The influence of solar wind parameters on pseudobreakups, substorms and polar auroral arcs

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The influence of solar wind parameters on
pseudobreakups, substorms and polar auroral arcs

• Anita Kullen

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Content

• Polar auroral arcs
• Dependence on solar wind parameters
• Different polar arc types
• Polar arc models
• Substorms and pseudobreakups
• Dependence on solar wind parameters
• The place of pseudobreakups in a substorm cycle
• Different pseudobreakup types
• Summary

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Method

• Polar UV images and ACE data are taken from three
  winter months in 1998/99.
• All polar arcs, pseudobreakups and substorms are
  selected that appear on Polar UV images.
• Solar wind parameters for each type of auroral
  phenomenon are analyzed statistically.

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All substorms of one month overlaid on ACE solar
wind data
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All pseudobreakups of one month overlaid on ACE
solar wind data
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All polar arcs of one month overlaid on ACE solar
wind data
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Occurrence frequency
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Polar auroral arcs

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The dependence of polar arcs on different solar
wind parameters
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The dependence of polar arcs on the anti-epsilon
parameter
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Results

• Large-scale polar arcs occur preferably during
  northward IMF Bz and high solar wind energy flux.
  This relation can be expressed with the
  anti-epsilon parameter

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Classification into different polar arc types
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The IMF By dependent motion of polar arcs
(Valladares et al., 1994)

• Static polar arcs (oval-aligned, midnight arcs)
  appear on the dawn side for dawnward IMF and on
  the duskside for duskward IMF.
• Polewardly moving arcs (moving, bending arcs)
  move from dusk to dawn for dawnward IMF and from
  dawn to dusk for duskward IMF.

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The dependence of different polar arc types on
the IMF clock angle

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The dependence of different polar arc types on
IMF changes
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Results

• Oval-aligned arcs occur during constant IMF.
• Moving arcs occur after an IMF By sign change.
• Bending arcs occur after an IMF Bz sign change.
• Midnight and multiple arcs occur during varying
  IMF.

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Polar arc models

• The tail is twisted when an oval-aligned arc
  appears.
• The tail changes its twist when a moving arc
  appears.
• A tailward moving plasma sheet tounge is
  connected to a midnight arc.

(Makita et al., 1991)
(Kullen, 1999, Kullen and Janhunen, 2004)
(Rezhenov, 1995)
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Substorms and pseudobreakups

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Classification into different substorm types

• Pseudobreakups onset without expansion
• The substorm size is estimated from the location
  of the equatorward oval boundary at 0 MLT.
• Small-oval substorms gt 63 CGlat
• Medium-oval substorms 60-63 CGlat
• Large-oval substorms lt 60 CGlat

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The dependence of pseudo- breakups and substorms
on different solar wind parameters
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The dependence of pseudo- breakups and substorms
on IMF Bz
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The dependence of pseudobreakups and substorms on
epsilon and AE index
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Results

• Results from other studies
• (Sergeev et a., 1986 Koskinen et al., 1993
  Nakamura et al., 1994 etc.)
• Pseudobreakups have the same ionospheric and
  magnetospheric signatures as substorm breakup.
• Results from this study
• There is a systematic shift of all solar wind
  parameters from low values for pseudobreakups to
  increasingly higher values for substorms of
  increasing strength.
• Conclusion
• Pseudobreakups are the weakest type of
  substorms, appearing when there is a very low
  energy transfer into the magnetosphere.

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All pseudobreakups overlaid on AE index data
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Results

• Pseudobreakups appear during quiet times, during
  substorm growth phase or during substorm
  recovery.
• Pseudobreakups do not appear in large substorm
  cycles

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Classification into different pseudobreakup types

• Single pseudobreakups
• Growth phase pseudobreakups
• onset within 30 minutes before substorm onset
• Recovery phase pseudobreakups
• onset when substorm recovery signatures are
  still visible

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The dependence of different pseudobreakup types
on IMF signs
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The dependence of different pseudobreakup types
on epsilon and AE index
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Results

• Single pseudobreakups
• appear during quiet times. They do not differ
  much from very weak substorms.
• Growth phase pseudobreakups
• appear after an IMF southturn, just before weak
  substorms.
• Recovery phase pseudobreakups
• appear after IMF northturn triggered substorms,
  much poleward of the main oval. They may in fact
  be some kind of poleward auroral intensification.

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Summary

• Substorms need less solar wind energy than polar
  arcs due to the better energy transfer during
  southward IMF.