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.