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

This study is intended to reveal the oscillation and propagation characteri stics of ULF waves observed near the dayside magnetopause. A comparative st udy of such ULF wave phenomena is made by using the data obtained from the successive skimmings of the dayside magnetopause by the GEOTAIL Satellite p erformed on three successive days of 9, Is, and 27 December 1994. The instr umentations of GEOTAIL are good for such a task, since the satellite simult aneously measured the magnetic and electric fields, and low energy plasma d ata. Based the observed data, we studied the dynamic spectral characteristi cs of both magnetic and electric fields. The results revealed that the domi nant ULF waves appearing in the dynamic spectra were Pc 3 and Pc 5 oscillat ions. The Pc 3 oscillations were observed during a limited local time aroun d noon without an extension to the dawn and dusk flanks, and dominantly app eared at a frequency of similar to 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 ch aracteristic was also recognized. The Poynting Bur of the Pc 3 signals show ed that the energy flux was about 10 nJ/m(2)s on average, the strongest bei ng along the magnetic field line. Pc 5 oscillations showed another dominant spectral power which appeared in the radial component of the electric fiel d, suggesting that the resonance oscillations were well established. Howeve r, the Pc 5 oscillations in the subsolar region did not show any earthward propagation characteristics.