Article

# Quasi-perpendicular Shock Structure and Processes

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Imperial College London Now at Space and Atmospheric Physics, The Blackett Laboratory London UK
(Impact Factor: 6.28). 06/2005; 118(1):161-203. DOI: 10.1007/s11214-005-3827-0

ABSTRACT

Many of the achievements of cluster investigations in the field of investigating quasi-perpendicular shock transitions are discussed. Cluster has been able to probe the internal shock scales and motion via now-standard four spacecraft techniques. Non-planarity of the shock can be caused by large scale curvature or by rippling and waves around the shock. The finite shock width, combined with the presence of waves around the shock, results in uncertainty in the shock time of around a second. It was found that the timing method and the models are good estimators of the shock orientation.

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• "[3] Particles of solar wind origin can be accelerated at the terrestrial bow shock by various acceleration mechanisms. These could be reflected ion beams seen at the quasi‐ perpendicular bow shock and so‐called diffuse particles associated with the quasi‐parallel bow shock [Bale et al., 2005; Eastwood et al., 2005]. At the quasi‐perpendicular bow shock energetic ions of solar wind origin can be accelerated by shock drift acceleration, and then travel upstream to the large distances [Anagnostopoulos and Kaliabetsos, 1994; Anagnostopoulos et al., 2009]. "
##### Article: On the origin of the energetic ion events measured upstream of the Earth's bow shock by STEREO, Cluster, and Geotail
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ABSTRACT: In 2007 during the declining phase of the solar cycle the energetic upstream ion events occurred mainly after a corotating interaction region passed the Earth's magnetosphere. We study the relation between these upstream events observed from about 70 to 1750 R<SUB>E</SUB> away from the Earth and observations in the vicinity of the terrestrial bow shock (up to 30 R<SUB>E</SUB>). For this purpose, simultaneous measurements of energetic ions from STEREO A and STEREO B (far upstream region) and from Cluster and Geotail (near the bow shock) are used. In all cases the energetic ions far upstream are associated with the upstream ion events near the bow shock. The upstream events are observed simultaneously mainly when the magnetic field is pointing along the line joining those satellites in the far upstream region with those near the terrestrial bow shock. The upstream events near the bow shock often coincide with sunward directed electron bursts, increased AE index (>200 nT), nonexponential proton spectra, and most important the presence of O<SUP>+</SUP> ions, all of which imply at least partly a magnetospheric origin. In ˜57% of cases the upstream ion events near the bow shock are associated with electron bursts and/or with the presence of O<SUP>+</SUP>, and ˜40% of the latter events are associated with electron bursts at STEREO A. Although we present strong evidence that the events are partially of magnetospheric origin, we do not exclude the presence of the ions accelerated at the bow shock.
Journal of Geophysical Research Atmospheres 02/2011; 116(A2):A02210. DOI:10.1029/2010JA015561 · 3.43 Impact Factor
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• "The solid and dashed curves denote ideal MHD calculations for perpendicular (θ Bn = 90 • ) shocks at γ = 5/3, 2 and 3. bow (solid marks) and interplanetary (light marks) shocks based on data of various authors. The values of ρ 2 /ρ 1 in these dependences were taken from (Zastenker et al., 1983) and (Formisano et al., 1973; Greenstadt et al., 1980; Bame et al., 1979; Bale et al., 2005) for interplanetary and bow shocks respectively. In some cases, the calculation of the Alfvén Mach number was based on hour-averaged OMNI data (http://omniweb.gsfc.nasa.gov/) on the magnetic field, SW density and velocity (for the bow shock). "
##### Article: Estimated relations at a shock driven by a coronal mass ejection
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ABSTRACT: Analysis of SOHO/LASCO C3 data reveals a discontinuity, interpreted as a shock wave, in plasma density radial profiles in a restricted region ahead of each of ten selected coronal mass ejections (CME) along their travel directions. In various events, shock wave velocity $V\approx$ 800-2500 km s$^{-1}$. Comparing the dependence of Alfv\'{e}n Mach number $M_A$ on shock wave strength $\rho_2/\rho_1$, measured at $R > 10R_\odot$ from the center of the Sun, to ideal MHD calculations suggests that the effective adiabatic index $\gamma$, characterizing the processes inside the shock front, is largely between 2 and 5/3. This corresponds to the effective number of degrees of freedom of motion 2 to 3. A similar dependence, $M_A(\rho_2/\rho_1)$, was derived for the Earth's bow shock and interplanetary collisionless shock waves. All this supports the assumption that the discontinuities in front of CMEs are collisionless shock waves. Comment: 22 pages, 12 figures
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• "In this paper, our analysis will cover time scales above 1 s (Fig. 10), hence the differences of measurements between the satellites are indistinguishable. The selected time interval, defined by the onset of the solar wind supersonic/subsonic transitions, begins when Cluster-1 crosses the shock front of a quasi-perpendicular bow shock by entering into the solar wind at the time indicated by a dashed line in the upper panel of Fig. 2, and ends when Cluster-1 departs from the solar wind by entering into the transition (foreshock ) region of a quasi-parallel bow shock at the time indicated by a dashed line in the lower panel of Fig. 2. In contrast to a quasi-perpendicular shock (Bale et al., 2005a) characterized by sharp transitions of the modulus of the ion bulk flow velocity |V i | and magnetic field |B|, a quasi-parallel shock (Burgess et al., 2005) is characterized by a transition region with repeated shock crossings, as seen in Fig. 2. This quasiparallel shock event has been analyzed by a number of papers (Eastwood et al., 2003; Stasiewicz et al., 2003; Behlke et al., 2004; Lucek et al., 2004). "
##### Article: Cluster and ACE observations of phase synchronization in intermittent magnetic field turbulence: A comparative study of shocked and unshocked solar wind
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ABSTRACT: We apply two distinct nonlinear techniques, kurtosis and phase coherence index, to analyze the modulus of interplanetary magnetic field data |B| measured by Cluster and ACE spacecraft from 1 to 3 February 2002. High degree of phase synchronization is found across a wide range of time scales, from 1 s to 104 s, in the magnetic field fluctuations, both in the shocked solar wind upstream of Earth&apos;s bow shock and in the unshocked ambient solar wind at the L1 Lagrangian point. This is the first direct measurement of phase coherence in the ambient solar wind turbulence. We show that phase synchronization related to nonlinear multiscale interactions is the origin of the departure from Gaussianity in the intermittent magnetic field turbulence. In particular, we demonstrate that at small scales near the spectral break the intermittency level of Cluster is lower than ACE, which may be a signature of the reflected ions from the shock.
Annales Geophysicae 04/2009; 27(4). DOI:10.5194/angeo-27-1789-2009 · 1.71 Impact Factor