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At least 955 records · Page 53
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NASA NTRS1987

Effect of wave localization on plasma instabilities

The Anderson model of wave localization in random media is involved to study the effect of solar wind density turbulence on plasma processes associated with the solar type III radio burst. ISEE-3 satellite data indicate that a possible model for the type III process is the parametric decay of Langmuir waves excited by solar flare electron streams into daughter electromagnetic and ion acoustic waves. The threshold for this instability, however, is much higher than observed Langmuir wave levels because of rapid wave convection of the transverse electromagnetic daughter wave in the case where the solar wind is assumed homogeneous. Langmuir and transverse waves near critical density satisfy the Ioffe-Reigel criteria for wave localization in the solar wind with observed density fluctuations -1 percent. Numerical simulations of wave propagation in random media confirm the localization length predictions of Escande and Souillard for stationary density fluctations. For mobile density fluctuations localized wave packets spread at the propagation velocity of the density fluctuations rather than the group velocity of the waves. Computer simulations using a linearized hybrid code show that an electron beam will excite localized Langmuir waves in a plasma with density turbulence. An action principle approach is used to develop a theory of non-linear wave processes when waves are localized. A theory of resonant particles diffusion by localized waves is developed to explain the saturation of the beam-plasma instability. It is argued that localization of electromagnetic waves will allow the instability threshold to be exceeded for the parametric decay discussed above.

Levedahl, William Kirk↗
NASA NTRS1988

Three-dimensional magnetosheath plasma ion distributions from 200 eV to 2 MeV

This paper presents initial measurements, made with ISEE 1 plasma and energetic-particle instruments, of the three-dimensional magnetosheath plasma ion flow and the spectrum over the energy range of 200 eV to 2 MeV, obtained on two magnetosheath traversals, one on the dawn (December 19, 1977) and the other on the dusk (July 7, 1978) flanks of the magnetosphere. The data suggest that the magnetosheath plasma ion population often consisted of a shocked solar wind component, of energy not greater than 5 keV, and a magnetospheric high-energy (not below 5 keV) component. The shocked solar wind component generally behaved independently of the magnetic field direction, indicating that the magnetic field was carried along in the bulk plasma flow. The high-energy tail was highly modulated by the magnetic field.

Williams, D. J.↗
NASA NTRS1988

Electron heating and the potential jump across fast mode shocks

Two different methods were applied to determine the cross-shock potential jump in the de Hoffmann-Teller reference frame, using a data set that represented 66 crossings of the terrestrial bow shock and 14 interplanetary shocks observed by various ISEE spacecraft, and one crossing each of the Jovian bow shock and the Uranian bow shock made by the Voyager spacecraft. Results for estimates of the electrostatic potential based on an estimate of the jump in electron enthalpy correlated well with estimates based on Liouville's theorem, although the Liouville-determined values were systematically the higher of the two, suggesting that significant irreversible processes contribute to the shape of the downstream distribution. The potential jump corresponds to approximately 12-15 percent of the incident ion ram kinetic energy, and was found not to be controlled by the Mach number, plasma beta, shock geometry, or electron to ion temperature ratios.

Schwartz, Steven J.↗
NASA NTRS1988

Boundary layer dynamics in the description of magnetospheric substorms

This paper presents an analysis of eleven magnetospheric substorm events for which good-quality ground-based magnetometer data and ISEE satellite data were both available. It is shown that the magnetotail particle and field observations associated with a substorm expansive phase can be explained through the spatial movement of the boundary layers and central plasma sheet in the magnetotail. The sweeping of these regions past the satellite, even in the absence of temporal variations within the various regions, can lead to a set of plasma flow observations typical of what is observed in the magnetotail during substorm activity.

Eastman, T. E.↗
NASA NTRS1989

Large-scale fluctuations in the solar wind at 1 AU - 1978-1982

The large-scale fluctuations in the strength of the magnetic field B and the bulk speed V at 1 AU were investigated on the basis of hourly averages of IMP 8 and ISEE 3 data compiled by Couzens and King (1986). The power spectra of the intermediate frequency fluctuations in B at 1 AU had the form of a power law with exponent 1.92 + or - 0.06 during the 1978-1982 interval. The contributions of jumps to the spectra of the large-scale fluctuations in B and V were studied for the interval from days 226 to 365, 1978, which is representative of other such intervals. Of the jumps in B, 22 percent have the signature of a forward or reverse shock.

Burlaga, L. F.↗
NASA NTRS1989

A statistical study of ELF-VLF plasma waves at the magnetopause

ISEE 1 plasma wave data are used to study the broadband ELF-VLF plasma waves at the magnetopause. Enhanced wave intensities are detected at 85 percent of all magnetopause crossings. Wave amplitudes vary from event to event and even with a single event. Wave spectra averaged over many passes, however, are similar at dawn, noon, and dusk local hours. The only parameter correlated with wave intensity is the magnitude of the Z component of the magnetosheath magnetic field. The results place strong constraints on any proposed generation mechanism for the broadband magnetopause boundary layer waves.

