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J.-A. Sauvaud 1 , C. Jacquey 1 , M. Oka 2 1 IRAP (CESR), UPS‐CNRS,Toulouse, France

A multi­spacecraft study of the changes of the near-Earth plasma sheet and lobe driven by multiple substorms. J.-A. Sauvaud 1 , C. Jacquey 1 , M. Oka 2 1 IRAP (CESR), UPS‐CNRS,Toulouse, France 2 SSL, Berkeley, UCB, USA. Acknowledgments to CSSAR, LANL, CAA, CDPP, IMAGE, SPDF, WDC-2. Overview.

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J.-A. Sauvaud 1 , C. Jacquey 1 , M. Oka 2 1 IRAP (CESR), UPS‐CNRS,Toulouse, France

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  1. A multi­spacecraft study of the changes of the near-Earth plasma sheet and lobe driven by multiple substorms J.-A. Sauvaud1, C. Jacquey1, M. Oka2 1 IRAP (CESR), UPS‐CNRS,Toulouse, France 2 SSL, Berkeley, UCB, USA Acknowledgments to CSSAR, LANL, CAA, CDPP, IMAGE, SPDF, WDC-2

  2. Overview • Lobe Signatures of substorms  Quasi-empty region: almost no local magnetic source Remote sensing of the cross-tail current dynamics • Travelling Compression Region (TCR) • Cross-Tail current Disruption • Dipolarisations observations by DoubleStar and Cluster and LANL: August 31, 2005 events.

  3. TAILWARD PROPAGATING CURRENT DISRUPTION OBSERVED IN THE MID-TAIL LOBES Jacquey et al., 1991, 1993, Ohtani et al., 1992, Jacquey and Sauvaud, 1994, Jacquey, 2000 Earth Ro : 7~15 RE V : 150 ~350 km/s ISEE: Xgsm = -20.7 RE, Ygsm = -0.2 RE, Zgsm = 8.3 RE

  4. INTERBALL – IMP 8 November 24, 1996 Interball Xgsm = -26.4RE Ygsm = 1.3RE Zgsm = 9.3RE IMP-8 Xgsm = -36.2RE Ygsm = -3RE Zgsm = 10.4RE BxBefore > BxAfter Time Scale ~ 20 minutes X = 9.8 RE Vx = - 350 km/s (Jacquey, 2000)

  5. Toward the Earth 15-20 min. BX BX BZ BZ XO Lui, 1978, Jacquey et al., 1991, 1993, Ohtani et al., 1992, Jacquey and Sauvaud, 1994 Sauvaud and Winckler, 1980 Kaufmann, 1987

  6. TCR versus CD: TCR with South-North BZ transition propagates Earthward Bx after ~ Bx before Time scale ~ 30 sec Bz: weak southward turning followed by a northward turning 36 sec Eartward prpogation Slavin et al., 2005

  7. DISRUPTION/DIPOLARIZATION + OXYGEN Traveling Dipolarization associated with a strong impulsive electric field (-vxB) O+ H+ E/L = B/T L = 15 RE

  8. MULTIPLE DIPOLARIZATIONS IN THE LOBE ions ions

  9. Dipolarisations on August 31, 2005 • We focus on dipolarisation events: • corresponding to global magnetotail reconfiguration • corresponding to significant energy dissipation events • i.e. associated with a substorm expansion

  10. Tailward propagating current reductions observed by Cluster and Double Star XDSP-1 ~ -10 RE XCLUSTER ~ -17 RE DSP-1 in the North hemisphere CLUSTER in the South hemisphere GTL in the magnetosheath LANL

  11. AUGUST 31, 2005 15 Pressure GEOTAIL SW 10 ACE PSW (nPa) 5 0 Dst BzIMF SW CLUSTER By Bz Bx Storm conditions  The magnetosphere is populated by a significant amount of 0+ (e.g. Kistler et al.; Sauvaud et al.)

