Vela 4 plasma observations near the Earth’s bow shock
TL;DR: In this paper, the Vela 4B analyzer was used to detect the earth's bow shock in the magnetosheath of the earth, and it was shown that the jump in proton temperature is 2 to 4 times greater than the jump of electron temperature.
Abstract: Concurrent measurements of electron and proton differential energy spectrums (each spectrum measurement requiring from 0.1 to 0.3 sec) have been obtained near the earth’s bow shock with the Vela 4B electrostatic analyzer. The following results have been derived from an analysis of 26 shock crossings during May and June 1967: (1) The jump in proton temperature is 2 to 4 times greater than the jump in electron temperature. (2) In the magnetosheath the proton temperature is nearly always greater than the electron temperature. (3) Te/Tp, upstream from the shock ranges between 0.6 and 4, and the shock remains well defined over this range. (4) Electron thermalization usually occurs in much less than 3 sec and has been observed to occur in ≈ 0.03 sec. (5) The magnetosheath electron velocity distribution is flat-topped or sometimes somewhat concave in shape within at least a few RE of the shock. (6) Evidence has been found that electrons are thermalized in a thin region upstream from the region in which most of the proton thermalization occurs. The observed increase in Te/Tp resulting from electron preheating may account for destabilization of electrostatic ion waves that may then produce strong ion heating by nonlinear Landau damping. Representative proton and electron velocity distributions from which the above results were derived are presented.
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TL;DR: In this paper, Chandra's 1 ″ angular resolution corresponds to linear resolution of less than a kiloparsec, which is smaller than some interesting linear scales in the intracluster plasma.
738 citations
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TL;DR: In this paper, the average characteristics of solar wind electron velocity distributions as well as the range and nature of their variations are presented, and the largest-scale parameter variations appear to come most often in association with high-speed streams.
Abstract: Average characteristics of solar wind electron velocity distributions as well as the range and nature of their variations are presented. The measured distributions are generally symmetric about the heat flux direction and are adequately parameterized by the superposition of a nearly bi-Maxwellian function which characterizes the low-energy electrons and a bi-Maxwellian function which characterizes a distinct, ubiquitous component of higher-energy electrons. An alternate self-consistent description of the higher-energy component is presented in terms of an unbound population of hot electrons with energy greater than some breakpoint energy of ≃60 V. The largest-scale parameter variations appear to come most often in association with high-speed streams. The salient electron parameter variations associated with these structures are presented and discussed. The mechanism by which interplanetary electrons conduct heat is convection of the hot component relative to the bulk speed. Arguments are presented which favor the local regulation of the solar wind heat flux at 1 AU.
690 citations
TL;DR: In this paper, a detailed description of plasmasmas in the distant polar magnetosphere has been provided by the Heos 2 satellite, which revealed the presence of a persistent layer of tailward-flowing magnetosheath-like plasma inside of and adjacent to the magnetopause.
Abstract: Comprehensive plasma observations carried out on board the Heos 2 satellite have provided the first systematic description of plasmas in the distant polar magnetosphere. These observations have revealed the presence of a persistent layer of tailward-flowing magnetosheathlike plasma inside of and adjacent to the magnetopause. This region has been termed the ‘plasma mantle.’ The mantle has been found to extend over the entire surface of the magnetosphere tailward of the polar cusp and northward of the plasma sheet. Vela observations of a ‘magnetotail boundary layer’ obtained in the vicinity of the plasma sheet by Hones and coworkers refer to the same phenomenon. The salient features of the plasma mantle as provided by Heos measurements from February to December 1972 can be summarized as follows: (1) The mantle was found to be present in over 70% of the passes through the polar magnetosphere in the region described above. (2) Its thickness varies greatly, ranging up to ≳ 4 RE, and does not appear to depend significantly on position or the state of the magnetosphere as measured by Kp. (3) A tailward-directed bulk flow parallel to the local terrestrial magnetic field was nearly always distinctly measurable. It was found to lie usually between 100 and 200 km s−1 and was always less than the concurrent flow speed in the nearby magneto sheath. (4) The flow speed in the mantle is positively correlated with the flow speeds in the magnetosheath and solar wind but depends only very weakly, if at all, on distance from the polar cusp, i.e., on XGSM. (5) A narrow region of low density and/or low flow speed plasma, i.e., a ‘gap,’ 0.1–0.2 RE thick, is frequently observed between the plasma mantle and the magnetopause. (6) The mantle protons are normally significantly cooler along B than perpendicular, i.e., T∥ < T⊥. (7) The proton density, temperature, and bulk speed all tend to decrease gradually with depth inside the magnetopause, but this trend can at times be obscured by fluctuations and magnetopause motions. At the inner edge of the mantle the proton distribution is often very narrow in both energy and angle, i.e., relatively cold, before it finally disappears below the 100-eV threshold of the instrument. It is concluded, after an appraisal of several possible mechanisms, that the most probable cause for the formation of the mantle is the day side merging of terrestrial and interplanetary field lines.
