1. Sources of < 10 keV ring current ions: supply mechanism?
M. Yamauchi, R. Lundin, H. Nilsson (IRF-Kiruna),
Y. Ebihara (Nagoya U.)
I. Dandouras, H. Reme (CESR, Toulouse)
Substorm : production of plasma
Sub-keV ring current : fossil of substorm
Question: source of sub-keV ring current?
IMC workshop, Espoo,

2. Sub-keV Ring Current? m>2 H+ Eastward (electric) drift
15 MLT
Sub-keV Ring Current?
cavity in sub-keV range
Eastward (electric) drift
Westward (magnetic) drift
Noon Early morning Late morning
only < 1 keV also > 1 keV also > 1 keV

3. Statistics Morning peak Energy decrease with MLT
poleward
Viking 14 MLT
Statistics
eastward drift
Morning peak
Energy decrease with MLT
Cluster = Viking ≠ Freja (less) 
(1) Moves eastward
(2) Decrease in time
(3) Freja is below mirror altitude
6 MLT
9 MLT
12 MLT
15 MLT
18 MLT
Time-lag (hr) from substorm onset

4. Sub-keV component is fossil of substorm activity
UT 00: : : :00
day (12 MLT)
Midnight (3 MLT)
difference
Substorm onset
Summary
Sub-keV component is fossil of substorm activity
Mirror altitude > 2000 km
Seen at low-altitude
(after substorm)

5. However: Questions (1) Too quick response (2) H+ - O+ difference
(3) Freja-Cluster difference in both composition and distribution
mainly O+
mainly H+

6. H+ - O+ difference

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

8. Oxygen feature H+: both directions O+: one direction PA PA
Substorm onset
O+ structure is only at keV range (20 km/s ~ 50 km/s).
0.05 keV O+ takes 20~30 min to travel from the ionosphere to the Cluster location along B in best case.
Therefore, O+ should not have mirror-bounced, and this is confirmed from nearly uni-direction pitch angle.
Again, 20~30 min elapsed time (with morning source) !
H+: both directions
O+: one direction PA PA

9. O+ trajectory (30 min trajectory)
Tsyganenko T89 B-model & Weimer 2001 E-model
Backward trace of 0.1 keV O+ (reference point S/C-3)
Pitch angle: 0°, 45°, 90°, 135°, 180°
Again, morning source

10. Inter-SC time-of-flight confirms the timing
V(10 keV) = VE-VB << VE
10 keV
0.1 keV H+
23:40 UT
+0.1° ° °
23:40UT: No
23:40 UT
23:50UT: Yes
9 MLT
Substorm onset
23:50 UT
V(0.1 keV) ~ VE
23:50 UT O+
∆t < 13 min
(100 eV/SC-3 & 10 keV/SC-4)
 t < 30 min
 drift = VE * t < km
 started at 7~9 MLT.

11. Questions Q1.The source location (MLT + altitude)
Q2.The source population (O+ source and H+ source can be different).
Q3. Source energy, i.e., relation between two (keV+wedge) components.
Q4.The exact relation to substorms
Q5. Supply mechanism
To invest these problems, we need
* More observation/analyses
* Numerical mapping

12. Source ? Observation = Back-trace to 8 Re Back-trace to 8 Re
Bursty cold (0.1~0.2/cc)
Isotropic Maxwellian
(T=1 keV, N=0.5/cc)

13. Re-construction by simulation
both component together

14. Summary
Wedge-like dispersed sub-keV ring current is a fossil of substorm activity carried by VExB ≥ VB-drift.
O+ source is different from H+ source.
The source is cold ions, which is supplied from midnight to morning.
A sample of morning source: event (next figure).

15. IMAGE/FUV Ground ∆B 0611:40 UT evening-midnight: 2000 nT 0613:40 UT
event
evening-midnight: 2000 nT
Wide morning source of upward current (O+ escape) nearly simultaneously with substorm onset
0613:40 UT
0615:40 UT
morning: 2000 nT
Yamauchi, Iyemori, Frey, & Henderson, 2006 JGR

17. Summary of event
Case study from event (9 MLT) shows that
* The "wedge" suddenly appeared in the magnetic flux tube in which no signature was recognized 10 minutes before.
* The dispersion is formed within 3 Re distance from the spacecraft within 30 minutes before the observation.
* Observed oxygen ions of the "wedge" were not mirrored, i.e., they directly came from northern ionosphere (ionospheric source) minutes before.
 Dispersion started and O+ is ejected from the morning (6~7 MLT).

18. Ground ∆B + auroral image
0611:40 UT
0615:40 UT
evening-midnight
Ground ∆B + auroral image
IQA≈01 LT
0613:40 UT
morning
0617:40 UT