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Analysis of Substorms during the Second THEMIS Tail Season

Analysis of Substorms during the Second THEMIS Tail Season V. Angelopoulos 1 , 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)

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Analysis of Substorms during the Second THEMIS Tail Season

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  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 2009. 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 • Feb. 15, 2009 • Feb. 23, 2009 • Feb. 27, 2009 • Summary of findings

  3. TH-B TH-C TH-D TH-E TH-A P1 P2 P3 P4 P5 First year baseline orbit (FY08) YGSE Tail 12008-02-02 Dayside 12008-08-08 XGSE Second year baseline orbit (FY09) YGSE Dayside 22009-09-16 Tail 22009-02-18 XGSE Angelopoulos, 2008 Space Sci. Rev.

  4. 2009 Tail Season dzNS [Re] Time [d] dzNS [Re] Y-GSM [Re] dzNS [Re] X-GSM [Re] • Dec 2008-Feb 2009 orbits much Results x<-10 Re, dy<2 Re, 4 probes • closer to neutral sheet than in Tail1 dzNS < 1 Re: 31h+ 60h+10h=101h • Due to overlap with shadow about dzNS < 2 Re: 44h+ 94h+37h=175h • 90h within 1 Re useful Nominal criteria: 64h+101h+94h=259h P1 P2 Feb 27 Feb 23 Feb 15 Feb 07 Feb 27 Feb 23 Jan 26 Feb 15 Feb 07 Jan 26 Blue = conjunctions

  5. Compare with: 2008 tail season Midnight Pre-midnight Feb-26 Mar-01 Feb-22 Feb-18 Feb-14 Feb-10 Feb-6 Jan-29 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, 2009Substorms Cloudybut 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 • Tailward flows on P1 (TH-B) and Earthward flows on P4 (TH-E) • 0635UT onset • Tailward flows on P1 (TH-B) and Earthward flows on P4 (TH-E) • 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

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