Observation of high kinetic energy density jets in the Earth’s magnetosheath

Observation of high kinetic energy density jets in the Earth’s magnetosheath

E. Amata1, S. P. Savin2, R. Treuman3,G. Consolini1, D. Ambrosino, M.F. Marcucci1 , L. Trenchi1.

1. IFSI - INAF, Rome, Italy2. IKI, Moscow, Russia

3. ISSI, Bern, Switzerland

(Ermanno.Amata@ifsi-roma.inaf.it)

OUTLINE

• MSH flow: basic properties.

• The 21 March 2002 event.

• The 17 March 2001 event.

• The 26 March 2005 event.

• Summary.

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

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.

Wk_MSH = 0.7 Wk_SW

OUTLINE

• MSH flow: basic properties.

• The 21 March 2002 event.

• The 17 March 2001 event.

• The 26 March 2005 event.

• Summary.

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

21 March 2002. Cluster inbound crossing.(Retinò et al., 2006)

VSW~ 470 km/s, n ~ 4 cm-3.

Vectors show SW and MSH velocities.

100 km/s

We use ACE, WIND and IMP 8 as solar wind monitors.

Y (

RE)

X (RE)

WIND (27 March 2002)

WIND (17 March 2001)

IMP8 (17 March 2001)

17 March 2001.WIND: -22, -195, 7 RE

IMP8: 13, 20, 13 RE

27 March 2002.WIND: 79, -15, 6 RE ACE

We use WIND as solar wind monitor.

Wk far exceeds the solar wind WkSW.

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 consider two periods: 10.00-11.00 (presence of N and V peaks)11.00-11.30 (no N and V peaks)

High Kinetic energy density Plasma Jets

HKPJ

Wk > 6.7 keV/cm-3

Wk > 1.5 <WkSW>

KeV

Between 11:00 and 11:20 UT Mms~ 1.

Between 09:42 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 > 6.7 keV/cm3, Mms ~ 1.62

For Wk > 10 keV/cm3, Mms ~ 1.9

83 HKPJ are found between 09.40 and 11.00 UT.

<<∆t> ~ 28 s, i.e. ~ 6000 km.

The characteristic HKPJ angular spread is ~20°-30°.

The strongest HKPJ’s have Wk ~ 16 keV/cm3 and a characteristic scale ~6 s, i.e. 1000-1500 km, i.e. several proton gyroradii.

OUTLINE

• MSH flow: basic properties.

• The 21 March 2002 event.

• The 17 March 2001 event.

• The 26 March 2005 event.

• Summary.

ACE GSM mag. field

IMP8

c c X (RE)

WIND

Y (

RE)

Red jet. Mainly due to high speed (dV ~ 63%, dN ~ 4 %)Direction close to MSH flow.

M.sphere

Green jet. Mainly due to high speedDirection closer to X axis. i.e. towards MP.

Bz > 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.

Gradients are of the order of 100 km .

X dimensions (cyan shadowing)are ~ 1000-2000 km.

OUTLINE

• MSH flow: basic properties.

• The 21 March 2002 event.

• The 17 March 2001 event.

• The 26 March 2005 event.

• Summary.

XZ GSE XY GSE

X

Z

Y

X

Cluster

DS

Bow Shock

Cluster & DS orbital tracks between 02 and 04 UT on March 26, 2005.

ACE Vz ~ -30 km/s

ACE Vx ~ -690 km/s

DS

Cluster 3

DS

Cluster 3

(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

XZ GSE XY GSE

MSH/Jet flow Angle

Double Star

Cluster

10° 14°

Wk_jet ~ 3. Wk_MSH

~ 1.5 Wk_SW

βMSH βjet Mms_MSH Mms_jet

D.Star 4.2 10 0.6 1.5

Cluster 7.5 14 0.7 1.3

X

Z

X

Y

OUTLINE

• MSH flow: basic properties.

• The 21 March 2002 event.

• The 17 March 2001 event.

• The 26 March 2005 event.

• 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 > 1.5 Wk_SW

Summary

HKPJ’s 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.

The flow in HKPJ’s is on average directed between the ambient MSH flow direction and the SW flow direction.

The temperature in HKPJ’s is lower than in the surrounding MSH, while WT is higher (due to N).

The strongest HKPJ’s 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.

We always find that Mms > 1.3 and that βjet > βMSH

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).

Are they generated at the BS itself or in the MSH?

Questions

We do not know the origin of HKPJ’s.

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 HKPJ’s?

Increase the statistics.

Answer the questions.

Future work

Thank you