Abstract
Abstract. Field-aligned ion beams (FABs) originate at the quasi-perpendicular Earth's bow shock and constitute an important ion population in the foreshock region. The bulk velocity of these FABs depends significantly on the shock normal angle, which is the angle between shock normal and upstream interplanetary magnetic field (IMF). This dependency may therefore be taken as an indicator of the local structure of the shock. Applying the direct reflection model to Cluster measurements, we have developed a method that uses proton FABs in the foreshock region for remote sensing of the local shock structure. The comparison of the model results with the multi-spacecraft observations of FAB events shows very good agreement in terms of wave amplitude and frequency of surface waves at the shock front.
Highlights
The global shape of Earth’s bow shock is well known and can be modeled by using a magnetohydrodynamics approach
From top to bottom this figure shows the distance of the spacecraft to the shock front determined by timing analysis, the beams bulk speeds and the shock normal angles determined by the models
The blue lines show the θBn calculated with the preestablished local structure according to the forward model; the green lines show the θBn calculated with Eqs. (2), (3) and constraint that n is out of B–Vsw plane with the selected angle; the red lines show the θBn calculated with the similar way as green lines but n is within the B–Vsw plane
Summary
The global shape of Earth’s bow shock is well known and can be modeled by using a magnetohydrodynamics approach. The details of the local structure of the bow shock are still not very well understood. The various shock regions are commonly distinguished by the shock normal angle (θBn), which is the angle between the upstream IMF and the normal (n) to the shock front. Angles of θBn≤45◦ correspond to the quasi-parallel regime whereas angles of θBn≥45◦ are corresponding to quasi-perpendicular shock regions, respectively. Both the shock structure and presence of ion population are quite different at those two distinct regions.
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