1. High-Speed Plasma Flows Observed in the Magnetotail during Geomagemtically Quiet Times: Relationship between Magnetic Reconnection, Substorm and High-Speed Plasma Flows
Motoharu Nowada (野和田 基晴)1, George K. Parks2, Sui-yan Fu1, Zu-yin Pu1, Vassilis Angelopoulos3, Charles W. Carlson2, Hans-Ulrich Auster4
1: ISPAT/SESS, Peking University
2: SSL, University of California, Berkeley
3: IGPP, University of California Los Angeles
4: Technische Universität, Braunschweig, Deutsuland
2/24/2019
2011 ILWS Workshop No. 3567

2. Characteristics of the high-speed plasma flows (HSPFs) in the terrestrial magnetotail…
1. Location: GSM-X = -10 Re – -30 Re (at the CPS) 2. Velocity: 300 – 400 km/s (Vx) or higher than ~300 km/s (V⊥) 3. Duration: From about 1 min. to 10 min. 4. Generation Mechanism: Magnetotail Magnetic reconnection, Some instability driven by current etc… Others: Observed during geomagnetically both active (GATs) and quiet (GQTs) times. 6. Questions: The HSPFs (in particular, at GQTs) are associated with substorm… ? How the HSPFs during quiet times are related with magnetic reconnection ?

3. On the HSPFs during geomagnetically quiet times…
GEOTAIL observation from January 1998 to April The 4 HSPF events at very quiet auroral activity times were only selected [Ieda et al., 2003].
I. The clear HSPFs are almost always associated with auroral brightenings [Fairfield et al., 1999; Ieda et al., 2001, 2003, Nakamura et al., 2001].
Therefore, the HSPF’s occurrence during an absent of (or very weak) auroral activity is rare [Ieda et al., 2003].
II. The magnetic reconnection does not necessarily trigger the (global) substorm in the magnetotail at geomagnetically quiet times [Ohtani et al., 2002].
2/24/2019
2011 ILWS Workshop No. 3567

4. Main characterstics of these HSPFs during geomagnetically quiet condition
- THEMIS
1. Sun-tailward plasma velocity (GSM-X component of the plasma velocity: |Vx|) is higher than 300 km/s.
2. GSM-X < 0 [Re] (Nightside) and -18 < GSM-Y < 18 [Re] (avoiding the MPCL crossing data).
3. β value (ratio between the plasma pressure and magnetic pressure) is higher than 0.5 (CPS (PS) region).
- Ground
4. Kp index range is between -1 and +1 and AL/AU indices are lower than ±40 nT.
5. Auroral activation is absent or not outstanding (confirmed by THEMIS-ASI).

5. 4 Events of “Magnetotail High-Speed Plasma Flows during Geomagnetically Quiet Times”
Date (yyyy/mm/dd)
Time Intervals (UT)
Flow Orientation
THEMIS Probes I
2008/01/31
09:45 – 10:01
Earthward
P3 (D) and
P4 (E) II
2010/03/24
04:25:40 – 04:30:30
P3 (D) and P4(E)
III
2009/03/27
00:10 – 00:19 (TH-B)
00:56:00 – 00:58:30 (TH-B)
00:59 – 01:02 (TH-C)
Earthward
P1 (B) and P2 (C) IV
2010/01/31
08:43:30 – 09:10:00
Tailward

6. Event I: January 31, 2008
I. THEMIS-D and -E observed the high-speed plasma flows (HSPFs).
II. THEMIS-C and -A did not observe the HSPFs

7. Event I: January 31, 2008

8. Event I: January 31, 2008 During the HSPFs… I. Bt: Enhancement
Dipolarization 
Dipolarization ↑
During the HSPFs…
I. Bt: Enhancement
II. Bz: Northward direction and fluctuating

9. Pi2 range: 6.7 mHz - 25 mHz (40 s – 150 s)
Event I: January 31, 2008
Pi2 range: 6.7 mHz - 25 mHz (40 s – 150 s)

10. Event I: January 31, 2008 THEMIS-ASI 09:40 – 09:50 UT THEMIS-ASI
Footpoints of THEMIS

11. Event II: March 24, 2010 I. THEMIS-D and -E observed the HSPFs.
II. The other probes did not see them.

12. Event II: March 24, 2010

13. Event II: March 24, 2010
I. The magnetic field intensity enhances in association with the HSPFs.
II. Simultaneous intensity of the Bz component enhances.
III. The orientation of the Bz component is northward.
Dipolarization
Dipolarization↑

14. Pi2 range: 6.7 mHz - 25 mHz (40 s – 150 s)
Event II: March 24, 2010
Pi2 range: 6.7 mHz - 25 mHz (40 s – 150 s)
I. The power spectra at the footpoint ground stations.
II. Very weak power associated with the Pi 2 waves is detected.

15. Event II: March 24, 2010 THEMIS-ASI 04:20 – 04:30 UT
Footpoints of THEMIS

16. Summary Bt Bz V⊥ GSM-X and -Y [Re] Pi 2 wave
[km/s]
GSM-X and -Y [Re] Bt Bz
Aurora Activation
Pi 2 wave
Kp, AU/AL
[nT]
2008/1/31
(-12, -3.5)
(-11, -4.5) + △ NW × ○ 1-
8/-10
2010/3/24
250-
300
(-10.5, -0.8)
(-10.5, -1)
17/-16
2009/3/27
(-16, -6)
(-18, -6) +-
NWD 0+
10/-15
2010/1/31
(-32, -17)
(-55, -14)
20/0 I II
III IV
“+” means “Enhancement”, and “-” means “Decrease”.
“△” means “Fluctuation” or “Very weak Pi 2”.

