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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 24, issue 12
Ann. Geophys., 24, 3421–3432, 2006
https://doi.org/10.5194/angeo-24-3421-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 24, 3421–3432, 2006
https://doi.org/10.5194/angeo-24-3421-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.

  21 Dec 2006

21 Dec 2006

Dayside aurorae and polar arcs under south-east IMF orientation

P. E. Sandholt1, M. Dyrland2, and C. J. Farrugia3 P. E. Sandholt et al.
  • 1Department of Physics, University of Oslo, Oslo, Norway
  • 2The University Centre in Svalbard, Longyearbyen, Norway
  • 3Space Science Center, University of New Hampshire, Durham, USA

Abstract. We document a characteristic spatial and temporal structure of the aurora in the postnoon sector present during a 10-h-long interval of very steady southeast IMF orientation (clock angle=135°) ending in a sharp south-to-north transition. Focus is placed on the detailed morphology of auroral forms/activities corresponding to merging and lobe convection cells obtained from SuperDARN convection data and Greenland magnetograms. The ground optical instruments at Ny Ålesund, Svalbard (76° MLAT) recorded different auroral forms/activities as the station moved to higher magnetic local times (MLTs) in the 13:00–17:00 MLT sector. Whereas the 13:00–15:00 MLT sector is characterized by classical poleward moving auroral forms (PMAFs) associated with merging cell transients, the aurora in the 15:00–17:00 MLT sector shows instead a characteristic latitudinal bifurcation consisting of standard oval forms and polar arcs, and a corresponding composite pattern of merging and lobe convection cells. The merging and lobe cells respond to the southward and northward IMF transitions by activation/fading and fading/activation, respectively. A sequence of brightening events is characterized by successive activations progressing in latitude from the merging cell regime to the lobe cell regime. Emphasis is placed on the association between polar arc brightenings and the activation of the channel of enhanced sunward flow in the lobe cell. The observations are discussed in relation to recent work on solar wind-magnetosphere-ionosphere interconnection topology.

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