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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Magnetic fields, plasmas, and coronal holes: The inner solar system

In situ magnetic field and plasma observations within 1 AU which describe MDH stream flows and Alfvenic fluctuations, the latest theories of those phenomena are discussed. Understanding of streams and fluctuations was enhanced by the acquisition of nearly complete sets of high resolution plasma and magnetic data simultaneously at two or more points by IMPs 6, 7, and 8, Mariner-Venus-Mercury, HELIOS 1, and HELIOS 2. Observations demonstrate that streams can have very thin boundaries in latitude and longitude near the sun. This has necessitated a revision of earlier views of stream dynamics, for it is now clear that magnetic pressure is a major factor in the dynamics of stream in the inner solar system and that nonlinear phenomena are significant much closer to the sun than previously believed. Simultaneous IMP 6, 7, and 8 observations of Alfvenic fluctuations indicate that they are probably not simply transverse Alfven waves and suggest that Alfvenic fluctuations are better described as nonplanar, large-amplitude, general Alfven waves moving through an inhomogeneous and discontinuous medium, and coupled to a compressive mode.

Burlaga, L. F.↗
NASA NTRS1997

Exterior and Interior Polar Cusps: Observations from Hawkeye

Hawkeye plasma, magnetic field, and plasma wave instruments directly sampled the throat of the northern polar cusp as the orientation of the Interplanetary Magnetic Field (IMF) changed from southward to northward on July 3, 1974. Two distinct regions in the polar cusp were identified based on magnetic field, plasma flow and magnetic and electric noise: the interior and exterior cusps. The observations show highly variable flows in the exterior portion of the cusp and constantly strong dawn-dusk flows in the interior portion during periods of strong IMF By component. Results of a minimum variance analysis of the magnetic field at each cusp interface crossing provides evidence that the magnetopause surface normal deviated highly from empirical models. During intervals of relatively steady solar wind dynamic pressure, the motion of the cusp relative to the slow moving spacecraft was modulated by the varying IMF clock angle as observed by IMP 8 in the upstream solar wind. The motion did not show a correlation with internal processes monitored by the A E index. We propose that observed plasma flow patterns and cusp motion are results of reconnection between the IMF and the magnetospheric magnetic field. Flow velocity observed in the interior cusp is consistent with stress balance for a reconnection process. This unique interval provides an opportunity for detailed studies of the plasma, magnetic field, and plasma wave properties in both the exterior and interior cusp.

Chen, S.-H.↗
NASA NTRS1989

Small scale irregularities in Comet Halley's plasma mantle - An attempt at self-consistent analysis of plasma and magnetic field data

VEGA-1 measurements of the plasma density and magnetic field in the coma of Comet Halley show characteristic signatures over a significant portion of the outbound pass. It is found that the assumption that there is a balance between the thermal and magnetic pressures in these features can be used to obtain estimates of the plasma temperature as a function of distance from the nucleus. These estimates indicate that the ions cool from about 1.5 x 10 to the 6th K at 10 to the 5th km to 2 x 10 to the 5th K at 5 x 10 to the 4th km. The technique used here represents a novel approach whereby temperature measurements can be made in situations where only plasma density and magnetic field data are available.

Vaisberg, O. L.↗
NASA NTRS1973

Analysis and synthesis of coronal and interplanetary energetic particle, plasma, and magnetic field observations over three solar rotations.

In a previous paper (Krimigis et al., 1971), simultaneous observations in 1967 of solar particle events at low (less than 1 MeV) energies were presented. In the present paper, the full complement of simultaneous plasma, magnetic field, and energetic particle data is combined, and a complete analysis is made of all the events discussed in the original paper. The essential concept of 'collimated convection' is introduced, whereby the bulk velocity along the field lines of low-energy solar particles is independent of solar local plasma velocity, and the particles are strongly collimated along the field line with no transverse velocity component other than that of the field line itself. Collimated convection effects are shown to exist in small-scale convection and large-scale evolution of particle fluxes; the particle fluxes are, in turn, used to delineate the small-scale and large-scale evolution of the interplanetary magnetic field. Use of collimated convection is made in demonstrating a technique whereby energetic particle intensity profiles in the interplanetary medium can be related to equatorial high coronal magnetic field structures, by using the instantaneous solar wind velocity. This technique is applied in mapping particle intensities from Mariner 5 onto H alpha synoptic charts of chromospheric magnetic field structures for Carrington rotations 1523 to 1525.

