1. Magnetospheric solitary structure maintained by 3000 km/s ions as a cause of westward moving auroral bulge at 19 MLT
M. Yamauchi1, I. Dandouras2, P.W. Daly3, G. Stenberg4, H. Frey5, P.-A. Lindqvist6, Y. Ebihara7, R. Lundin1, H. Nilsson1, H. Reme2, M. Andre4, E. Kronberg3, and A. Balogh8
(1) IRF, Kiruna, Sweden, (2) CESR, Toulouse, France, (3) MPS, Katlenburg-Lindau, Germany, (4) IRF, Uppsala, Sweden, (5) UCB/SSL, Berkeley, CA, USA, (6) Alfvén Lab., KTH, Stockholm, Sweden, (7) IAR, Nagoya U., Nagoya, Japan, (8) Blackett Lab., ICL, London, UK
Cluster workshop,

2. Cluster Perigee
S/C
* Z ≈ 0 RE
* 60 GMLat
* 19 MLT
sun
tail

3. overview ions > 5000 km/s ions ≈ 3000 km/s P/A 0.01~40 keV P/A
06:42
06:44
06:46
06:48
IMAGE
(FUV)

4. Sudden change in field ExB (>50 km/s) is observed
e.g., 57 km/s : He+ ~ 70 eV
H+ ~ 17 eV

5. Timing (B ≠ E) propagate (1) single peak of E:
lead by SC-3 by 1~10 sec
(2) Pi2-like rarefaction of B:
simultaneous at all SC

6. Timing from ExB convection
SC-3 leads against SC-1 by 10 sec: agree with field data

7. Timing  Sunward propagation of E
& E is nearly // to Propagation direction
1000~2000 km

8. 06:43 UT event (arrival of auroral bulge)
Sunward propagation (5~10 km/s) of DC field
* depletion of |B|≈BZ up to 25%
* polarization E≈-EX of up to 10 mV/m
* ExB convection (up to 50 km/s) of cold He+
(without O+)

9. increase in ion flux decrease in ion flux H+ < 90 keV

10. increase in ion flux decrease in ion flux He < 350 keV
O < 0.9 MeV
O > 1.4 MeV
He > 700 keV
decrease in ion flux

11. All relevant ion channel
3000 km/s = 50 keV (H), 190 keV (He), 740 keV (O)
5000 km/s = 130 keV (H), 500 keV (He), 2 MeV (O)

12. 06:43 UT event (arrival of auroral bulge)
(a) Sunward propagation (5~10 km/s) of DC field
* depletion of |B|≈BZ up to 25%
* polarization E≈-EX of up to 10 mV/m
* ExB convection (up to 50 km/s) of cold He+
(b) Net flux Increase of selectively 3000 km/s ions
* ∆P3000km/s = 3 nPa = - ∆PB.
* net decrease of other energetic particles.

13. Drift motion VB  energy (mass independent) 50 keV H+ drift = 15 km/s
190 keV He+ drift = 60 km/s
740 keV O+ drift = 220 km/s
Simultaneous appearance & much faster than the motion of the E-structure  a solitary structure to maintain the flux peak
VExB = constant (energy  mass)

14. ion-scale ? H+ He+ O+ RB(H+) ≤ gradient ≤ RB(He+) << RB(O+)
gradient is less than 500 km (5~10 km x 50 sec)
cf. RB (= mv/qB) for B ≈ 200 nT condition
50 keV
200 keV
1 MeV H+
v = 3000 km/s
RB = 150 km
v = 6000 km/s
RB = 300 km
v = km/s
RB = 700 km
He+
v = 1500 km/s
RB = 600 km
v = 7000 km/s
RB = 1400 km O+
v = 700 km/s
RB = 1200 km
v = 3500 km/s
RB = 3000 km
RB(H+) ≤ gradient ≤ RB(He+) << RB(O+)

15. 06:43 UT event (arrival of auroral bulge)
(a) Sunward propagation (5~10 km/s) of DC field
* depletion of |B|≈BZ up to 25%
* polarization E≈-EX of up to 10 mV/m
* ExB convection (up to 50 km/s) of cold He+
(b) Net flux Increase of selectively 3000 km/s ions
* ∆P3000km/s = 3 nPa = - ∆PB.
* net decrease of other energetic particles.
* propagating solitary structure.
* scale size ~ gyro radius

16. overview ions > 5000 km/s ions ≈ 3000 km/s P/A 0.01~40 keV P/A
06:42
06:44
06:46
06:48
IMAGE
(FUV)

17. // keV ion
At around 06:44 UT, appearance of 7 keV // O+ from both hemisphere, within 40 sec difference

18. 06:43 UT event (arrival of auroral bulge)
(a) Sunward propagation (5~10 km/s) of DC field
* depletion of |B|≈BZ up to 25%
* polarization E≈-EX of up to 10 mV/m
* ExB convection (up to 50 km/s) of cold He+
(b) Net flux Increase of selectively 3000 km/s ions
* ∆P3000km/s = 3 nPa = - ∆PB.
* Net decrease of other energetic particles.
* propagating solitary structure.
* scale size ~ gyro radius
(c) Conjugate with auroral bulge
* Parallel O+ of ≈ 7 keV is detected

19. conclusion
1000~2000 km
Cluster observed westward moving auroral bulge at 19 MLT on is caused by a solitary structure in the magnetosphere.
The solitary structure consists of polarization E-field (up to 10 mV/m) and depletion of B≈Bz.
This solitary structure is maintained by energetic ions of 3000 km/s speed for all ions.
Size (gradient < 500 km) of this solitary structure is comparable to the ion gyro radius of carrier ions.

