Magnetic reconnection X-line crossing by THEMIS-B on February 7, 2009

Hall effect

Magnetic islands

Electron energization?

February 7, 2009 TH-C and TH-B

TH-B: Tailward to earthward flow reversal

TH-C: Earthward flow

TH-BTH-C

TH-BTH-C

AE

TH-C B

TH-C

TH-B

TH-C V

TH-C ions

TH-B B

TH-B V

TH-B ions

Vx

Vx

TH-B X-line crossing

- 40 minutes of burst data- Earthward to tailward flow reversal- BZ reversal: negative to positive- Multiple current sheet crossings

Hall magnetic field?

Vx

TH-B B(GSM)

TH-B V(GSM)

TH-B ions

Bz

Flow reversal

toward Earth

BY (mostly) consistent with Hall magnetic field- especially in the tailward flow

BX

(nT)

Vx (km/s)By > 0

By < 0

Vx (km/s)

BX

(nT)

Entire flow reversal (04:03-04:27 UT) With biggest magnetic island removed

By<0By>0

By>0By<0

By<0

By<0

By>0

By>0

toward Earth

1 2

3 4

1 2

3 4

1 2

3 4

Lower energy electrons toward the X-line

Bx = - 9 nTVx = - 180 km/s

Direction of low energy electrons consistent with being the Hall current carrier

Higher energy electrons away from the X-line

Hall electrons at the lobe/PS boundary

TH-B ions

TH-B B

Hall electronsHigh energy electrons

toward Earth 1 2

3 4

Hall electrons

Bx = 12 nT

Bx = -9 nT

Bx = 13 nT

Hall electrons at the lobe/plasma sheet boundary in all four quadrants- excellent coverage of the reconnection region

Hall electrons at the lobe/PS boundary could potentially be used for timing of reconnection onset tailward of X-line

toward Earth

Bx = -12 nT

1 2

3 4

Magnetic islands near flow reversal

Several magnetic islands embedded inhigh speed flows

?

Flow reversalVx

TH-B B

TH-B ions

TH-B V

Magnetic islands: BZ reversals opposite in earthward and tailward flow

in tailward flowin earthward flow

Vx

Vx

earthward jet

tailward jet

TH-B V

TH-B V

TH-B B

TH-B B

TH-B ions

TH-B ions

BZ BZ

Energetic electrons?

X-line crossing

(Background not yet removed)

This event is ideal for studyingelectron energization near an X-line and in magnetic islands

But first we need to remove Sun linecontamination

TH-B ions

TH-B B

Bz

TH-B V

TH-Bhigh energyelectrons(df)

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

Electric Field

04:06:43 - 04:06:46 UT

Will look for Hall Ez (to be reconstructed from Ex and Ey)

BGSM

VGSM

EDSL(p burst)

BGSM

VGSM

EDSL(p burst)