Fast time-resolved spectra of electrostatic turbulence in the earth's bow shock
Fast time-resolved spectra of earth bow shock electrostatic turbulence based on broadband analog electric data from OGO-5
Coroniti, F. V.↗
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Average and unusual locations of the earth's magnetopause and bow shock
Average and unusual locations of magnetopause and bow shock positions observed by IMP spacecraft
Fairfield, D. H.↗
Study on multi-satellite, multi-measurement of the structure of the earth's bow shock
The pulsation model of the earth's bow shock proposed a nonuniform shock having both perpendicular (abrupt, monotonic) and oblique (oscillatory, multigradient) properties simultaneously, depending on local orientation of the shock surface to the interplanetary field B sub sw in parallel planes defined by B sub sw and solar wind velocity. Multiple, concurrent, satellite observations of the shock and solar wind conditions were used. Twenty-six potentially useful intervals of concurrent Explorer 33 and 35 data acquisition were examined, of which six were selected for closer study. In addition, two years of OGO-5 and HEOS 1 magnetometer data were examined for possible conjunctions to these spacecraft having applicable data. One case of clear nonuniformity and several of field-dependent structure were documented. A computational aid, called pulsation index, was developed.
Source record↗
Large-scale coherence and high velocities of the earth's bow shock on February 12, 1969.
The earth's bow shock exhibited a clean laminar profile at low Mach number as it crossed and recrossed Ogo 5, Heos 1, and Explorer 33 on February 12, 1969. The approximate 120 earth radii distance between Heos and Explorer during one set of crossings indicated the abrupt character of the laminar shock 'front' and the absence of magnetosheath turbulence both in the dayside hemisphere above the ecliptic and in the flank of the shock 75 earth radii behind the earth and below the ecliptic. The abruptness of the shock and coplanarity of the loci of Ogo and Heos with the local shock normal permit the most reliable estimates yet obtained of shock velocities along the normal. These mean velocities ranged from 11 to at least 100 km/sec over distances of 2-7 earth radii.
Greenstadt, E. W.↗
Study of relation between Pc 3 micropulsations and magnetosheath fluctuations, and multisatellite investigation of earth's bow shock
The validity is investigated of a suggested model according to which Pc 3 and/or Pc 4 micropulsations are excited by magnetosheath field (and plasma) fluctuations arising in the quasi-parallel structure of the subsolar bow shock. The influence of solar wind plasma parameters on local shock structure and on the configuration of the entire bow shock system is included. Simultaneous data from two or more spacecraft and from multiple diagnostics is used to evaluate the geometrical factor, field-to-shock normal angle, or its B-X equivalent, and the principal plasma parameters. Results are presented and discussed.
Greenstadt, E. W.↗
Monte Carlo simulation of charged particles upstream of the earth's bow shock
A simple model of the earth's bow shock is presented and compared with ISEE-1 observations of diffuse ions upstream of the shock. Ion behavior is modeled in a test particle simulation using Monte Carlo techniques for a plane parallel shock at which cold solar wind ions are heated sufficiently to allow diffusion back upstream. Fitting of the model to the observations indicates that the diffusion coefficient must increase faster than linearly with velocity, and provides an upper limit to the acceleration efficiency defined as the proportion of incoming solar wind ions accelerated and observed upstream. Results suggest that astrophysical shocks are capable of accelerating ions directly from the thermal plasma without the need for a distinct preenergizing injection stage.
Ellison, D. C.↗
Electrostatic noise at the plasma frequency beyond the earth's bow shock
Scarf et al. (1971) and Dunckel (1974) have shown that there are, very frequently, intense electrostatic waves whose frequency is near the plasma frequency upstream of the earth's bow shock and that these waves are correlated with the presence of energetic electrons from the bow shock. Also, Fredericks et al. (1971) have postulated a two-stream instability. The paper investigates these phenomena further, by comparing electrostatic noise at or near the ambient solar wind plasma frequency with times when the interplanetary magnetic field probably connects to the shock. Evidence is presented that Scarf et al. and Fredericks et al. were correct in their explanation of the phenomenon, and that the double-humped distribution would be expected only in a region too small to be resolved by the plasma measurements made so far.
