真夏の磁気圏界面磁束乗換現象 flux transfer events and solar wind energy entry at...

Download 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

Post on 10-Feb-2016

47 views

Category:

Documents

0 download

Embed Size (px)

DESCRIPTION

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. - PowerPoint PPT Presentation

TRANSCRIPT

  • Flux transfer events and solar wind energy entry at Earths magnetopauseHiroshi HasegawaISAS/JAXAContributers: the ISSI team, J. P. McFadden (SSL, UCB), & V. Angelopoulos (IGPP, UCLA)

    STP seminar on 19 May 2010

  • Active objects (emitter)Pulsars (spin period)Sun: solar wind( spin period ~13.5 day at Earth)Jupiter: radio wave, B induced in Europa, etc.(~spin period ~10-11 hours)

    Passive objects (receiver)Earths magnetosphere: semi-annual variation ( revolution period =0.5 year)Magnetic dipole tilt & periodic phenomenaFrom Wikipedia

  • 13.5-day period in the solar windMursula & Zieger (JGR, 1996)VSWTSWNSWKpDue to magnetic latitude dependence of the solar wind

  • Russell-McPherron effect at EarthMcPherron et al., 2009Semi-annual variation of geomagnetic activityRussell & McPherron, 1973

  • 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.Outline

  • XYZFlux Transfer Event (FTE) at magnetopauseBL: north-southBMBN|B|Bipolar BN & enhanced |B|.Believed to result from transient, localized, or multiple X-line reconnection, or their combination.Russell & Elphic, 1978

  • Models of FTE generationLocalized & transient reconnectionRussell & Elphic, 1978Transient but ~2D reconnectionScholer, 1988; Southwood et al., 1988Multiple X-line reconnectionLee & Fu, 1985; Sonnerup, 1987Little is known about the FTE generation processes and effects on magnetospheric phenomena.

  • Differences among FTE models: spatio-temporal properties of reconnectionKey factors to SW energy entry into the tail

    TemporalSpatialTopology changeRate (ERX), continuity, and/or duration of reconnection.Length (L) of X-line.Number of X-line (not all X-lines change magnetic topology!).

    Time-averaged B flux per unit length

    Time-averaged B flux integrated over the tail widthClosed to Open? (leading to transport and storage of B flux into the tail)

  • Raeder, AnnGeo, 2006FTE formation under large dipole tiltSequential Multiple X-line Reconnection: SMXR

  • 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.3. New X forms near the location of the old X formation, generating a flux rope between the two Xs.123

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

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

  • FTEs (some bipolar, some tripolar)A, B, C, D, ETHEMIS 2007-06-14 (10, 4, -2) Re in GSM

  • Evidence of FTE from MXR near solstice~BNTHEMIS data on 2007-06-14(10, 4, -2) Re in GSMNorthward then southward jetsFTE between the jets

  • 2D field map recovered from TH-C & -D dataGrad-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 normalSouth-east subsolar

  • B tensionCentrifugal forceReconnection northward of the FTEWaln relation(Sonnerup et al., 1987)Waln testNegative slopeconsistent with jet southward of X, where flows are anti-field-aligned in the HT frame.

  • Particle signatures of reconnection on both sides of the FTEPA ~0 deg ionPA ~180 deg ionPA ~0 deg elePA ~180 deg eleTHB on sheath side saw both || and anti-|| electron beams, indicating that field lines are reconnected on both south and north sides of the FTE.FTE

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

  • 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.Summary

  • 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.

  • In p.4 of Lui et al. (GRL, 2008):In p.6-7 of Lui et al. (JGR, 2008):Coordinate systemThis should be GSE.

  • Orientation of flux rope (z) axisA spurious magnetic island, resulting from incorrect choice of the flux rope axisOur result

  • Recovered structure is not in a magneto-hydrostatic equilibriumNo 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.

  • GSM comp. of the GS axesX = (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/sVHT*x = -137.2 km/sOur more reasonable result

  • TH-A ionPitch angle (PA) ~0 deg

    PA ~180 degEscaping Msp ions(SC north of X)

    electronPA ~0 deg

    PA ~180 degBi-dir ele(multiple X)Top: sheath ionsBottom: MSBL

  • 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 Earths 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.References:

  • Grad-Shafranov reconstruction technique (Hau & Sonnerup, 1999)(A spatial initial value problem)

    AssumptionsPlasma structures are: in magnetohydrostatic equilibria (time-independent). Pt, p, & Bz are functions of A only (constant on same field lines). 2-D (no spatial gradient in the z direction)Grad-Shafranov (GS) equation (e.g., Sturrock, 1994)Magnetic field tension balances with force from the gradient of total (magnetic + plasma) pressure.

  • XA 2D structureXYZ (invariant axis)Reconstruction procedureYReconstruction planeLx = VST_X* T (analyzed interval)

    X axis: sc trajectory in x-y planeVST_XSpatial integrationVST (VHT)(in the x-z plane)

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

Recommended

View more >