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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 8
Ann. Geophys., 17, 996–1011, 1999
https://doi.org/10.1007/s00585-999-0996-2
© European Geosciences Union 1999
Ann. Geophys., 17, 996–1011, 1999
https://doi.org/10.1007/s00585-999-0996-2
© European Geosciences Union 1999

  31 Aug 1999

31 Aug 1999

Reconfiguration and closure of lobe flux by reconnection during northward IMF: possible evidence for signatures in cusp/cleft auroral emissions

M. Lockwood2,1 and J. Moen3 M. Lockwood and J. Moen
  • 1Rutherford Appleton Laboratory, Chilton, UK
  • 2Also Guest Lecturer at the University Courses on Svalbard
  • 3University Courses on Svalbard, Longyearbyen, Svalbard, Norway

Abstract. Observations are presented of the response of the dayside cusp/cleft aurora to changes in both the clock and elevation angles of the interplanetary magnetic field (IMF) vector, as monitored by the WIND spacecraft. The auroral observations are made in 630 nm light at the winter solstice near magnetic noon, using an all-sky camera and a meridian-scanning photometer on the island of Spitsbergen. The dominant change was the response to a northward turning of the IMF which caused a poleward retreat of the dayside aurora. A second, higher-latitude band of aurora was seen to form following the northward turning, which is interpreted as the effect of lobe reconnection which reconfigures open flux. We suggest that this was made possible in the winter hemisphere, despite the effect of the Earth's dipole tilt, by a relatively large negative X component of the IMF. A series of five events then formed in the poleward band and these propagated in a southwestward direction and faded at the equatorward edge of the lower-latitude band as it migrated poleward. It is shown that the auroral observations are consistent with overdraped lobe flux being generated by lobe reconnection in the winter hemisphere and subsequently being re-closed by lobe reconnection in the summer hemisphere. We propose that the balance between the reconnection rates at these two sites is modulated by the IMF elevation angle, such that when the IMF points more directly northward, the summer lobe reconnection site dominates, re-closing all overdraped lobe flux and eventually becoming disconnected from the Northern Hemisphere.

Key words. Magnetospheric physics (magnetopause · cusp and boundary layers; solar-wind-magnetosphere interactions) · Space plasma physics (magnetic reconnection)

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