1. Analysis of Substorms during the Second THEMIS Tail Season
V. Angelopoulos1, A. Runov(1), X. Z. Zhou(1), S. Frey(2), J. P. McFadden(2), D. Larson(2), S. Mende(2), H. Frey(2), J. Bonnell(2), U. Auster(3), K. H. Glassmeier(3), O. LeContel(4) and A. Roux(4)
(1) IGPP/ESS, University of California, Los Angeles, California, USA
(2) Space Sciences Laboratory, University of California, Berkeley, California, USA
(3) IGEP, TU Braunschweig and MPS, Katlenburg-Lindau, Germany
(4) Laboratoire de Physique des Plasmas, Ecole Polytechnique, Palaiseau, France
During the second tail season the P1, P2 orbits were redesigned to reside closer to the neutral sheet in order to capture reconnection events in the midtail and correlate mid-tail particle signatures with substorm onset and near-Earth dipolarization. We review the substorms that have been observed thus far and perform timing analysis on several of them: Major conjunctions of January 26th, Feb 7th, Feb 15th, Feb 23rd and, Feb 27th Due to the low solar and geomagnetic activity in the first half of 2009, the substorms encountered were localized and often the ionospheric conductivity was low enough that magnetic signatures are small or absent. This presents the opportunity to compare small with large substorms from multiple vantage points in the tail. Based on ACE and STEREO correlations, it is expected that Feb 23rd will be an active time, high quality conjunction. The extra benefit from Cluster placement in that event will also be discussed. Preliminary results show that small substorms and high latitude substorms have all features of injections, fast flows dipolarizations and reconnection that are found in larger substorms, but are more confined in their local time extent on the ground and seemingly also in the magnetosphere.

2. Overview 2nd Tail Season Orbits Jan. 26, 2009 Feb. 07, 2009
Summary of findings

3. First year baseline orbit (FY08)
YGSE
Tail
Dayside
XGSE
TH-B
TH-C
TH-D
TH-E
TH-A P1 P2 P3 P4 P5
Second year baseline orbit (FY09)
YGSE
Dayside
Tail
XGSE
Angelopoulos, 2008
Space Sci. Rev.

4. 2009 Tail Season
Dec 2008-Feb orbits much Results x<-10 Re, dy<2 Re, 4 probes
closer to neutral sheet than in Tail dzNS < 1 Re: h+ 60h+10h=101h
Due to overlap with shadow about dzNS < 2 Re: h+ 94h+37h=175h
90h within 1 Re useful Nominal criteria: 64h+101h+94h=259h P1
Feb 15
Feb 23
Feb 27 P2
Feb 07
Jan 26
Feb 07
Feb 15
Feb 23
Feb 27
Jan 26
dzNS [Re]
Time [d]
Y-GSM [Re]
X-GSM [Re]
Blue = conjunctions

5. Compare with: 2008 tail season Midnight Pre-midnight
Feb-26
Feb-18
Feb-22
Mar-01
Feb-14
Feb-10
Jan-29
Feb-6
Feb-2
Feb-26
Jan-29

6. Jan 26, 2009 Substorms
TH-B

7. Jan 26, 2009 Substorms

8. Jan 26, 2009 comments Lines defined based on near-Earth dipolarization
Activations at SNKQ (6:29UT), GILL (intens.: 0640UT), RANK(NS arcs:0647UT) GILL (Intens. 0704UT, 0708UT, 0710UT…), FSIM new onset/intens. (0714UT), GILL (Intens. of prior onset? 0730UT, see 2 pages earlier)
TH-A has delayed response due to its latitude (1Re below TH-D, TH-E)
Multiple tail activations seen prior to substorm onset, uncorrelated to each other
Likely due to off-midnight placement and extreme localization effects
Likely radial alignment does not correspond to meridional alignment far from midnight
Intense auroral currents are related to intense activation on all probes, including inner probes.
More global
Preconditioning of ionospheric conductivity a possibility

9. Feb 07, 2009 Substorms
Cloudy but there!

10. Feb 07, 2009 Substorms

11. Feb 07, 2009 Comments
Probes were closer in the dawn side of onset meridian
Auroral onset ~0341UT, ~0358 UT (KUUJ), poleward ~0404UT (RANK)
See Movie by Emma Spanwick
Significant activity at P1, P2 prior to 0400UT does not correspond to dipolarization at P3, P4
Only when auroral currents (THEMIS-AL) were significant did P3, P3 indicate dipolarization
Auroral signatures accompanied 0400 UT onset but could be higher latitude (PBIs?) and could have been missed earlier. Unclear where poleward boundary of plasma sheet is.

12. Feb 15, 2009 Substorms
TH-B

13. Feb 15, 2009 Substorms
Activity at NRSQ at 3:24 UT, appears to extend through Eastern Canada to GILL.

14. Feb 15, 2009 Substorms
Fiducial based on earliest dipolarization: 3:18 UT

15. Feb 15, 2009 Comments
Intense dipolarization associated with small AE signature
Yet auroral intensification was significant, expanded far poleward
THEMIS-AE responded only 20 minutes later, despite good coverage
Likely ionospheric conductivity effects influence response
Role of preconditioning may be significant in generating global response

16. Feb 23, 2009 Substorms
TH-B
CL-2

17. Feb 23, 2009 Substorms
Fiducial based on earliest dipolarization: 8:18 UT

18. Feb 23, 2009 D-E-A

19. Feb 23, 2009 Comments Similar to Feb 15
Probes were closer to dawn sector so may have missed the primary activation
Flow localization effects in –Y direction affects interpretation significantly

20. Feb 27, 0226UT 2009 Substorm

21. Feb 27, 0226UT 2009 Substorm

22. Feb 27, 0635UT 2009 Substorm

23. Feb 27, 0742UT 2009 Substorm

24. Feb 27, 0635 & 0742UT 2009 Substorms

25. Feb 27, 2009 Comments Three substorms 0226UT onset 0635UT onset
Tailward flows on P1 (TH-B) and Earthward flows on P4 (TH-E)
0635UT onset
0742UT onset
Activity was already tailward of P1 at 20Re

26. THEMIS 2nd tail season: Summary
Events reveal immediately that:
Precursor activity is important in preconditioning ionospheric conductivity
Z-location is critical not only at 20-30Re but also for inner probes:
Timing depends critically on distance from neutral sheet
A number of nice events are ameanable to timing and propagation delay analysis