The quasiperiodic (QP) waves accompanied by simultaneous energetic electron precipitations in the high-latitude ionosphere were recorded by the sun-synchronous circular orbit China Seismo-Electromagnetic Satellite (CSES). The new features of QP waves observed by CSES are the well-pronounced rising-tone structures and very short repetition periods, which are not ofen reported by previous studies. The repetition period of QP waves varies from~1 to over 20 s, with wave spectral properties displaying dynamic structures and clear cutoff frequencies. The majority of QP waves appear at geomagnetic latitudes from~50°to 65°, and L shell from~3.5 to 4, mostly inside the plasmapause. The QP waves obliquely propagate towards decreasing L shell directions with right-handed polarization, with wave normal angles varying from~30°to 50°. Out of the 68 events examined, 19 of them show synchronous variations of ultralow frequency (ULF) magnetic field pulsations in certain portions of the wave event. The energetic electrons predominately precipitate in a double-peak pattern (~400 to 550 keV and~700 to 800 keV). No clear periodic precipitating fluxes were found. The estimated time interval of energetic electrons driving free energy to modulate the whistler-mode waves varies from 0.04 to 30°s, which is roughly consistent with the observed repetition periods (10 to over 20 s). For the fast repetition period (~1 to 2s) QP wave, it is likely caused by the bouncing of the extremely/very low frequency (ELF/VLF) whistler-mode wave packets from the conjugate ionosphere.

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This study reports the temporal and spatial distributions of the extremely/very low frequency (ELF/VLF) wave activities and the energetic electron fluxes in the ionosphere during an intense storm (geomagnetic activity index Dst of approximately −174 nT) that occurred on 26 August 2018, based on the observations by a set of detectors onboard the China Seismo-Electromagnetic Satellite (CSES). A good correlation of the ionospheric ELF/VLF wave activities with energetic electron precipitations during the various storm evolution phases was revealed. The strongest ELF/VLF emissions at a broad frequency band extending up to 20 kHz occurred from the near-end main phase to the early recovery phase of the storm, while the wave activities mainly appeared at the frequency range below 6 kHz during other phases. Variations in the precipitating fluxes were also spotted in correspondence with changing geomagnetic activity, with the max values primarily appearing outside of the plasmapause during active conditions. The energetic electrons at energies below 1.5 MeV got strong enhancements during the whole storm time on both the day and night side. Examinations of the half-orbit data showed that under the quiet condition, the CSES was able to depict the outer/inner radiation belt as well as the slot region well, whereas under disturbed conditions, such regions became less sharply defined. The regions poleward from geomagnetic latitudes over 50° were found to host the most robust electron precipitation regardless of the quiet or active conditions, and in the equatorward regions below 30°, flux enhancements were mainly observed during storm time and only occasionally in quiet time. The nightside ionosphere also showed remarkable temporal variability along with the storm evolution process but with relatively weaker wave activities and similar level of fluxes enhancement compared to the ones in the dayside ionosphere. The ELF/VLF whistler-mode waves recorded by the CSES mainly included structure-less VLF waves, structured VLF quasi-periodic emissions, and structure-less ELF hiss waves. A wave vector analysis showed that during storm time, these ELF/VLF whistler-mode waves obliquely propagated, mostly likely from the radiation belt toward the Earth direction. We suggest that energetic electrons in the high latitude ionosphere are most likely transported from the outer radiation belt as a consequence of their interactions with ELF/VLF waves.

We present observations on the local proton cyclotron band emissions (PCBEs), which is one type of hiss wave in the upper ionosphere, recorded by the China Seismo‐Electromagnetic Satellite (CSES). The PCBEs are characterized by narrow‐band electromagnetic emissions along the local proton cyclotron frequency (fnormalcnormalp ${f}_{\mathrm{c}\mathrm{p}}$), exhibiting a sharp cutoff effect. The lower cutoff frequency (fnormalcnormalunormalt−normallnormalonormalw ${f}_{\mathrm{c}\mathrm{u}\mathrm{t}-\mathrm{l}\mathrm{o}\mathrm{w}}$) is closely along the local fnormalcnormalp ${f}_{\mathrm{c}\mathrm{p}}$, decreasing with magnetic latitude, while the upper cutoff frequency (fnormalcnormalunormalt−normalunormalp ${f}_{\mathrm{c}\mathrm{u}\mathrm{t}-\mathrm{u}\mathrm{p}}$) is diffuse and deviates from the local fnormalcnormalp ${f}_{\mathrm{c}\mathrm{p}}$. We developed an algorithm to automatically extract PCBEs from CSES's massive electromagnetic data and statistically examined their occurrence and bandwidth's dependence on location and season. The global morphology of PCBEs in 2019 shows that they primarily occur in the mid‐high magnetic latitude (approximately 20°–55°) dayside ionosphere, with the maximum occurrence happening around the South Atlantic Anomaly region. Their bandwidth shows a decreasing tendency with magnetic latitude and strong seasonal dependence, with a wider bandwidth in local winter and a narrower one in local summer. The ratio of fnormalcnormalunormalt−normallnormalonormalw ${f}_{\mathrm{c}\mathrm{u}\mathrm{t}-\mathrm{l}\mathrm{o}\mathrm{w}}$ and fnormalcnormalp ${f}_{\mathrm{c}\mathrm{p}}$ also shows a seasonal dependence, with greater values in local summer and smaller values in local winter. This characteristic of fnormalcnormalunormalt−normallnormalonormalw ${f}_{\mathrm{c}\mathrm{u}\mathrm{t}-\mathrm{l}\mathrm{o}\mathrm{w}}$ is similar to that of the H+‐He+ cutoff frequency (fnormalcnormalunormalt−normalinormalonormaln ${f}_{\mathrm{c}\mathrm{u}\mathrm{t}-\mathrm{i}\mathrm{o}\mathrm{n}}$). This study provides statistical characteristics of occurrence and the cutoff features of PCBEs based on the CSES operating in the upper ionosphere.

In recent decades, with the successful operation of satellites in low earth orbit (LEO) space, many types of electromagnetic (EM) waves in the ULF/ELF/VLF (Ultra/Extreme/Very low frequency) range get well recorded in the ionosphere: for example, the most commonly observed ionospheric hiss waves (e.g.,