types of ion populations and waves observed to exist in the earth's foreshock region. The present calculation has the objective to quantitatively test the picture obtained for the earth's foreshock region. An analysis is conducted of the coupled spatial and temporal evolution of upstream protons and hydromagnetic waves by means of a simple model in which the protons are represented by counterstreaming beams which resonate with hydromagnetic waves, exciting the outward propagating modes and damping the inward propagating modes at a single wave number.

Lee, M. A.↗
NASA NTRS1985

Electron plasma waves upstream of the earth's bow shock

Electrostatic waves are observed around the plasma frequency fpe in the electron foreshock, together with electrons backstreaming from the bow shock. Using data from the sounder aboard ISEE 1, it is shown that this noise, previously understood as narrow band Langmuir waves more or less widened by Doppler shift or nonlinear effects, is in fact composed of two distinct parts: one is a narrow band noise, emitted just above fpe, and observed at the upstream boundary of the electron foreshock. This component has been interpreted as Langmuir waves emitted by a beam-plasma instability. It is suggested that it is of sufficiently large amplitude and monochromatic enough to trap resonant electrons. The other is a broad band noise, more impulsive than the narrow band noise, observed well above and/or well below fpe, deeper in the electron foreshock. The broad band noise has an average spectrum with a typical bi-exponential shape; its peak frequency is not exactly equal to fpe and depends on the Deybe length. This peak frequency also depends on the velocity for which the electron distribution has maximum skew. An experimental determination of the dispersion relation of the broad band noise shows that this noise, as well as the narrow band noise, may be due to the instability of a hot beam in a plasma.

Lacombe, C.↗
NASA NTRS1985

Slow-mode shocks - A semipermanent feature of the distant geomagnetic tail

A survey is made of the relative frequency of encounters with slow-mode shocks observed by ISEE 3 in the distant geomagnetic tail. The association of these shocks with the phase of substorm activity as evidenced by enhanced currents in the auroral ionosphere and enhanced energetic-particle populations at geostationary orbit is also documented. During the 25 days between January 18 and February 11, 1983, 26 unambiguous examples of slow shocks were observed. Although a very strong association with the level of geomagnetic activity is found, shocks were observed during all phases of substorm activity including one during quiet conditions. Slow-mode shocks must therefore be a semipermanent feature of the bounding surfaces which separate lobe and plasma sheet particle populations in the distant geomagnetic tail.

Feldman, W. C.↗
NASA NTRS1985

High time resolution characteristics of intermediate ion distributions upstream of the earth's bow shock

High time resolution particle data upstream of the bow shock during time intervals that have been identified as having intermediate ion distributions often show high amplitude oscillations in the ion fluxes of energy 2 and 6 keV. These ion oscillations, observed with the particle instruments of the University of California, Berkeley, on the ISEE 1 and 2 spacecraft, are at the same frequency (about 0.04 Hz) as the magnetic field oscillations. Typically, the 6-keV ion flux increases then the 2-keV flux increases followed by a decrease in the 2-keV flux and then the 6-keV flux decreases. This process repeats many times. Although there is no entirely satisfactory explanation, the presence of these ion flux oscillations suggests that distributions often are misidentified as intermediate ion distributions.

Potter, D. W.↗
NASA NTRS1984

3 keV to 2 MeV observations of four gamma-ray bursts

Simultaneous X and gamma ray spectra were obtained for four gamma ray burst events using satellite instrumentation. The P78-1 satellite proportional counters recorded X-ray data in the 3-10 keV range, while Pioneer Venus Orbiter and ISEE 3 sensors had a 3 keV lower limit for events. The positively correlated data covered the events GB 790307, 790325, 790504, and 790731. The time histories of the X and gamma ray energies did not correlate well. The post-gamma ray phase of GB 790307 displayed features of simple cooling, and in conjunction with soft X-ray data suggested an origin in an optically thin fireball. However, the data were equally well-fitted by a model of an emitting hot spot on a neutron star. The data negated any concept that gamma ray bursts evolve similarly to classical X-ray bursts.

