First 10 months (Feb 2007-Dec 2007) Prime mission at a glance (FY07-FY09) First 10 months (Feb 2007-Dec 2007) TH-B TH-C TH-D TH-E TH-A P1 P2 P3 P4 P5 First year baseline orbit (FY08) 2007-03-23 Tail 1 2008-02-02 2007-06-03 YGSE Dayside 1 2008-08-08 Launch= 2007-02-17 2007-07-15 XGSE Second year baseline orbit (FY09) 2007-08-30 2007-12-04 Tail 2 2009-02-18 Dayside 2 2009-09-16

Discovery of entry mechanism of cold dense magnetospheric plasma First dissection of a detached FTE Discoveries Dusk MP Sphere Sheath Sibeck et al., GRL, 2008 Discovery of entry mechanism of cold dense magnetospheric plasma Oieroset et al., GRL, 2008; Li et al., JGR 2008 Liu et al., GRL, 2008 First detection of remote signatures of FTE's

A comparison between the electric field and –Vi x B, observed by THEMIS during the current sheet thinning. Their remarkable disagreement indicates violation of the “frozen-in” condition (presented by J. McFadden et al.).

Substorm study on Feb 26, 2008 Substorm onset Auroral signature Probe locations

Other substorm signatures: Currents, Pulsations

Tail substorm signatures: Fields, Flows, Distributions V┴ V║ P1 P2 ions V┴ P1 P2 electrons V║ Electrons: Similar to Hoshino et al., 2001 Ions: Similar to Hoshino et al., 1998

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

TRx TAI TCD 3rd 1st 2nd 3rd 1st 2nd Timing on the ground and in space: electrons ions 3rd 1st 2nd

2nd 1st 3rd Inside out model Outside-In model 2nd 1st 3rd 3rd 2nd 1st Note: this is not the classical time sequence: Aurora brightens before near Earth dipolarization This holds true on several events considered (Gabrielse et al; 2008; Liu et al., 2008; Runov et al., 2008; Mende et al., 2008) Inside out model Outside-In model 2nd 1st 3rd 3rd 2nd 1st Reconnection Aurora Current Disruption 3rd 1st 2nd

Summary, Future Work and Implications On several events when THEMIS was well positioned, reconnection preceded substorm onset and current disruption. Need to understand generality of results (next winter) Are spontaneous and externally driven substorms different? Are very low latitude onsets (65o) different from these (67o-68o) On all events the aurora responded too quickly (~90s) for Alfven wave communication. Need to investigate coupling mechanism: Dispersive Alfven waves, whistlers or electrons can travel fast enough. IMPLICATIONS Spontaneous reconnection can be destabilized but how? Need to understand instability preconditioning, criterion, drivers Study how pre-substorm aurora maps to the tail How is growth phase aurora created How do field aligned currents distort mapping How does pre-substorm energy storage result in: Auroral intensification, Equatorward motion? Results may change our concepts of flux circulation, tail stability, MI coupling

Data availability http://themis.ssl.berkeley.edu