## 4 Discussion
Specifically, Figure 9 shows an example of the existence of whistler-mode waves with both non-structured (at the geomagnetic latitudes over 55\({}^{\circ}\)) and structured QP waves (at latitudes of 30\({}^{\circ}\) to 40\({}^{\circ}\)) at frequencies from 900 to 1200 Hz, as well as ELF hiss waves below the local proton cyclotron frequency \(f_{\rm cp}\). Thanks to the availability of waveform data below 2.5 kHz along the whole orbit trajectory, we could conduct a wave vector analysis to discuss the propagation features for these typical ELF/VLF whistler-mode emissions that occurred during the storm time. The wave propagation parameters for the ELF/VLF waves are shown in Figure 12, and they were computed by the singular value decomposition method [46] under the geomagnetic field aligned coordinate system (FAC) of the CSES (see details in Section 3.2 of the work of [PERSON] et al. [20]). Figure 12 shows the wave vector analysis results for the ELF/VLF waves at northern high geomagnetic latitude regions (corresponding to the right part of Figure 9). The ellipticity value (Figure 12c), which is the ratio of the axes of polarization ellipse (+1 means right-hand circular polarization, \(-\)1 means left-hand circular polarization, and 0 means linear polarization), indicated that waves (900 Hz \(<\)_f_\(<\) 2000 Hz) and hiss waves (_f_\(<\)_f\({}_{\rm cp}\)) were of the right-handed polarized whistler-mode and their wave normal angles (\(\Theta_{\rm k}\)) (Figure 12d) generally varied in the range of around 40\({}^{\circ}\) to 65\({}^{\circ}\). This suggested that waves obliquely propagated to the background magnetic field. Figure 12e shows the azimuthal angles (\(\varphi_{\rm k}\)) (\(\pm\)180\({}^{\circ}\): decreasing \(L\) shell direction; 0\({}^{\circ}\): increasing \(L\) shell direction), which present values near 180\({}^{\circ}\), suggesting that the observed ELF/VLF waves propagated towards the Earth direction (that is, in the decreasing \(L\) shell direction). The planarity of waves (Figure 12f), which represents the wave propagation mode, exhibited a value mostly equal to +1, meaning that the observed waves were coming towards the spacecraft as plane waves. The Poynting fluxes (\(E\times H\)) were computed by the six components of the electromagnetic waves [20]. It can be seen from Figure 12 that Poynting fluxes (S) mainly dominated in the perpendicular direction to the background magnetic field instead of the parallel directions. Figure 11: Same as Figure 10 but for orbit No. 0031290 on 27 August 2018. According to Figure 12, the ELF/VLF whistler-mode waves obliquely propagated from the outer radiation belt towards the satellite along the Earth direction. Such peculiarity agreed with previous studies [17; 29] that highlighted that in the high latitude ionosphere, these particles most likely propagate from the outer radiation belt and precipitate into the ionosphere (or into the atmosphere) as a consequence of their interactions with ELF/VLF waves. [PERSON] et al. [9] and [PERSON] et al. [47] interpreted the generation of ELF/VLF waves in the ionosphere as mostly likely being due to the strong temperature anisotropy after solar wind energetic particle injections during storm time, which provides free energy for wave excitation to amplify the ELF/VLF waves in the upper ionosphere.