Akebono satellite observations of Dispersive Alfven waves and the ionospheric Alfven resonator in the cusp region

In the cusp region at altitudes of a few thousands of km, burst-like fluctuations of electric and magnetic fields are often observed in the ULF range of 0.2-5 Hz on the Akebono satellite. We have found that these bursts occasionally have clear harmonic structures in small-scale upward field-aligned current regions. The Alfven resonator between the bottom of the Auroral acceleration region and the ionospheric E layer is one of the candidates of these harmonic structures. The model of Lysak et al. [1991] calculated the phase shifts of electric and magnetic field as a function of frequency using the ionospheric Alfven resonator model. Grzesiak. [2001] succeeded in demonstrating that satellite measurements coincide with the model given by Lysak. Pilipenko et al. [2001] investigated the resonance condition of dispersive Alfven wave between the bottom of the auroral acceleration and the E layer. Based on these previous results, we compared electric and magnetic field data obtained by the Akebono satellite with the Lysak model, using the cross-wavelet analysis method. Further, considering that small-scale upward and downward field-aligned currents would be produced by dispersive Alfven waves, we compared the measured ratios of electric and magnetic field with the resonance condition of dispersive Alfven waves.