Filbert, P. C.↗
The Transverse Acceleration Instability for Bow Shocks in the Nonlinear Regime
We continue our study of the stability of thin isothermal bow shocks. We follow the transverse.
Bow Shocks↗
Diffusion and convection of energetic electrons behind the earth's bow shock
Diffusion effects on energy spectrum of electron group analyzed during downwind convection in bow shock transition region of earth
ELECTRON ENERGY↗
The Planetesimal Bow Shock Model for Chondrule Formation: More Detailed Simulations in the Near Vicinity of the Planetesimal
Gas dynamic shock waves in a low temperature nebula have been considered to be a leading candidate mechanism for providing the repetitive, short-duration heating events that are believed to have been responsible for the formation of chondrules in chondrites. It has been found, for example, that shocks with Mach numbers greater than 4 or 5 would be capable of rapidly melting 0.1-1 mm sized silicate particles as required by meteoritic data. Near the nebula midplane where chondrite parent bodies are believed to have formed, possible energy sources for generating multiple shocks include mass concentrations in a gravitationally unstable nebula, tidal interactions of proto-Jupiter with the nebula, and bow waves upstream of planetesimals scattered gravitationally into eccentric orbits by proto- Jupiter. In a recent study, we have found that chondrule precursors that are melted following passage through a planetesimal bow shock would likely cool at rates that are too rapid to be consistent with meteoritic evidence. However, that study was limited to the bowshock exterior to about 1.5 planetesimal radii (measured perpendicular to the symmetry axis) to avoid complications interior to this distance where large pressure gradients and lateral flow occur as the gas flows around the planetesimal. In this paper, we reconsider the planetesimal bow shock model and report more detailed numerical simulations of chondrule precursor heating, cooling, and dynamical histories in the near vicinity of a representative planetesimal.
Hood, Lon L.↗
Magnetic reconnection and kinetic waves generated in the Earth's quasi-parallel bow shock
Magnetic reconnection in quasi-parallel shocks, relevant to the Earth’s bow shock, is studied by means of two-dimensional full particle-in-cell simulations. As the Alfvénic Mach number increases, the propagation direction of the waves excited in the transition region changes, and the shock becomes more turbulent with more reconnection sites. In the higher Mach number shock, abundant electron-only reconnection sites are generated with scales on the order of the ion skin depth or less. Non-reconnecting current sheets can also generate electron jets and energy dissipation can occur there as well. However, non-reconnecting current sheets with the magnetic field reversal typically show a smaller energy dissipation rate than reconnecting current sheets. In the shock transition region, two types of waves are responsible for driving reconnection: one has a wavelength around three ion skin depths (d i ), and the other has a wavelength less than 1 d i . Here, electron and ion distribution functions show that in regions where the former type of waves is excited, there are two ion beams and a single-peaked electron distribution. In contrast, in regions where the latter type of waves is excited, there are multiple electron and ion beams. The waves propagating obliquely to the magnetic field bend the magnetic field lines, and magnetic reconnection occurs where oppositely directed field lines come into contact.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
The two-dimensional structure of diffuse ions associated with the earth's bow shock
The lateral distribution of upstream, diffuse energetic ions resulting from shock acceleration at an idealized model bow shock is investigated, where the model consists of a uniform planar shock along which steady source ion injection takes place over a finite region of the shock. The solution exhibits growth toward a peak ion concentration whose location beneath the point of initial magnetic connection with the shock is sensitive to the model parameters. It is found that a plateau forms if the source size is large in comparison to the scale length of ion distribution function's growth, and that cross-field diffusion strongly enhances the diffuse ion concentration near the leading edge of the source.
Skadron, G.↗
Microinstabilities associated with a high Mach number, perpendicular bow shock
Instability analyses incorporating insights gained through ISEE observations and hybrid simulations are used in an examination of the instabilities associated with a high Mach number perpendicular shock akin to the earth's bow shock. In the regions in front of, and at, the shock transition the cross-field instabilities are subdivided into the ion-ion streaming, kinetic cross-field streaming, and drift lower hybrid instability low frequency modes, as well as the electron cyclotron drift, ion sound, and electron whisker instability high frequency modes. Further downstream, ion ring-like and anisotropy-driven instabilities are considered. The implications of these results for wave signatures, plasma heating and acceleration are noted.
