Transcript 'Source Location of the Wedge-like Dispersed Ring Current

Sub-keV Ring Current Ions: Source,
Transport, and O+/H+ difference
M. Yamauchi, R. Lundin, H. Nilsson, S. Arvelius (IRF-Kiruna),
Y. Ebihara (NIPR),
and Cluster-CIS team
"Wedge-like dispersion"
eastward drift
H+
westward drift
eastward drift
Sub-keV trapped ions are seen almost all
satellites at around L=4-6. They are
wedge-like energy-latitude dispersed as
shown in both Viking data (mid-altitude)
and Cluster data (equatorial plane). They
are trapped ions drifting eastward, i.e., the
ExB drift (including corotation) is stronger
than the magnetic drift (B and curvature)
at this energy range.
We show (1) Viking statistics
(2) Cluster event studies.
Previous Works
sub-keV ion precipitation @ subauroral region):
•Aureol 1 (400~2500km): Sauvaud et al., 1980
00-06 MLT: increases after substorms.
* DMSP F6/F7 (800 km):Newell & Meng, 1986
0830 MLT: correlated with Kp with some
hours delay, and event may last a day.
Ebihara et al., 2001
Reversed
dispersion
Both
dispersions
* Viking (2~3 RE): Yamauchi et al., 1996a,b
"Wedge-like dispersed structures"
modulation by pc-5 pulsation.
* Simulation: Ebihara et al., 2001
drift model (ExB, |B|, and curvature)
many hours after nightside injection
dispersion patterns + MLT dependence.
* Freja/Viking/Cluster: Yamauchi et al., 2005
morning peak
O+ at low-altitude / H+ at high-altitude
* others: Shelley et al., 1972; Chappel et al., 1982
Cluster
(2001-2003)
extend >1keV
limited < 1keV
(1) Viking
backward superposed
epoch analyses
Probabilities of observing
the wedge-like structure
after the start of AE
activity. Probability is
calculated from numbers
of traversals with/without
the structure for each 3-hr
bin (3-hr running sum) for
each 3-hr MLT bin.
6 MLT
9 MLT
12 MLT
15 MLT
The peak probability
moves eastward, while
the peak value of the
probability decrease as
the peak moves eastward.
Evacuation is seen (the
probability is even lower
than asymptotic one)
18 MLT
Time-lag (hours)
Viking Summary
The wedge-like structure
drifts eastward, and is a
fossil of substorm activity
(model is right!). Decay
time is several hours
(charge exchange model is
right!).
MLT
5~7
Minimum Asymptotic
Quiet case Quiet case
After end of After end of
300 nT
300 nT activity
activity
1~3h (0%) 8~9h (30%)
Maximum
Clear case
After start
of 400 nT
activity
0~3h (85%)
8~10
2~3h (5%) 9~10h (50%)
2~4h (75%)
11~13 3~5h (10%) 10~11h (70%) 4~6h (70%)
14~16 4~6h (35%) 12~13h (80%) 6~7h (50%)
17~19 6~8h (50%) 14~16h (100%) 10h (25%)
However, it appears much
earlier than prediction,
suggesting that a substantial
amount of "wedge" might be
formed in the morning sector
during substorms. We need to
identify the source location
from event study.
We have several possibilities
(2) Cluster
Ion source dispersion scenario
night
night
No !
night
morning
(A)
morning
morning
(B) (C) (D)
(A) Strong electric field push ions quickly.
(B) Scattering of <10 keV ions
(C) Energetic ions precipitate and sputter
ionospheric ions into the space.
(D) Unknown local energization process.
 Need to find events when the wedge
is formed during a substorm.
 We found one case. Wedge is
seen only at outbound.
 Case study!
H+
O+
H+
+1°
S/C-1
No Yes
No
O+
Yes
H+
O+
2001-10-21
23:40-24:00 UT
Relative S/C position:
all at 9.0±0.1 MLT
No
S/C-4
0° -1° -2°
No
No
S/C-3
H+
? Yes
O+
Observation summary
time-of-flight principal
S/C-1 (23:45 UT), S/C-4 (23:50 UT), and S/C3 (23:40 UT) passed through the same
magnetic flux tube at 9 MLT (L≈4).
Wedge-like dispersion at 23:50 UT.
