NearEarth Magnetotail Reconnection and Plasmoid Formation in Connection With a Substorm Onset on 27

1
Near-Earth Magnetotail Reconnection and Plasmoid
Formation in Connection With a Substorm Onset on
27 August 2001

• S. Eriksson1, M. Oieroset2, D. N. Baker1, C.
  Mouikis3,
• M. W. Dunlop4, H. Reme5, R. E. Ergun1, and A.
  Balogh6
• 1 Laboratory for Atmospheric and Space Physics,
  University of Colorado at Boulder, USA
• 2 Space Sciences Laboratory, University of
  California at Berkeley, USA
• 3 Space Science Center, University of New
  Hampshire, USA
• 4 Rutherford Appleton Laboratory, UK
• 5 Centre dEtude Spatiale des Rayonnements,
  France
• 6 Imperial College, UK

Contact information eriksson_at_lasp.colorado.edu
2
Outline

• Introduction
• Tail reconnection and slow-mode shocks
• deHoffmann-Teller and Walen analyses
• Cluster observations and Walen analyses
• August 27 2001 from 0350 UT to 0435 UT
• (post-midnight event)
• Summary

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Tail Reconnection and Slow-mode Shocks
Hill, T.W., JGR, 80, 4689, 1975
Feldman et al., JGR, 92, 83, 1987

• Acceleration in tail reconnection is assumed to
  take place across a slow-mode shock connected to
  the diffusion region. Configuration essentially
  that of Petschek 1964 (above right).

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Tail Reconnection and Slow-mode Shocks
Hill, T.W., JGR, 80, 4689, 1975
Feldman et al., JGR, 92, 83, 1987

• Slow-mode shocks are defined in ideal MHD by an
  increased plasma pressure and a decreased B-field
  strength where the B-field bends toward the shock
  normal.

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Tail Reconnection and Slow-mode Shocks
Hill, T.W., JGR, 80, 4689, 1975
Feldman et al., JGR, 92, 83, 1987

• Slow-mode shocks were first observed in the
  tail by e.g. Feldman et al. 1984, 1987 using
  the Rankine-Hugoniot jump conditions. Also
  suggested by Oieroset et al. 2000 who
  successfully used the Walen analysis on Wind data
  60 Re downtail.

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deHoffmann-Teller Analysis
Khrabrov and Sonnerup, ISSI Sci.rep., 1998

• The existence of an HT frame indicates the
  presence of a quasi-stationary coherent pattern
  of magnetic field and plasma velocity. The HT
  interval should include data points on either
  side of the boundary.

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deHoffmann-Teller Analysis
Khrabrov and Sonnerup, ISSI Sci.rep., 1998

• A Galilean HT frame transformation allows for
  the identification and analysis of such coherent
  structures (e.g. slow-mode shocks) moving past an
  observing platform.

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Walen Analysis as a Test of Reconnection
(Not a slow shock since B does not bend toward
normal)

• Reconnection predicts that the generated
  rotational discontinuity (finite normal B-field
  component) propagates away from the diffusion
  region at a field-aligned phase speed in the HT
  shock frame and its magnitude is determined by
  the type and strength of the shock.

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Walen Analysis as a Test of Reconnection
(Not a slow shock since B does not bend toward
normal)

• The sign of the Walen slope depends on whether
  the B-field is parallel or antiparallel to the
  flow direction.

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Walen Analysis in the Magnetotail
Walen slope
Oieroset et al., JGR, 105, 25,247, 2000.

• Region I earthward jet, Bxgt0, RWlt0
• Region II tailward jet, Bxgt0, RWgt0

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Walen Analyses at Wind (x -60 Re)
Oieroset et al., JGR, 105, 25,247, 2000.

• Earthward jet interval
• Negative Bx
• Walen slope should be positive

Note that there is no ion composition in the Wind
data set and that these slopes were derived
assuming 100 H.
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Cluster Location August 27 2001
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Cluster Observations on August 27 2001
Density (CODIF)
Plasma b (CODIF)
A
B
C
Ion speed (HIA)
Vx, Vy, Vz
Bx, By, Bz
Magnetic field magnitude
Alfven Mach number Note MAlt1
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Cluster Observations on August 27 2001
Density (CODIF)
Plasma b (CODIF)
A
B
C
Ion speed (HIA)
Vx, Vy, Vz
Bx, By, Bz
Magnetic field magnitude
Approximate substorm onset in global UV images at
0406-0408 UT Baker et al., GRL, 2002
Alfven Mach number Note MAlt1
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Comparison with the Substorm of April 24 1979
Bx
Bx
sc1 sc3
Overview of ISEE 2 magnetic field (GSE) and
plasma data near substorm onset. H
ones et al.,1986 Feldman et al., 1987
By
By
Bz
Bz
Pp
beta
Vx
Vx
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Comparison with the Plasmoid of April 24 1979
Cluster magnetic field hodogram (GSM)
Three-dimensional magnetic field structure of
plasmoid at substorm onset from Hones et al.,
GRL, 1982.
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Walen Analyses on August 27 2001(A) Tailward
Region II Jets 0400-0403 UT
sc1

• Positive Bx
• Tailward jets
• Prediction
• Positive Region II
• Walen slope

sc3
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Walen Analyses on August 27 2001(B) Earthward
Region I Jets 0406-0410 UT

• Positive Bx
• Earthward jets
• Prediction
• Negative Region I
• Walen slope

sc1 0406-0408 UT
sc3 0409-0410 UT
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Walen Analyses on August 27 2001(C) Earthward
Region I Jets 0426-0428 UT
sc1

• Positive Bx
• Earthward jets
• Prediction
• Negative Region I
• Walen slope

sc3
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B
A
C
x black y green z red
Angle between V and B .
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Substorm of 27 August 2001
(A)
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Substorm of 27 August 2001
(B)
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Substorm of 27 August 2001
(B)
(C)
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Note on Importance of Density for the Walen Slope
A mix of 5 O ions and 95 H results in an
effective mass m1.75mp and a lower Alfven speed,
that effectively should increase the Walen slope
.
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Impact of mmp Assumption
O fraction 0.8 - 4.8 Avg O fraction
1.8 Walen slope0.73
Assume 100 H Walen slope0.65
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Summary

• The Walen test together with the location of
  Cluster north of the neutral sheet confirms the
  presence of a slow mode shock on the tailward
  side of the near-Earth X-line on August 27, 2001
  that most likely accelerated the ions.
• The Walen test for some earthward jets may
  indicate a correct slope (sign), although the
  quality of the HT frame is lower.
• The earthward jets seem to be more field-aligned
  which implies that ideal MHD (and thus the HT
  analysis) breaks down.
• The use of ion composition data from CODIF
  improved the Walen slope.