Tsurutani, Bruce T.↗
NASA NTRS1988

Multipoint measurements of magnetotail dynamics

The role of multipoint spacecraft measurements in revealing the morphology of magnetospheric substorm is described. Information has been provided on the storage of energy in the tail during the growth phase, the thinning of the plasma sheet relative to onset, reconfiguration and energy loss after onset, and how these phenomena are controlled by the IMF. Smaller-scale phenomena that need to be observed on finer time scales and detected in more limited spatial regions were studied by ISEE 1 and 2 and a number of spacecraft near geosyncronous orbit.

Fairfield, D. H.↗
NASA NTRS1988

Comparison of plasma sheet ion composition with the IMF and solar wind plasma

Plasma sheet energetic ion data (0.1- to 16 keV/e) obtained by the Plasma Composition Experiment on ISEE-1 between 10 and 23 earth radii are compared with concurrent IMF and solar wind plasma data. The densities of H(+) and He(++) ions in the plasma sheet are found to be the highest, and the most nearly proportional to the solar wind density, when the IMF B(z) is not northward. The density of terrestrial O(+) ions increases strongly with increasing magnitude of the IMF, in apparent agreement with the notion that the IMF plays a fundamental role in the electric coupling between the solar wind and the ionosphere.

Lennartsson, W.↗
NASA NTRS1988

Multi-point measurements of ULF wave phases using a multi-channel energetic ion detector

The oscillation of differential fluxes of energetic ions modulated by a ULF wave often shows a phase shift between measurements in back-to-back detectors with look directions perpendicular to the ambient magnetic field. In a plasma of a single ion species, the phase difference is caused by displacement of the effective measurement positions by one ion gyroradius to each side of the detector. As the wave phase is periodic, the observed phase shift can correspond to a family of possible wavelengths. Simultaneous measurements of the flux modulations in different energy channels, which are equivalent to measurements of the wave phase at different positions, may make it possible to single out a unique wavelength consistent with all the measurements. Using the medium-energy-particle experiments ISEE-1 and 2, each of which may serve as a back-to-back detector, the above method was applied to a compressional Pc 5 wave observed near the equatorial plane at L between about 7 and 11. The transverse propagation properties of the wave were determined unambiguously.

Lin, N.↗
NASA NTRS1988

Radial Alfven velocity profiles in the magnetosphere and their relation to ULF wave field-line resonances

The radial Alfven velocity, V(A), in the magnetosphere was investigated using magnetic field and plasma data from the ISEE-1 spacecraft. The harmonic frequency structure calculated from these data was compared with the observed resonant wave structure in the frequency range 5-100 mHz and over the region L = 3-9. It was found that the frequency of these resonances depend on the A(V), which is a function of the magnetic field strength and plasma density. The toroidal mode resonance frequency structure was modeled for the first four harmonics, with excellent agreement between the modeled and observed harmonics for a passs which does not show a plasmapause gradient. In the presence of a steep plasmapause gradient, the model was found to predict a correspondingly steep increase in the resonance frequencies at the plasmapause, by about 5 mHz for the first harmonic and by 20 mHz for the fourth harmonic. Special consideration is given to the effect of heavy ion mass loading on the modeling.

Fraser, B. J.↗
NASA NTRS1989

Thermodynamic properties of the heliospheric plasma

A global-scale study is conducted of the radial evolution of the solar wind's temperature (T), number density (n), and entropy (s) thermodynamic properties, on the basis of plasma data from such sources as IMP and ISEE 3, in conjunction with an MHD simulation model. The radial evolution of T and s indicates that the heliospheric plasma is subjected to a heating process; this heating is interpreted to be largely due to the cumulative effect of the shock process with increasing distance from the sun. This simulation model is also used to extrapolate the thermodynamic properties of the solar wind from Voyager 2 to the region of the outer heliosphere that is bounded by the termination shock.

Whang, Y. C.↗
NASA NTRS1989

Modeling of an interplanetary disturbance event tracked by the interplanetary scintillation method

The interplanetary disturbance event of August 25-29, 1978 was modeled in an attempt to reproduce the corresponding interplanetary scintillation observations and simultaneous ISEE-3 satellite data. A shock wave generated from the region of a disappearing filament on August 23 is shown to account for the observed shock wave structure, but not the broad high-speed stream behind the shock wave. A shock wave generated by the sudden activation of the coronal hole on the same day is able to account for the high-speed stream.

