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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 10
Ann. Geophys., 17, 1245–1250, 1999
https://doi.org/10.1007/s00585-999-1245-4
© European Geosciences Union 1999
Ann. Geophys., 17, 1245–1250, 1999
https://doi.org/10.1007/s00585-999-1245-4
© European Geosciences Union 1999

  31 Oct 1999

31 Oct 1999

The Earth's passage of the April 11, 1997 coronal ejecta: geomagnetic field fluctuations at high and low latitude during northward interplanetary magnetic field conditions

S. Lepidi2,1, P. Francia1, U. Villante1, A. Meloni2, A. J. Lazarus3, and R. P. Lepping4 S. Lepidi et al.
  • 1Dipartimento di Fisica, Università dell'Aquila, L'Aquila, Italy
  • E-mail: stefania.lepidi@aquila.infn.it
  • 2Istituto Nazionale di Geofisica, Roma, Italy
  • 3Center for Space Research, MIT, Cambridge, USA
  • 4Laboratory for Extraterrestrial Physics, NASA/GSFC, Greenbelt, USA

Abstract. An analysis of the low frequency geomagnetic field fluctuations at an Antarctic (Terra Nova Bay) and a low latitude (L'Aquila, Italy) station during the Earth's passage of a coronal ejecta on April 11, 1997 shows that major solar wind pressure variations were followed at both stations by a high fluctuation level. During northward interplanetary magnetic field conditions and when Terra Nova Bay is close to the local geomagnetic noon, coherent fluctuations, at the same frequency (3.6 mHz) and with polarization characteristics indicating an antisunward propagation, were observed simultaneously at the two stations. An analysis of simultaneous measurements from geosynchronous satellites shows evidence for pulsations at approximately the same frequencies also in the magnetospheric field. The observed waves might then be interpreted as oscillation modes, triggered by an external stimulation, extending to a major portion of the Earth's magnetosphere.

Key words. Magnetospheric physics (MHD waves and instabilities; solar wind-magnetosphere interactions)

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