No low-energy signature at 23:40 UT.
Butterfly-trapped distribution
 Bounce inside the geomagnetic bottle.
 Difference between 23:40 UT and
23:50 UT in the same flux tube means
an temporal variation although observation
is made in the opposite hemisphere.
VE: eastward ExB drift speed = energy
independent, MLT dependent
VB: westward magnetic (|B|+curvature) drift
velocity = energy dependent
VE >> VB at low energy (<100 eV) and VE ~
VB at high energy (value depends on E-field
strength). From dispersion curve, the lastcoming ions are 10-20 keV. Therefore,
VE ~ VB at 20 keV in the present case.
V1 = VE-VB ~ VE @ 0.1 keV
V2 = VE-VB << VE @ 10 keV
t
t+∆t
0.1 keV
10 keV
V1*t = V2*(t+∆t)
V1 ~ VE
V2 ~ VE-VB
or
(t+∆t)/∆t = V1/(V1-V2)
~ VE/VB
(note : VB@10 keV)
= (E/B)*(q*R*B/3*W*g)
~ E [mV/m]/g or
t = ∆t*E [mV/m]/g - ∆t
for observation near equatorial plane, where
E and B are the field strengths,
q is the charge,
R = 4 RE is the geocentric distance,
W = 10 keV is the ion energy, and
g ~ 1, 0.9 &0.7 for 90°, 40° & 0° pitch
angles
Dispersion analysis
1~3 mV/m
Pitch angle of the "wedge" is about 40~90°
(g=0.9~1.0)  t ≤ (1.1*E[mV/s] - 1) * ∆t
Electric field is 1~3 mV/m for half an hour
 t = 0.1~2.3*∆t & VE = 3~10 km/s
(a) 0.1 keV @ 23:50 UT, S/C-1 
Nothing @ 23:40 UT, S/C-3 : temporal chance
(b) 10 keV @ 23:53 UT, S/C-1 
Nothing @ 23:40 UT, S/C-3 : temporal change
(c) 0.1 keV @ 23:50 UT, S/C-1 
10 keV @ 23:53 UT, S/C-1 : temporal or spatial
Combination of (a)+(b) : it is temporal change
 ∆t < 13 min  t < 30 min before 23:40 UT
 drift distance = VE * t < 20000 km
 dispersion started at 7~9 MLT.
Combination of (b)+(c) : if temporal
 ∆t~3 min  t = 0.5~8 min before 23:50 UT
 drift distance = VE * t = 100~5000 km
 dispersion started at 8~9 MLT.
On the other hand, we observed O+ "wedge"
at 0.05-0.3 keV (20 km/s ~ 50 km/s). The
0.05 keV O+ takes 20~30 min to travel from
the ionosphere to the Cluster location along
B in best case. From this:
(1) Source timing is about 20~30 min
before, i.e., at 23:20~23:30 UT.
(2) The combination (b)+(c) cannot be
true, i.e., the observed dispersion is mostly
the spatial structure.
(3) O+ pitch angle is uni-direction, i.e.,
should not have been mirror-bounced,
endorsing point (1).
H+/O+ differences
O+ motion ≠ H+ motion
The 2001-10-21 event showed a
clear O+/H+ difference inside the
wedge, with H+ bounce-averaged
feature (with butterfly pitch-angle
distribution), whereas O+ is not
bounce-averaged.
O+ source ≠ H+ source
H+
O+
Statistically the wedge-like structure
is O+ rich at low-altitudes (Freja)
whereas it is H+ rich as high-altitudes
(Cluster).
correlated & anti-correlated
Correlation part means that H+ and
These fact suggests that O+ source
O+ has the same bounce-average
could be different from H+ source.
drift motion. Then, how can we
We found couple of good Cluster
understand the anti-correlation
examples that endorse this idea
part just 15 minutes later?
Summary and conclusions
(1) The dispersion might start in the morning for a substantial
numbers of the wedge-like structure. This is suggested by
the local time distribution, superposed epoch analyses, and a
case study on the 2001-10-21 event (source <30 min, <3 RE
distance).
(2) Pitch-angle distribution, particularly for O+, suggest
ionospheric source (consistent with morning source).
(3) In addition to the altitude dependence of the O+/H+ ratio, O+
are sometimes behaving in a different way from H+.
