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Tung-Shin Hsu 1 and R L McPherron 1 ,

A Statistical Analysis of the Effects of Fast Plasma Flows on the Pi 2 Pulsations and Its Associated Magnetospheric Reconfiguration. Tung-Shin Hsu 1 and R L McPherron 1 , Yasong Ge 1 , Joseph Borovsky 2 , Hui Zhang 1 , Vassilis Angelopoulos 1 , Christopher Russell 1 IGPP/UCLA

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Tung-Shin Hsu 1 and R L McPherron 1 ,

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  1. A Statistical Analysis of the Effects of Fast Plasma Flows on the Pi 2 Pulsations and Its Associated Magnetospheric Reconfiguration Tung-Shin Hsu1 and R L McPherron1, Yasong Ge1, Joseph Borovsky2, Hui Zhang1, Vassilis Angelopoulos1, Christopher Russell1 IGPP/UCLA Las Almos National Lab GEM 2008, Midway, Utah June 22 – June 27, 2008

  2. Selection of THEMIS Flow Burst Events • All of the events are beyond -5 Re • CCNV nightside Pi 2 is used. • Vxgsm is used for selection of events. • A sliding 5-min time windows is used for selection of possible flow bursts events. • Threshold value is set at 150 km/sec. • Inside this 5-min time window, there must be at least 30 second beyond 150 km/s. • Visual inspection is used to selected the onset time instead of the maximum Vx peak time. • If multiple S/C detect flow, the earliest flow onset time is used.

  3. Superposed THEMIS Vx at Different Location

  4. Superposed Bz at Different Locations

  5. Superposed Pi 2 Power at Flow Burst

  6. Superposed Pi2 power and Vx • Pi2-Flow: 45%, Pi2-No Flow: 25%, Pi2-weak Flow: 30% • The superposed Vx and Pi 2 power by Pi 2 onsets is very similar to the behavior by plasma flow onsets. • This strongly suggests that Pi 2 and plasma flow have a very close relationship.

  7. Near Earth Neutral Line (?) [Shiokawa et al., 1997; Zhang et al., 2007; Birn et al., 1999; Roux et al., 1991; Pu et al., 1997; Cao et al., 2008] • It seems like that the flow braking as well as the Bz dipolarization occurs in the 8~15 Re in the tail. • This is consistent with the suggestion of the flux pile up neutral line model.

  8. Introduction • Pi 2 is important for substorm studies. • Several case studies has suggested Pi 2s are associated with plasma flows. • Hsu and McPherron [2007] suggested that substorms Pi 2s have high probability of flow association. • However, a recent statistical study [Kim et al. 2007] suggests that only 6% ~26% of probability of flow associated Pi 2s. • This probability seems too low if the Pi 2s are generated by the tail plasma flows. • With the launch of the THEMIS, we can re-examine this question with multi-points observations

  9. Position and Time Separation of Plasma Flow Events It seems that the time separation of the Plasma flow events is bout 6~8 minutes

  10. Pi 2- Flow Relationship Is Not Simple

  11. Superposed THEMIS Vx at Different Location • It seems that the plasma flows are decelerated toward the earth. • Inside the synchronous orbit, there is no flow detection. • The flow speed are approximately the same at 21 to 25 Re. • The braking of the plasma flows starts at 19 Re and is most significant from 15 to 9 Re.

  12. Summary (1) • Some of the plasma flow bursts may not penetrate deep enough to the near-Earth region to generate Pi 2s. • When there is a plasma flow burst, there is a high probability to see ground Pi 2s (~75%). • When there is a Pi 2, there is reasonable chance (45%) to see plasma flows in the tail • The Pi 2s duration is corresponding well with the plasma flow duration. • Pi 2s and plasma flows can cause intensification of auroral electrojets.

  13. Summary (2) • This suggests that the plasma flows is very likely the source of the Pi 2s. • The plasma flows are very likely carrying magnetic flux and are associated with magnetospheric reconfiguration. • The reconnection site seems at ~20-25 Re. • The flux pile up region (flow braking region) seems at ~8-15 Re in the tail. • The cluster between flow bursts and AL onsets suggests flow bursts is important to substorm dynamics.

  14. Superposed Bz at Different Locations • The dipolarization is not obvious as the S/C goes further from the Earth. • From 7 Re to 15 Re, there is a significant dipolarization while the flows are clearly decelerated. • Inside the 6.6 Re orbit, the flow is barely detected as well as the dipolarization (SCW effect?)

  15. Probability of Vx with Pi2 • The probability of association between flow bursts and Pi 2 is higher when more than one S/C detected flows. • This may suggest that some of the flow may not penetrate to the near earth region to initiate Pi 2 waves • It is not unusual that only 3~4 S/C has plasma observation.

  16. Time Delay between AL onsets and Flow Bursts There is a cluster between AL Onsets and flow bursts which may suggest flow bursts is Important to substorm onsets.

  17. How about Pi2 Events-Flows Association?

  18. Selection of Pi 2 Events • Only substorm associated Pi 2s are examined. • A +/- 2 hours time windows centered by AL onset is created for examination of the association between Pi 2s and plasma flows. • Every Possible Pi 2s are picked and marked the possible association. • If there is a auto detected plasma flow event within +/- 5 min, it is marked as an associated event. • Total: 774 Pi 2 events. • 353 associated with flow (45%)

  19. Pi 2s without Plasma Flows

  20. Pi 2s with Plasma Flows • The duration of the plasma flow is about 5~10 minutes. • The Pi 2s duration is also about 5~10 minutes • The near earth region shows plasma perturbation when no plasma flows associated with Pi 2s • The deceleration of the plasma flow is also observed in the superposed curves (by Pi 2 onsets).

  21. Intensification of Auroral Electrojet with Plasma Flows

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