Dayside magnetopause Pc 3 and Pc 5 ULF waves observed by the GEOTAIL Satellite

This study is intended to reveal the oscillation and propagation characteristics of ULF waves observed near the dayside magnetopause. A comparative study of such ULF wave phenomena is made by using the data obtained from the successive skimmings of the dayside magnetopause by the GEOTAIL Satellite performed on three successive days of 9, 18, and 27 December 1994. The instrumentations of GEOTAIL are good for such a task, since the satellite simultaneously measured the magnetic and electric fields, and low energy plasma data. Based the observed data, we studied the dynamic spectral characteristics of both magnetic and electric fields. The results revealed that the dominant ULF waves appearing in the dynamic spectra were Pc 3 and Pc 5 oscillations. The Pc 3 oscillations were observed during a limited local time around noon without an extension to the dawn and dusk flanks, and dominantly appeared at a frequency of ~25 mHz in the azimuthal component of the magnetic field. This frequency component showed clear resonant oscillation characteristics. In addition to this, a fast mode earthward propagation characteristic was also recognized. The Poynting flux of the Pc 3 signals showed that the energy flux was about 10 nJ/m2s on average, the strongest being along the magnetic field line. Pc 5 oscillations showed another dominant spectral power which appeared in the radial component of the electric field, suggesting that the resonance oscillations were well established. However, the Pc 5 oscillations in the subsolar region did not show any earthward propagation characteristics.