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Cluster workshop, 2009-5-15

Magnetospheric solitary structure maintained by 3000 km/s ions as a cause of westward moving auroral bulge at 19 MLT.

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Cluster workshop, 2009-5-15

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  1. Magnetospheric solitary structure maintained by 3000 km/s ions as a cause of westward moving auroral bulge at 19 MLT M. Yamauchi1, I. Dandouras2, P.W. Daly3, G. Stenberg4, H. Frey5, P.-A. Lindqvist6, Y. Ebihara7, R. Lundin1, H. Nilsson1, H. Reme2, M. Andre4, E. Kronberg3, and A. Balogh8 (1) IRF, Kiruna, Sweden, (2) CESR, Toulouse, France, (3) MPS, Katlenburg-Lindau, Germany, (4) IRF, Uppsala, Sweden, (5) UCB/SSL, Berkeley, CA, USA, (6) Alfvén Lab., KTH, Stockholm, Sweden, (7) IAR, Nagoya U., Nagoya, Japan, (8) Blackett Lab., ICL, London, UK Cluster workshop, 2009-5-15

  2. Cluster Perigee S/C * Z ≈ 0 RE * 60 GMLat * 19 MLT sun tail

  3. overview ions > 5000 km/s ions ≈ 3000 km/s P/A 0.01~40 keV P/A 06:42 06:44 06:46 06:48 IMAGE (FUV)

  4. Sudden change in field ExB (>50 km/s) is observed e.g., 57 km/s : He+~ 70 eV H+ ~ 17 eV

  5. Timing (B ≠ E) propagate (1) single peak of E: lead by SC-3 by 1~10 sec (2) Pi2-like rarefaction of B: simultaneous at all SC

  6. Timing from ExB convection SC-3 leads against SC-1 by 10 sec: agree with field data

  7. & E is nearly // to Propagation direction Timing  Sunward propagation of E 1000~2000 km

  8. 06:43 UT event (arrival of auroral bulge) Sunward propagation (5~10 km/s) of DC field * depletion of |B|≈BZ up to 25% * polarization E≈-EX of up to 10 mV/m * ExB convection (up to 50 km/s) of cold He+ (without O+)

  9. increase in ion flux decrease in ion flux H+ < 90 keV H+ > 160 keV

  10. increase in ion flux He < 350 keV O < 0.9 MeV O > 1.4 MeV He > 700 keV decrease in ion flux

  11. All relevant ion channel 3000 km/s = 50 keV (H), 190 keV (He), 740 keV (O) 5000 km/s = 130 keV (H), 500 keV (He), 2 MeV (O)

  12. 06:43 UT event (arrival of auroral bulge) (a) Sunward propagation (5~10 km/s) of DC field * depletion of |B|≈BZ up to 25% * polarization E≈-EX of up to 10 mV/m * ExB convection (up to 50 km/s) of cold He+ (b) Net flux Increase of selectively 3000 km/s ions * ∆P3000km/s = 3 nPa = - ∆PB. * net decrease of other energetic particles.

  13. Drift motion VB energy (mass independent) 50 keV H+ drift = 15 km/s 190 keV He+ drift = 60 km/s 740 keV O+ drift = 220 km/s Simultaneous appearance & much faster than the motion of the E-structure  a solitary structure to maintain the flux peak VExB= constant (energy  mass)

  14. ion-scale ? gradient is less than 500 km (5~10 km x 50 sec) cf. RB (= mv/qB) for B ≈ 200 nT condition RB(H+) ≤ gradient ≤ RB(He+) << RB(O+)

  15. 06:43 UT event (arrival of auroral bulge) (a) Sunward propagation (5~10 km/s) of DC field * depletion of |B|≈BZ up to 25% * polarization E≈-EX of up to 10 mV/m * ExB convection (up to 50 km/s) of cold He+ (b) Net flux Increase of selectively 3000 km/s ions * ∆P3000km/s = 3 nPa = - ∆PB. * net decrease of other energetic particles. * propagating solitary structure. * scale size ~ gyro radius

  16. overview ions > 5000 km/s ions ≈ 3000 km/s P/A 0.01~40 keV P/A 06:42 06:44 06:46 06:48 IMAGE (FUV)

  17. // keV ion At around 06:44 UT, appearance of 7 keV // O+ from both hemisphere, within 40 sec difference

  18. 06:43 UT event (arrival of auroral bulge) (a) Sunward propagation (5~10 km/s) of DC field * depletion of |B|≈BZ up to 25% * polarization E≈-EX of up to 10 mV/m * ExB convection (up to 50 km/s) of cold He+ (b) Net flux Increase of selectively 3000 km/s ions * ∆P3000km/s = 3 nPa = - ∆PB. * Net decrease of other energetic particles. * propagating solitary structure. * scale size ~ gyro radius (c) Conjugate with auroral bulge * Parallel O+ of ≈ 7 keV is detected

  19. conclusion 1000~2000 km Cluster observed westward moving auroral bulge at 19 MLT on 2002-5-19 is caused by a solitary structure in the magnetosphere. The solitary structure consists of polarization E-field (up to 10 mV/m) and depletion of B≈Bz. This solitary structure is maintained by energetic ions of 3000 km/s speed for all ions. Size (gradient < 500 km) of this solitary structure is comparable to the ion gyro radius of carrier ions.

