Observation of high kinetic energy density jets in the Earth’s magnetosheath E. Amata 1, S. P. Savin 2, R. Treuman 3, G. Consolini 1, D. Ambrosino, M.F. Marcucci 1, L. Trenchi IFSI - INAF, Rome, Italy 2. IKI, Moscow, Russia 3. ISSI, Bern, Switzerland

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. W k_MSH = 0.7 W k_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 Cluster outbound crossing. V SW ~ 330 km/s 21 March Cluster inbound crossing. (Retinò et al., 2006) V SW ~ 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 (R E ) X (R E ) WIND (27 March 2002) WIND (17 March 2001) IMP8 (17 March 2001) 17 March WIND: -22, -195, 7 R E IMP8: 13, 20, 13 R E 27 March WIND: 79, -15, 6 R E ACE

We use WIND as solar wind monitor. W k far exceeds the solar wind W kSW. March 27, 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: (presence of N and V peaks) (no N and V peaks)

High Kinetic energy density Plasma Jets HKPJ W k > 6.7 keV/cm -3 W k > 1.5 KeV

Between 11:00 and 11:20 UT  M ms  ~ 1. Between 09:42 and UT,  M ms  ~1.34 and  M A  ~3.8. This suggests that a super-magnetosonic population adds to that with low M ms. For W k > 6.7 keV/cm 3,  M ms  ~ 1.62 For W k > 10 keV/cm 3,  M ms  ~ HKPJ are found between and UT. ~ 28 s, i.e. ~ 6000 km. The characteristic HKPJ angular spread is ~20°-30°. The strongest HKPJ’s have W k ~ 16 keV/cm 3 and a characteristic scale ~6 s, i.e 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 (R E ) WIND Y (R E )

Red jet. Mainly due to high speed (dV ~ 63%, dN ~ 4 %) Direction close to MSH flow. M.sphere Green jet. Mainly due to high speed Direction closer to X axis. i.e. towards MP. B z > 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 ~ 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 V z ~ -30 km/s ACE V x ~ -690 km/s DS Cluster 3

DS Cluster 3

(km/s) DS VxDS VyDS VzCl VxCl VyCl Vz Jet MSH XZ GSEXY GSE MSH/Jet flow Angle Double Star Cluster 10° 14° W k_jet ~ 3. W k_MSH ~ 1.5 W k_SW β MSH β jet M ms_MSH M ms_jet D.Star Cluster 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: W k_jet > 1.5 W k_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 W T is higher (due to N). The strongest HKPJ’s have W k ~ keV/cm 3 and scales of km, i.e. several proton gyroradii, while their peaks and gradients have scales of the order of the proton gyroradius. We always find that M ms > 1.3 and that β jet > β MSH 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

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