1. Substorm current wedge, Alfven waves, ion injections, Pi2 pulsations, and ion outflows:
A THEMIS look
The THEMIS team

2. Background Most relevant: Bauer et al. (1995):
Neutral sheet oscillations associated with substorm current wedge
Maynard et al. (1996) :
Poynting flux of Alfven waves associated with substorm current wedge ……

3. THEMIS AE index
Substorm
March 23, 2007
Overview plot Y X

4. Previously discussed: Wave-particle signatures prior to main onset
Increasing particles
energies
anticorrelated
~60 s – Pi2

5. anti-correlated
same period
no anti-correlation,
only similar periodicity

6. Vector plots (hodogram)
Onset
Onset
waves previously
presented
more waves; today’s focus Bx
Dipolarization Bz Bz
Current sheet Bx
THEMIS
Time
Vector plots (hodogram)

7. Wave modes
total B 1
Poloidal (compressional) mode dominates at pre-cursor breakup
Resonances are mostly compressional 2 X 1 2 3
Poloidal and toroidal components (Alfven wave) dominate at expansion phase onset
 substorm current wedge? Y 3 Z

8. Focus on low-frequency component
Ions Bt Bx By D E Bz C
Focus on low-frequency
component A D C E B
By is stronger for C (Alfvenic)
D and E are more compressional

9. nearly circular polarized
THEMIS C Bx Bz Bz Bx
Rotation
Bx, By, Bz
L, M, N
11:00
12:00
nearly circular polarized

10. Alfven wave Bx By Bz
Bx, By, Bz
L, M, N
nearly circular polarized

11. C D A B C E D B A E E-vector = ( ) angle = E-vector = ( ) angle =

12. Y X

13. Ion outflow on auroral field lines
Ion injection
caused by Alfven waves ?
caused by ion injections ?
Alfven waves

14. Comparison with ground stations
210 MM
Note: So far, no data available from high-latitude 210M stations (data provider: Shiokawa and Yumoto)
THEMIS
210MM
THEMIS
Note: 210MM lies on the same meridian as THEMIS

15. THEMIS 210MM giant pulsations gigantic pulsation Period: ~135 sec
unusually long period for low latitude
typical period for high latitude
more complic. pattern across all stations

16. Comparison: Particles and Pi2
THEMIS SST
Decaying amplitude
Largest pulse first
278 keV
time-shifted: - 30 sec
(THEMIS and 210MM)
Ground data
Note: Alfven transit time
Period: ~135 sec

17. Five key observations: Questions:1
Alfven waves (circularly polarized) observed at onset of substorm and onset of ion injection
Ion outflow on same field lines as Alfven waves and ion injections
Ground shows very large, long-period Pi2 (~135 sec)
Ion flux at THEMIS is temporally correlated with ground Pi2 (~135 s)
Ion flux characteristics resemble ground Pi2 (first pulse, decaying amplitude, period)
Period of ion injections : ~135 sec
Bounce period ~21 s for 278 keV ion
Drift period >10 min
Thus, is this periodicity caused by BBF?
Secondary and tertiary injections show dispersion ( trace back particles)
Ion injections are variable at different s/c
are variable
Period of pulsations are different at different azimuthal locations
Alfven waves are caused by onset of inductive field? Ion injections cause Alfven waves?
Unusual Pi2 period for low-latitude. What drives the Pi2 frequency? Energetic ions?
What about pressure, velocity variations? 2 3 4 5

18. End