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

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

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)

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 1000~2000 km

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 H+ < 90 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)

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.

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)

ion-scale ? H+ He+ O+ RB(H+) ≤ gradient ≤ RB(He+) << RB(O+) gradient is less than 500 km (5~10 km x 50 sec) cf. RB (= mv/qB) for B ≈ 200 nT condition 50 keV 200 keV 1 MeV H+ v = 3000 km/s RB = 150 km v = 6000 km/s RB = 300 km v = 14000 km/s RB = 700 km He+ v = 1500 km/s RB = 600 km v = 7000 km/s RB = 1400 km O+ v = 700 km/s RB = 1200 km v = 3500 km/s RB = 3000 km RB(H+) ≤ gradient ≤ RB(He+) << RB(O+)

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

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)

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

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

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.

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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

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?

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?

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

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

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

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

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

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.

sunward propagation profile E

Global condition: minor storm Dst ≈ -60 nT

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

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.

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

µB conservation: W  W//, but 06:43

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

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.

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

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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

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