Transcript Evolution of Dayside Magnetopause Reconnection Exhaust Regions and FTE Genesis: THEMIS Observations S. Eriksson1, J.T.

Evolution of Dayside
Magnetopause Reconnection
Exhaust Regions and FTE
Genesis: THEMIS Observations
S. Eriksson1, J.T. Gosling1, V. Angelopoulos2,
J.P. McFadden2, K.-H. Glassmeier3, A. Roux4,
H.-U. Auster3, O. le Contel4, and R.E. Ergun1
1LASP,
University of Colorado, Boulder, CO, USA
2SSL, University of California, Berkeley, CA, USA
3IGEP, Technische Universitat, Braunschweig, Germany
4CETP, Velizy, France
Contact: [email protected]
Cluster
Geotail
Cluster
TC1
Themis
Themis
Geotail
TC1
acknowledgment: ISAS/JAXA “Conjunction Event Finder” http://www.darts.isas.jaxa.jp/stp/cef/cef.cgi
2130-2330 UT
Solar wind context:
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.
Walen relation satisfied at TH-B and TH-C
TH-B
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]
FTE motion
Apparent s/c trajectories
in FTE rest frame
BGEO
BIMF
BIMF
ZGSM
YGSM
[VIEW FROM SUN]
FTE motion
Apparent s/c trajectories
in FTE rest frame
BGEO
BIMF
BIMF
ZGSM
YGSM
[VIEW FROM ABOVE]
YGSM
XGSM
BGEO
BIMF
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).
magnetosheath
[acknowledment: L. Andersson]
NMP
magnetosphere
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 TH-D,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 TH-C,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 TH-C,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.