First systematic identification of triple-mode Auroral Kilometric Radiation using Arase polarization data

Auroral kilometric radiation (AKR), a fundamental plasma emission in Earth's magnetosphere, exhibits three characteristic modes: the right-handed extraordinary (R-X), left-handed ordinary (L-O) and left-handed extraordinary (L-X) modes. The role of AKR in magnetosphere−ionosphere−atmosphere coupling depends sensitively on its wave mode. While previous studies have primarily focused on the dominant R-X mode, we present the first systematic identification of all three modes using a practical polarization analysis method based on Arase satellite observations. This method employs a spin-axis-relative Ratio: when the satellite's spin axis aligns with the background magnetic field, a positive (negative) Ratio indicates the right-handed (left-handed) polarization, with reversal under anti-parallel conditions. Combined polarization-frequency analysis reveals that R-X, L-O, and L-X modes can exist in both dayside and nightside regions, with power spectral densities up to 10^-6 \rmmV^2\rmm^-2\rmHz^-1 . This study resolves long-standing ambiguities in AKR mode classification and has implications for understanding AKR-induced electron dynamics.