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    ABSTRACT: The ion mass analyzer (IMA) on board Mars Express revealed bundled structures of ions in the energy domain within a distance of a proton gyroradius from the Martian bow shock. Seven prominent traversals during 2005 were examined when the energy-bunched structure was observed together with pick-up ions of exospheric origin, the latter of which is used to determine the local magnetic field orientation from its circular trajectory in velocity space. These seven traversals include different bow shock configurations: (a) quasi-perpendicular shock with its specular direction of the solar wind more perpendicular to the magnetic field (QT), (b) quasi-perpendicular shock with its specular reflection direction of the solar wind more along the magnetic field (FS), and (c) quasi-parallel (QL) shock. In all seven cases, the velocity components of the energy-bunched structure are consistent with multiple specular reflections of the solar wind at the bow shock up to at least two reflections. The accelerated solar wind ions after two specular reflections have large parallel components with respect to the magnetic field for the QL shock whereas the field-aligned speed is much smaller than the perpendicular speed for the QT shock. The reflected ions escape into the solar wind when and only when the reflection is in the field-aligned direction.
    Earth, Planets, and Space. 04/2012; 64(2):2853-.
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    ABSTRACT: Among several mechanisms issued from simulation and theoretical studies proposed to account for the nonstationarity of quasi-perpendicular supercritical shocks, one process-the so-called self-reformation-driven by the accumulation of reflected ions in the foot has been intensively analyzed with simulations. Present results based on experimental CLUSTER mission clearly evidence signatures of this self-reformation process for the terrestrial bow shock. The study based on magnetic field measurements includes two parts: (i) a detailed analysis of one typical shock crossing for almost perpendicular shock directions where the risk of pollution by other nonstationarity mechanisms is minimal. A special attention is drawn on appropriate treatment of data to avoid any wrong interpretation. One key result is that the ramp width can reach a very narrow value covering a few electron inertial lengths only; (ii) a statistical analysis allows relating the signatures of this nonstationarity with different plasma conditions and shock regimes. Present results are discussed in comparison with previous simulation works.
    Twelfth International Solar Wind Conference. 03/2010;
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    ABSTRACT: The Earth’s bow shock is the most studied example of a collisionless shock in the solar system. It is also widely used to model or predict the behaviour at other astrophysical shock systems. Spacecraft observations, theoretical modelling and numerical simulations have led to a detailed understanding of the bow shock structure, the spatial organization of the components making up the shock interaction system, as well as fundamental shock processes such as particle heating and acceleration. In this paper we review the observations of accelerated ions at and upstream of the terrestrial bow shock and discuss the models and theories used to explain them. We describe the global morphology of the quasi-perpendicular and quasi-parallel shock regions and the foreshock. The acceleration processes for field-aligned beams and diffuse ion distribution types are discussed with connection to foreshock morphology and shock structure. The different possible mechanisms for extracting solar wind ions into the acceleration processes are also described. Despite several decades of study, there still remain some unsolved problems concerning ion acceleration at the bow shock, and we summarize these challenges.
    Space Science Reviews 11/2012; 173(1-4). · 5.87 Impact Factor

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