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
~MP
nor
mal
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) axisA 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).
PBJVVtV
)(× ×
)(002
2
2
2
AjAdPd
yA
xA
zt
),)(,,( 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
xAxA tdxVxd HT ˆ
)( xABy
Grad-Shafranov equation
2
,2
2
,
)(21),(),( y
yAy
yAyxAyyxA
yxyx
yyAyxBy
yByxByyxB
yxx
yx
xxx
,
2
2
,
),(),(),(
AdPd
xA
yA t
02
2
2
2
spatial integration in y direction
))(,,( ABxAyAB z
(2nd order Taylor exp.)
(1st order Taylor exp.)
)(002
2
2
2
AjAdPd
yA
xA
zt
GS eq.
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