Tung-Shin Hsu 1 and R L McPherron 1 ,
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Transcript of Tung-Shin Hsu 1 and R L McPherron 1 ,
A Statistical Analysis of the Effects A Statistical Analysis of the Effects of Fast Plasma Flows on the Pi 2 of Fast Plasma Flows on the Pi 2
Pulsations and Its Associated Pulsations and Its Associated Magnetospheric ReconfigurationMagnetospheric Reconfiguration
Tung-Shin Hsu1 and R L McPherron1, Yasong Ge1, Joseph Borovsky2, Hui Zhang1, Vassilis Angelopoulos1, Christopher Russell1
1.IGPP/UCLA2.Las Almos National LabGEM 2008, Midway, Utah
June 22 – June 27, 2008
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.
Superposed THEMIS Vx at Different Location
Superposed Bz at Different Locations
Superposed Pi 2 Power at Flow Burst
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.
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.
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
Position and Time Separation of Plasma Flow Events
It seems that the time separation of the Plasma flow events is bout 6~8 minutes
Pi 2- Flow Relationship Is Not Simple
• 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.
Superposed THEMIS Vx at Different Location
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.
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.
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?)
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.
Time Delay between AL onsets and Flow Bursts
There is a cluster between AL Onsets and flow bursts whichmay suggest flow bursts is Important to substorm onsets.
How about Pi2 Events-Flows Association?
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%)
Pi 2s without Plasma Flows
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).
Intensification of Auroral Electrojet with Plasma Flows