Solar Energetic Particles: From the Corona to the Magnetotail
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Keywords:
Magnetosheath
Interplanetary medium
Field line
Solar energetic particles
Bow wave
The origin of large‐amplitude hydromagnetic waves in the Venus magnetosheath down‐stream of the quasi‐parallel bow shock is investigated by means of numerical simulation. It is shown that the most likely source of these waves is the bow shock itself, rather than an instability involving the solar wind and oxygen ions of planetary origin. Pickup of O + ions by these waves is also examined and shown to be in agreement with previous test particle calculations. The effect of mass loading on the structure of the shock is also discussed.
Magnetosheath
Bow wave
Atmosphere of Venus
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Abstract Localized magnetosheath jets with high dynamic pressure are frequently observed downstream of Earth's bow shock. When such a fast magnetosheath jet compresses the ambient magnetosheath plasma, an earthward compressional bow wave could form. Such bow waves have been predicted by simulations but have never been observed. Using multipoint Time History of Events and Macroscale Interactions during Substroms (THEMIS) observations, we report the first observation where such a bow wave driven by an intrinsically formed magnetosheath jet can reflect and accelerate particles up to tens of kiloelectron volt for ions and 100 keV for electrons. By analyzing the ion distributions, we infer how particles reach the spacecraft from the bow wave demonstrating good agreement with our model of single particle motion. Our study implies that particle acceleration at magnetosheath jets could contribute significantly to particle acceleration at shocks in general.
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Bow wave
Particle (ecology)
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Abstract. The Double Star TC-1 magnetosheath pass on 26 February 2004 is used to investigate magnetic field fluctuations. Strong compressional signatures which last for more than an hour have been found near the magnetopause behind a quasi-perpendicular bow shock. These compressional structures are most likely mirror mode waves. There is a clear wave transition in the magnetosheath which probably results from the change of the interplanetary magnetic field (IMF) cone angle. The wave characteristics in the magnetosheath are strongly controlled by the type of the upstream bow shock.
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Bow wave
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A causal relationship between midlatitude magnetosheath energetic ions and bow shock magnetic geometry was previously established for ion energy up to 200 keV e −1 for the May 4, 1998, storm event. This study demonstrates that magnetosheath ions with energies above 200 keV up to 1 MeV simply extend the ion spectrum to form a power law tail. Results of cross‐correlation analysis suggest that these ions also come directly from the quasi‐parallel bow shock, not the magnetosphere. This is confirmed by a comparison of energetic ion fluxes simultaneously measured in the magnetosheath and at the quasi‐parallel bow shock when both regions are likely connected by the magnetic field lines. We suggest that ions are accelerated at the quasi‐parallel bow shock to energies as high as 1 MeV and subsequently transported into the magnetosheath during this event.
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Bow wave
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Magnetosheath jets are localized fast flows with enhanced dynamic pressure. When they supermagnetosonically compress the ambient magnetosheath plasma, a bow wave or shock can form ahead of them. Such a bow wave was recently observed to accelerate ions and possibly electrons. The ion acceleration process was previously analyzed, but the electron acceleration process remains largely unexplored. Here we use multi-point observations by Time History of Events and Macroscale during Substorms from three events to determine whether and how magnetosheath jet-driven bow waves can accelerate electrons. We show that when suprathermal electrons in the ambient magnetosheath convect towards a bow wave, some electrons are shock-drift accelerated and reflected towards the ambient magnetosheath and others continue moving downstream of the bow wave resulting in bi-directional motion. Our study indicates that magnetosheath jet-driven bow waves can result in additional energization of suprathermal electrons in the magnetosheath. It implies that magnetosheath jets can increase the efficiency of electron acceleration at planetary bow shocks or other similar astrophysical environments.
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Bow wave
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Magnetosheath
Bow wave
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Abstract Cluster multipoint measurements are used to study two successive magnetosheath flux transfer events (FTEs). Magnetic field lines in the leading region are found to be closed magnetospheric field lines. For event 1 these field lines are wounded up by a large current structure oriented eastward and moving poleward. Conversely, the trailing region corresponds to opened magnetic field lines. For both events the leading edge of the FTEs is a tangential discontinuity separating the magnetosheath from closed field lines. In the case of event 1 magnetosheath ions are accelerated through the FTE trailing edge via a rotational discontinuity and penetrate on closed field lines through a second discontinuity. Thus, the ion jet is accelerated equatorward of the spacecraft but the backtracking of the discontinuities and the lack of dispersion show that ion acceleration occurs at less than 2 R E from Cluster. On the other hand the extrapolation forward indicates that the FTE bulge steepens as in simulations of Dorelli and Bhattacharjee ( ). Evidence is given for the penetration of magnetosheath ions inside the core of the FTE, on closed field lines. Magnetosheath electrons are accelerated in parallel and antiparallel directions on open and on closed field lines, thus breaking the frozen‐in condition. Event 2 is also split in two distinct regions but no evidence is found for accelerated bidirectional magnetosheath electrons. For event 2 the two discontinuities at the trailing region are stacked together when they are crossed by the spacecraft, suggesting that the current splitting is a reconnection signature.
Magnetosheath
Field line
Current sheet
Classification of discontinuities
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We investigate the scatter‐free propagation of low‐energy (1–5 keV) protons in the magnetosheath by following test particle trajectories in a model of the magnetosheath fields previously obtained from gasdynamic simulations. We concentrate on those ions energized by near‐specular reflection at the quasi‐perpendicular shock: the reflected‐gyrating ions. Our results indicate that for the most common orientations of the interplanetary field, it is unlikely that such ions when scattered in pitch angle behind the near‐perpendicular bow shock (θ Bn ⩾80°) can contribute to upstream field‐aligned beams leaving the bow shock at shock‐normal angles (θ Bn ) greater than 45°. Reflected‐gyrating ions similarly scattered behind the quasi‐perpendicular shock (θ Bn ⩾45°) are more likely to contribute to such beams by leaking from the bow shock close to where they entered the magnetosheath.
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Bow wave
Pitch angle
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Plasma and magnetic field data detected by NASA GGS/Polar and Wind during the May 4, 1998, storm event are analyzed to demonstrate for the first time a causal relation between the magnetosheath energetic ions and bow shock magnetic geometry. Intense magnetosheath energetic ions observed upstream from the cusp are from the quasi‐parallel bow shock and show properties indicating that they are a possible source of cusp energetic ions.
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Bow wave
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Times when energetic ions are absent and present in ISEE 1 magnetosheath plasma spectrograms are correlated with ISEE 3 IMF orientation measurements. The study indicates that when the plasma at the spacecraft is traced along a streamline to the bow shock surface, the angle between the surface normal at that point and the IMF is greater than 60° when the energetic ions are absent and less than 60° when they are present. The pattern is consistent with the ions coming from the same regions of the bow shock where intermediate and diffuse ions are found on the upstream side. The 60° criterion is used to draw schematic patterns of the location of energetic ions in the magnetosheath as a function of IMF orientation. Some orientations result in layers adjacent to the magnetopause and other orientations give layers adjacent to the bow shock.
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Bow wave
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