  12. CLUSTER B Bz V E

  13. AUGUST 31, 2005 Double STAR - CLUSTER DSP CLUSTER Cluster is in the south lobe (Bx <0)

  14. The 15:35 event: Disruption preceded by a current filament First disruption : dB = 9 nT BX BZ

  15. CLUSTER

  16. The 15:35 event Pi-2 TC2 TC2 Cluster Cluster Tailward velocity from the Bz shape: -600 to 300 km/s Tailward velocity from the Bx shape from the four Cluster : -300 km/s

  17. The 21:00 event TC-2 Cluster Computed tailward velocity: -92 km/s Measured tailward velocities: from -425 to -106 km/s

  18. Possible interpretation: Time delays could result from the density gradient (i.e VA gradient) in the PSBL/Lobe Wave front

  19. Current disruption/reduction • Related to substorm onset • Tailward propagating • Observed later in the far tail as plasmoids

  20. Current disruption/reduction and reconnection A B Particle-in-cell simulation, see Oka et al., PRL, 2008

  21. Disruption and injections at geosynchronous orbit Δ ≈ 5 - 7 minutes

  22. Summary and conclusions Initiation of current disruption, ≈10 RE Tailward propagating current disruption (90~300 km/s) • Inductive electric field • (1~3 mV/m) E Fast plasma sheet thinning • Plasma injections observed several • minutes later at geosychronous orbit • Differential timing analysis at CLUSTER suggest that there is a • significant gradient of the Alfven speed in the lobe in the Z-direction E In this study, we focus on dipolarisation events corresponding to substorms, i.e., to global magnetic reconfiguration and energy dissipation DSP LANL CLUSTER Data obtained after the onset are in remarkable agreement with results of particle-in-cell simulations of reconnection, the cause of reconnection stays unknown

  23. Disruption and injections at geosynchronous orbit

  24. Propagation velocity From the 4 spacecraft : R = 1466 km t = 4 sec V= 300 km/s Tailward

  25. BX max: • Dt = 113 s  V ~ 380 km/s • ~ Solar Wind speed • Dipolarisation tailward propagation: • Dt = 225 ~462 s • Assuming a propagation purely along X •  V = 90~190 km/s • During the ~5 first minutes, BZ is roughly constant at TC1. • The current reduction is at the TC1 location and does not propagate immediately • TC1 is initially out (dawnward) of the current wedge

  26. Disruption and injections at geosynchronous orbit

  27. Disruption and injections at geosynchronous orbit

  28. Current reduction front (BZ min): • Dt = 225 ~462 s • Assuming a propagation purely along X •  V = 90~190 km/s • Start of the current reduction (BX max): • Dt = 113 s  V ~ 380 km/s • During the ~5 first minutes, BZ is roughly constant at TC1. • The current reduction is at the TC1 location and does not propagate immediately • TC1 is initially out (dawnward) of the current wedge

  29. August 31, 2005 LOS ALAMOS SATELLITES AT 6.6 RE CLUSTER-3 Injections LANL Dipolarization CLUSTER

  30. 255 RE Substorm associated wave propagation over 255 RE STEREO-B AE Time delay STEREO V=1800 km/s

  31. Conclusions • In this study, we focus on dipolarisation events corresponding to substorms, i.e., to global magnetic reconfiguration and energy dissipation • In the last event, the current reduction (i.e. dipolarisation) CLEARLY propagate tailward at velocity ranging between 90 and 190 km/s (value obtained with too rough models). • Sub-structures seen on the BX component (profile of the beginning of the event) appears to propagate tailward at larger velocity (~380 km/s) • The different Cluster spacecraft detected the BZ negative change (Current reduction approach) with significant delays. The most outward of the PS detect the BZ change first. • The passage of the current reduction front is associated with an enhancement of the convection in the lobes, interpreted as the effect of the inductive electric field (1-3 mV/m). • The injection of plasma at geostationary orbit occurred several minutes after dipolarization at Cluster.

  32. Current reduction front (BZ min): • Dt = 225 ~462 s • Assuming a propagation purely along X •  V = 90~190 km/s • Start of the current reduction (BX max): • Dt = 113 s  V ~ 380 km/s • During the ~5 first minutes, BZ is roughly constant at TC1. • The current reduction is at the TC1 location and does not propagate immediately • TC1 is initially out (dawnward) of the current wedge

  33. Trop de traits

  34. G12 B E C D Mid-tail Near-Earth tail Presented at ICS-9, Jacquey et al.

  35. At least 2 types of dipolarisations Type I: No global reconfiguration, no global energy dissipation Type II: Both global reconfiguration and global energy dissipation

  36. Comparison with the timing inferred from mid-tail probes < 1’ 55 sec < 1’ 25 sec -2’43’’ -163 sec < 1’ 10 sec

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