Sources of < 10 keV ring current ions: supply mechanism?

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Sources of lt 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, 2008-7
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Sub-keV Ring Current?
mgt2 H
15 MLT
cavity in sub-keV range
Eastward (electric) drift
Westward (magnetic) drift
Noon Early morning Late
morning
only lt 1 keV also gt 1 keV also gt 1 keV
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Statistics
poleward
Viking 14 MLT
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
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Summary
UT 0030 0100 0130
0200
day (12 MLT)
Midnight (3 MLT)
difference
Substorm onset
Sub-keV component is fossil of substorm
activity Mirror altitude gt 2000 km
Seen at low-altitude (after substorm)
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However Questions
(1) Too quick response (2) H - O difference (3)
Freja-Cluster difference in both composition and
distribution
mainly O mainly H
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H - O difference
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Case study 2001-10-21 event
Substorm onset
H O
South North
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Oxygen feature
Substorm onset
O structure is only at 0.05-0.3 keV range (20
km/s 50 km/s). 0.05 keV O takes 2030 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, 2030 min elapsed time (with morning
source) !
H both directions O one direction
PA
PA
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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
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Inter-SC time-of-flight confirms the timing
V(10 keV) VE-VB ltlt VE
10 keV
0.1 keV
H
2340 UT
0.1 0 -0.1
2340 UT
SC-3 _at_ 2340UT No
SC-1,4 _at_ 2350UT Yes
9 MLT
Substorm onset
2350 UT
V(0.1 keV) VE
2350 UT
?t lt 13 min (100 eV/SC-3 10 keV/SC-4) ? t lt 30
min ? drift VE t lt 20000 km ? started at
79 MLT.
O
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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 (keVwedge) components. Q4.The exact
relation to substorms Q5. Supply mechanism
To invest these problems, we need More
observation/analyses Numerical mapping
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Source ?
Observation
Back-trace to 8 Re
Back-trace to 8 Re
Bursty cold (0.10.2/cc)
Isotropic Maxwellian (T1 keV, N0.5/cc)
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Re-construction by simulation
both component together
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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 2003-10-29 event (next figure).
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2003-10-29 event
IMAGE/FUV
Ground ?B
061140 UT
evening-midnight 2000 nT
Wide morning source of upward current (O escape)
nearly simultaneously with substorm onset
061340 UT
061540 UT
morning 2000 nT
Yamauchi, Iyemori, Frey, Henderson, 2006 JGR
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(No Transcript)
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Summary of 2001-10-21 event

• Case study from 2001-10-21 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) 20-30 minutes
  before.
• ? Dispersion started and O is ejected from the
  morning (67 MLT).

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Ground ?B auroral image
061140 UT
061540 UT
evening-midnight
IQA01 LT
morning
061340 UT
061740 UT