528 citations
TL;DR: Stix's treatment of zero-damped electrostatic waves in a Maxwellian plasma is extended to the nonlinear regime in this paper, where Stationary Bernstein-Greene-Krusk almodes which propagate with ion acoustic speed are constructed.
Abstract: Stix's treatment of zero-damped electrostatic waves in a Maxwellian plasma is extended to the nonlinear regime. Stationary Bernstein-Greene-Krusk almodes which propagate with ion acoustic speed are constructed. This subclass consists of solitary, snoidal (=periodical waves, like ocean waves, which can be written in terms of Jacobian elliptic functions) and sinusoidal waves. A discrimination of those waves can be given by a single parameter, the steepness parameter, which contains nonlinearity, trapping of particles and dispersion. It turns out that Sadgeev's soliton represents a special case of the class solitons having the largest width and the lowest velocity. Hence a modified Korteweg-de-Vries equation must exist with a stronger nonlinearity.
521 citations
TL;DR: In this paper, it was concluded that solar wind plasma can penetrate to low altitudes through the high-latitude cusp in the magnetopause, which is often referred to as the neutral point.
Abstract: Daytime high-latitude fluxes of low-energy ( 107 cm−2 ster−1 sec−1 with typical energy fluxes in the range 0.01 to 0.1 ergs cm−2 ster−1 sec−1. It is concluded that solar wind plasma can penetrate to low altitudes through the high-latitude cusp in the magnetopause, which is often referred to as the neutral point. This flux is related to a number of geophysical phenomena, including magnetospheric surface currents, daytime auroras, VLF and LF emissions, ionospheric irregularities, and geomagnetic fluctuations.
515 citations
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TL;DR: MHD equations applied to hypersonic flow of solar plasma around magnetosphere and approximation with simpler equations of gas dynamics were used to simulate the solar plasma in the magnetosphere.
920 citations
TL;DR: In this paper, the initial results of the detailed measurements of the interplanetary magnetic field and the interaction of the solar wind with the geomagnetic field are presented, with extreme values as low as 1 and as high as 10 γ.
Abstract: 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.
451 citations
449 citations
TL;DR: In this paper, it was concluded that the waves are associated with the earth's bow shock since they only occur when projection of the interplanetary field observed at the spacecraft intersects the shock.
Abstract: Fifty orbits of Explorer 34 data have been used to study 0.01–0.05 Hz transverse waves in the interplanetary medium region between the bow shock and the spacecraft apogee of 34 RE. It is concluded that the waves are associated with the earth's bow shock since they only occur when projection of the interplanetary field observed at the spacecraft intersects the shock. The waves are observed 18.5% of the time when a total of 134 days of interplanetary data is considered, but more than 90% of the time when the field has the proper orientation with respect to the bow shock. On the basis of this result it is suggested that these waves with 20–100 second periods are a permanent feature of the solar wind-earth interaction. The transverse component of the waves is typically several gammas in amplitude in 4–8 gamma fields. The disturbance vector in the XY plane generally exhibits the same sense of rotation in a coordinate system where the field is oriented along the positive z axis. Attenuation of wave amplitudes with distance from the bow shock is estimated to be only a factor of 2 when the spacecraft is 15 RE from the bow shock. The absence of waves at particular field orientations, even though the field line intersects the shock, is interpreted as a propagation effect. This observation is the basis for calculations that yield an average velocity in the plasma frame of 2.7 ± 0.4 times the solar wind velocity. Whistler propagation and local generation by two-stream instability are discussed as alternate theoretical explanations for the presence of the waves. It is suggested that the data favor the latter mechanism.
345 citations