17. Conclusion
During the High-Speed Plasma Flows (HSPFs) at geomagnetically quiet times…
- the auroral activation was not observed.
- the PI 2 waves are not always observed.
 “Magnetic reconnection” might not necessary condition to generate the HSPFs.
 The HSPFs occur in association with not only “pure substorm” but also “substorm-like phenomena” (pseudo-substorm).
In association with the HSPFs during geomagnetically quiet times…
- Enhancements of the magnetic field intensity and the Bz component
 Magnetic flux piling up and dipolarization
- The magnetic field fluctuations
 Some instability is occurred (is triggered ?) by the HSPFs.
2/24/2019
2011 ILWS Workshop No. 3567

18. That’s All. Thank You For Your Attention !!
2/24/2019
2011 ILWS Workshop No. 3567

19. Extra Slides
2/24/2019
2011 ILWS Workshop No. 3567

20. On the HSPFs during geomagnetically quiet times…
I. The clear HSPFs are almost always associated with auroral brightenings [Fairfield et al., 1999; Ieda et al., 2001, 2003, Nakamura et al., 2001].
II. Occurrence of the HSPFs during an absent of (or very weak) auroral activity is rare [Ieda et al., 2003].
III. The magnetic reconnection does not necessarily trigger the (global) substorm in the magnetotail at geomagnetically quiet times [Ohtani et al., 2002].
2/24/2019
2011 ILWS Workshop No. 3567

21. On the HSPFs during geomagnetically quiet times…
I. The clear HSPFs are almost always associated with auroral brightenings [Fairfield et al., 1999; Ieda et al., 2001, 2003, Nakamura et al., 2001].
Therefore, the HSPF’s occurrence during an absent of (or very weak) auroral activity is rare [Ieda et al., 2003].
II. The magnetic reconnection does not necessarily trigger the (global) substorm in the magnetotail at geomagnetically quiet times [Ohtani et al., 2002].
2/24/2019
2011 ILWS Workshop No. 3567

22. On the HSPFs during geomagnetically quiet times…
GEOTAIL observation from January 1998 to April The 4 HSPF events at very quiet auroral activity periods were only selected [Ieda et al., 2003].
2/24/2019
2011 ILWS Workshop No. 3567

23. Event I: January 31, 2008
I. In this event, the high-speed plasma flows are occurring periodically.
II. Perturbations of the magnetic field are observed in association with the high-speed plasma flows.
III. The magnetic intensity (magnetic pressure) is seemed to enhance, but the plasma pressure seemed to decrease in association with the high-speed plasma flows.

24. Event II: March 24, 2010
I. THEMIS-D and -E observed the HSPFs during the periodical (wavy) variations of the plasma velocity.
II. The magnetic pressure enhanced, but the plasma pressure decreased when the HSPFs were observed.
 Is this evidence for the pile up of the magnetic flux in the magnetotail associated with the HSPFs ?

25. Event III: March 27, 2009 (Quiet)
I. THEMIS-B and -C observed the HSPFs.
II. The other probes did not see them.

26. Event III: March 27, 2009 (Quiet)
I. The first HSPFs observed by THEMIS-B was not observed by THEMIS-C.
II. The two HSPF events detected by THEMIS-B were occurring under very low β condition (β ≤ 0.5)
III. The second HSPF event observed by THEMIS-B was seen by THEMIS-C, but the magnetic field and plasma structures are different each other.

27. Event III: March 27, 2009 (Quiet)

28. Event III: March 27, 2009 (Quiet)

29. Event III: March 27, 2009 (Quiet)
Pi2 range: 6.7 mHz - 25 mHz (40 s – 150 s)
I. The power spectra at the footpoint ground stations.
II. Very weak power associated with the Pi 2 waves is detected.

30. Event III: March 27, 2009 (Quiet)
THEMIS-ASI
00:00 – 00:10 UT
THEMIS-ASI
00:50 – 01:00 UT
THEMIS-ASI
01:00 – 01:10 UT
Footpoints of THEMIS

31. Event IV: January 31, 2010 (Quiet)
I. THEMIS-B and -C observed the HSPFs.
II. The other probes did not see them.

32. Event IV: January 31, 2010 (Quiet)
THEMIS-B and -C might be located near the LLBL ? Or
THEMIS-B and -C experienced the magnetopause crossing ? If so, the polarity change of Bx (this case should be “outbound crossing”) is opposite (from positive to negative).
I. Both THEMIS-B and -C observed the tailward HSPFs.

33. Event IV: January 31, 2010 (Quiet)

34. Event IV: January 31, 2010 (Quiet)

35. Event IV: January 31, 2010 (Quiet)
Pi2 range: 6.7 mHz - 25 mHz (40 s – 150 s)
I. The power spectra at the footpoint ground stations.
II. Very weak power associated with the Pi 2 waves is detected.

36. Event IV: January 31, 2010 (Quiet)
THEMIS-ASI
08:40 – 08:50 UT
THEMIS-ASI
08:50 – 09:00 UT
Footpoints of THEMIS