Latitudinal distribution of auroral kilometric radiation ordinary and extraordinary wave modes observed by KAGUYA

The auroral kilometric radiations (AKR) are intense radio emissions originating from the Earth's auroral region. An important property of the AKR is its polarization. The AKR is believed to be generated by the cyclotron maser mechanism because the polarization is dominated by right-handed extraordinary (R-X) mode with small contribution of left-handed ordinary (L-O) one. However, intense L-O mode was also observed from low latitude spacecraft, Jikiken and Akebono. Hashimoto interpreted such L-O mode as a result of propagation effects through density gradients near the source and through the plasmapause. The KAGUYA mission gave a good opportunity to make a stochastic analysis of the AKR polarization from lunar orbits. The waveform capture instrument (WFC) was a plasma wave receiver on-board the KAGUYA spacecraft. The frequency sweep receiver WFC-H, which was a subsystem of the WFC, continuously observed power spectrum and polarizations of waves in a frequency range from 1 kHz to 1 MHz for about one year mission period.