Dual source populations of substorm-associated ring current ions

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Dual source populations of substorm-associated
ring current ions

• M. Yamauchi (IRF, Kiruna)
• Y. Ebihara (Nagoya U.)
• I. Dandouras, H. Reme (CESR, Toulouse)

Past work Sub-keV ring current ions fossil of
substorm drift eastward Present work Source
population?
Cluster workshop, Uppsala, 2009.5
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Sub-keV ring current ions are often observed
Traditional view of ring current gt 5 keV only
westward drift, BUT
mgt2 H
cavity in sub-keV range
15 MLT
cavity
Westward (magnetic) drift
cavity
Eastward (ExB) drift
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Statistics fossil of substorm
6 MLT 9 MLT 12 MLT 15 MLT 18 MLT

• (1) Moves eastward
• (2) Decrease in time for both probability and
  energy

Time-lag (hours)
(Yamauchi and Lundin, 2006)
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Morning sector dual population
We first classified the ion pattern in the
morning sector. Then, we take statistics of the
patterns against peak AE during last 6 hr.
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Note) The wedge-like structure appears in the
early morning sector about 56 hours after
high-AE activity
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Observation summary
Peak AE during latest 6 hours vs Pattern in
spectrogram

Peak AE (a) (b) (c) (d)
lt 300 nT 0 4 26 10
300500 nT 0 8 17 1
gt 500 nT 5 33 3 4
Pattern in Spectrogram
? (c) and (d) ? (c), sometimes (b) ? (b),
sometimes (a)
Past AE activity (peak value during 6 hr)
determines the pattern (o o) Mono-energetic
band (o) decays faster than wedge-like structure
(o) Energy of mono-energetic band ( strength
of ExB) reflects AE value
Question Relation between two (o o)
components, i.e. source population?
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Numerical tracing
Observation
AE 100200 nT, with peak of 400 nT 6 hr before.
mapping relation
(0.20.6/cc)
Back-trace to 8 Re
Back-trace to 8 Re
Cold
Isotropic Maxwellian (T1 keV, N0.5/cc)
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Forward simulation
both component together
band-2 westward drift band-1 eastward
drift wedge
Simultaneous reconstruction of three components
confirms rational of our source estimate.
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Conclusion
Wedge-like dispersed sub-keV ions are originated
from cold ions in the plasma sheet (0.10.5 cm-3).
? cf. recent observation of cold ion filling
example of filling