Multiple Ion Acceleration at Martian Bow Shock

1
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 dEtude 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.
2
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.
3
Figure 2 examined traversals
Figure 3
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)
4
Figure 4
BS
BS
BS
BS
Other examples with multi-bundled structure
BS
5
Fig 5 Summary
QT
FS
QL
QT
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. // acceleration (3a, 6b, 7a)
escape after the second reflection.
escape
acceleration
acceleration
oblique accel.
// acceleration
QT
FS
QT
QL
escape
escape
acceleration
oblique accel.
// acceleration
// accel.