Sub-keV Phenomena of Dayside Ring Current

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?
Traditional view of the ring current gt 5 keV
only
2002-7-20
ions H He O
Sub-keV Cavity
Cluster (SC-1) CIS data over perigee traversal at
noon
3
Example 1 wedge-like structure
However
poleward
eastward drift
Viking
14 MLT
westward drift eastward drift
Cluster
Perigee, 11 MLT
4
Motion and source
Viking probability of event
6 MLT 9 MLT 12 MLT 15 MLT 18 MLT
Cluster
Time-lag (hours)
Backward Superposed Epoch Analyses using 700
traversals.
5
Case study 2001-10-21 event
Substorm onset
H O
South North
6
Inter-SC time-of-flight (at 9.0 MLT)
H O
0.1 0 -0.1
V(10 keV) VE-VB ltlt VE
SC-4
0.1 keV
10 keV
2340 UT
2340 UT
SC-4 _at_ 2350 UT Yes
2350 UT
SC-3 _at_ 2340 UT No
H O
V(0.1 keV) VE
2350 UT
SC-3
?t lt 13 min (100 eV/C-3 10 keV/C-4) ? t lt 30
min ? drift distance VE t lt 20000 km ?
started at 79 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 He O
e- i
heating?
heating?
No dispersion ? not drifted ? local
energization Energy normally lt 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 gt900 eV 5-900 eV
ion (C1)
ion (C3)
0645 0650 0655
0700
H (C4)
10
Feature-1 Timing
064830
simultaneous at all SC in 12sec resolution
SC-1 leading
ion (C1)
SC-3 60s behind SC-1
ion (C3)
0642 0646
0650
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 064830 UT
V n dB dE B0
ion
14
more wave broadband stagnant
150 nT ? ?P 4 Hz
ion dE dB S// E/B
?He?
dBZ
BB-EM
spin effects
stagnant
dBX
15
Feature-4 DC field
Substorm-level disturbance simultaneous with
heating
064830 UT heating
EY potential B
SC separation up to 1 min ? temporal structure
0640 0645
0650 0655
already from 0643 UT
16
Feature-5 gt5 keV component
ion ion ion
E 0.00540 keV P/A (gt 5 keV) P/A (lt 0.2
keV)
0643 precursor
064830 heating
H HeO
sudden decrease
17
for gt 100 keV component
ion e- H He He C , N O
18
Feature-6 Precursor
strong ExB drift
? (spin)
19
direction of drift rotate
//
?
Y (duskward)
drift direction
X (sunward)
- UxB (estimated E) direction
20
and agree with DC E-field
EXlt0
0600 0620 0640
0700
EYgt0
EYlt0
ExB drift velocity 2535 km/s ? 3-6 eV for H,
13-25 eV for He, 50-100 eV for O
40 42 44 46
48 50
21
Feature-7 Composition
(1) From energy peak plasmaspheric He rich
//
?
Precursor (0644 UT)
Heating (0649 UT)

• 0
• 180
• 360

H He O
?
//
18 eV 70 eV
He O
ratio4 O/He or He/H
10 100 eV
10 100 eV
22
Composition Precursor part
O He
He becomes detection range only when E is
strong.
23
Composition
(2) TOF mass analyser He rich
precursor
heating
H He He O
contamination
0643 0644 0645 0646 0647
0648 0649
24
Composition
(3) gt100 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 gt5 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 gt 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
all at 064830 UT (12s resolution)
SC-1 leading
25150 eV 5-25 eV
ET PA
25150 eV 5-25 eV
SC-3 60s behind SC-1
25150 eV 5-25 eV
ET PA
25150 eV 5-25 eV
SC-4 25s behind SC-1
ET PA
O 30500 eV
0642 0644 0646 0648 0650
0652 0654 0656
31
Particle vs. wave
4s spin plots of ion
32
Feature-

33
Feature-

34
more wave
Yes, of course
0645 0700
dE dB S// E/B
0630 0700 0730
35
Cluster Examples
Westward (magnetic) drift
Eastward (electric) drift
Noon Early morning
Late morning
only lt 1 keV also gt 1 keV also gt 1 keV