Wu, C. S.↗
Magnetic reconnection and kinetic waves generated in the Earth's quasi-parallel bow shock
Magnetic reconnection in quasi-parallel shocks, relevant to the Earth's bow shock, is studied by means of two-dimensional full particle-in-cell simulations. As the Alfvénic Mach number increases, the propagation direction of the waves excited in the transition region changes, and the shock becomes more turbulent with more reconnection sites. In the higher Mach number shock, abundant electron-only reconnection sites are generated with scales on the order of the ion skin depth or less. Non-reconnecting current sheets can also generate electron jets and energy dissipation can occur there as well. However, non-reconnecting current sheets with the magnetic field reversal typically show a smaller energy dissipation rate than reconnecting current sheets. In the shock transition region, two types of waves are responsible for driving reconnection: one has a wavelength around three ion skin depths (di), and the other has a wavelength less than 1 di. Electron and ion distribution functions show that in regions where the former type of waves is excited, there are two ion beams and a single-peaked electron distribution. In contrast, in regions where the latter type of waves is excited, there are multiple electron and ion beams. The waves propagating obliquely to the magnetic field bend the magnetic field lines, and magnetic reconnection occurs where oppositely directed field lines come into contact.
N. Bessho↗
Predictions of lithium interactions with earth's bow shock in the presence of wave activity
The results of a test-particle simulation studying the movement of a lithium tracer ion injected upstream of the bow shock are reported. Wave activity consists of parallel and antiparallel propagating Alfven waves characterized by a frequency power spectrum within a frequency or range of amplitudes defined separately in the upstream and downstream regions. The results show that even a moderate level of wave activity can substantially change the results obtained in the absence of waves. Among the effects observed are: (1) increased ion transmission; (2) both the average energy gain and spread about the average are increased for transmitted and reflected particles; (3) the average final pitch angle for transmitted particles tends to 90 deg, and the spread of reflected particles is reduced; and (4) the spatial dispersion of the ions on the bow shock after a single encounter is increased.
Decker, R. B.↗
The distant bow shock and magnetotail of Venus - Magnetic field and plasma wave observations
An examination of the magnetic field and plasma wave data obtained by the Pioneer Venus orbiter in the wake region behind Venus discloses a well developed bow shock whose location is similar to that observed on previous missions in contrast to the dayside bow shock. Venus also has a well developed magnetotail in which the field strenght is enhanced over magnetosheath values and in which the magnetic field is aligned approximately with the solar wind direction. The boundary between magnetosheath and magnetotail is also marked by a change in the plasma wave spectrum.
Russell, C. T.↗
Observations of gyrating ions in the foot of the nearly perpendicular bow shock
A beam of secondary ions which gyrate about the magnetic field have been detected by ISEE-1 satellite measurements of ion velocity distributions during a high Mach number bow shock crossing under nearly perpendicular conditions. The ions are encountered as the satellite enters the region ahead of the foot of the shock, and their behavior is that of solar wind ions reflected off the shock and then returned to it under the combined influence of magnetic field deflection and interplanetary electric field acceleration. Beam densities increase from 0.2 to 30% of the total plasma density as the main shock is approached, and the ion beam is not degraded through interaction with the counterstreaming solar wind upstream of the ramp. The gyrating ions provide strong dispersion in velocity space, and therefore constitute the first step in the process by which solar wind streaming energy is converted into the thermal energy of the ions at the bow shock.
Paschmann, G.↗
Energetic ions upstream of planetary bow shocks - Fermi acceleration or leakage?
Observations of energetic ions upstream of earth, Jupiter, and Saturn are examined. The velocity dispersions, energy spectra, and ion compositions for the three planets are described. Fermi acceleration and leakage are analyzed as the potential mechanism for the presence of energetic particles upstream of planetary bow shocks. It is noted that energetic ions upstream of planetary bow shock originate from within the planetary magnetosphere, and leakage is the mechanism for the energetic particles.
Krimigis, S. M.↗