Determination of the Substorm Initiation Region From a Major Conjunction Interval of THEMIS Satellites. A T Y Lui, V Angelopoulos, S B Mende, O LeContel, H Frey, E Donovan, D G Sibeck, W Liu, H U Auster, X Li, M Nose, and M O Fillingim Outline Conjunction of THEMIS and GOES 11 &12 satellites
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A T Y Lui, V Angelopoulos, S B Mende, O LeContel, H Frey, E Donovan, D G Sibeck, W Liu, H U Auster, X Li, M Nose, and M O Fillingim
Conjunction of THEMIS and GOES 11 &12 satellites
Auroral activity (AU/AL indices and GBO observations)
Time history of substorm disturbances (including GOES 11&12)
Summary and Conclusions
AU/AL indices During Conjunction on 2008 Jan 29, 07-09 UT.
During the conjunction interval, there were one isolated substorm and another substorm with multiple intensifications. The three time indicators correspond closely to onsets of substorm activity seen by THEMIS satellites.
Satellite Projections on 2008 Jan 29, 07-09 UT.
AE stations are shown in blue, THEMIS GBO stations in green, and THEMIS satellite projections along magnetic field lines in red. The projected satellite locations are well embedded within these stations.
Auroral Activity at Fort Smith (FSMI) on 2008 Jan 29, 07-09 UT.
First auroral substorm onset at ~0714 UT starting slightly to the east - note the relatively undisturbed arc (no breakup activity) poleward of the onset arc.
Second substorm onset at ~0742 UT starting slightly to the west - note undisturbed arc poleward of onset arc.
Third substorm activity at ~0832 UT from the west of the station.
Auroral Activity at Fort Simpson (FSIM) on 2008 Jan 29, 07-09 UT.
• Fort Simpson (FSIM) is west of FSMI.
• Substorm activity seen was similar to that at FSMI, i.e., arc brightening followed by poleward expansion at ~0714 UT and ~0742 UT and with relatively undisturbed poleward arc.
• Auroral substorm activity at the poleward boundary starting at ~0831 UT.
Keograms From 4 GBO Stations on 2008 Jan 29, 07-09 UT.
• From top to bottom are keograms from FSMI, FSIM, Inuvik (INUV), and Fort Yukon (FYKN).
• INUV & FYKN are west of and at higher latitudes than the former two stations.
• Onset at ~0742 UT reached INUV & FYKN with poleward expansion at ~0813 UT.
•Another activation at ~0828 UT at the poleward boundary for INUV & FYKN.
Double oval: retreating equatorward at FSIM but expanding poleward at INUV & FYKN
Movie From GBO Stations on 2008 Jan 29, 07-09 UT.
THEMIS B (P1) on 2008 Jan 29, 07-09 UT.
• No dipolarization seen by P1 at X ~ –30 Re.
• Negative Bz but no tailward plasma flows seen near the first substorm onset.
• P1 exited the plasma sheet later with negative Bz and earthward plasma flows, implying plasma sheet thinning after (not before) the substorm expansion onset in the mid-tail region.
• It remained in the tail lobe for the rest of the interval.
THEMIS C (P2) on 2008 Jan 29, 07-09 UT.
• Two dipolarizations seen by P2 at X ~ –18 Re, negative Bz and no tailward plasma flows for first substorm onset.
• Negligible earthward plasma flow seen prior to the 2nd dipolarization.
• Strong earthward plasma flows (~500 km/s) seen prior to the third dipolarization.
THEMIS D (P3) on 2008 Jan 29, 07-09 UT.
• Three dipolarizations seen by P3 at X ~ –11 Re with time corresponding well to ground auroral onsets of activity.
• Weak earthward plasma flows (<150 km/s) seen prior to the first dipolarization.
• Negligible earthward plasma flows (<50 km/s) prior to the second and third dipolarizations.
THEMIS E (P4) on 2008 Jan 29, 07-09 UT.
• Three dipolarizations seen by P4 at X ~ –11 Re, similar to P3 closeby. However, there are big differences between P3 & P4 in temporal profiles of Vx and Bz during dipolarizations.
• Weak earthward plasma flows (<100 km/s) seen prior to the first dipolarization.
• Tailward plasma flows prior to 2nd dipolarization.
• Weak earthward plasma flows (<200 km/s) prior to the 3rd dipolarization.
THEMIS A (P5) on 2008 Jan 29, 07-09 UT.
• Two dipolarizations seen by P5 at X~ –8 Re, similar to P2 at X~ –18 Re.
• Weak earthward plasma flows (~100 km/s) seen prior to the 2nd dipolarization.
• Very weak earthward plasma flows (<50 km/s) seen prior to the 3rd dipolarization.
Observations from GOES 11 & 12 satellites on 2008 Jan 29, 07-09 UT.
• Dipolarization most prominent for first substorm onset.
• GOES 12 at post-midnight observed a larger Bz increase than GOES 11 at pre-midnight, suggesting first onset was located in the post-midnight.
THEMIS Vix and Bz on 2008 Jan 29, 07-09 UT.
For 0714 UT, temporal sequence: D/E => B
For 0742 UT, temporal sequence: A => D/E => C
For 0828 UT, temporal sequence: C => E => D => A
Time History of Events on 2008 Jan 29, 07-09 UT.
No Magnetic Reconnection on Open Field Lines on 2008 Jan 29, 07-09 UT.