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Cluster Workshop 2009-05-13

Cluster Workshop 2009-05-13. Space and Plasma Physics School of Electrical Engineering Royal Institute of Technology Stockholm Sweden. Small-scale plasmoids in the magnetosheath and the solar wind Tomas Karlsson, Nils Brenning, Georgios Spanopoulos. Cluster Workshop 2009-05-13. Introduction.

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Cluster Workshop 2009-05-13

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  1. Cluster Workshop 2009-05-13 Space and Plasma PhysicsSchool of Electrical EngineeringRoyal Institute of TechnologyStockholmSweden Small-scale plasmoids in the magnetosheath and the solar windTomas Karlsson, Nils Brenning, Georgios Spanopoulos

  2. Cluster Workshop 2009-05-13 Introduction Reconnection Dominating process for transfer of energy and plasma Impulsive penetration Alternative/complementary model proposed by Lemair ca 1976 Lemair, 1991

  3. Cluster Workshop 2009-05-13 Introduction Recent observations by Lundin et al. have revealed localized regions of magnetosheath plasma inside the magnetosphere Lundin, 2003

  4. Cluster Workshop 2009-05-13 Impulsive penetrationGeometry of penetrating elements unclear Lemair, 1977 Lemair, 1991

  5. Cluster Workshop 2009-05-13 Penetration mechanisms Magnetic expulsion(followed by localized reconnection) Self-polarizationEp = - vx B Ma, 1991 Brenning, 2005

  6. Cluster Workshop 2009-05-13 Three possibilities [Brenning et al .2005] 100 SONG 1990 • B expulsion ∆B/B =100% • Polarization EP = -v0xB • Rejection BOUNDARY 1 FORBIDDEN REGION 10 MAGNETIC EXPULSION LINDBERG 1978 BOUNDARY 2 ISHIZUKA 1982 0.1 TRANSITION SELF POLA-RIZATION MISHIN 1986 0.01

  7. Cluster Workshop 2009-05-13 Methodology Instruments • EFW (S/C potential to get ne [Pedersen et al, 2001]) • CIS HIA (plasma bulk velocity) • FGM (magnetic field data)

  8. Cluster Workshop 2009-05-13 Calibration using WHISPER 021218, 030101, 030102, 030413 WHISPER ne (cm-3) C.f. Escoubet et al., 1997, Pedersen et al., 2001 Uprobe (V)

  9. Cluster Workshop 2009-05-13 Methodology Event selection • Main point is not to confuse plasmoids with double crossings of MP or BS • No appreciable change in drift velocity, in particular no sign changes • Keep to the ”middle” of the magetosheath • No ”nested structures” • Consider typical plasma density values: • MS ~ 10 cm-3 • SW ~ 5 cm-3 • MS (Lobe) < 1cm-3 • Other criteria • All events over thresholdne/nBG > 1.5(boxcar avergage with T = 3600 s)

  10. Cluster Workshop 2009-05-13 2002-12-23/24

  11. Cluster Workshop 2009-05-13 021223overview ne ne/ ne,BG |B| Bx By Density signatures associated with magnetic field variations Bz vx vy vz

  12. v Cluster Workshop 2009-05-13 Methodology Analysis of 3D structure – scale sizes • Order according to minimum variance analysis (MVA) •  x’, y’ ; • Planar = dn < 15 % • Move into plasma drift frame (HIA velocity) y’ x’ x’’ = x’ + vxt y’’ = y’ + vyt z’’ = z’ + vzt

  13. Cluster Workshop 2009-05-13 Methodology Analysis of 3D structure – scale sizes • Move into plasma drift frame (cont’d) ne(t) t (s) ne (x’’) x’’ (RE)

  14. Cluster Workshop 2009-05-13 B n2 (z) Distribution of angle between MVA normal and average magnetic field n3 (y) n1 (x) N (n1,B)

  15. Cluster Workshop 2009-05-13 Orientation: X-Y (GSE)

  16. ne(t) ne(x) Cluster Workshop 2009-05-13 Methodology Analysis of 3D structure – scale sizes • Get scale size along normal vector from MVA • Estimate scale sizes perpendicular to normal

  17. 2002-12-23 (36 040 s) Dx S/C 1 Dy Dz v Cluster Workshop 2009-05-13 Estimation of scale sizes • Along x-direction: width of half maximum of D ne • y and z: in effect only four measurement points

  18. Cluster Workshop 2009-05-13 Determination of scale sizes 1. Extrapolate 3. No signal on 1-3 S/C Use several different methods: ne ne Dz < S/C separation 5. Inconsistency ne z z w 2. Half width of single event 4. Cross correlation < thres. z ne ne Dz < S/C separation Dz > w Dz > Max(S/C separation,w) w z x

  19. Cluster Workshop 2009-05-13 2002-12-23 (39 315 s) z,B Method 1a t (s) ne(x) x (RE) y ne(y) y (RE) Method 5 Along B ne(z) x z (RE) 1a + 5 =

  20. Cluster Workshop 2009-05-13 2002-12-23 (36 740 s) Method 2

  21. Cluster Workshop 2009-05-13 Scale sizes: x-y ly (RE) ly = 10 lx ly = lx lx(RE)

  22. Cluster Workshop 2009-05-13 Scale sizes: x-z lz (RE) lz = 10 lx lz = lx lx(RE)

  23. Cluster Workshop 2009-05-13 Scale sizes: y-z lz (RE) lz = ly lx(RE)

  24. Cluster Workshop 2009-05-13 Penetration parameters 1.5 Expulsion Rejection Self-polarization

  25. Cluster Workshop 2009-05-13 Conclusions I • Plasmoids in MS often shaped like saucers or flattened flux tubes, with 0.1 RE < Dx < 14 RE • Plasmoids orientated after bow shock/MP • Parameters are such that magnetic expulsion will be likely mechanism for impulsive penetration, instead of self-polarization.

