Abstract
Abstract. The structure of low-latitude continuous pulsations termed Pc3, which are naturally occurring MHD waves in the Earth's magnetosphere, were studied by comparing ground and satellite magnetic field measurements. Data from two induction magnetometers, located at Hermanus and Sutherland in South Africa were used in conjunction with Challenging Minisatellite Payload (CHAMP) satellite observations to study a Pc3 event observed on 15 February 2003, at a time when CHAMP was passing over the ground stations. We observed a number of discrete frequency oscillations for the fast mode wave, one of which drives a field line resonance (FLR) at characteristic latitude as detected by both ground and satellite measurements. Consequently, our observations confirmed the compressional wave as being the driver of the field line resonance. The toroidal mode frequency observed on CHAMP experienced a Doppler frequency shift due to the rapid motion across the resonance region. Polarization hodograms in the resonance region clearly showed the expected 90° rotation of the field line resonant magnetic field components.
Highlights
Geomagnetic pulsations are the magnetic signature of ultra low frequency (ULF) waves, which are naturally occurring magnetohydrodynamic (MHD) waves in the Earth’s magnetosphere
The fast mode compressional waves can drive field line resonances, which can be pictured as standing waves along geomagnetic field lines with ends fixed at conjugate ionospheres
In this paper we studied a Pc3 geomagnetic pulsation event at a time when the Challenging Minisatellite Payload (CHAMP) satellite passed over the HER ground station
Summary
Geomagnetic pulsations are the magnetic signature of ultra low frequency (ULF) waves, which are naturally occurring magnetohydrodynamic (MHD) waves in the Earth’s magnetosphere. Depending on their waveform and wave period the pulsations were classified into two groups by IAGA in 1963. This study is about the class of continuous pulsations, termed Pc3 and characterised by a period ranging from 10 to 45 s, which occur at low, mid, and high latitudes. The main source of Pc3 pulsations is thought to be upstream waves in the Earth’s foreshock region (Russell et al, 1983); the wave structure may be affected by cavity modes (Menk et al, 2000). The fast mode compressional waves can drive field line resonances, which can be pictured as standing waves along geomagnetic field lines with ends fixed at conjugate ionospheres
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