Title: Dual source populations of substorm-associated ring current ions
1Dual 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
2Sub-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
3Statistics 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)
4Morning 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.
5Note) The wedge-like structure appears in the
early morning sector about 56 hours after
high-AE activity
6Observation 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?
7Numerical 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)
8Forward simulation
both component together
band-2 westward drift band-1 eastward
drift wedge
Simultaneous reconstruction of three components
confirms rational of our source estimate.
9Conclusion
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