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真夏の磁気圏界面磁束乗換現象 Flux transfer events and solar wind energy entry at Earth’s magnetopause

真夏の磁気圏界面磁束乗換現象 Flux transfer events and solar wind energy entry at Earth’s magnetopause. Hiroshi Hasegawa 　（長谷川　洋） ISAS/JAXA Contributers: the ISSI team, J. P. McFadden (SSL, UCB), & V. Angelopoulos (IGPP, UCLA) STP seminar on 19 May 2010. Magnetic dipole tilt & periodic phenomena.

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真夏の磁気圏界面磁束乗換現象 Flux transfer events and solar wind energy entry at Earth’s magnetopause

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  1. 真夏の磁気圏界面磁束乗換現象Flux transfer events and solar wind energy entry at Earth’s magnetopause Hiroshi Hasegawa　（長谷川　洋） ISAS/JAXA Contributers: the ISSI team, J. P. McFadden (SSL, UCB), & V. Angelopoulos (IGPP, UCLA) STP seminar on 19 May 2010

  2. Magnetic dipole tilt & periodic phenomena From Wikipedia • Active objects (emitter) • Pulsars (spinperiod) • Sun: solar wind (½ spin period ~13.5 day at Earth) • Jupiter: radio wave, B induced in Europa,etc. (~spin period ~10-11 hours) • Passive objects (receiver) • Earth’s magnetosphere: semi-annual variation (½ revolution period =0.5 year)

  3. 13.5-day period in the solar wind VSW TSW NSW Kp Mursula & Zieger (JGR, 1996) Due to magnetic latitude dependence of the solar wind

  4. Russell-McPherron effect at Earth Russell & McPherron, 1973 Semi-annual variation of geomagnetic activity McPherron et al., 2009

  5. Outline • Relationship between models of flux transfer events (FTEs) and solar wind energy entry. • Possible role of an FTE generation process (multiple X-line reconnection) in the semi-annual variation of geomagnetic activity. • Evidence for FTEs resulting from multiple X-line reconnection: THEMIS observations.

  6. Flux Transfer Event (FTE) at magnetopause Russell & Elphic, 1978 BL: north-south BM BN |B| Z • Bipolar BN & enhanced |B|. • Believed to result from transient, localized, or multiple X-line reconnection, or their combination. Y X

  7. Models of FTE generation Localized & transient reconnection Russell & Elphic, 1978 Little is known about the FTE generation processes and effects on magnetospheric phenomena. Transient but ~2D reconnection Scholer, 1988; Southwood et al., 1988 Multiple X-line reconnection Lee & Fu, 1985; Sonnerup, 1987

  8. Differences among FTE models: spatio-temporal propertiesof reconnection Key factors to SW energy entry into the tail

  9. FTE formation under large dipole tilt Sequential Multiple X-line Reconnection: SMXR Raeder, AnnGeo, 2006

  10. 1 In the SMXR model,1. Initial X forms between the subsolar point and B equator.2. It moves into the winter hemisphere, and becomes inactive. 2 3 3. New X forms near the location of the old X formation, generating a flux rope between the two Xs.

  11. Without dipole tilt, continuous topology change from closed to open can occur.Efficient energy entry With dipole tilt, new X-line first has to consume already open field lines to reconnect closed field lines.Less efficient energy entry

  12. Seasonal dependence of geomag activity Russell & McPherron, 1973 Less efficient energy entry from SMXR may explain part of the lower geomag activity for larger dipole tilt.

  13. A, B, C, D, E THEMIS 2007-06-14 (10, 4, -2) Re in GSM FTEs (some bipolar, some tripolar)

  14. Evidence of FTE from MXR near solstice THEMIS data on 2007-06-14(10, 4, -2) Re in GSM Northward then southward jets FTE between the jets ~BN

  15. 2D field map recovered from TH-C & -D data Grad-Shafranov reconstruction (Hau & Sonnerup, 1999; Hasegawa et al., 2005)- Flux rope moving southward: VHT=(-46, 11, -103) km/sbetween the two jets- Elongation along N- Enhanced Bz & pconsistent with compression by the two converging jets ~MP normal South-east ⇔ subsolar

  16. Reconnection northward of the FTE Walén test Negative slope：consistent with jet southward of X, where flows are anti-field-aligned in the HT frame. Centrifugal force B tension Walén relation (Sonnerup et al., 1987)

  17. Particle signaturesof reconnection on both sides of the FTE THBon sheath side saw both || and anti-|| electron beams, indicating that field lines are reconnected on both south and north sides of the FTE. PA ~0 deg ion PA ~180 deg ion PA ~0 deg ele PA ~180 deg ele FTE

  18. The FTE is consistent with SMXR model South-east ⇔ subsolar • Multiple X-line reconnection near solstice. • Flux rope traveling into the winter hemisphere. • Subsolar X-lineactivated later than southward X.