Akasofu, S.-I.↗
NASA NTRS1989

Impulsive acceleration and scatter-free transport of about 1 MeV per nucleon ions in (He-3)-rich solar particle events

Impulsive solar energetic particle (SEP) events are studied to: (1) describe a distinct class of SEP ion events observed in interplanetary space, and (2) test models of focused transport through detailed comparisons of numerical model prediction with the data. An attempt will also be made to describe the transport and scattering properties of the interplanetary medium during the times these events are observed and to derive source injection profiles in these events. ISEE 3 and Helios 1 magnetic field and plasma data are used to locate the approximate coronal connection points of the spacecraft to organize the particle anisotropy data and to constrain some free parameters in the modeling of flare events.

Mason, G. M.↗
NASA NTRS1989

Solar sources of interplanetary southward Bz events responsible for major magnetic storms (1978-1979)

The solar sources of interplanetary southward Bz events responsible for major magnetic storms observed in the August 1978-December 1979 period were studied using a full complement of solar wind plasma and field data from ISEE 3. It was found that, of the ten major storms observed, seven were initiated by active region flares, and three were associated with prominence eruptions in solar quiet regions. Nine of the storms were associated with interplanetary shocks. However, a comparison of the solar events' characteristics and those of the resulting interplanetary shocks indicated that standard solar parameters did not correlate with the strengths of the resulting shocks at 1 AU.

Tang, Frances↗
NASA NTRS1989

On the source of diffuse, suprathermal ions observed in the vicinity of the earth's bow shock

ISEE 2 data from the Fast Plasma Experiment were used to search for upstream 'diffuse' suprathermal ion events observed at times when the local IMF was nearly radial and the spacecraft was positioned at local times greater than 1530. For these observing conditions, which correspond to a local theta-Bn of about 45 deg, the field lines sampled should be at least 4 earth radii from the earth's magnetopause. A number of diffuse ion events which satisfy these conditions were found, and two of them are described in detail. The results show that the events are observed in association with large-amplitude low-frequency magnetic field fluctuations; the suprathermal particle velocity distributions are roughly isotropic in the solar wind frame, and the spectra extend smoohtly to energies beyond 40 keV. It is suggested that diffuse ion events observed in the vicinity of the bow shock at energies below 40 keV are primarily caused by shock processes.

Gosling, J. T.↗
NASA NTRS1989

Energetic (0.1- to 16-keV/e) magnetospheric ion composition at different levels of solar F10.7

The effects of varying solar activity (as measured by the daily F10.7 index) on the composition of energetic magnetospheric ions H(+), He(2+), He(+), and O(+) were investigated using data obtained in the near-equatorial magnetosphere, between L = 3 and R = 23 earth radii, by the Plasma Composition Experiment on ISEE-1. The strongest effect was found in the number densities of the He(+) and the O(+) ions, which were found to increase by factors of about 3-5 and 5-10, respectively, over the full range of the F10.7. The peak density of the O(+) is about 20 times that of He(+) and is the highest at L of about 3-5. Both species showed a decreasing energy with increasing F10.7 at a radius less than 10 earth radii, from about 4-5 keV at low F10.7 to about 2-3 keV at high F10.7.

Lennartsson, W.↗
NASA NTRS1989

Magnetospheric plasma pressures in the midnight meridian - Observations from 2.5 to 35 R(E)

Plasma pressure data from the ISEE 2 fast plasma experiment (FPE) are statistically analyzed to determine the plasma sheet pressure versus distance in the midnight local time sector of the near-earth (12-35 earth radii) magnetotail plasma sheet. In regions where the bulk of the plasma pressure is contributed by particles in the energy range of the FPE (70 eV to 40 keV for ions), the statistically determined peak plasma pressures vary with distance similarly to previously determined lobe magnetic pressures. Estimates of plasma pressures in the 'transition' region (7-12 earth radii), where the magnetic field topology changes rapidly from a dipolar to a taillike configuration, are compared with the observed pressure profiles. Quiet time observations and estimates are combined to provide profiles of the equatorial plasma pressure along the midnight meridian between 2.5 and 35 earth radii.

Spence, Harlan E.↗
NASA NTRS1989

Energetic particle diffusion coefficients upstream of quasi-parallel interplanetary shocks

The properties of about 30 to 130-keV/e protons and alpha particles upstream of six quasi-parallel interplanetary shocks that passed by the ISEE 3 spacecraft during 1978-1979 were analyzed, and the values for the upstream energegic particle diffusion coefficient, kappa, in these six events were deduced for a number of energies and upstream positions. These observations were compared with predictions of Lee's (1983) theory of shock acceleration. It was found that the observations verified the prediction of the A/Q dependence (where A and Q are the particle atomic mass and ionization state, respectively) of kappa for alpha and proton particles upstream of the quasi-parallel shocks.

Tan, L. C.↗