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Ann. Geophys., 20, 1143-1152, 2002
www.ann-geophys.net/20/1143/2002/
© European Geosciences Union 2002
Geomagnetic field fluctuations during the passage at the Earth’s orbit of the tail of the 15–16 July 2000 ejecta
P. Francia1, S. Lepidi2, and K. Yumoto3
1Dipartimento di Fisica, Università dell’Aquila, Via Vetoio, 67010 Coppito-L’Aquila, Italy
2Istituto Nazionale di Geofisica e Vulcanologia, Castello Cinquecentesco, 67100 L’Aquila, Italy
33Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, 812-81, Japan
Correspondence to: P. Francia
(patrizia.francia@aquila.infn.it)
Abstract. In this work we present
the analysis of the geomagnetic field fluctuations observed at different ground
stations (approximately along two latitudinal arrays, separated by several
hours in local time) during the passage at the Earth’s orbit of the tail of
the 15–16 July 2000 coronal ejecta. The time interval of interest is
characterized by northward interplanetary magnetic field conditions and several
changes in the solar wind dynamic pressure. We found at all stations, both in
the local morning and in the local evening, simultaneous and highly coherent
waves at the same discrete frequencies (~ 1.8 and ~ 3.6 mHz) and suggest a
possible interpretation in terms of global compressional modes driven by an
impulsive variation of the solar wind pressure. Along the array situated in the
morning sector, at the highest latitudes, the higher frequency mode seems to
couple with the local field line resonance; on the other hand, along the array
situated in the evening sector, the characteristics of the observed
fluctuations suggest that the highest latitude station could be located at the
footprint of open field lines. Our results also show that solar wind pressure
variations observed during the recovery phase of the storm do not find
correspondence in the geomagnetic field variations, regardless of local time
and latitude; conversely, some hours later continuous solar wind pressure
variations find a close correspondence in the geomagnetic field variations at
all stations.
Key words. Magnetospheric physics
(solar wind-magnetosphere interaction; MHD waves and instabilities)
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