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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. Amata 1 , S. P. Savin 2 , R. Treuman 3 , G. Consolini 1 , D. Ambrosino, M.F. Marcucci 1 , L. Trenchi 1 . 1. IFSI - INAF, Rome, Italy 2. IKI, Moscow, Russia 3. ISSI, Bern, Switzerland.

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

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  1. 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, Italy 2. IKI, Moscow, Russia 3. ISSI, Bern, Switzerland (Ermanno.Amata@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 > 6.7 keV/cm-3 Wk >1.5 <WkSW> KeV High Kinetic energy density Plasma Jets HKPJ

  9. 83 HKPJ are found between 09.40 and 11.00 UT. <<∆t> ~ 28 s, i.e. ~ 6000 km. 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. The characteristic HKPJ angular spread is ~20°-30°. 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

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

  11. ACE GSM mag. field Y (RE) WIND IMP8 c c X (RE)

  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 > 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. M.sphere 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. OUTLINE • MSH flow: basic properties. • The 21 March 2002 event. • The 17 March 2001 event. • The 26 March 2005 event. • Summary.

  14. Cluster & DS orbital tracks between 02 and 04 UT on March 26, 2005. Z Bow Shock Cluster DS X X XZ GSE Y XY GSE

  15. ACE Vz ~ -30 km/s DS ACE Vx ~ -690 km/s Cluster 3

  16. DS Cluster 3

  17. Wk_jet ~ 3. Wk_MSH ~ 1.5 Wk_SW Z XZ GSE XY GSE X X Y

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

  19. 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 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. We always find that Mms > 1.3 and that βjet > βMSH 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. 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).

  20. Questions We do not know the origin of HKPJ’s. 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 HKPJ’s? Future work Increase the statistics. Answer the questions.

  21. Thank you

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