Fig. 1.
From: Ion acceleration by multiple reflections at Martian bow shock
Extractions from Yamauchi et al. (2011). (a) Energy-time spectrograms of the electron energy flux and ion energy flux (keV cm−2 s−1 keV−1) observed by ELS and IMA, respectively, during 11:30–12:05 UT, 12 July 2005. Both spectrograms show the average of all 16 azimuthal directions. The nearly 3-min (192 sec) cycle seen in the proton data is due to the scanning cycle of the IMA entrance (elevation) direction from θ = 0 (−45°) to θ = 15 (+45°). Solar wind protons are seen at around 0.7 keV (contaminated by He++ at around 1.4 keV) every 192 sec scanning cycle. DRM denotes the Mars-centric distance with a unit of Martian raduis. (b) The proton data during 11:46:00–11:49:12 UT for azimuthal sectors φ = 1∼4 (counts per every 100 ms measurement), and integration of all sectors (counts per second). The first pixels correspond to −45° elevation (θ = 0) and the last pixels to +45° elevation (θ = 15). Different branches of the multiple stripes are marked by horizontal bars with different colors. (c) Velocity scatter plots in the V L -V N projection (upper panel) and in the V L -V M projection (lower panel) during the same scan as (b), i.e., 11:46:00–11:49:12 UT. The local Cartesian coordinates L-M-N are derived such that the lowest-energy ring distribution at around 2 keV, marked by blue dashed line in (b) and blue empty circles in (c), forms a gyrating circular trajectory (blue dashed circle in (c)) in the V L -V M projection with zero average V N , such that N points along the magnetic field (Yamauchi et al., 2011). The velocity space points with 5 counts or more during the 100 ms measurement period (this threshold is increased to 10 counts per 100 ms measurement for the solar wind that is marked by light blue pluses) are plotted in the spacecraft reference frame except for ϕ = 0 which is strongly contaminated from the other sectors. Identified ion populations in (b) are marked by different symbols (legend at right) using the same colors as (b). The modeled bow shock normal direction (n) is given by black arrows. The orange and red arrows show in the V L -V M projection of the calculated jumps by the first and second specular reflections, starting from the solar wind velocity for the first reflection (orange) and from the end point of the observed second ring (corresponds to second injection) for the second reflection. Gyration trajectories of these reflected ions are given by orange and red dashed circles. The horizontal blue, orange, and red lines in the V L -V N projection indicates the calculated field-aligned velocities (V N ) of the solar wind, first reflected ions, and second reflected ions, respectively.