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| Titel |
Determining the axial direction of high-shear flux transfer events |
| VerfasserIn |
Robert Fear, Steve Milan, Kjellmar Oksavik, Arne Pedersen |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250052142
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| Zusammenfassung |
| Flux transfer events are bursts of dayside reconnection, which give rise to local perturbations
of the magnetic field which can be observed by spacecraft near the magnetopause. A key
difference between the original model proposed by Russell & Elphic (1978) to explain the
observed signatures, and subsequent models (Lee & Fu, 1985; Southwood et al.,
1988; Scholer, 1988) is that when the magnetic shear across the magnetopause is
close to 180°, the Russell & Elphic model will give rise to a structure whose axis is
oriented north-south, whereas the subsequent models will result in a dawn-dusk
oriented structure. Several techniques for determining the axial direction of such
structures have been suggested: minimum variance analysis on the magnetic field (e.g.
Kharbrov & Sonnerup, 1998; Xiao et al., 2004), minimisation of the axial electric
field (Sonnerup & Hasegawa, 2005), and Grad Shafnarov reconstruction (Hau &
Sonnerup, 1999; Sonnerup et al., 2004). We apply these techniques to a series of flux
transfer events observed by Cluster at a high-shear magnetopause crossing on 27th
March 2007 (an interval previously studied by Fear et al., 2010). Minimum variance
analysis on the signatures caused by the draping of unreconnected magnetic flux
around the flux transfer events consistently results in an axial direction which is
directed dawn-dusk. However, the electric field technique, applied to flux transfer
events which are penetrated by the spacecraft, results in a mixture of north-south and
dawn-dusk axes. Testing these axial directions with Grad Shafnarov reconstruction
suggests that the axes of events which appear to be oriented dawn-dusk might be
more reliably determined than the axes of events which appear to be north-south. |
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