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Onsets and Flapping Studied using a Dynamic Harris Sheet Model

Onsets and Flapping Studied using a Dynamic Harris Sheet Model. M. Connors 1 , R. Lerner 1 , G. Jaugey 2 , B. Lavraud 3 , M. Volwerk 4 , R. L. McPherron 5 1 Athabasca U., 2 U. Joseph Fourier, 3 LANL, 4 Österreichische Ak. Wissensch. , 5 UCLA.

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Onsets and Flapping Studied using a Dynamic Harris Sheet Model

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  1. Onsets and Flapping Studied using a Dynamic Harris Sheet Model M. Connors1, R. Lerner1, G. Jaugey2, B. Lavraud3, M. Volwerk4, R. L. McPherron5 1Athabasca U., 2U. Joseph Fourier, 3LANL, 4Österreichische Ak. Wissensch., 5UCLA STAMMS-2 Orleans, France September 2007 Image: Mikko Syrjäsuo

  2. Athabasca University Geophysical Observatory (AUGO) A comprehensive observatory in western Canada ideally located for THEMIS conjunctions (see poster) 54.72 N, 246.7 E CGM (2005) 62.0, 306.5 L=4.55 Founded 2002 (UCLA mag 1998)

  3. Plasma sheet - Harris model • Plasma sheet : hot plasma • n = 3 cm-3 • Eth ~ 4200 eV • B ~ 10 nT • β ~ 6 • z>0 => Bx>0 , z<0 => Bx<0 Bo • Harris model • Magnetic field : where By=Bz=0 and Bo = Blobes • Current density : derived from

  4. Method for Harris sheet fitting • The Levenberg-Marquardt nonlinear fitting method was used for BX(Z0,L,B0) during the slow traversal of Cluster through the plasma sheet • The Levenberg-Marquardt nonlinear fitting method was used for BX(Z0,L) with B0 held constant during flapping • Thompson et al. (2005 JGR) used a similar fitting technique

  5. Cluster Plasma sheet crossingSeptember 22th, 2001 • Plasma sheet crossing at ~ 5 UT • B reverse • low |B| • more energized particles • Harris form

  6. Harris fitAugust 3rd, 2003 Results • Bo = B(lobes) = 26.8 nT => realistic ( Theory ~30 nT ) • Zo = -1.64 Re => not centred (z axis) => movement of the plasma sheet in the Z direction => flapping • L = 0.63 Re => thickness of the plasma sheet Questions • Are the parameters related ? • What influences the parameters ? Bo Zo

  7. Flapping study • Flapping affects fits during slow passage of Cluster through plasma sheet BUT, Plasma sheet crossing is too long flapping are very fast => Good Harris study could come from flap fits • Harris flapping study : • fit again using Z separation of the spacecraft rather than the Z motion over time • Bo is known ( Harris crossing study) • Harris fit to find L, Zo • awaited results : L constant and Zo function of time flapping real crossing

  8. Flapping studyAugust 23rd , 2002 • Results • L ~ 0.89 Re • Zo is a function of time => Vz Zo(t) => velocity of the flapping Vz • Questions • Vz same as Cluster data ? • The current is Harris current ? • => Vz and J L ~ cst during flapping

  9. Flapping studyAugust 23rd , 2002 Jfit(blue) • Vz (cluster data) > Vz fit • 11 UT => +60 km.s-1 • Current fit realistic (compared to the data in black) • Vy ≈ or > Vz !! => First hypothesis (flap only in Z direction) false • our fit needs some changes !!

  10. Conclusions on Flapping • Our method for the fit gives good results for the plasma sheet thickness, the Zo evolution and also the current. • Nevertheless, our hypothesis of only Z motion of the plasma sheet is false. It’s moving also at least in the Y direction. • We are working to improve our fit assuming that the plasma sheet can be tilted yet planar (3-d Harris fit). • This approach would differ from least-variance methods

  11. Statistical Trends • 71 plasma sheet crossings in the public data set were fit • The only significant trend was of B0 vs P • L(B0) seemed to show the opposite behaviour than expected, thicker for higher lobe field • The lack of relationships is likely due to use of overly long time periods

  12. Pressure Variation • Beff is the lobe field as calculated from the measured B and particle data • Ptotal also arises from this and shows an influence on B0

  13. Pressure Statistics • The lobe field varies with solar wind pressure (ACE) • We did not find other strong dependencies on solar wind parameters

  14. August 21 2002 ca. 8 UT Canada Conjugacy Event

  15. Active Period with good conjugacy to Churchill meridian at onset at 7.9 UT

  16. Ground Pi2 also starts 7.9 UT (MCMU is to west)

  17. Cluster Pi2 starts at 8.1 UT

  18. Features of 21 Aug 2002 event • Plasmoid signature in Bz at onset time • Flow reversal from –X bursts to +X bursts indicating tailward motion of the X-line • Flapping after onset • Current enhancement at onset • Very clear activations of all signatures at onset

  19. B signatures: activation, flapping

  20. Plasmoid: bipolar BZ

  21. Flow direction changes as neutral line moves outward

  22. July 27 2003: Inference from Flapping • Unusual evening Ps6/omega band event recorded by magnetometer and THEMIS test camera at Athabasca • Cluster in morning sector; ground data sparse; spacecraft spacing very close • Multiple flappings where BX goes to 0 but not beyond

  23. Bifurcated Current Sheet? • Bx several times went to 0 but not beyond • Could bifurcated current sheet be related to Ps 6?

  24. Summary • Enhanced facilities in Canada benefit THEMIS and Cluster • 1-d Harris fit can be applied for PS crossing or for flapping • 3-d Harris fit may be needed and is being worked on • Conjugate studies can now be more frequent and with better data

  25. Acknowledgements • Canadian Space Agency and University of Alberta for CARISMA data • A. Balogh, ICSTM, for Cluster FGM data • This work funded by Canada Research Chairs, Canada Foundation for Innovation, AU, and NSERC

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