* non-bounce-average feature (2001-10-21 event).
* correlation and anti-correlation in a single traversal.  ???
Future task : understand the source of the wedge-like structure
for both O+ and H+. This final target is still far away.
END
What is "wedge-like dispersion" / What is the problem?
Sub-keV trapped ions seen almost all
satellites at around L=4-6. They are wedgelike energy-latitude dispersed as shown in
both Viking data (mid-altitude) and Cluster
data (equatorial plane). See Poster XY0868
by Yamauchi and Lundin in this session.
Data analyses and simulation confirmed that
they are drifting trapped ions (I.e., Cluster
should see the same phenomena as Viking).
Past analyses raised two main questions.
westward drift
eastward drift
(1) Past identification of "wedge" observed
by Cluster was in-appropriate because the
resultant distribution does not agree with
the simulation or other satellites. We need
to refine the criterion.
(2) Past statistics suggests that the source
can be in the morning sector during
substorms. We need to identify the source
location from event study.
New criterion and statistics
Past criterion: completely isolated from > 5 keV ring current.
 Only (a) is identified as "wedge" but not (b) or (c)
New criterion: isolated from > 5 keV component at the wedge
location, as long as wedge is extended from sub-keV.
 All of (a), (b), and (c) are identified as "wedge"
New statistics shows morning peak, which is consistent with the
other statistics and simulation.
(b)+(c)
(a)
Present Work (1) Case study : It requires isolated substorm activity +
Simulation indicates:
* Drift slowly eastward
* Originated from past
substorm-related injections into
the ring current region 5~20
hours before.
However,
No solid data analyses has
been done to confirm the
dynamic part of the model.
Are they drifting?
If so, velocity?
Are they nightside origin?
Are they related to
substorms?
If so, time lag?
(1)case study
(2) statistics
consecutive traversals, but even best case can be interpreted in
many way.
Result : 1
6 MLT
Probabilities of
observing the wedgelike structure after the
end of AE activity.
(cf. (2) in explanation)
9 MLT
Quiet probability
corresponds to the last
injection
12 MLT
Lowest quiet
probability start
increase (=last wedge
passing through) start
to increase at later
time-lag at larger MLT,
it moves eastward,
while the value itself
increase eastward.
15 MLT
18 MLT
Time-lag (hours)
Conclusions : wedge-like structures
1. The structure is related to the past AE activity but not directly to Dst
2. After hourly AE>400 nT, the majority of the structure reaches the noon,
and nearly half of them reaches the early afternoon sector.
3. The structures in the evening sector most likely have traveled by
eastward drift rather than directly from the nightside by westward drift.
4. The response at 6 MLT is nearly immediate after high AE activities.
Source of wedge shifts or extends to the early morning, e.g., 4-5 MLT.
5. The drift speed for hourly AE>400 nT is somewhat faster than model
prediction even taking into account of the morning-shift of source.
6. The decay time of several hours at all MLT is consist with the charge
exchange life time.
7. Sub-keV ions are sometimes evacuated right after the onset of
substorm or storm.
100
100
80
80
60
40
20
0
6
8
0
4
6
4
6
8
10
2
4
6
8
10
40
0
2
4
6
8
peak / clear structure
10
20
% traversals
40
20
0
100
100
80
80
hours from "end" of activity
100 200 300 400 500
Peak probabilities vs AE threshold
20
40
12
0
60
60
0
2
2
Best threshold value values are 400 nT for
start of activity and 300 nT for end of activity
0
80
20
4
AE threshold (nT) for "end"
60
40
6
AE threshould (nT) for "end"
80
10
8
20
80
60
0
0
100 200 300 400 500
100
AE(hr)<500nT
8
8
2
0
0
6
6
100
20
4
4
timing / quiet traversal
8
100
40
2
2
40
10
AE(hr)<400nT
8
0
60
80
60
0
4
80
0
6
18 M LT
0
0
20
4
6
100
40
2
15 M LT
100
60
0
20
8
% traversals
2
AE(hr)<300nT
0
12 M LT
80
20
timing / clear structure
40
100
40
Optimum time-lag vs AE threshold
9 M LT
80
60
6 M LT
60
100
% traversals
4
% traversals
2
AE(hr)<200nT
0
quiet traversals
0
2
4
6
8
10
12
0
100 200 300 400 500
AE threshold (nT) for "end"
60
40
20
0
0
2
4
6
8
10
12
hours from "end" of activity
minimum / quiet traversal
peak probability (%)
% traversals
AE(hr)<100nT
with clear structure
More statistics (∑3h)
hours from "end"
For different AE threshold values
100
80
60
40
20
0
100 200 300 400 500
AE threshold (nT) for "end"
Result of superposed epoch analyses (∑3h)
From end of activity (cf (2) in explanation)
From start of activity (cf (1) in explanation)
6 MLT
9 MLT
12 MLT
15 MLT
18 MLT
Time-lag (hours)
Time-lag (hours)
Previous Works
sub-keV ion precipitation @ subauroral region):
* Aureol 1 (400~2500 km): Sauvaud et al., 1981
00-06 MLT:
increases some hours after substorms.
