Abstract
Abstract. On 7 November 2005 various ground based and spaced based instruments registered five wave packets with frequencies in the Pc4 range. The most prominent of the five wave packets was observed in ground based magnetometer data spanning almost all latitudes on the dayside magnetosphere. The propagation from the dayside into the tail is deduced from Poynting flux calculations of Cluster data and an onset time analysis of the ground based magnetometer data. This suggests an upstream source. Backstreaming ions are identified to be the most probable source mechanism for this event. Due to the fortunate configuration of the Cluster satellites, the harmonic structure of the wave is analysed and compared with cross-phase spectra from ground data. We present evidence that the driving wave resonantly interacted with geomagnetic field lines. The data suggests that resonant driving occurred at stations where the driving frequency was harmonically related to the local fundamental frequency, creating FLR-like signatures.
Highlights
In the dayside magnetosphere, ultra-low frequency (ULF) pulsations with spectral power in the Pc4 frequency range are abundant
Through similar wave-particle interactions ions injected during substorms drive Pc4 pulsations with high azimuthal wave numbers predominantly in the morning sector (Baddeley et al, 2002)
When the orientation of the interplanetary magnetic field (IMF) is roughlyparallel to the normal vector of the bow shock, ions can be reflected at the boundary and travel upstream
Summary
Ultra-low frequency (ULF) pulsations with spectral power in the Pc4 frequency range are abundant. When the orientation of the interplanetary magnetic field (IMF) is roughly (anti-)parallel to the normal vector of the bow shock, ions can be reflected at the boundary and travel upstream They resonantly interact with naturally occurring waves, amplifying them (Barnes, 1970; Sentman et al, 1981). High latitude Pc5 pulsations often have distinctive characteristics and they have are known as field line resonances (FLR) Dungey proposed that they are standing Alfven waves on geomagnetic field lines, a concept that has been confirmed by a number of studies In this paper we discuss a highly coherent Pc4 pulsation with a m number around unity It is a global phenomenon, occurring at both low and high latitudes, over 12 h of magnetic local time (MLT). We explore the possibility of it being a FLR and investigate its source using ground and space based magnetometer data
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