1. 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)

2. 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

3. 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

4. Motion and source Cluster Viking probability of event 6 MLT 9 MLT
Time-lag (hours)
Backward Superposed Epoch Analyses using 700 traversals.

5. Case study : event
Substorm onset H+ O+
South North

6. 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.

7. 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

8. 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.

9. Unusual heating on 2002-5-19 Energy range: >900 eV & 5-900 eV
ion+ (C1)
ion+ (C3)
H+ (C4)

10. 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)

11. cf. SC-location

12. Feature-2: Pitch angle:
Mostly // direction
4s spin plots of ion //
 (spin)  //

13. Feature-3: Wave simultaneous! 4s spin plots of ion SC-1: 06:48:30 UT VdB dE B0
ion

14. more wave: broadband + stagnant
150 nT  ΩP = 4 Hz
ion dE dB
S//
E/B
ΩHe?
dBZ
BB-EM
spin effects
stagnant
dBX

15. 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

16. 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

17. for > 100 keV component
ion+ e- H+
He+ & He+ +
C +, N + & O+

18. Feature-6: Precursor
strong ExB drift
 (spin)

19. direction of drift: rotate// 
drift direction
Y (duskward)
X (sunward)
- UxB (estimated E) direction

20. 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+

21. 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]

22. Composition: Precursor part
He+
He+ becomes detection range only when |E| is strong.

23. Composition H+ He++ He+ O+ (2) TOF mass analyser: He+ rich precursor
heating H+
He++
He+ O+
contamination

24. Composition
(3) >100 keV: plasmaspheric He+
precursor heating

25. Feature-8: magnetospheric condition
Not special (just a minor storm/substorm)

26. Feature-9 : ground conj. Nothing special only 50 nT activity
precursor heating

27. 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 !

28. 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

29. Thank you

30. 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

31. Particle vs. wave
4s spin plots of ion

32. Feature-#
**: **

33. Feature-#
**: **

34. more: wave
Yes, of course dE dB
S//
E/B

35. Cluster Examples Eastward (electric) drift Westward (magnetic) drift
Noon Early morning Late morning
only < 1 keV also > 1 keV also > 1 keV