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

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 ……

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

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

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

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)

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

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

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

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

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

Y X

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

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

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

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

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

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