1. Joint Cluster-THEMIS SWT 1 Sep 23-26, 2008 Vassilis Angelopoulos, James P. McFadden, Davin Larson, Charles W. Carlson, Stephen B. Mende, Harald Frey, Tai Phan, David G. Sibeck, Karl- Heinz Glassmeier, Uli Auster, Eric Donovan, Ian R. Mann, I. Jonathan Rae, Christopher T. Russell, Andrei Runov, Xu-Zhi Zhou, Larry Kepko Also: Thanks to Sabine Frey for the orbits and Sergey Apatenkov for SCW modeling Overview and event selection Satellite locations and overview Ground Timing –Auroral Intensification –Poleward Expansion –Pi2 pulsations Reconnection Onset Timing Current Disruption Timing Timing Synopsis Substorm Picture Revis(it)ed THEMIS: Tail Reconnection triggering substorm onset

2. Joint Cluster-THEMIS SWT 2 Sep 23-26, 2008 Orbit was a North-South scan. As a result: –P1, P2 at 30 and 20 R E saw tailward flows/beams only when dZ NS <1R E –When P1, P2 had 5R E >dZ NS >1R E they observed classical NFTEs at onset Earthward flows are more frequent than tailward (plasma sheet expansion) Energetic particle beams were not observed (though we planned for them) A number of events (Feb. 16 to Mar. 1) are amenable to timing 1 st Tail Neutral Sheet Crossings 1 st tail season (Jan-Mar 2008) Feb-14 Feb-10 Feb-6 Feb-2 Feb-18 Feb-22 Feb-26 Midnight Pre-midnight Jan-29 Mar-01 Jan-29 Feb-26

3. Joint Cluster-THEMIS SWT 3 Sep 23-26, 2008 Substorm study on Feb 26, 2008 Probe locations P2 P3 P4 P5 P1 2008-02-26 04:50UT x y

4. Joint Cluster-THEMIS SWT 4 Sep 23-26, 2008 First Event Second Event

5. Joint Cluster-THEMIS SWT 5 Sep 23-26, 2008 First EventSecond Event

6. Joint Cluster-THEMIS SWT 6 Sep 23-26, 2008 First Event Second Event Pi2 Signatures

7. Joint Cluster-THEMIS SWT 7 Sep 23-26, 2008 P1 (TH-B) P2 (TH-C) First Event P1

8. Joint Cluster-THEMIS SWT 8 Sep 23-26, 2008 Tail substorm signatures: Flows, Reconnection, Dipolarization Second Event

9. Joint Cluster-THEMIS SWT 9 Sep 23-26, 2008 Middle Panels: Transformation to deHoffman-Teller frame Bottom panels: Walen test of stress balance Caveats: - Need to include energetic particle contribution to velocity - Aliasing from temporal variations

10. Joint Cluster-THEMIS SWT 10 Sep 23-26, 2008 Middle Panels: Transformation to deHoffman-Teller frame Bottom panels: Walen test of stress balance Caveats: - Need to include energetic particle contribution to velocity - Aliasing from temporal variations Note: When peak velocity considered match to Alfven speed is better

11. Joint Cluster-THEMIS SWT 11 Sep 23-26, 2008 Combined substorm signatures for the second event: AE, Pulsations, Aurora

12. Joint Cluster-THEMIS SWT 12 Sep 23-26, 2008 T Rx T AI T CD 3 rd 1 st 2 nd 3 rd 1 st 2 nd Timing of ground and space:

13. Joint Cluster-THEMIS SWT 13 Sep 23-26, 2008 Note: this is not the classical time sequence: Aurora brightens before near Earth dipolarization This holds true on several events considered Inside out model 1 st 2 nd 3 rd Aurora Current Disruption Reconnection 3 rd 1 st Outside-In model 2 nd 3 rd 1 st 2 nd THEMIS finds: Clarification

14. Joint Cluster-THEMIS SWT 14 Sep 23-26, 2008 Caveats and Open questions Caveats The plasma sheet was cold (Ti ~ 1keV) and dense (1/cc) –Communication speeds slow: perhaps reason for the long delays? The first onset (0400 UT) might not be an isolated substorm (TBD). –Have requested Greenland mags and will collate KUUJ data Open Questions How does Rx communicate with and power aurora so fast (96s)? What preconditions tail to reconnect? –Spontaneous tearing? –Driven by ballooning or KH instabilities and cross-scale coupling? How can mapping be so distorted? –Need to model stretching using THEMIS data for validation (MHD, Tsyganenko) Non-monotonic flux tube volume evolution vs. distance ought to be sources of current? Consequences of tail stretching for tail stability, particle dynamics and wave growth?