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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 26, issue 8
Ann. Geophys., 26, 2191–2202, 2008
https://doi.org/10.5194/angeo-26-2191-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 26, 2191–2202, 2008
https://doi.org/10.5194/angeo-26-2191-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

  04 Aug 2008

04 Aug 2008

Polar observations of ion/electron bursts at the pre-dawn polar cap boundary: evidence for internal reconnection of overdraped lobe flux

P. E. Sandholt1 and C. J. Farrugia2 P. E. Sandholt and C. J. Farrugia
  • 1Department of Physics, University of Oslo, Oslo, Norway
  • 2Space Science Center, University of New Hampshire, Durham

Abstract. Observations made by Polar of ion-electron bursts on the dawn side of the polar cap are presented. They occurred when conditions external to the magnetosphere corresponded to that of the sheath region of a magnetic cloud, which was characterized by very high densities/dynamic pressure and a magnetic field which was strong in all components and which was tilted antisunward (Bx<0) and northward (Bz>0) with its clock angle lying between 20 and 90° (By: 8–15 nT). A clear temporal development in the energy range spanned by the individual ion bursts (from 0.2–2 keV to 1–10 keV) was present. We relate this to a corresponding temporal evolution in the cloud sheath field and plasma. We analyze the solar wind-magnetosphere aspects of the observations using the concepts of (i) (i) overdraped lobe flux, (ii) Bx- and By-regulated sequential reconnections in opposite hemispheres (magnetopause and internal modes), and (iii) newly-closed magnetic flux. In particular, we find that the most energetic ion bursts (accompanied by bi-directionally streaming electrons at 1–10 keV and intense magnetosheath-origin fluxes) are located on newly closed field lines generated by internal reconnection occurring between overdraped lobe field lines and the closed geomagnetic field. This result corroborates a topology of lobe reconnection under conditions of dipole tilt and/or nonzero IMF Bx component advanced by Watanabe et al. (2006), which in our case is adapted to nonzero IMF By conditions.

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