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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.

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Presentation on theme: "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."— Presentation transcript:

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/design and Sergey Apatenkov for SCW modeling Mission overview, and the substorm problem Overview and event selection Event #1 2008-02-26 (reconnection onset) Other events (2008-02-16, 22: reconnection onset) Counter example: 2008-01-29 Substorm Picture Revis(it)ed Remaining questions THEMIS: Tail Reconnection triggering substorm onset

2 Joint Cluster-THEMIS SWT 2 Sep 23-26, 2008 Introduction: Definitions Substorms, the three main elements Current Disruption Auroral Eruption Reconnection X Y X Z X Y Courtesy: H. Frey Courtesy: Pulkkinen & Wiltberger

3 Joint Cluster-THEMIS SWT 3 Sep 23-26, 2008 The current disruption region: Ballooning Three plasma forces in equilibrium: –F Curvature +F Plasma +F Bfield =0 –Assume  V undulation –If  F p >  F C it grows –Plasma expelled –Linear instability criterion is: –0 <  C <  P (2+  )/4  C,  P,  B : inverse scale sizes  and  C low enough: »6<R<10 R E Mode stable in linear MHD regime… …but unstable in the non-linear (right), in the Hall-MHD and fully kinetic regimes FPFP FBFB FCFC JJ JJ JJ Earth Tail Roux et al., 1985 Horton et al., 2005

4 Joint Cluster-THEMIS SWT 4 Sep 23-26, 2008 InstabilityFrequencyWave numberFeatures BI << f ci kL px ~ 1, yz-planeVarious forms of BI CCI ~(0.01-0.1)f LH k  i ~ 1-10, yz-plane ions ^ heated; electrons || heated; jE < 0 occurs CDAI ~ (0.1-5)f ci kv A /f ci ~ 0.1-1, xz-plane || current disrupted to cause current disruption DKI/DSI ~ f ci k  i ~ 1, yz-plane Slow growth at realistic ion/electron mass ratio EADI << f ci kL px ~ 1, yz-planeFrom simulation KHI (0.1-2)v A /L cs kL cs ~ 1-15, yz-planeCan distort current sheet LHDI ~ f LH k  e ~ 1, yz-plane At current sheet boundary TI << f ci kL cs ~ 0.1-1, xz-planeElectron compression, slow growth WHERE: f ci = proton gyrofrequency; f LH = lower hybrid frequency L cs = current sheet thickness; L px = pressure gradient scale size  i = proton gyroradius; v A = Alfvén speed The current disruption region: A zoo of instabilities

5 Joint Cluster-THEMIS SWT 5 Sep 23-26, 2008 The reconnection (Rx) region The phenomenon Rapid release of magnetic energy into plasma energy –Performed by acceleration and heating of outflow plasma Rate depends on local Alfvén speed and outflow capability Proposed at the Sun and later in the magnetosphere Plasma resistivity alone is too low to explain fast onset, but… Petschek showed that shock formation around Rx line makes the rate insensitive to the value of the resistivity

6 Joint Cluster-THEMIS SWT 6 Sep 23-26, 2008 The reconnection (Rx) region … the phenomenon Reconnection rate depends on external flow coupling to whistler waves –Whistlers control reconnection rate as they mediate electron physics to ion outflow –Rate insensitive to simulation model as long as whistler mode is accounted for –Hall MHD is adequate for rate regardless of term is responsible for collisionless resistivity Electron skin depth: Ion skin depth: Electron beta: Electron inertia Hall term Electron pressure Alfvén waves Whistler waves Dispersive Alfvén waves Pritchett and Coroniti, 2001

7 Joint Cluster-THEMIS SWT 7 Sep 23-26, 2008 A simpler task: Distinguish Between Two Models for Substorm Onset Current Disruption: Implosion at 10R E Magnetic Reconnection: Explosion at 25R E

8 Joint Cluster-THEMIS SWT 8 Sep 23-26, 2008 THEMIS Mission elements Probe conjunctions along Sun-Earth line recur once per 4 days over North America. Ground based observatories completely cover North American sector; determine auroral breakup within 1-3s … … while THEMIS’s space-based probes determine onset of Current Disruption and Reconnection each within <10s. : Ground Based Observatory