  19. Summary • Relationship between models of flux transfer events (FTEs) and solar wind energy entry. • Possible role of an FTE generation process (multiple X-line reconnection) in the semi-annual variation of geomagnetic activity. • Evidence for FTEs resulting from multiple X-line reconnection: THEMIS observations near solstice.

  20. An addition: correct interpretation ofLui et al. (JGR, 2008) Three serious mistakes: • The coordinate system is wrong. • The chosen flux rope orientation is not optimal. • Magneto-hydrostatic force balance is not at all satisfied in their composite map.

  21. Coordinate system In p.4 of Lui et al. (GRL, 2008): In p.6-7 of Lui et al. (JGR, 2008): This should be “GSE”.

  22. Orientation of flux rope (z) axis A spurious magnetic island, resulting from incorrect choice of the flux rope axis Our result

  23. Recovered structure is not in a magneto-hydrostatic equilibrium No sufficient pressure gradient to balance the spurious kink (tension) of the field lines. If the map was right, the GS method could not and should not be used.

  24. Our more reasonable result GSM comp. of the GS axes X = (0.3991, -0.8363, 0.3758) Y = (0.7389, 0.5361, 0.4082) Z = (-0.5428, 0.1148, 0.8320) VHT = (-102.8, 124.9, 22.1) km/s VHT*x = -137.2 km/s

  25. TH-A ion Pitch angle (PA) ~0 deg PA ~180 deg Escaping Msp ions (SC north of X) electron PA ~0 deg PA ~180 deg Bi-dir ele (multiple X) Top: sheath ions Bottom: MSBL

  26. References: • Hasegawa, H., et al. (2005), Optimal reconstruction of magnetopause structures from Cluster data, Ann. Geophys., 23, 973-982. • Hau, L.-N., and B. U. O. Sonnerup (1999), Two-dimensional coherent structures in the magnetopause: Recovery of static equilibria from single-spacecraft data, JGR, 104, 6899-6917. • Lee, L. C., and Z. F. Fu (1985), A theory of magnetic flux transfer at the Earth’s magnetopause, GRL, 12, 105-108. • Lui, A. T. Y., et al. (2008), Reconstruction of a magnetic flux rope from THEMIS observations, Geophys. Res. Lett., 35, L17S05, doi:10.1029/2007GL032933. • Lui, A. T. Y., et al. (2008), Reconstruction of a flux transfer event based on observations from five THEMIS satellites, J. Geophys. Res., 113, A00C01, doi:10.1029/2008JA013189. • McPherron, R. L., et al. (2009), Role of the Russell-McPherron effect in the acceleration of relativistic electrons, JASTP, 71, 1032-1044. • Mursula, K., and B. Zieger (1996), The 13.5-day periodicity in the Sun, solar wind, and geomagnetic activity: The last three solar cycles, J. Geophys. Res., 101(A12), 27,077-27,090. • Raeder, J. (2006), Flux Transfer Events: 1. generation mechanism for strong southward IMF, Ann. Geophys., 24, 381-392. • Russell, C. T., and R. L. McPherron (1973), The magnetotail and substorms, Space Sci. Rev., 15, 205-266. • Russell, C. T., and R. C. Elphic (1978), Initial ISEE magnetometer results: magnetopause observations, Space Sci. Rev., 22, 681-715. • Scholer, M. (1988), Magnetic flux transfer at the magnetopause based on single X-line bursty reconnection, Geophys. Res. Lett., 15, 291-245. • Sonnerup, B. U. O. (1987), On the stress balance in flux transfer events, JGR, 92(A8), 8613-8620. • Sonnerup, B. U. O., et al. (1987), Magnetopause properties from AMPTE/IRM observations of the convection electric field: Method development, J. Geophys. Res., 92, 12,137-12,159. • Southwood, D. J., et al. (1988), What are flux transfer events?, Planet. Space Sci., 36, 503-508.

  27. × × Grad-Shafranov reconstruction technique (Hau & Sonnerup, 1999) (A spatial initial value problem) Assumptions Plasma structures are: •in magnetohydrostatic equilibria (time-independent). Magnetic field tension balances with force from the gradient of total (magnetic + plasma) pressure. •2-D (no spatial gradient in the z direction) Grad-Shafranov (GS) equation(e.g., Sturrock, 1994) Pt, p, &Bzare functions ofAonly (constant on same field lines).

  28. Reconstruction procedure A 2D structure Reconstruction plane Y Spatial integration Y VST_X X X VST(VHT) (in the x-z plane) Lx = VST_X* T (analyzed interval) X axis: sc trajectory in x-y plane Z (invariant axis)

  29. Spatial initial value problem (Sonnerup & Guo, 1996) Grad-Shafranov equation spatial integration in -/+y direction (2nd order Taylor exp.) (1st order Taylor exp.) GS eq.

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