S. Eriksson 1 , J.T. Gosling 1 , V. Angelopoulos 2 ,
J.P. McFadden 2 , K.-H. Glassmeier 3 , A. Roux 4 ,
H.-U. Auster 3 , O. le Contel 4 , and R.E. Ergun 1
1 LASP, University of Colorado, Boulder, CO, USA
2 SSL, University of California, Berkeley, CA, USA
3 IGEP, Technische Universitat, Braunschweig, Germany
4 CETP, Velizy, France
Contact : eriksson@lasp.colorado.edu

TC1
Cluster
Themis
Geotail
Themis
TC1
Cluster
Geotail acknowledgment: ISAS/JAXA “Conjunction Event Finder” http://www.darts.isas.jaxa.jp/stp/cef/cef.cgi

2130-2330 UT

08 June 2007 2100-0000 UT
ACE solar wind data shifted to match
TH-B clock angle. Wind shifted to match ACE (Bx, By, |B|).
Rw=(257.5, 50.6, 22.7) Re (GSE)
Ra=(233.9, -40.4, 10.3) Re (GSE) dR=95 Re
Steady solar wind speed and IMF conditions.
Gradual dynamic pressure increase
(1 to 1.5 nPa) at TH-B magnetopause transition.

MP B
D
C
E
A

MP

MP

Cluster 3 obs. (31 January 2001) of low-energy 10-100 eV dispersed cold ionospheric ions due to magnetopause motion electric field. Adiabatic H+ acceleration and deceleration [Sauvaud et al., AG, 2001].
Themis observed very similar signatures as the FTEs passed the s/c and the same process was likely responsible for the ion dispersion. However,
Sauvaud et al. [2001] did not infer relative FTE motion, rather magnetopause boundary crossings.

TH-B
Walen relation satisfied at TH-B and TH-C
TH-C

Nakamura and Scholer [2000] hybrid simulation of dayside reconnection (guide field By>0).
Expanding bulge assumed to be the signature of FTE.
Hall fields appear at magnetosheathside current sheet (red circle).
A similar Hall field is observed at
Themis, but for northward jet (not southward as in simulation). Likely due to opposite IMF By.

Hodogram in agreement with
Hall field as simulated by
Nakamura and Scholer [2000]

Some of the first observations of accelerated plasma due to reconnection.
ISEE-1 (top) and ISEE-2 (bottom).
[Sonnerup et al., 1981]
THEMIS speed observations are very similar on 8 June 2007 with the addition of FTEs.

Predicted proton distributions just inside (left) and outside the magnetopause (right).
Cowley, Rev.Geophys., 1982

Russell and Elphic [1979] famous observations of FTEs (ISEE-1 and ISEE-2).
Very similar to THEMIS FTEs on 8 June 2007. However, four THEMIS probes on either side of magnetopause provides new context for relation of FTEs to
“quasi-steady” reconnection region.

[VIEW FROM SUN]
B
IMF
B
GEO
FTE motion
Apparent s/c trajectories in FTE rest frame
B
IMF
Z
GSM
Y
GSM

[VIEW FROM SUN]
B
IMF
B
GEO
FTE motion
Apparent s/c trajectories in FTE rest frame
B
IMF
Z
GSM
Y
GSM

[VIEW FROM ABOVE]
B
IMF
B
GEO
Apparent inward motion of two
FTE branches in s/c rest frame as the entire flux tube is brought northward to explain opposite
BN polarity (if not a relocation of X-line northward of s/c).
[acknowledment: L. Andersson] magnetosphere magnetosheath
N
MP
Y
GSM
X
GSM

Summary/Conclusions:
• Four THEMIS probes ( B , D , C , E ) transition the postnoon subsolar magnetopause in a pearl-on-string configuration on 8 June 2007 2130-2330 UT when the
IMF was southward and IMF By<0. TH-A was earthward of the magnetopause. Cowley [1982] predicts positive then negative bipolar BN for FTEs for these IMF conditions.
• When TH-B observed northward reconnection jets and an FTE within this reconnection layer, then THD , C , E
~simultaneously observed the FTE inside the magnetosphere in agreement with Cowley [1982] bipolar prediction. Field strength decreases away from TH-B suggesting TH-B closest to FTE and that FTE was generated inside the boundary layer.

Summary/Conclusions:
• When TH-D transitioned the magnetopause, it too observed an FTE in the magnetopause boundary layer that was observed in the magnetosheath by TH-B and inside the magnetosphere by THC , E . All four probes observed the positive-then-negative bipolar BN in agreement with Cowley [1982]. The strongest field strength was observed at TH-D with decreasing intensity away from TH-D suggesting this FTE, too, was generated within the boundary layer.
• TH-C then transitioned a highly laminar reconnection exhaust with no clear FTEs being observed there. No
FTE was observed at the other probes either.

Summary/Conclusions:
• TH-E entered the boundary layer less than 5 min after
TH-C left it. It did not observe a laminar field configuration as observed by TH-C . However, unlike the
TH-C crossing, TH-E did observe a strong FTE that was observed in the magnetosheath by THC , D . TH-B may have observed the very edge of its compression region.
• Unlike all other FTEs during this 2 hour period, the bipolar BN sequence related to the last TH-E magnetopause crossing seemed negative-then-positive with a southward plasma flow deflection suggesting a southern hemisphere connectedness (and an X-line above Themis)….

Summary/Conclusions:
• ….however, the magnetosheath conditions were steady.
An apparent inward FTE motion of both branches as
FTE approaches in a northward direction is consistent with opposite bipolar sequence on either side of the magnetopause.
• The axial FTE field appeared to be predominantly in the
BM-direction when the FTE was observed within the boundary layer whereas dominated by the BL-direction when observed away from the magnetopause.

Summary/Conclusions:
• The laminar TH-C magnetopause exhaust and its magnetic field configuration is quite reminiscent of socalled bifurcated current sheets bounding solar wind reconnection exhausts [e.g., Gosling et al., 2005]. Two well-defined current sheets was observed by TH-C [see
Nakamura and Scholer, 2000].
• Hall field observed by, e.g., TH-C at this outer current sheet of the bifurcated current sheets in agreement with
Nakamura and Scholer [2000].

Summary/Conclusions:
• The SCM power in the 48 Hz band showed a nearperfect correlation with reconnection exhausts at TH-B and TH-C . The same 48 Hz band enhancement was observed at TH-D and TH-E when they crossed the magnetopause boundary layer, suggesting that the subsolar reconnection site was active throughout the
2200-2335 UT period, despite the FTE observations.
• The 48 Hz band activity may be related to lower hybrid drift instability [e.g., Gary and Eastman, 1979; Cowley,
1982] which may be important for the generation of the magnetopause boundary layer formation.

Summary/Conclusions:
• The low-energy ion dispersion signatures observed in the magnetosphere at the time of the FTEs are very reminiscent of local ion acceleration caused by the passing FTE [e.g., Gosling et al., 1990; Sauvaud et al.,
2001].
• These THEMIS observations clearly connect the FTE genesis with the magnetopause boundary layer. A structured exhaust configuration was observed when the
FTE was observed as opposed to the laminar TH-C event. What came first (FTE or structured exhaust) remains to be determined.