Roelof, E. C.↗
NASA NTRS1989

Correlated plasma wave, magnetic field, and energetic ion observations in the ion pickup region of Comet Giacobini-Zinner

Relationships between simultaneous plasma wave, magnetic field, and energetic heavy ion data obtained by the International Cometary Explorer (ICE) spacecraft in the large-scale solar wind particle pickup region surrounding Comet Giacobini-Zinner are examined. In particular, consideration is given to the conditions under which electrostatic emissions at frequencies of a few kilohertz and electromagnetic waves at a few tens of hertz are observed. It is shown that the data are consistent with the view that the kilohertz electrostatic emissions result from a beam-type instability excited by the pickup photoelectron population when the angle alpha between the magnetic field and the plasma velocity vectors is not too large. The data also suggest that the few tens of hertz electromagnetic waves may be excited by a ring-type instability associated with the pickup ion population, which occurs when the magnetic field is near to orthogonality with the flow.

Richardson, I. G.↗
NASA NTRS1985

Filamental quenching of the current-driven ion-cyclotron instability

Since their discovery by D'Angelo and Motley (1962), ion-cyclotron waves have been an area of active research. Drummond and Rosenbluth (1962) have first conducted a theoretical analysis of the current-driven ion-cyclotron wave instability, taking into account a uniform, magnetized plasma, without magnetic shear, in which electrons drift along B field lines with the same drift velocity at all points in the plasma. Bakshi et al. (1983) have found conditions for which the instability is completely quenched. This phenomenon has been referred to as filamental quenching. The present investigation is concerned with a systematic test of the filamental quenching effect. It is found that filamental quenching operates at widths of the current channel comparable to the local Larmor radius, in agreement with the conclusions of Bakshi et al.

Cartier, S. L.↗
NASA NTRS1993

Stability of an inhomogeneous two-component plasma with magnetic viscosity

The stability of a semiinfinite quasi-neutral inhomogeneous plasma with magnetic viscosity has been discussed by using JWKB approximation in which the parameters are regarded slowing varying. Dispersion relation is obtained and discussed. It is found that the inhomogeneous system is unstable for all perturbations with k(y) = 0. A dispersion relation for homogeneous plasma is also obtained and discussed. It is shown that fast and slow-MHD waves propagate in the homogeneous plasma in the limit of almost perpendicular propagation under certain conditions.

Kumar, Nagendra↗
NASA NTRS1979

Interplanetary particles and fields, November 22 - December 6, 1977: Helios, Voyager, and IMP observations between 0.6 AU and 1.6 AU

The principal interplanetary events observed are described and analyzed. Three flow systems were observed: (1) a corotating stream and a stream interface associated with a coronal hole; (2) a shock wave and an energetic particle event associated with a 2-B flare; and (3) an isolated shock wave of uncertain origin. Data from 28 experiments and 6 spacecraft provide measurements of solar wind plasma, magnetic fields, plasma waves, radio waves, energetic electrons, and low energy protons.

Burlaga, L. F.↗
NASA NTRS2016

Penetration of Magnetosheath Plasma into Dayside Magnetosphere: Magnetic Field in Plasma Filaments - 2.

In this paper, we examined plasma structures (filaments), observed in the dayside magnetosphere but containing magnetosheath plasma. These filaments show the stable antisunward motion (while the ambient magnetospheric plasma moved in the opposite direction) and the existence of a strip of magnetospheric plasma, separating these filaments from the magnetosheath. These results, however, contradict both theoretical studies and simulations by Schindler (1979), Ma et al. (1991), Dai and Woodward (1994, 1998), and other researchers, who reported that the motion of such filaments through the magnetosphere is possible only when their magnetic field is directed very close to the ambient magnetic field, which is not the situation that is observed. In this study, we show that this seeming contradiction may be related to different events as the theoretical studies and simulations are related to the case when the filament magnetic field is about aligned with filament orientation, whereas the observations show that the magnetic field in these filaments may be rotating. In this case, the rotating magnetic field, changing incessantly its direction, drastically affects the penetration of plasma filaments into the magnetosphere. In this case, the filaments with rotating magnetic field, even if in each moment it is significantly inclined to the ambient magnetic field, may propagate through the magnetosphere, if their average (for the rotation period) magnetic field is aligned with the ambient magnetic field. This shows that neglecting the rotation of magnetic field in these filaments may lead to wrong results.

Lyatsky, Wladislaw↗
NASA NTRS1978

Plasma flows and magnetic field vectors in the plasma sheet during substorms

A detailed study of the plasma flow and the magnetic field vector in the plasma sheet during magnetospheric substorms is made to determine whether plasma flows are field-aligned or crossfield. It is shown that there is generally a large magnetic field-aligned component in the rapid plasma flow observed in the plasma sheet during substorms. In particular, the larger the observed flow speed, the closer the observed flow direction is aligned with the magnetic field line. There is no clear association between the plasma flow direction and the sign of the Bz component of the magnetic field during plasma sheet thinnings at substorms. The rapid plasma flows observed in the magnetotail are predominantly magnetic field-aligned.

Lui, A. T. Y.↗