* DMSP F6/F7 (800 km):Newell and Meng, 1986
0830 MLT: correlated with Kp with some
hours delay, and event may last a day.
* Viking (2~3 RE): Yamauchi et al., 1996a,b
"Wedge-like dispersed structures"
modulation by pc-5 pulsation
* Simulation: Ebihara et al., 2001
drift model (ExB, grad|B|, and curvature)
many hours after nightside injection
dispersion patterns + MLT dependence
* Freja/Viking/Cluster: Yamauchi et al., 2005
05-19 MLT: morning peak
altitude comparison: O+/H+ ratio change
* Others: Shelley et al., 1972; Chappel et al., 1982
Ordinary
(Type 1)
Both
(island)
Reversed
(Type 2)
Viking Observation
Reversed
(Type 2)
Both
(island)
Ebihara et al., 2001
Present Work
Simple AE correlation?  misleading
Simulation indicates:
Afternoon sector show negative correlation.
Thus, one may not take direct correlation.
* Drift slowly eastward
Are they drifting? If so,
velocity? from where?
Related to substorms?
If so, time lag?
(1) simple statistics
(2) case study
(3) advanced statistics
% traversals
However, no solid data
analyses has been done to
confirm the dynamic part of
the model.
75
80
198
192
159
77 # traversals
with clear structure (>oo)
50
25
0
hourly
AE<50
50 ~ 100 100 ~ 200 200 ~ 400
400 ~
[nT]
Simple Dst correlation?  misleading
Before all, only 58 out of 700 are during Dst < -30 nT.
Magnetic storm activity is not the direct cause.
159
209
280
58 # traversals
100
% traversals
* Originated from past
substorm-related injections
into the ring current region
5~20 hours before.
100
75
with clear structure (>oo)
50
25
0
Dst > 0
0 ~ -10
-10 ~ -30
< -30
[nT]
(2) Case study
It requires isolated
substorm activity +
consecutive
traversals = rare.
Even the best case
(860912) show
superficial anticorrelation
(1) Backward Superposed Epoch Analyses
* Probabilities with/without “wedge”
signature at various MLT in dayside
is obtained for different time-lags
from latest AE increase.
(a) Ideal AE profile gives three
characteristic times (1)(2)(3).
(b) & (c) We must fight against reality
Hope statistics helps.
Total only 700 traversals, sorted by
* 3-hour MLT bins
* 3-hour windows (running
summation) for the time-lag
* add all types of dispersions
Case study
We have several possibilities
Ion source dispersion scenario
night
night
No !
night
morning
(A)
morning
morning
(B) (C) (D)
(A) Strong electric field push ions quickly.
(B) Scattering of <10 keV ions
(C) Energetic ions precipitate and sputter
ionospheric ions into the space.
(D) Unknown local energization process.
 Need to find events when the wedge is
formed during substorms. We found one
case. Wedge is seen only at
outbound.
General context (deduced from ENA image)
ENA image indicates
(1) strong E
(2) No energetic H+ in the
late morning sector
(3) qualitative difference
between O+ and H+
Strong E  scenario (A)
in the Table:
Ions < 10 keV could have
convected to the morning
sector quickly without
forming the dispersion.
No energetic H+ 
difficult for scenario (B) in
the Table unless electron is
important
H+ - O+ difference  At
least O+ wedge can be
formed local
post-midnight preference
= strong E (could be ~10 mV/s)