Diapositiva 1

1
Observation of high kinetic energy density jets
in the Earths magnetosheath
E. Amata1, S. P. Savin2, R. Treuman3, G.
Consolini1, D. Ambrosino, M.F. Marcucci1 , L.
Trenchi1. 1. IFSI - INAF, Rome, Italy 2. IKI,
Moscow, Russia 3. ISSI, Bern, Switzerland

(Ermanno.Amata_at_ifsi-roma.inaf.it)
2
OUTLINE

• MSH flow basic properties.
• The 21 March 2002 event.
• The 17 March 2001 event.
• The 26 March 2005 event.
• Summary.

3

• Bow shock
• - conversion of kinetic energy into thermal
  energy
• - slowing down to sub-alfvénic and
  sub-magnetosonic flow.

Wk_MSH 0.7 Wk_SW
Magnetopause keeps MSH flow away from
magnetosphere.
Magnetic reconnection at the magnetopause -
plasma jets, - penetration of plasma in the
magnetosphere, - D-shaped distributions, -
reflected distributions in the MSH.
We describe here several examples of jets which
are not due to magnetic reconnection at the
magnetopause.
4
OUTLINE

• MSH flow basic properties.
• The 21 March 2002 event.
• The 17 March 2001 event.
• The 26 March 2005 event.
• Summary.

5
We show two periods during which jets were
observed in the northern and southern MSH
17 March 2001. Cluster outbound crossing. VSW
330 km/s
Vectors show SW and MSH velocities.
100 km/s
21 March 2002. Cluster inbound crossing. (Retinò
et al., 2006) VSW 470 km/s, n 4 cm-3.
6
We use ACE, WIND and IMP 8 as solar wind monitors.
Y (RE)
WIND (17 March 2001)
17 March 2001. WIND -22, -195, 7 RE IMP8 13,
20, 13 RE
WIND (27 March 2002)
27 March 2002. WIND 79, -15, 6 RE ACE
IMP8 (17 March 2001)
X (RE)
7
March 27, 2002. Period already studied by Retinò
et al. (2006) reconnection in the MSH at scales
of 100 km. We look at larger scales.
Many peaks are seen in N and V.
We use WIND as solar wind monitor.
Wk far exceeds the solar wind WkSW.
We consider two periods 10.00-11.00 (presence
of N and V peaks) 11.00-11.30 (no N and V peaks)
8
Wk gt 6.7 keV/cm-3 Wk gt 1.5 ltWkSWgt
High Kinetic energy density Plasma Jets HKPJ
9
83 HKPJ are found between 09.40 and 11.00 UT.
ltlt?tgt 28 s, i.e. 6000 km.
The strongest HKPJs have Wk 16 keV/cm3 and a
characteristic scale 6 s, i.e. 1000-1500 km,
i.e. several proton gyroradii.
The characteristic HKPJ angular spread is
20-30.
Between 1100 and 1120 UT ?Mms? 1. Between
0942 and 11.00 UT, ?Mms?1.34 and
?MA?3.8. This suggests that a
super-magnetosonic population adds to that with
low Mms. For Wk gt 6.7 keV/cm3, ?Mms? 1.62
For Wk gt 10 keV/cm3, ?Mms? 1.9
10
OUTLINE

• MSH flow basic properties.
• The 21 March 2002 event.
• The 17 March 2001 event.
• The 26 March 2005 event.
• Summary.

11
(No Transcript)
12
Red jet. Mainly due to high speed (dV 63, dN
4 ) Direction close to MSH flow.
Green jet. Mainly due to high speed Direction
closer to X axis. i.e. towards MP.
Bz gt 0 in the MSH and in the SW. MSH and
internal field locally roughly parallel. No
D-shaped distributions in the m.sphere. No
reflected populations in the MSH. We exclude
both local and low-latitude reconnection for the
blue and cyan jets.
The distance between the Cluster spacecraft was
600 km.
X dimensions (cyan shadowing) are 1000-2000 km.
Gradients are of the order of 100 km .
13
(No Transcript)
14
OUTLINE

• MSH flow basic properties.
• The 21 March 2002 event.
• The 17 March 2001 event.
• The 26 March 2005 event.
• Summary.

15
Cluster DS orbital tracks between 02 and 04 UT
on March 26, 2005.
Z
Bow Shock
Cluster
DS
X
X
Y
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
DS
Cluster 3
20
DS
Cluster 3
21
(km/s) DS Vx DS Vy DS Vz Cl Vx Cl Vy Cl Vz
Jet -350 -200 50 -330 0 200
MSH -180 -150 30 -150 0 150
Wk_jet 3. Wk_MSH 1.5 Wk_SW
MSH/Jet flow Angle MSH/Jet flow Angle
Double Star Cluster
10 14
ßMSH ßjet Mms_MSH Mms_jet
D.Star 4.2 10 0.6 1.5
Cluster 7.5 14 0.7 1.3
Z
X
X
Y
22
OUTLINE

• MSH flow basic properties.
• The 21 March 2002 event.
• The 17 March 2001 event.
• The 26 March 2005 event.
• Summary.

23
Summary
We identified many cases of high kinetic energy
density plasma jets (HKPJ) in the MSH. To define
such a jet we use the condition Wk_jet gt 1.5
Wk_SW
HKPJs are due to N and V increases. They are
found in Interball (not shown here), Cluster and
Double Star, at any distance from the BS and from
the MP.
We always find that Mms gt 1.3 and that ßjet gt
ßMSH
The flow in HKPJs is on average directed between
the ambient MSH flow direction and the SW flow
direction.
The temperature in HKPJs is lower than in the
surrounding MSH, while WT is higher (due to N).
The strongest HKPJs have Wk 10-20 keV/cm3 and
scales of 1000-2000 km, i.e. several proton
gyroradii, while their peaks and gradients have
scales of the order of the proton gyroradius.
None of the examined jets seems to be due to
reconnection at the MP.
Often the jets head towards the MP (in one case
with a 20 angle relative to the MP normal).
24
Questions
We do not know the origin of HKPJs.
Are they generated at the BS itself or in the MSH?
The magnetic field in the MSH is too low to
account for their extra energy density.
Nevertheless, what is the relation between the
reconnecting thin current sheets studied by
Retinò et al. (2006) and the larger scale HKPJs?
Future work
Increase the statistics. Answer the questions.
25
Thank you