Ion Acceleration at Martian Bow Shock
Transcript of Ion Acceleration at Martian Bow Shock
Ion Accelerationat Martian
Bow ShockM. Yamauchi1, Y. Futaana1, R. Lundin1,A. Fedorov2, J.-A. Sauvaud2, E. Dubinin3,J.D. Winningham4, R.A. Frahm4,S. Barabash1, and M. Holmstron1.
1 IRF, Kiruna, Sweden2 CESR, Toulouse, France3 MPS, Katlenburg-Lindau, Germany4 SwRI, San Antonio, USA
ASPERA/IMA on board Mars Expresssometimes observes double-ringdistribution in the solar wind referenceframe. The second ring has much higherenergy than the first ring originated fromzero-velocity (newly ionized) ions.
Here, we show two examples that show twodifferent formation processes of the secondring.
(1) 2005-6-3 event (06:00~06:31 UT):perpendicular acceleration.
Selected events
SW=600 km/s
(2) 2005-8-5 event (08:21~10:33 UT):parallel and anti-parallel acceleration, andanother type of perpendicular acceleration.
SW=400 km/s
In raw data (one scan), all ion counts ofmore than 1 keV are manually classified intothe solar wind, the first ring distribution(#1), the second ring distribution (#5), andthe others (#1.5, #2, #2.5, #3).
During the classification, we also comparedthese counts in the energy-anglespectrograms because counts are alreadyclustered in the spectrograms.
The last two categories (#1.5~#5) areclassified after we find IMF orientation from#1 (first ring). The IMF orientation isobtained from Minimum/Maximum Variancemethod (these ion must be distributedcircular in the velocity space because allions makes gyro-trajectory from the sameinitial velocity).
The last category (#1.5~#3) provides hintson acceleration process (direction andhistory) toward the second ring (#5).
Method
?
(1)
2005-6-3 event
discrete energy
+X = sunward
Bow Shock
#1
#5
SW#3
second ring ring
⊥ accel.
B
+ Y
- Y
N = (+0.5, -0.4~+0.2, +0.8)
#3
#1#1
#5
SW SW
#3
2005-8-5 event
(1)
(2)(2)
Jumping energy
(1)
(2)
(1)
+ R = +Y & +Z (45°)
- R = -Y & -Z (225°)
+X = sunward
Bow Shock SW
B#1.5=part of ring
#2.5=#1.5 + V//
#2=#1.5 - V//
#3 = #2.5 + ⊥ accel.
#1=ring
N = (0.17, -0.85, -0.49)
SW
#1
#2
#2.5
#1
#3
Jumping energy!
summaryAcceleration outside the bow shock is notsimple with at least two differentmechanisms.
1. Acceleration takes place on ions flowinga specific direction, i.e., at one angle invelocity space (#1.5).
2. We found a signature of parallelacceleration in both directions (#2, #2.5)even outside the bow shock.
3. We found two types of perpendicularaccelerations, in fixed direction (#3)tailward along the bow-shock surface, andexperiencing gyration during acceleration(#3.5).
4. The acceleration is non-continuous inenergy, and this discrete energy is stablefor several minutes.5. Both accelerations are connected tosecond ring at specific velocity (#5).
6. The spiral motion (#3.5) help estimatingthe IMF polarity.
cf. upstream of Venus Bow shock
ASPERA/IMA on board Mars Expresssometimes observes double-ringdistribution in the solar wind referenceframe. The second ring has much higherenergy than the first ring originated fromzero-velocity (newly ionized) ions.
Here, we show two examples that show twodifferent formation processes of the secondring.
(1) 2005-6-3 event (06:00~06:31 UT):perpendicular acceleration.
(2) 2005-7-12 event (11:35~11:50 UT):acceleration.
(3) 2005-7-29 event (17:29~17:52 UT):perpendicular acceleration.
(4) 2005-8-5 event (08:21~10:33 UT):parallel and anti-parallel acceleration, andanother type of perpendicular acceleration.
Abstract
#1
#3#5#3
#1He+H+
He+H+
He+H+
He+H+
#2.5
#1
#2
#2.5
#1
He+H+
He+H+
#3
#2.5
#1
#3
#1