Institute of Geophysics and Planetary Physics University of California, Los Angeles

1. Institute of Geophysics and Planetary Physics University of California, Los Angeles THEMIS observations at a substorm onset on March 1, 2008 A. Runov1, V. Angelopoulos1, X.-Z. Zhou1, V.A. Sergeev2, M. V. Kubyshkina2, S. Apatenkov2, I. Voronkov3, J. McFadden4, D. Larson4, K.-H. Glassmeier5, U. Auster5, W. Magnes6, R. Nakamura6, C. T. Russell1, I. Mann7, S. Mende2, H. Frey2, L. Kepko8, and H.J. Singer9 1. IGPP/ESS, UCLA, Los Angeles, CA, USA 2. St. Petersburg State University, St. Petersburg, Russia 3. Athabasca University, Edmonton, Alberta, Canada 4. SSL, University of California at Berkeley, CA, USA 5. TUBS, Braunschweig, Germany 6. IWF OEAW, Graz, Austria 7. University of Alberta, Edmonton, Alberta, Canada 8. SSC, University of New Hampshire, Durham, NH, USA 9. NOAA Space Weather Prediction Center, Boulder, CO, USA Correspondence to: arunov@igpp.ucla.edu

2. THEMIS GBO: Auroral onsets 2nd (major) intensification 0152:27 UT SNKQ 1st (minor) intensification 0148:42 UT GBAY P1 P1 P2 P2 P3 P3 P4 SNKQ P4 G12 GBAY G10 G10 G12 01:54:30UT 01:48:50UT

3. WIND (time shifted) GBAY DRBY LOYS KUUJ CHGB

4. THEMIS and GOES observations 08-03-01/0100 – 0210 UT 01:48:50UT 0148:42

5. Observations in the mid-tail PS • P2: X=-17.4 RE • Tailward fast flows • Bz and By variations • Ion & electron energization

6. Observations in the mid-tail PS • P1: X=-22.7 RE • Same as at P2, but ~30 s later on

7. Timing of ion fluxes (SST and ESA) variations during the first tailward flow P2 SST: 50 – 200 keV ESA: 5 – 21 keV • P2/THC: Tailward flux • 60 keV-Ion flux increases at 0148:25 UT; • 190 keV flux increases at 0148:55 UT. • Inversed Velocity Dispersion (IVD, Sarafopoulos and Sarris, 1988) • SC are in the PS: IVD due to the acceleration by the inductive electric field (Taktakishvili et al., 1993) • SC are close to the acceleration region (1-3 RE) P1

8. Electron PA distributions at P1 and P2 First tailward flow 0148:25

9. Observations in the near-Earth PS • P4: X=-8.0 RE • ~6 min later than the first activity in the mid-tail PS; • Magnetic field (and cross-tail current) reduction; • Dipolarization; • Bursty Ion and electron energization • A step-like increase of plasma density and pressure.

10. Observations in the near-Earth PS • P3: X=-9.3 RE • The same as at P4, but ~40 s later on • Tailward propagation of the step-like plasma pressure front at a velocity of 150 km/s.

11. Magnetic field variations at P3, P4, GOES 10, GOES 12 • P3 and P4 FGM measurements • (field-aligned coordinates): • Main field (Bz) at P3 and P4 continuously increases (growth phase) until ~0955 UT • Perpendicular components, • δBy and δBx started at 0148:20 – 0148:40 UT, indicating outward FAC underneath the SC. • GOES 10 (PEN coordinates): • Positive δBn (eastward!) at 0148- 0155 UT G10 was underneath of the FAC GOES10, 12: • Dipolarization at ~0154:20 UT

12. 2008-03-01/0140 – 0205 UT Event Timing 0148:25 high-energy electron flux increase at P2 (transient reconnection?) 0148:25 ~60 keV ion flux increase at P2 (acceleration by the inductive E-field) 0148:40 dBy at P3, P4, G10 (FAC) 0148:42 minor auroral onset at GBAY (pseudo-breakup) 0148:45 Pi2 onset at GBAY 0148:45 Tailward fast ion flow, dBy & dBz at P2 0149:30 Tailward fast ion flow, dBy and dBz at P1 0152:21 Auroral onset at SNKQ (substorm) 0153:30 Dipolarization at G12 0154:20 Dipolarization at P4 0154:30 Tailward flow, dBy & dBz at P1 0154:40 Drop of Bt at P4 (cross-tail current reduction/disruption) 0155:00 Tailward flow at P2 0155:21 Auroral onset at KUUJ 0155:50 Dipolarization at P3 0155:50 dVy and dVz at P3 0155:50 Drop of Bt at P3

13. A Possible Scenario • The observations suggest a two-step development of the activity: • First step: An initial disturbance (probably reconnection) in the mid magnetotail (X~-15 - -17 RE) led to the particle acceleration, the Bz and By perturbations, the plasma bulk flow, and the FAC formation, associated with the first (minor) auroral activation (precursor). The FAC was, likely, generated by the Earthward reconnection outflow. The cross tail current in the near-Earth magnetotail (X~-9 RE) continued building up. • Second step: The rapid reduction (disruption) of the cross-tail current due to hot plasma pile-up, associated with the major onset, developed in the near-Earth plasma sheet. The second tailward flow, observed by P1 and P2, was, likely, generated by a process in the mid tail (probably reconnection), acting simultaneously with (and independent from) the current disruption, observed by P3 and P4 in the near-Earth plasma sheet.

14. Back up slides

15. March 1, 2008 THEMIS major conjunction event 01:54:30UT 0148:50 UT 0155:00 UT