  26. DB Cluster Workshop 2009-05-13 Dia- or paramagnetic? 2003-05-01 2002-12-23 ne(cm-3) ne(cm-3) 500 s 500 s B (nT) B (nT) t (s) t (s)

  27. Cluster Workshop 2009-05-13 Dia- or paramagnetic? DB/B (%) lx(RE)

  28. ne (cm-3) ne (cm-3) ne (cm-3) ne (cm-3) B (nT) B (nT) B (nT) B (nT) Cluster Workshop 2009-05-13 Solar wind or magnetosheath? 700 s t (s) t (s) t (s) t (s)

  29. ne (cm-3) ne (cm-3) ne (cm-3) ne (cm-3) B (nT) B (nT) B (nT) B (nT) Cluster Workshop 2009-05-13 700 s SW MSh t t MSh SW t t

  30. Cluster Workshop 2009-05-13 Dia- or paramagnetic? Magnetosheath Solar wind DB/B (%) lx(RE)

  31. Cluster Workshop 2009-05-13 Dia- or paramagnetic? Magnetosheath Solar wind DB/B (%) Dt (s)

  32. Cluster Workshop 2009-05-13 Conclusions II • Smaller plasmoids – paramagnetic • Larger plasmoids – diamagnetic • Larger plasmoids found in the pristine solar wind. Compressed at bow shock? • Smaller plasmoids are leakage of compressional waves from foreshock?

  33. Thank you for your attention! Cluster Workshop 2009-05-13

  34. Cluster Workshop 2009-05-13 2002-12-23 (36 040 s) 1 2 3 4 Signature of diamagnetic behaviour

  35. x 1 2 3 4 z y x Cluster Workshop 2009-05-13 2002-12-23 (36 040 s) 1 2 3 4 EandDB 1 2 3 4

  36. x 1 2 3 4 z y x Cluster Workshop 2009-05-13 2002-12-23 (36 040 s) EandDB • Current sheets separate regions with different ne • Current may be electron Hall current? • Current sheet widths are of the order of 0.2 RE ≈ 2 rgi • (rgi≈ 800 km)

  37. Cluster Workshop 2009-05-13 2002-12-23 (36 040 s)

  38. Cluster Workshop 2009-05-13 2002-12-23 (36 040 s) • Increased density and temperature (large-scale) • Compensated by decrease in magnetic pressure (and perpendicular cooling at the highest densities?) • No electron data available (at present at least) • AW at the end of the pressure gradient. ne B T// T p, pB, pi , pi // AW?

  39. Cluster Workshop 2009-05-13 2002-12-23 (36 740 s) ne • Similar properties to prevoius case. • What will the electron temperature signature be? A cooling to keep the pressure constant??? • Or is this plasmoid expanding? B T// T p, pB, pi , pi //

  40. 10.00 10.10 10.20 10.30 10.40 10.50 Cluster Workshop 2009-05-13 2002-12-23 – Lion roars Data provided by Ondrej Santolik Signature of diamagnetic behaviour and self-polarization. • Lion roars are associated with anisotropies in electron distribution in magnetosheath. • ’Type A’ (30 % occurence rate) associated with dip in magnetic field (Zhang et al., 1998).

  41. Cluster Workshop 2009-05-13 2002-12-23 • The lion roars are there all the time (we are in MS!), but become more intense at plasmoids, and frequency decreases. • Direction of the Poynting flux varies from centre to edges. Can this effect the electron temperatures?

  42. Cluster Workshop 2009-05-13 Conclusions III • Excess thermal pressure balanced by diamagnetic effect. • Diamagnetic effect associated with thick current sheets at the plasmoid density gradients. • Plasmoids are associated with Type A lion roars. (Propagation direction varies with position in plasmoid)

  43. Thank you for your attention (again)! Cluster Workshop 2009-05-13

  44. Extra material

  45. Cluster Workshop 2009-05-13 B in MVA coordinates, corrected according to direction of B Bx (min. var. direction) By (~ max. var. direction) Bz (~ background B direction)

  46. Cluster Workshop 2009-05-13 Methodology Event selection ne ne(S/C 1) ne/ ne,BG ne/ ne,BG ne vx vy vz SW excursion MSph/MS excursion

  47. Cluster Workshop 2009-05-13 Methodology II. Event selection A magnetopause boundary wave could give a similar signature in density, but… vwave = vMS ?? v = const around the disturbance ??? nMsph < 1 cm-3 vMS vwave magnetosheath magnetosphere vMsph

  48. Cluster Workshop 2009-05-13 Calibration using WHISPER

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