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