Multiple Ion Acceleration at Martian Bow Shock M. Yamauchi1, Y. Futaana1, M. Holmström1, R. Lundin1, S. Barabash1, A. Fedorov2, J.-A. Sauvaud2, R.A. Frahm3, J.D. Winningham3, and E. Dubinin4 (1) Swedish Institude of Space Physics, Kiruna, Sweden, (2) Centre d’Etude Spatiale des Rayonnements, Toulouse, France, (3) Southwest Research Institute, San Antonio, Texas, USA (4) Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany IUGG, 6 July, 2011 (A102, #4402)

Analyses The ion mass analyzer (IMA) on board Mars Express (MEX) revealed multi-bundled energy structure of ions within a distance of a proton gyroradius from the Martian bow shock. By using pick-up ions of exospheric origin to determine the local magnetic field orientation from thier circular trajectory in velocity space, the velocity distribution of these multi-bundled structure is obtained. Figure 1 shows an example of observation. The velocity distribution is compared with specularly reflected solar wind and once-reflected solar wind that returns back to the bow shock after gyration (injection velocity is taken from observation). Seven traversals (Figure 2) with three types of the bow shock configurations (Figures 3 and 4) are examined. The result (V^-V//) and V^-V^ plots) are shown in Figure 5. Calculated V// is also compared with the de Hoffman-Teller velocity to examine weather the reflected ions escape after second reflection.

Figure 1 (a) Energy-time spectrograms near the bow shock (BS). The nearly 3-min cycle in the proton data is due to the scanning cycle of entrance direction from -45° to +45°. Solar wind protons (SW) are seen at around 0.7 keV. (b) One of 3-min scans is expanded for different azimuthal (f) directions, and (c) plotted in the ^-// projection (upper panel) and ^-^ projection (lower panel). Identified ion populations in (b) are marked by different symbols (legend at right) in (c) using the same colors as (b). The orange and red arrows are calculated jumps by the first and second specular reflection. Gyration trajectories of these reflected ions are given by orange and red dashed circles/lines. BS SW n: BS normal direction.

Figure 2: Figure 3 examined traversals Three types of bow shocks: quasi-parallel (QL) shock, quasi-perpendicular shock with its specular reflection direction of the solar wind more along than perpendicular with respect to the magnetic field (FS), and the other quasi-perpendicular shock (QT)

BS BS BS BS Figure 4 Other examples with multi-bundled structure BS

QT QT FS QL Figure 5a // acceleration ^ acceleration ^ acceleration oblique acceleration Figure 5a escape

QT QT QL FS Figure 5b oblique acceleration ^ acceleration ^ & // escape escape

Summary In all cases, the second branch marked by orange colors is consistent with specular reflections of the solar wind at the bow shock for both parallel and perpendicular directions. In all cases with multiple ring observations, the third branch marked by red colors is consistent with specular reflections of the second reflection at the bow shock for both parallel and perpendicular directions. All events with parallel acceleration (#3a, #6b, #7a) correspond to escape beyond the uncertainty after the second reflection. The events with perpendicular acceleration correspond to trapping, although the uncertainty is large for these cases.