9 Joint Cluster-THEMIS SWT 9 Sep 23-26, 2008 Mission overview Instrument I&T UCB Mission I&T UCB Encapsulation & launch BGS Operations UCB Probe instruments: ESA: ElectroStatic Analyzer (coIs: Carlson and McFadden) SST: Solid State Telescopes (coI: Larson) FGM: FluxGate Magnetometer (coIs: Glassmeier, Auster & Baumjohann) SCM: SearchCoil Magnetometer (coI: Roux) EFI: Electric Field Instrument (coI: Bonnell) Ground SST ESA EFIa EFIs FGM SCM T spin =3s Release D2925-10 @ CCAS

10 Joint Cluster-THEMIS SWT 10 Sep 23-26, 2008 Launch= 2007-02-17 2007-03-23 2007-06-03 2007-07-15 2007-08-30 2007-12-04 X GSE Y GSE TH-B TH-C TH-D TH-E TH-A P1 P2 P3 P4 P5 First 10 months Angelopoulos, 2008 Space Sci. Rev. Submitted

11 Joint Cluster-THEMIS SWT 11 Sep 23-26, 2008 Tail 1 2008-02-02 Dayside 1 2008-08-08 X GSE Y GSE TH-B TH-C TH-D TH-E TH-A P1 P2 P3 P4 P5 First year baseline orbit Angelopoulos, 2008 Space Sci. Rev. Submitted

12 Joint Cluster-THEMIS SWT 12 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

13 Joint Cluster-THEMIS SWT 13 Sep 23-26, 2008 Substorm study on Feb 26, 2008 Probe locations P2 P3 P4 P5 P1 2008-02-26 04:50UT x y

14 Joint Cluster-THEMIS SWT 14 Sep 23-26, 2008 First Event Second Event

15 Joint Cluster-THEMIS SWT 15 Sep 23-26, 2008 First EventSecond Event

16 Joint Cluster-THEMIS SWT 16 Sep 23-26, 2008 First Event Second Event Pi2 Signatures

17 Joint Cluster-THEMIS SWT 17 Sep 23-26, 2008 P1 (TH-B) P2 (TH-C) First Event P1

18 Joint Cluster-THEMIS SWT 18 Sep 23-26, 2008 Tail substorm signatures: Flows, Reconnection, Dipolarization Second Event

19 Joint Cluster-THEMIS SWT 19 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

20 Joint Cluster-THEMIS SWT 20 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

21 Joint Cluster-THEMIS SWT 21 Sep 23-26, 2008 Combined substorm signatures for the second event: AE, Pulsations, Aurora

22 Joint Cluster-THEMIS SWT 22 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:

23 Joint Cluster-THEMIS SWT 23 Sep 23-26, 2008 A different opinion: 2008-01-29 [Lui et al, 2008] P1 P2 P5 P3 P4 P1 P2 P5 P3 P4 Flows Velocity

24 Joint Cluster-THEMIS SWT 24 Sep 23-26, 2008 P1 (TH-B) Detail 2008-01-29 V z < 0 means Northward, Toward the neutral sheet Negative Bz implies tailward moving flux rope, near neutral sheet.

25 Joint Cluster-THEMIS SWT 25 Sep 23-26, 2008 2008-Feb-16 event Liu et al., 2008

26 Joint Cluster-THEMIS SWT 26 Sep 23-26, 2008 2008-Feb-22 event Gabrielse et al., 2008

27 Joint Cluster-THEMIS SWT 27 Sep 23-26, 2008 2008-Mar-01 event Runov et al., 2008

28 Joint Cluster-THEMIS SWT 28 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: Summary

29 Joint Cluster-THEMIS SWT 29 Sep 23-26, 2008 Caveats Caveats on Feb 26 event: 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 Caveat on all 1 st tail season events: There have been no events with 4 probes exactly at the neutral sheet –No simultaneous observations of reconnection outflows and current disruption Remedy: Second tail season –Reconfigured orbit to result in more neutral sheet encounters 2009 four-probe conjunctions: Nominal criteria: dzNS < 5 Re 63h+100h+93h=256h (comparable to 2008) Near neutral sheet:dzNS < 2 Re: 43h+ 95h+37h=175h Exactly at neutral sheet:dzNS < 1 Re: 30h+ 63h+10h=103h

30 Joint Cluster-THEMIS SWT 30 Sep 23-26, 2008 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?

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