Walen and Slow-mode Shock Analyses Applied to High-Speed Flows of the Near-Earth Magnetotail

1
Walen and Slow-mode Shock Analyses Applied to
High-Speed Flows of the Near-Earth Magnetotail

• S. Eriksson1, C. Mouikis2, M. W. Dunlop3, M.
  Oieroset4,
• D. N. Baker1, C. Cully1, H. Reme5, and A. Balogh6
• 1 Laboratory for Atmospheric and Space Physics,
  University of Colorado, Boulder, USA
• 2 Space Science Center, University of New
  Hampshire, Durham, USA
• 3 Rutherford Appleton Laboratory, Chilton, UK
• 4 Space Sciences Laboratory, University of
  California, Berkeley, USA
• 5 Centre dEtude Spatiale des Rayonnements,
  Toulouse, France
• 6 Imperial College, London, UK

Contact information eriksson_at_lasp.colorado.edu
2
Outline

• Introduction
• Tail reconnection and slow-mode shocks
• deHoffmann-Teller and Walen analyses
• Slow-mode shock criteria
• Cluster observations
• 2001-08-27 from 0350 UT to 0435 UT
• 2001-09-15 from 0355 UT to 0520 UT
• 2002-08-21 from 0750 UT to 0840 UT
• 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 (SS)
  connected to the diffusion region.
• SS generated due to near-symmetric conditions
  (comparable plasma density and magnetic field
  strength) on either side of the current layer.
• 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 were first observed in the
  tail by e.g. Feldman et al. 1984, 1987 using
  the Rankine-Hugoniot (RH) jump conditions on ISEE
  2 data.
• Later confirmed by Geotail RH observations
  e.g. Saito et al., 1995 Seon et al., 1996 and
  by Wind data Oieroset et al., 2000 using the
  shear-stress balance test on Wind data 60 Re
  downtail.

5
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.

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Shear-Stress Balance (Walen) Test

• Disturbance generated by reconnection propagates
  away from the diffusion region at a field-aligned
  phase speed in the HT shock frame determined by
  the type and strength of the shock.

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Shear-Stress Balance (Walen) Test

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

• Earthward jet
• 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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Slow-mode Shock Criteria
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Cluster Observations on 2001-08-27
A
B
C
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Walen Analyses 2001-08-27
A Tailward flows in Northern Hemisphere
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Walen Analyses 2001-08-27
B Earthward flows in Northern Hemisphere
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Walen Analyses 2001-08-27
C Earthward flows in Northern Hemisphere
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Shock Analysis on 2001-08-27
A
B
C
A
C
16
Shock Normal Optimization 2001-08-27
17
Cluster Observations on 2001-09-15
A
B
C
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Walen Analyses 2001-09-15
A Tailward flows in Northern Hemisphere
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Walen Analyses 2001-09-15
B Tailward flows in Northern Hemisphere
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Walen Analyses 2001-09-15
C Tailward flows in Southern Hemisphere
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Shock Analysis on 2001-09-15
B
A
C
A
B
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Cluster Observations on 2002-08-21
A
B
C
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Walen Analyses 2002-08-21
A Tailward flows in Northern Hemisphere
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Walen Analyses 2002-08-21
B Tailward flows in Northern Hemisphere
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Walen Analyses 2002-08-21
C Tailward flows in Southern Hemisphere
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Shock Analysis on 2002-08-21
B
A
C
B
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Summary

• The Walen test together with the location of
  Cluster suggest the presence of slow-mode shocks
  on the tailward sides of near-Earth X-lines
  (Xgt-19 Re) for three events 2001-08-27,
  2001-09-15, 2002-08-21.
• Earthward jets seemingly fail the Walen test more
  readily than tailward jets.
• Joint Walen and RH analyses generally confirm the
  presence of slow-mode shocks during accelerated
  tailward flows. Based on three events and several
  jets.
• Shock-normal analyses suggest that magnetic
  coplanarity theorem results in a normal near the
  optimized (minimum RH deviations) direction.