Ducted Propagation of Whistler Mode Waves Observed by the Arase Satellite

Ducted propagation of whistler‐mode waves has attracted attention as a process that explains how whistler‐mode waves propagate to high latitudes, resulting in the loss of relativistic electrons to the atmosphere and changes in the upper atmosphere due to electron precipitation. However, few studies have compared the observed density ducts and wave propagation characteristics to theoretical predictions in detail, particularly for low‐density ducts. We present four patterns of ducting modes as electron density increases or decreases, as observed by the Arase satellite. (a) Lower‐band (LB) waves propagating along a high‐density duct with small wave normal angles (WNAs), (b) LB waves propagating along a low‐density duct with a wide distribution of WNAs up to above the Gendrin Angle, (c) LB waves propagating along a low‐density duct with WNAs around the Gendrin Angle, and (d) upper‐band waves propagating along a low‐density duct with small WNAs. We derived the WNAs for these cases, and their characteristics were consistent with the ducting theory. Based on this theory, we calculated the frequency range in which the waves were likely to be trapped in the ducts. We compared this frequency range with the power spectra of the recorded whistler‐mode waves and found consistency between the theory and observations. Furthermore, it is suggested that the WNAs for cases (b) and (c) have azimuthal distributions based on a comparison of the WNA analysis of the simple simulated waveforms and the observed data.