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Sub-keV Phenomena of Dayside Ring Current
M. Yamauchi, R. Lundin, H. Nilsson (IRF-Kiruna), Dandouras, H. Reme (CESR, Toulouse), G. Stenberg, M. Andre (IRF, Uppsala), P.-A. Lindquvist (KTH, Stockholm), Y. Ebihara (Nagoya U.), C. Vallat (ESTEC, Nordwijk), P.W. Daly (MPS, Katlenburg-Lindau), A. Balogh (ICL, London)
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Sub-keV Ring Current? ions H+ He+ O+ Sub-keV Cavity
Traditional view of the ring current : > 5 keV only ions H+ He+ O+ Sub-keV Cavity Cluster (SC-1) CIS data over perigee traversal at noon
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Example 1: wedge-like structure
However Example 1: wedge-like structure poleward eastward drift Viking 14 MLT westward drift eastward drift Cluster Perigee, 11 MLT
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Motion and source Cluster Viking probability of event 6 MLT 9 MLT
Time-lag (hours) Backward Superposed Epoch Analyses using 700 traversals.
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Case study : event Substorm onset H+ O+ South North
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Inter-SC time-of-flight (at 9.0 MLT)
+0.1° ° ° V(10 keV) = VE-VB << VE SC-4 10 keV 0.1 keV 23:40 UT 23:40 UT 23:50 UT: Yes 23:50 UT 23:40 UT: No H+ O+ V(0.1 keV) ~ VE 23:50 UT SC-3 ∆t < 13 min (100 eV/C-3 & 10 keV/C-4) t < 30 min drift distance = VE * t < km started at 7~9 MLT.
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Wedge-summary Wedge-like dispersed sub-keV ring current is a fossil of substorm activity (model is right!) by VExB ≥ VB-drift. It's source extends from midnight to morning (both statistics and case study) O+ source is different from H+ source
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Example 2: heating Viking , 8 MLT Cluster , 19 MLT ions H+ e- He+ i+
No dispersion not drifted local energization Energy normally < 100 eV observed all local time Only one extremely intense event over 5 years Cluster obs.
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Unusual heating on 2002-5-19 Energy range: >900 eV & 5-900 eV
ion+ (C1) ion+ (C3) H+ (C4)
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Feature-1: Timing 06:48:30 simultaneous at all SC in 12sec resolution
SC-1: leading ion+ (C1) SC-3: 60s behind SC-1 ion+ (C3) SC-4: 25s behind SC-1 H+ (C4)
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cf. SC-location
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Feature-2: Pitch angle:
Mostly // direction 4s spin plots of ion // (spin) //
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Feature-3: Wave simultaneous! 4s spin plots of ion SC-1: 06:48:30 UT V
dB dE B0 ion
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more wave: broadband + stagnant
150 nT ΩP = 4 Hz ion dE dB S// E/B ΩHe? dBZ BB-EM spin effects stagnant dBX
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Feature-4: DC field EY potential B
Substorm-level disturbance simultaneous with heating 06:48:30 UT = heating EY potential B SC separation up to 1 min: temporal structure already from 0643 UT
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Feature-5: >5 keV component
ion+ E = 0.005~40 keV P/A (> 5 keV) P/A (< 0.2 keV) 06:43 precursor 06:48:30: heating H+ He++~O+ sudden decrease
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for > 100 keV component ion+ e- H+ He+ & He+ + C +, N + & O+
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Feature-6: Precursor strong ExB drift (spin)
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direction of drift: rotate
// drift direction Y (duskward) X (sunward) - UxB (estimated E) direction
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and agree with DC E-field
EX<0 EY>0 EY<0 ExB drift velocity = 25~35 km/s 3-6 eV for H+, eV for He+, eV for O+
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Feature-7: Composition
(1) From energy peak: plasmaspheric He+ rich // Precursor (06:44 UT) Heating (06:49 UT) = 0° = 180° = 360° // H+ He+ O+ 18 eV eV He+ O+ ratio=4: O+/He+ or He+/H+ [eV] [eV]
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Composition: Precursor part
He+ He+ becomes detection range only when |E| is strong.
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Composition H+ He++ He+ O+ (2) TOF mass analyser: He+ rich precursor
heating H+ He++ He+ O+ contamination
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Composition (3) >100 keV: plasmaspheric He+ precursor heating
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Feature-8: magnetospheric condition
Not special (just a minor storm/substorm)
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Feature-9 : ground conj. Nothing special only 50 nT activity
precursor heating
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Indications from data (heating):
1. Simultaneous at SC-1, 4 and -3 sudden activation 2. Bi-directional along B local hearing (not propagated) 3. Simultaneous wave with randomly changing Pointing flux direction even the wave is locally generated? 4. DC disturbance in B and E substorm-level activity? 5. Change in >5 keV large-scale configuration change 6. Precursor with cold ExB drift, no energization related ??? 7. Rich in He+ for cold, sub-keV and 100 keV component plasmaspheric He+ is supplied well before the event? 8. Only minor magnetospheric activity Mystery !
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Summary Sub-keV part of dayside ring current is not empty!
Wedge-like dispersed sub-keV ions (statistics + case study) Fossil of substorm with eastward by VExB > VB-drift Some are originated from morning sector O+ source is different from H+ source Heating (case study, unusual event, not well understood) Local heating at equatorial plane by sudden onset He+ rich Precursor with strong DC E-field (and E-B drift) Not clear ground signature, before substorm onset
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Thank you
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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
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Particle vs. wave 4s spin plots of ion
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Feature-# **: **
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Feature-# **: **
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more: wave Yes, of course dE dB S// E/B
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Cluster Examples Eastward (electric) drift Westward (magnetic) drift
Noon Early morning Late morning only < 1 keV also > 1 keV also > 1 keV
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