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 IRF seminer 2009-2-19

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

Many interesting topics (1) 06:43 UT event (auroral bulge)  today (2) 06:48 UT event (faded arc) (3) Incoherent inter-SC difference (4) Decoupling technique of different plasma using conservation of magnetic moment

Cluster location * Z ≈ 0 RE S/C * 19 MLT * 60 GMLat sun tail

IMAGE/FUV 06:26~06:56 UT 06:26 UT 06:34 UT 06:42 UT 06:50 06:28 UT 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

Global condition: minor storm Dst ≈ -60 nT

IMAGE/FUV 06:26~06:56 UT 06:26 UT 06:34 UT 06:42 UT 06:50 06:28 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

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.

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)

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.

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

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

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

Timing  Sunward propagation of E & E is nearly // to Propagation direction

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

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+)

increase in ion flux decrease in ion flux // 45°  35 keV H+ < 90 keV H+ > 160 keV

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

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)

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

µB conservation: W  W// 06:43 06:48:30

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

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

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 8~9 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 decrease of other energetic particles.

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

Drift motion VB  energy (mass independent) VExB = constant (energy  mass)

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 10 keV 100 keV 1 MeV H+ v = 1400 km/s RB = 70 km v = 4000 km/s RB = 200 km v = 14000 km/s RB = 700 km He+ v = 700 km/s RB = 140 km v = 2000 km/s RB = 400 km v = 7000 km/s RB = 1400 km O+ v = 350 km/s RB = 300 km v = 1000 km/s RB = 800 km v = 3500 km/s RB = 3000 km

correlation to DC field

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

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

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

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

Westward surging aurora Present understanding Akasofu et al., 1966 Fujii et al., 1994 Ober et al. 2001

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.

sunward propagation profile E

Qualitative difference within Rgyro

conclusion The observations indicate a new type solitary structure in the magnetosphere as the cause of the westward moving auroral bulge: (1) Composed of polarization electric field in the propagation direction and magnetic depletion (2) Maintained by flux enhancement of 3000 km/s ions. Fluxes of the other ring current particles decreased. (3) About 2000 km width in the propagation direction and propagates sunward with about 10 km/s speed. (4) The 3000 km/s ions are the main carrier of the propagating diamagnetic current that caused the magnetic depletion propagating sunward.

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.

conclusion - continued (5) The polarization is maintained by different behaviors between energetic ions and electrons, and particularly the 90 ~ 160 keV protons and > 240 keV electrons are good candidates for the major charge carriers. (6) The potential drop in the propagation direction (about 10 kV tailward at equator) is the ultimate cause of the field-aligned potential drop (about 7 kV upward). (7) The sunward propagation of this solitary structure caused the sunward propagation of field-aligned potential drop and hence of the auroral bulge. Therefore, ring current protons at about 100 keV can be the major charge carrier for auroral electrodynamics in the evening sector.

End

Observation Summary (06:43 UT) 1. Sudden change in particle flux (> 40 keV, > 10 keV, and < 100 eV) when aurora bulge arrived Cluster’s conjugate ~19 MLT. 2. Change is simultaneous at all SC (SC-3 leading by 1~10 sec). 3. Simultaneous DC field change (tailward E~9mV/m, Pi2-like rarefaction |B|≈|BZ| up to 25%) without special wave activity. 4. Increase in medium energy (~3000 km/s) ion flux. Diamagnetic effect by ∆PP can quantitatively explain ∆PB. 5. Decrease in energetic e- (>30 keV) and ions (> 5000 km/s) 6. Temporal (about 1 min) change of pitch-angle of 10-40 keV to more field-aligned than perpendicular. 7. Bulk motion of cold He+ and H+ (no cold O+ or He++). The ion velocity (20km/s, duskward) agrees with the ExB velocity.

inter-SC difference (a) Qualitative and quantitative different changes in fluxes between different SC (b) However, ion gyro-radius (RB) >> inter-SC distance, i.e., it is not finite gyroradius effect. (c) Therefore, gradient is substantially large.

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

Timing for E  propagation

Cold ion moving in one (perpendicular) direction  (spin) Detail on Ion dynamics 15-60 eV for He+ 4-15 eV for H+ Cold ion moving in one (perpendicular) direction  (spin)

Composition = He+ No oxygen! H+ He++ He+ O+ 06:44:00 UT contamination 0643 0644 0645 0646 0647 0648 0649 4-15 eV for H+ ExB drift velocity = 25~50 km/s  15-60 eV for He+ 60-250 eV for O+

Ion convection = ExB SC-3 leads against SC-1 by 10 sec

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

How about CIS (MCP) data?

Inter-SC difference: trapped H+ for CIS

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

End

06:48 UT event (fading of auroral bulge) (a) Bi-parallel beams in the equatoral plane (b) Equatorial signature of the transpolar arc.

Observation of event #2 1. Simultaneous at SC-1, 4 and -3 within 1 sec  sudden activation 2. Bi-directional along B, and DC E-field disturbance  double parallel potential is carried by convection? 3. Wave with randomly changing Pointing flux direction (not shown here)  wave is caused by the bi-parallel beam 4. Decrease 5~70 keV  large-scale configuration change 5. More O+ than He+  not from cold plasma 6. Filamentation in the transpolar arc  but, the relation is not clear (?) 7. Only minor magnetospheric activity  Why do we observed only once in 5 years ?

DC field EY

Timing (ion = 12sec resolution) 06:43:00 06:48:30 leading 60s behind 25s behind

PA distribution + Wave again simultaneous 4s spin plots of ion SC-1: 06:48:30 UT V n dB dE B0 ion

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

energetic component change: < 70 keV only

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]

End

All info ET PA ET PA ET PA all at 06:48:30 UT (12s resolution) SC-1: leading 25~150 eV 5-25 eV ET PA 25~150 eV 5-25 eV SC-3: 60s behind SC-1 25~150 eV 5-25 eV ET PA 25~150 eV 5-25 eV SC-4: 25s behind SC-1 ET PA O+ 30~500 eV 0642 0644 0646 0648 0650 0652 0654 0656

Ground conj. Nothing special only 50 nT activity 06:43 06:48

µB conservation: W  W//