1. Magnetic reconnection X-line crossing by THEMIS-B on February 7, 2009
Hall effect
Magnetic islands
Electron energization?

2. TH-B: Tailward to earthward flow reversal TH-C: Earthward flow
February 7, 2009 TH-C and TH-B
TH-B: Tailward to earthward flow reversal
TH-C: Earthward flow AE
TH-C B
TH-C Vx
TH-C V
TH-C
TH-B
TH-C
ions
TH-B B
TH-B
TH-B V Vx
TH-C
TH-B
TH-B
ions

3. Earthward to tailward flow reversal BZ reversal: negative to positive
TH-B X-line crossing
- 40 minutes of burst data
Earthward to tailward flow reversal
BZ reversal: negative to positive
Multiple current sheet crossings
Flow reversal
TH-B B
(GSM) Bz
toward Earth
TH-B V
(GSM) Vx
TH-B
ions
Hall magnetic field?

4. BY (mostly) consistent with Hall magnetic field
- especially in the tailward flow
Entire flow reversal (04:03-04:27 UT)
With biggest magnetic island removed 1 2 1 2
By>0
By<0
By>0
By<0 BX
(nT) BX
(nT)
By<0 3 4
By>0
By<0 3 4
By>0
Vx (km/s)
Vx (km/s)
By > 0
By < 0 1 2
toward Earth 3 4

5. Hall electrons at the lobe/PS boundary
Lower energy electrons toward the X-line 1 2
toward Earth
Higher energy electrons away
from the X-line 3 4
High energy electrons
Hall electrons
TH-B B
TH-B
ions
Bx = - 9 nT
Vx = km/s
Direction of low energy electrons consistent with being the Hall current carrier

6. Hall electrons at the lobe/plasma sheet boundary in all four quadrants
- excellent coverage of the reconnection region 1 2
Bx = 13 nT
Bx = 12 nT
toward Earth 3 4
Hall electrons
Bx = -12 nT
Bx = -9 nT
Hall electrons at the lobe/PS boundary could potentially be used for timing of
reconnection onset tailward of X-line

7. Magnetic islands near flow reversal
Several magnetic islands embedded in
high speed flows ?
TH-B B
Flow reversal Vx
TH-B V
TH-B
ions

8. BZ reversals opposite in earthward and tailward flow
Magnetic islands:
BZ reversals opposite in earthward and tailward flow
in earthward flow
in tailward flow BZ BZ
TH-B B
TH-B B Vx
TH-B V
TH-B V Vx
TH-B
ions
TH-B
ions
tailward
jet
earthward
jet

9. This event is ideal for studying electron energization near an
Energetic electrons?
TH-B B Bz
This event is ideal for studying
electron energization near an
X-line and in magnetic islands
But first we need to remove Sun line
contamination
X-line crossing
TH-B V
TH-B
ions
TH-B
high energy
electrons
(df)
(Background not yet removed)

10. Summary: Feb. 7, 2009 reconnection X-line crossing
- 40 minutes (!) of burst data
- Excellent coverage of all four quadrants
- Diffusion region + islands
- Ideal for studying electron energization
Next step:
Energetic particles (Sun removed)
Electric field structures

11. Will look for Hall Ez (to be reconstructed from Ex and Ey)
Electric Field
BGSM
VGSM
EDSL
(p burst)
04:06: :06:46 UT
BGSM
VGSM
EDSL
(p burst)
Will look for Hall Ez (to be reconstructed from Ex and Ey)