  20. End

  21. Many other interesting topics (1) Qualitative inter-SC difference (2) Inter-SC time-of-flight examination (3) Decoupling technique of different plasma using conservation of magnetic moment

  22. Qualitative difference within Rgyro Distribution function  Difference cannot be explained by the slight difference in effective energy between SC. RB >> inter-SC distance  cannot be due to finite gyroradius effect.  gradient is substantially large?

  23. TOF effect or phase effect? TOF (7 keV O+ = 250 km/s & SC-1 -100km- SC-4 -150km- SC-3) or Phase-angle dependence?

  24. TOF (7 keV O+ = 250 km/s) SC-1/SC-4/SC-3 = 100 km/150 km or Phase-angle dependence?

  25. Energy-time dispersion (flux increase) time-of-flight? (No) ∆T ~ 10 sec for ∆VD~ 10 km/s  source < 1000 km  No finite gyroradius? (Yes) ∆T ~ 10 sec for ∆RB~ 100 km  agree with propagation VDB = 10~20 km/s VDB = 20~30 km/s VDB = 30~50 km/s VDB = 50~100 km/s

  26. Energetic electron vs B observed flux |B| Synchronize with B field variation

  27. µB = W/B conserved? not really increasing flux = real under µB = const df(µB) = 0  (∂f/∂W)B > 0  (∂f/∂B)W > 0

  28. Linear decoupling after decoupling the conservation of µB = W/B observed flux

  29. End

  30. Westward surging aurora Akasofu et al., 1966 Fujii et al., 1994 = strong upward FAC

  31. conclusion - continued The 3000 km/s ions are the main carrier of the propagating diamagnetic current that caused the magnetic depletion propagating sunward. The sunward propagation of this solitary structure caused the sunward propagation of field-aligned potential drop and hence of the auroral bulge.

  32. sunward propagation profile E

  33. Dst ≈ -60 nT Global condition: minor storm

  34. overview > 5000 km/s 3000 km/s 0.01~40 keV P/A P/A

  35. IMAGE/FUV 06:26~06:56 UT ~06:43 event S/C 06:26 UT 06:34 UT 06:42 UT 06:50 06:28 UT 06:36 UT 06:44 UT 06:52 06:30 UT 06:38 UT 06:46 UT 06:54 06:32 UT 06:40 UT 06:48 UT 06:56

  36. AE and Bx Main phase of minor storm (Dst ~ -60 nT). 2. Substorm onset at around 06:25 UT but ceased in ~10 min. 3. New activity started at around 06:38 UT. 4. Aurora bulge arrived Cluster’s conjugate ~19 MLT at around 06:42~06:44 UT.

  37. ion-scale ? All SC should observe the same behavior of ions if ion gyro-radius (RB = mv/qB) >> inter-S/C distance RB for B ≈ 200 nT condition

  38. µB conservation: W W//, but 06:43

  39. consolation S/C distance ≈ 100 km in z direction & 50 km in x-y direction ≈ RB for 10~20 keV H+ << RB for Ring current ions  H+ > 20 keV (O+ > 2 keV) should behave the same at all SCs if the gyrotropic assumption is correct

  40. 06:43 UT event (arrival of auroral bulge) (a) Sunward propagation (5~10 km/s) of DC field * depletion of |B|≈BZ up to 25% * polarization E≈-EX of up to 10 mV/m * ExB convection (up to 50 km/s) of cold He+ (without O+) (b) Net flux Increase of selectively 3000 km/s ions (∆P3000km/s = 3 nPa = - ∆PB). * Net flux decrease of other energetic particles. * Energy-time dispersion * 100 keV H+ ~ ∆E, and 50 keV H+ ~ ∆B (c) Ionospheric plasma that is accelerated by parallel potential of about 7 kV.

  41. But, there is inter-SC difference RAPID (SSD) data

  42. How about CIS (MCP) data?

  43. Inter-SC difference: trapped H+ for CIS

  44. inter-SC difference ! For flux increase: (1) SC-2 < SC-1 < SC4=SC3 H+: 80~160 keV He+: 200~300 keV (2) SC-2 > SC-1 > SC4=SC3 H+: ~60 keV O+: 500~600 keV Hybrid: (5) SC-2 > SC-1 > SC4 > SC3 O+: 400~500 keV For flux decrease: (3) SC-2 < SC-1 < SC4=SC2 He+: 400~700 keV (4) SC-2 > SC-1 > SC4=SC3 O+: ~400 keV

  45. End

  46. no wave@06:43 UT, wave@06:48 UT 150 nT  ΩP = 4 Hz ion dE dB S// E/B ΩHe? dBZ BB-EM spin effects stagnant dBX

  47. Composition from energy ratio (1) From energy peak: plasmaspheric He+ rich //  Precursor (06:44 UT) Heating (06:49 UT) • = 0° • = 180° • = 360°  // H+ He+ O+ 18eV 70eV H+ He+ ratio=4: O+/He+ or He+/H+ 10 100 [eV] 10 100 [eV]

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