Dynamic nonshock properties of large amplitude microscale Alfven waves in interplanetary medium, using plasma and magnetic field data from Mariner 5

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Large-amplitude Alfvén waves in the interplanetary medium, 2

A magnetospheric magnetic field model with a warped tail current sheet

Observations of electrons of energy 125 ev to ∼2 kev with the OGO 1 satellite and of electrons of energy 40 ev to ∼2 kev with OGO 3 (by means of modulated Faraday cup detectors) are used to investigate the low-energy electron population in the magnetosphere within the local-time range ∼17 to ∼22 hours. Intense fluxes of these electrons are confined to a spatial region, termed the plasma sheet, which is an extension of the magnetotail plasma sheet discovered by the Vela satellites and is identified with the soft electron band first detected by Gringauz. The plasma sheet extends over the entire local-time range studied in this investigation, from the magnetospheric tail past the dusk meridian toward the dayside magnetosphere. In latitude it is confined to within 4–6 RE of the geomagnetic and/or solar magnetospheric equatorial plane, in agreement with observations already reported from the Vela satellites; no electron fluxes are detected high above the equator, not even very near the magnetopause. In radial distance the plasma sheet is terminated by the magnetopause on the outside and by a well-defined sharp inner boundary on the inside. The inner boundary has been traced from the equatorial region to the highest latitudes investigated, ∼40°; during geomagnetically quiet periods, it is observed at an equatorial distance of 11 ± 1 RE and appears to extend to higher latitudes along magnetic field lines. Weak or no electron fluxes are found between the inner boundary of the plasma sheet and the outer boundary of the plasmasphere. Detection (by an indirect process) of the very high ion densities within the plasmasphere gives positions for its boundary in good agreement with other determinations. During periods of magnetic bay activity, the plasma sheet extends closer to the earth; the inner boundary of the plasma sheet is then found at equatorial distances of 6–8 RE. This is most simply interpreted as the result of an actual inward motion of the plasma during a bay. In one case, it was possible to associate the beginning of this motion with the onset of the bay and to estimate an average radial speed of ∼12 km/sec, from which an electric field corresponding to ∼48 kilovolts across the magnetospheric tail was inferred. Within the plasma sheet, the electron population is characterized by number densities from 0.3 to 30 cm−3 and mean energies from 50 to 1600 ev and higher, with a strong anticorrelation between density and mean energy, so that the electron energy density (∼1 kev cm−3) and energy flux (∼3 ergs cm−2 sec−1) show relatively little variation. The lower energies and higher densities tend to occur during periods of geomagnetic disturbance. The nonobservation of electrons in regions above the plasma sheet implies an upper limit on the electron number density of 5 × 10−2 cm−3 if their mean energy is assumed to be ∼50 ev (typical of the magnetosheath) and 10−2 cm−3 if the energy is ∼1 kev (typical of the plasma sheet). At the inner boundary of the plasma sheet there is a sharp softening of the electron spectrum with decreasing radial distance but apparently little change in the electron number density. The electron energy density decreases across the inner boundary roughly as ∼exp (distance/0.4 RE) during quiet periods; during times of magnetic bay activity the energy density decreases as ∼exp (distance/0.6 RE), and there is a more complicated spatial structure of density and mean energy.

A survey of low-energy electrons in the evening sector of the magnetosphere with OGO 1 and OGO 3.

The flow behind an interplanetary shock was analyzed through the use of magnetic field and plasma data from five spacecraft, with emphasis on the magnetic cloud identified by a characteristic variation of the latitude angle of the magnetic field. The size of the cloud was found to be about 0.5 AU in radial extent and greater than 30 deg in azimuthal extent, with its front boundary almost normal to the radial direction. Because the field direction of the magnetic cloud as it moved past the spacecraft was observed to rotate nearly parallel to a plane, it is thought that the field configuration of the cloud was essentially two-dimensional. These results further suggest that the lines of force in the magnetic cloud formed loops, but it could not be determined whether these loops were open or closed.

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Magnetic loop behind an interplanetary shock: Voyager, Helios and IMP-8 observations

Astrophysical magnetic fields and nonlinear dynamo theory

Green function solution to Maxwell equations for interplanetary and coronal magnetic fields above photosphere, considering field at source surface

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A model of interplanetary and coronal magnetic fields.

