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

• Active objects (emitter)– Pulsars (spin period)– 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)

Magnetic dipole tilt & periodic phenomenaFrom Wikipedia

13.5-day period in the solar wind

Mursula & Zieger (JGR, 1996)

VSW

TSW

NSW

Kp

Due to magnetic latitude dependence of the solar wind

Russell-McPherron effect at Earth

McPherron et al., 2009

Semi-annual variation of geomagnetic activity

Russell & McPherron, 1973

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.

XY

Z

Flux Transfer Event (FTE) at magnetopause

BL: north-south

BM

BN

|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, 1978

Transient but ~2D reconnectionScholer, 1988; Southwood et al., 1988

Multiple X-line reconnectionLee & Fu, 1985; Sonnerup, 1987

Little is known about the FTE generation processes and effects on magnetospheric phenomena.

Differences among FTE models: spatio-temporal properties of reconnection

Temporal Spatial Topology change

Rate (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 width

Closed to Open? (leading to transport and storage of B flux into the tail)

T

dtLtERX)(

T

dttERX)(

Key factors to SW energy entry into the tail

Raeder, AnnGeo, 2006

FTE formation under large dipole tilt

Sequential 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.

1

2 3

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

Russell & McPherron, 1973

Seasonal dependence of geomag activity

Less 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, E THEMIS 2007-06-14 (10, 4, -2) Re in GSM

Evidence of FTE from MXR near solstice

~BN

THEMIS data on 2007-06-14(10, 4, -2) Re in GSM

Northward then southward jets

FTE 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

~M

P n

orm

al

South-east ⇔ subsolar

0

)()(

BBVV

0

BVV HT

B tension

Centrifugal force

Reconnection northward of the FTE

Walén relation(Sonnerup et al., 1987)

Walén testNegative slope ： consistent with jet southward of X, where flows are anti-field-aligned in the HT frame.

Particle signatures of reconnection on both sides of the FTE

PA ~0 deg ion

PA ~180 deg ion

PA ~0 deg ele

PA ~180 deg ele

THB 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 model

• Multiple X-line reconnection near solstice.• Flux rope traveling into the winter hemisphere.• Subsolar X-line activated later than southward X.

South-east ⇔ subsolar

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.

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 system

This should be “GSE”.

Orientation of flux rope (z) axis

A spurious magnetic island, resulting from incorrect choice of the flux rope axis

Our result

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.

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/s

Our 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

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.

pBj

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

AssumptionsPlasma structures are: • in magnetohydrostatic equilibria (time-independent).

PBJVVt

V

)(× ×

)(002

2

2

2

AjAd

Pd

y

A

x

Az

t

),)(,,( ABxAyAB z

)2( 02 zt BpP

Pt, p, & Bz are functions of A only (constant on same field lines).

)( zAA

• 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.

X

A 2D structure

X

Y

Z (invariant axis)

Reconstruction procedure

YReconstruction plane

Lx = VST_X* T (analyzed interval)

X axis: sc trajectory in x-y plane

VST_X

Spatial integration

VST (VHT)(in the x-z

plane)

Spatial initial value problem (Sonnerup & Guo, 1996)

,)0,()0,(00

x

y

xdxxBxd

x

AxA tdxVxd HT ˆ

)( xABy

Grad-Shafranov equation

2

,

2

2

,

)(2

1),(),( y

y

Ay

y

AyxAyyxA

yxyx

yy

AyxBy

y

ByxByyxB

yx

x

yx

xxx

,

2

2

,

),(),(),(

Ad

Pd

x

A

y

A t02

2

2

2

spatial integration in y direction

))(,,( ABxAyAB z

(2nd order Taylor exp.)

(1st order Taylor exp.)

)(002

2

2

2

AjAd

Pd

y

A

x

Az

t

GS eq.