Laros, J. G.↗
NASA NTRS1984

Ionic charge states of N, Ne, Mg, Si and S in solar energetic particle events

The mean ionic charges and source-region temperatures of flare-accelerated N, Ne, Mg, Si and S in three large solar-energetic-particle events during 1978-1979 are determined from ISEE-3 observations, extending the findings of Hovestadt et al. (1981) and Gloeckler et al. (1981) for C, He, O, and Fe. The results are presented in tables and graphs, and the charge states are shown to correspond to different source temperatures even in the same flare, assuming equilibration in the hot plasma. The electron temperatures range from 2 x 10 to the 6th K for C, N, O, Si, and S, 4 x 10 to the 6th K for Ne and Fe, and 7 x 10 to the 6th K for Mg. The possibility that these temperature inconsistencies reflect different stages in the approach to equilibrium is considered.

Luhn, A.↗
NASA NTRS1984

The physical mechanisms of subcritical collisionless shock-wave formation

The key process in shock wave formation is related to energy dissipation, and the nature of the operative dissipation mechanism determines the basic character of the resulting shock. In the case of collisionless plasmas, the primary problem consists in the identification of the processes which can provide the necessary dissipation in relatively short spatial scale lengths. The present investigation is concerned with the various collisionless dissipation mechanisms which can operate in weak shocks, taking into account the effects of different mechanisms on shock structure. Particular attention is given to a restricted class of quasi-perpendicular low beta low Mach number shocks. Such shocks are traditionally called 'laminar shocks'. Resistive shocks are considered along with subcritical shocks observed with the aid of the ISEE spacecraft.

Mellott, M. M.↗
NASA NTRS1983

The interplanetary shock event of November 11/12 1978 - A comprehensive test of acceleration theory

A comprehensive study of the November 11, 12, 1978 shock event based on energetic particle, solar wind, magnetic field and wave data from the ISEE-3, -1 and -2 spacecraft has been undertaken both from the energetic and the collisionless shock point of view. The energy density of 10-50 keV protons accelerated by the shock is found to be equivalent to the upstream magnetic field energy density. The observations are in quantitative agreement with Lee's (1983) self consistent theory for the excitation of hydromagnetic waves and the acceleration of ions upstream of interplanetary shocks.

Wenzel, K.-P.↗
NASA NTRS1983

The September 1979 solar cosmic ray event

Observations of a long-lived solar particle event in September 1979, are presented. The energy flux observations were carried out simultaneously by the Voyager 2, ISEE-3, and IMP-8 satellites at widely separated radial positions. It is shown that the flux spectra of the particle population which arrived early at Voyager 2 extended to several MeV for each nucleon, although at energies above 1.5 MeV/nuc, the peak flux occurred one day later. The solar wind speed at Voyager 2 increased from about 600 km/s to 1000 km/s upon the arrival of the particles, causing rapid changes in the Voyager 2 connection longitude. It is suggested that the steepening observed in the maximum flux energy spectra above about 10 MeV/nuc at Voyager 2 may have been due to the injection of particles one day earlier.

Hamilton, D. C.↗
NASA NTRS1983

Ionization states of helium in He-3-rich solar energetic particle events

Results of a systematic study of the ionic charge state of helium in the energy range 0.6-1.0 MeV/nucleon for He-3-rich solar energetic particle events during the time period August 1978 to October 1979 are reported. The data have been obtained with the Max-Planck-Institut/University of Maryland experiment on ISEE-3. Whereas for solar energetic particle events with no enrichment of He-3 relative to He-4 surprisingly large abundances of singly ionized helium have been reported recently, He-3-rich solar energetic particle events do not show significant abundances of He-3(+). This result is consistent with current theories explaining large compositional anomalies by mass per charge dependent selective heating of the minor ion species.

Klecker, B.↗
NASA NTRS1983

Direct determination of the ionic charge distribution of heavy ions in Fe-rich solar energetic particle events

The first direct determination of the iron charge distribution in the energy range 0.3-1.0 MeV/nucleon during Fe-rich and He-3-rich solar energetic particle events is reported. The deterimination was made on the basis of ISEE-3 data for the event from August 1978 to October 1979. The enrichment of He-3 iron relative to oxygen was found to be directly correlated with the enrichment of He-3 to He-4. Average ion charge distributions were computed for: (1) He-3-rich periods which were also Fe-rich and had a He-3/He-4 ratio of 0.1 and (2) periods with a He-3/He-4 ratio of less than 0.1. It is found that the mean iron charge state for He-3-rich periods was in the range 19.5 (+ or - 1.5) and only 14 (+ or - 1) for the time periods with He-3/He-4 less than ratio of 0.1. The reduced data are found to be in good agreement with the theoretical predictions of Fisk (1978), suggesting a temperature in the source region above 5 million degrees K for Fe-rich and He-3-rich solar energetic particle events.