The dissipation range for interplanetary magnetic field fluctuations is formed by those fluctuations with spatial scales comparable to the gyroradius or ion inertial length of a thermal ion. It is reasonable to assume that the dissipation range represents the final fate of magnetic energy that is transferred from the largest spatial scales via nonlinear processes until kinetic coupling with the background plasma removes the energy from the spectrum and heats the background distribution. Typically, the dissipation range at 1 AU sets in at spacecraft frame frequencies of a few tenths of a hertz. It is characterized by a steepening of the power spectrum and often demonstrates a bias of the polarization or magnetic helicity spectrum. We examine Wind observations of inertial and dissipation range spectra in an attempt to better understand the processes that form the dissipation range and how these processes depend on the ambient solar wind parameters (interplanetary magnetic field intensity, ambient proton density and temperature, etc.). We focus on stationary intervals with well-defined inertial and dissipation range spectra. Our analysis shows that parallel-propagating waves, such as Alfven waves, are inconsistent with the data. MHD turbulence consisting of a partly slab and partly two-dimensional (2-D) composite geometry is consistent with the observations, while thermal paxticle interactions with the 2-D component may be responsible for the formation of the dissipation range. Kinetic Alfven waves propagating at large angles to the background magnetic field are also consistent with the observations and may form some portion of the 2-D turbulence component.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JA03394

Observational constraints on the dynamics of the interplanetary magnetic field dissipation range

Quasi-stationary co-rotating structure in interplanetary field observed with IMP-I SATELLITE during three solar rotations

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Quasi‐stationary corotating structure in the interplanetary medium

Extensive measurements of the magnetic field of the earth at distances greater than approximately 7Re (earth radii) have been performed by the Imp 1 satellite. These magnetic field measurements began on November 27, 1963, and ended on May 30, 1964. During this six-month interval the apogee-earth-sun angle in solar ecliptic coordinates decreased from 336° to 156°. The apogee of the satellite was 31.7Re, and the range of the magnetometers was between 0.25 and 300γ. This paper is concerned principally with the topology of the magnetic field within the magnetosphere and the position of both its boundary and the detached collisionless bow shock wave. The geomagnetic field is observed to trail out far behind the earth in the antisolar direction, thus forming a magnetic tail. Magnetic field strengths of approximately 10 to 30 γ are observed out to satellite apogee. The diameter of the magnetosphere at a distance of 30Re behind the earth is found to be approximately 40Re. The direction of the field is parallel to the earth-sun line and in the antisolar direction below the solar magnetospheric equatorial plane and in the solar direction above this plane. A neutral surface separating antisolar directed fields in the southern hemisphere from solar directed fields in the northern hemisphere has been detected over a large area. This experimental result suggests the development of quantitative theories explaining the aurora, gegenschein, day-night asymmetry, and formation of the radiation belts. On the basis of a preliminary review of the data, it appears that the geomagnetic field trails out far behind the earth following the flow field of the solar plasma to a distance far beyond the orbit of the moon. No termination of the magnetic tail is detected or suggested by the data. Thus the earth can be compared to the nucleus of a comet, the radiation belts and co-rotating magnetosphere being the coma and the magnetic tail being the cometary tail.

The Earth's magnetic tail

The interplanetary monitoring platform Imp 1, or Explorer 18, launched on November 27, 1963, has provided the first accurate measurements of interplanetary magnetic fields. The initial apogee of the satellite was 197,616 km on the sunlit side of the earth, with an apogee-earth-sun angle of 26°. This paper presents the initial results of the detailed measurements of the interplanetary magnetic field and the interaction of the solar wind with the geomagnetic field. The strength of the interplanetary magnetic field is found to vary between 4 and 7 γ, with extreme values as low as 1 and as high as 10 γ. The magnitude, however, is extremely stable over times of hours, although changes of direction are significant. The average direction of the interplanetary magnetic field is slightly below the plane of the ecliptic and approximately along the streaming angle predicted for a steady-state solar wind. A significant feature of the magnetic field measurements is the discovery of fields pointed diametrically opposite the streaming angle, indicating filamentary structure of the interplanetary field. Associated with the fields of opposite direction are null surfaces between the filaments and in the over-all field structure. The complex interaction of the solar wind and the geomagnetic field shows a variety of magnetic field fluctuations and transition characteristics. The detection of the collisionless magnetohydrodynamic shock wave at 13.4Re at the stagnation point associated with the super Alfvenic flow of solar plasma is one of the major results of this experiment. Details of the fluctuations are discussed, as well as the gross structure and shape of the magnetospheric surface (10.2Re at the subsolar point) and the shock wave from the subsolar point to the nighttime geomagnetic tail. The transition region between the shock wave and the magnetopause is one of high turbulence in the magnetic field. A unique aspect of the magnetic field data is the detection of the magnetohydrodynamic wake of the moon during the fifth orbit, when the satellite was eclipsed by the moon's magnetosphere while in interplanetary space. The implications of this experimental discovery are discussed.

Norman F. Ness

Papers

A model of interplanetary and coronal magnetic fields.

Observational constraints on the dynamics of the interplanetary magnetic field dissipation range

Quasi‐stationary corotating structure in the interplanetary medium

The Earth's magnetic tail

Initial results of the imp 1 magnetic field experiment