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

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

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?

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

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 = - 180 km/s Direction of low energy electrons consistent with being the Hall current carrier

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

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

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

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)

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

Will look for Hall Ez (to be reconstructed from Ex and Ey) Electric Field BGSM VGSM EDSL (p burst) 04:06:43 - 04:06:46 UT BGSM VGSM EDSL (p burst) Will look for Hall Ez (to be reconstructed from Ex and Ey)