Klecker, B.↗
NASA NTRS1983

The delayed energetic particle event of June 6-10, 1979

Energetic particle observations carried out with the ISEE-3 Medium-Energy Cosmic Ray experiment during the flare event of June 6-10, 1979 are reported. An expanded time history of the He nuclei particle spectra is given, and particle trajectory angles are identified with respect to the earth-sun line. The backward flow of the particle stream following the shock was analyzed, and it is found that the shock continued to accelerate particles beyond 1 AU from the sun. Polar plots of the number of protons counted in each sector of observation are given with their corresponding magnetic field directions.

Von Rosenvinge, T. T.↗
NASA NTRS1985

Coupling between the solar wind and the magnetosphere - CDAW 6

It is pointed out that an extensive study of the causes and manifestations of geomagnetic activity has been carried out as part of the sixth Coordinated Data Analysis Workshop, CDAW 6. The present investigation has the objective to determine the coupling between the solar wind and the magnetosphere for the two selected analysis intervals, taking into account, as a basis for the study, the interplanetary field and plasma observations from ISEE 3 and IMP 8 and the geomagnetic activity indicators developed by CDAW 6 participants. The method of analysis employed is discussed, giving attention to geomagnetic indices, upstream parameters, and a cross-correlation analysis. In a description of the obtained results, the March 22, 1979 event is considered along with the March 31 to April 1, 1979 event, and an intercomparison of the events. The relationship between interplanetary indices and the resulting geomagnetic activity for the two CDAW 6 intervals is illustrated.

Tsurutani, B. T.↗
NASA NTRS1985

Substorm effects on the plasma sheet ion composition on March 22, 1979 (CDAW 6)

One of the potentially most useful aspects of mass spectroscopy in magnetospheric research is related to the ability to distinguish between ions of solar wind and terrestrial origins. Knowing the source of the plasmas in various regions and under various geomagnetic conditions is crucial in improving the understanding of particle flows in the magnetosphere. Sharp et al. (1982) found that the plasma sheet ions in the 0.1- to 16-keV/e range, were predominantly of solar wind origin during low geomagnetic activity, while there was a large terrestrial component during active times. This paper presents a set of data from March 22, 1979. The reported investigation represents the first detailed case study of the relation between geomagnetic substorm activity and the ion composition in the plasma sheet. A decrease in solar wind ion flow at ISEE 1 and the subsequent increase in the flow of ionospheric ions is interpreted as evidence of a fundamental change in the particle flow pattern following the start of substorm activity.

Lennartsson, W.↗
NASA NTRS1985

Short-wavelength electrostatic waves in the earth's magnetosheath

Recent observations with the ISEE-1 spacecraft have found electric field emissions in the dayside magnetosheath whose frequency spectrum is modulated at twice the spacecraft spin period. The upper frequency cut-off in the frequency-time spectrum of the emissions has a characteristic parabola shape or festoon shape. The low frequency cutoff ranges from 100 Hz to 400 Hz, while the high frequency limit ranges from about 1 kHz to 4 kHz. The bandwidth is found to minimize for antenna orientations parallel to the wave vectors. The wave vector does not appear to be related to either the local magnetic field direction of the plasma flow velocity. The spacecraft observed frequency spectrum results from the spacecraft antenna response to the Doppler shifted wave vector spectrum which exists in the plasma. Imposed constraints on the plasma restframe wave vectors and frequencies indicate that the emissions occur within the frequency range from about 150 Hz to 1 kHz, with wavelengths between about 30 meters and 600 meters. These constraints strongly suggest that the festoon-shaped emissions are ion-acoustic waves. The small group velocity and k direction of the ion-acoustic mode are consistent with wave generation upstream at the bow shock and convection downstream to locations within the outer dayside magnetosheath.

Gallagher, D. L.↗