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Influence of Solar Wind Parameters on Polar Auroral Arcs

This study analyzes the dependence of polar auroral arcs on solar wind parameters and the different types of polar arcs. It also examines the influence of solar wind parameters on substorms and pseudobreakups, and classifies the different types of pseudobreakups based on their onset and occurrence. The results show the relationship between solar wind parameters and the occurrence and characteristics of polar arcs, substorms, and pseudobreakups.

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Influence of Solar Wind Parameters on Polar Auroral Arcs

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  1. The influence of solar wind parameters on pseudobreakups, substorms and polar auroral arcs Anita Kullen

  2. 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

  3. 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.

  4. All substorms of one month overlaid on ACE solar wind data

  5. All pseudobreakups of one month overlaid on ACE solar wind data

  6. All polar arcs of one month overlaid on ACE solar wind data

  7. Occurrence frequency

  8. Polar auroral arcs

  9. The dependence of polar arcs on different solar wind parameters

  10. The dependence of polar arcs on the anti-epsilon parameter

  11. 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:

  12. Classification into different polar arc types

  13. 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.

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

  15. The dependence of different polar arc types on IMF changes

  16. 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.

  17. 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)

  18. Substorms and pseudobreakups

  19. 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: > 63 CGlat • Medium-oval substorms: 60-63 CGlat • Large-oval substorms: < 60 CGlat

  20. The dependence of pseudo- breakups and substorms on different solar wind parameters

  21. The dependence of pseudo- breakups and substorms on IMF Bz

  22. The dependence of pseudobreakups and substorms on epsilon and AE index

  23. 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.

  24. All pseudobreakups overlaid on AE index data

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

  26. 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

  27. The dependence of different pseudobreakup types on IMF signs

  28. The dependence of different pseudobreakup types on epsilon and AE index

  29. 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.

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

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