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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 9
Ann. Geophys., 17, 1155–1165, 1999
https://doi.org/10.1007/s00585-999-1155-5
© European Geosciences Union 1999
Ann. Geophys., 17, 1155–1165, 1999
https://doi.org/10.1007/s00585-999-1155-5
© European Geosciences Union 1999

  30 Sep 1999

30 Sep 1999

The dynamic cusp aurora on 30 November 1997: response to southward turning of the IMF

P. E. Sandholt1, C. J. Farrugia2, and B. Lybekk3 P. E. Sandholt et al.
  • 1Department of Physics, University of Oslo, Oslo, Norway
  • 2Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, NH, USA
  • 3Department of Physics, University of Oslo, Oslo, Norway

Abstract. We document the detailed dynamics of the dayside aurora in the \sim1200-1600 MLT sector in response to a sharp southward turning of the interplanetary magnetic field (IMF) under negative IMF By conditions. Features not documented in previous work are elucidated by using two meridan scanning photometers (separated by 2 h) and an all-sky auroral imager in Ny Ålesund, Svalbard (75.5°MLAT) in combination with magnetograms from stations on Svalbard, covering the latitude range 71°75°MLAT. The initial auroral response may be divided into three phases consisting of: (1) intensification of both the red (630.0 nm) and green (557.7 nm) line emissions in the cusp aurora near 1200 MLT and ~100 km equatorward shift of its equatorward boundary, at ~75°MLAT, (2) eastward and poleward expansions of the cusp aurora, reaching the 1430 MLT meridian after 5-6 min, and (3) east-west expansion of the higher-latitude aurora (at ~77°78°MLAT) in the postnoon sector. The associated magnetic disturbance is characterized by an initial positive deflection of the X-component at stations located 100-400 km south of the aurora, corresponding to enhanced Sunward return flow associated with the merging convection cell in the post-noon sector. The sequence of partly overlapping poleward moving auroral forms (PMAFs) during the first 15 min, accompanied by corresponding pulsations in the convection current, was followed by a strong westward contraction of the cusp aurora when the ground magnetograms indicated a temporary return to the pre-onset level. These observations are discussed in relation to the Cowley-Lockwood model of ionospheric response to pulsed magnetopause reconnection.

Key words. Mangetospheric physics (magnetopause · cusp and boundary layers; solar wind-magnetosphere interactions; auroral phenomena)

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