20. End

21. Many other interesting topics
(1) Qualitative inter-SC difference
(2) Inter-SC time-of-flight examination
(3) Decoupling technique of different plasma using conservation of magnetic moment

22. Qualitative difference within Rgyro
Distribution function  Difference cannot be explained by the slight difference in effective energy between SC.
RB >> inter-SC distance  cannot be due to finite gyroradius effect.
 gradient is substantially large?

23. TOF effect or phase effect?
TOF (7 keV O+ = 250 km/s & SC km- SC km- SC-3)
or Phase-angle dependence?

24. TOF (7 keV O+ = 250 km/s) SC-1/SC-4/SC-3 = 100 km/150 km
or Phase-angle dependence?

26. Energy-time dispersion (flux increase)
time-of-flight? (No)
∆T ~ 10 sec for ∆VD ~ 10 km/s
 source < 1000 km  No
finite gyroradius? (Yes)
∆T ~ 10 sec for ∆RB ~ 100 km
 agree with propagation
VDB = 10~20 km/s
VDB = 20~30 km/s
VDB = 30~50 km/s
VDB = 50~100 km/s

27. Energetic electron vs B
observed flux
|B|
Synchronize with B field variation

28. µB = W/B conserved?  not really
increasing flux
= real
under µB = const
df(µB) = 0 
(∂f/∂W)B > 0 
(∂f/∂B)W > 0

29. Linear decoupling after decoupling the conservation of µB = W/B
observed flux

30. End

31. Westward surging aurora
Akasofu et al., 1966
Fujii et al., 1994
= strong upward FAC

32. conclusion - continued
The 3000 km/s ions are the main carrier of the propagating diamagnetic current that caused the magnetic depletion propagating sunward.
The sunward propagation of this solitary structure caused the sunward propagation of field-aligned potential drop and hence of the auroral bulge.

33. sunward propagation
profile E

34. Global condition: minor storm
Dst ≈ -60 nT

35. overview
> 5000 km/s
3000 km/s
0.01~40 keV
P/A
P/A

36. IMAGE/FUV 06:26~06:56 UT 06:26 UT 06:34 UT 06:42 UT 06:50 06:28 UT
~06:43 event
S/C
06:26 UT
06:34 UT
06:42 UT
06:50
06:28 UT
06:36 UT
06:44 UT
06:52
06:30 UT
06:38 UT
06:46 UT
06:54
06:32 UT
06:40 UT
06:48 UT
06:56

37. AE and Bx Main phase of minor storm (Dst ~ -60 nT).
2. Substorm onset at around 06:25 UT but ceased in ~10 min.
3. New activity started at around 06:38 UT.
4. Aurora bulge arrived Cluster’s conjugate ~19 MLT at around 06:42~06:44 UT.

38. ion-scale ?
All SC should observe the same behavior of ions if ion gyro-radius (RB = mv/qB) >> inter-S/C distance
RB for B ≈ 200 nT condition
10 keV
100 keV
1 MeV H+
v = 1400 km/s
RB = 70 km
v = 4000 km/s
RB = 200 km
v = km/s
RB = 700 km
He+
v = 700 km/s
RB = 140 km
v = 2000 km/s
RB = 400 km
v = 7000 km/s
RB = 1400 km O+
v = 350 km/s
RB = 300 km
v = 1000 km/s
RB = 800 km
v = 3500 km/s
RB = 3000 km

39. µB conservation: W  W//, but
06:43

40. consolation S/C distance ≈ 100 km in z direction
& 50 km in x-y direction
≈ RB for 10~20 keV H+
<< RB for Ring current ions
 H+ > 20 keV (O+ > 2 keV) should behave the same at all SCs if the gyrotropic assumption is correct

41. 06:43 UT event (arrival of auroral bulge)
(a) Sunward propagation (5~10 km/s) of DC field
* depletion of |B|≈BZ up to 25%
* polarization E≈-EX of up to 10 mV/m
* ExB convection (up to 50 km/s) of cold He+
(without O+)
(b) Net flux Increase of selectively 3000 km/s ions (∆P3000km/s = 3 nPa = - ∆PB).
* Net flux decrease of other energetic particles.
* Energy-time dispersion
* 100 keV H+ ~ ∆E, and 50 keV H+ ~ ∆B
(c) Ionospheric plasma that is accelerated by parallel potential of about 7 kV.

42. But, there is inter-SC difference
RAPID (SSD) data
But, there is inter-SC difference

43. How about CIS (MCP) data?

44. Inter-SC difference: trapped H+ for CIS

47. inter-SC difference ! For flux increase:
(1) SC-2 < SC-1 < SC4=SC3
H+: 80~160 keV
He+: 200~300 keV
(2) SC-2 > SC-1 > SC4=SC3
H+: ~60 keV
O+: 500~600 keV
Hybrid:
(5) SC-2 > SC-1 > SC4 > SC3
O+: 400~500 keV
For flux decrease:
(3) SC-2 < SC-1 < SC4=SC2
He+: 400~700 keV
(4) SC-2 > SC-1 > SC4=SC3
O+: ~400 keV

48. End

49. no wave@06:43 UT, wave@06:48 UT BB-EM stagnant 150 nT  ΩP = 4 Hz iondE dB
S//
E/B
ΩHe?
dBZ
BB-EM
spin effects
stagnant
dBX

50. Composition from energy ratio
(1) From energy peak: plasmaspheric He+ rich // 
Precursor (06:44 UT)
Heating (06:49 UT)
= 0°
= 180°
= 360°  //
H+ He+ O+
18eV 70eV
H+ He+
ratio=4: O+/He+ or He+/H+
[eV]
[eV]

51. End

52. Ground conj.
Nothing special
only 50 nT activity
06:43 06:48