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On May 21, a Ms6.4 earthquake occurred in Yangbi, Yunnan Province. Less than 5 ​h later, on May 21, follows a Ms7.4 earthquake in Madoi, Qinghai Province. In this study, multiple parameters are studied from CSES-01 satellite and GNSS. The parameters include the electron density from LAP, energetic particle flux from HEPP, electric field spectrum from EFD, induced magnetic field spectrum from SCM, and global TEC from ground-based GNSS receivers. In the time scale, all parameters changed on May 15, 17 and 18. The relative amplitude of Ne is more than 200%. In space scale, the clear enhancement focus on the southeast of the epicenter of Madoi, Qinghai, and the shape of the focus region is like a clockwise-30°-rotated rectangle, which is about 45° in length and 20° in width. Moreover, there appeared enhancement in the conjugated region. According to the day-to-day analysis of the low-frequency (75–90 Hz) spectrum of EFD and SCM payloads, the relationship of the increment on May 18 could be confirmed with the successive two earthquakes. The energetic particle fluxes enhanced on May 20. All those changes are located in the east of the following epicenter and appeared just several days before, which could be well explained by the Lithosphere-Atmosphere-Ionosphere theory.

The China-Seismo-Electromagnetic Satellite (CSES), which was launched in February 2018, carries the search coil magnetometer (SCM) and the electric field detector (EFD) to realize the high-resolution electromagnetic field and wave detection in the upper ionosphere. Due to the complexity and variability of the ionospheric environment, the stability of such a high sampling rate and high-precision electromagnetic field detection systems is always an essential link in data processing and the scientific application of CSES. This work evaluates the stability of the very-low-frequency (VLF) band detection by validating the systemic sampling-time differences between SCM and EFD in the VLF burst-mode observations. The optimal waveform data preprocessing method is put forward according to the noise levels of the VLF burst-mode observation and the inherent design characteristics of EFD. The VLF waveform data of EFD is rebuilt by filling the data gaps among the sampling sub-periods, making it with a similar sample length to SCM. Then by precisely intercepting the maximum and minimum values of the burst-mode waveforms, the variation of the sampling-time difference between EFD and SCM is statistically evaluated. Results show that during the three years’ operation, the sampling-time difference between EFD and SCM predominately keeps below 0.5 s, indicating good stability of EFD and SCM on orbit. Then we developed an automatic synchronization tool based on the similarity function and STA/LTA (short time average over long time average) characteristic function. This tool can effectively realize the precise synchronization between SCM and EFD in the VLF burst-mode observation. This work is helpful to upgrade the data quality of CSES and provides technical support for electromagnetic wave propagation studies.

The China Seismo-Electromagnetic Satellite (CSES) deploys three payloads to detect the electromagnetic environment in the ionosphere. The tri-axial fluxgate magnetometers (FGM), as part of the high precision magnetometer (HPM), measures the Earth magnetic vector field in a frequency range from direct current (DC) to 15 Hz. The tri-axial search coil magnetometer (SCM) detects the alternating current (AC) related magnetic field in a frequency range from several Hz to 20 kHz, and the electric field detector (EFD) measures the spatial electric field in a broad frequency band from DC to 3.5 MHz. This work mainly cross-calibrates the consistency of these three payloads in their overlapped detection frequency range and firstly evaluates CSES’s timing system and the sampling time differences between EFD and SCM. A sampling time synchronization method for EFD and SCM waveform data is put forward. The consistency between FGM and SCM in the ultra-low-frequency (ULF) range is validated by using the magnetic torque (MT) signal as a reference. A natural quasiperiodic electromagnetic wave event verifies SCM and EFD’s consistency in extremely low-frequency and very low-frequency (ELF/VLF) bands. This cross-calibration work is helpful to upgrade the data quality of CSES and brings valuable insights to similar electromagnetic detection solutions by low earth orbit satellites.

Based on the observations by the sun‐synchronous circular orbit China Seismo‐Electromagnetic Satellite(CSES), a typical case of the rising‐tone quasiperiodic (QP) emissions with a large period of around 2 min was reported to appear on the dayside on 23 October 2021. The frequency of QP waves ranges from 2,000 ∼ 3,000 Hz and the wave spectral structure consists of four elements with right‐handed polarization. Three elements of them are located at extremely low L‐shells from 2 ∼ 3.5. The periodic precipitating fluxes of 100 ∼ 400 keV electrons were found in the conjugate region also observed by CSES, which appeared in the same magnetic field lines with the elements of QP waves, respectively. By numerical simulations of quasi‐linear diffusion theory, we confirm that QP emissions can effectively precipitate energetic electrons near the loss cone into the atmosphere in the inner radiation belt. To our best knowledge, this is the first evidence that the rising‐tone QP whistler waves scatter electrons in the inner radiation belt. This new finding will help to deepen our understanding of the electron precipitation dynamics in radiation belt physics. The whistler‐mode quasiperiodic (QP) emissions with a repetition period from several seconds to several minutes have been reported by a large amount of satellites and ground‐based detector stations observations, and their generation mechanisms have been studied a lot. However, the reports about diffusion or acceleration effects on the relativistic electrons induced by QP waves are rare and only a little focused on the outer radiation belts. CSES satellite with the sun‐synchronous polar orbits at 507 km altitude provides an advantage to study the wave‐particle interaction in the extremely low L‐shell regions including the inner radiation belts. In this work, we present the rising‐tone QP whistler waves observed by CSES satellite in the inner radiation belt. Simultaneously, the periodic precipitating fluxes of 100–400 keV electrons were found in the same magnetic field lines with the elements of QP waves, respectively. To our knowledge, this provides the first evidence that QP emissions can effectively precipitate energetic electrons into the atmosphere in the inner radiation belt. This scenario is confirmed by our numerical simulations of quasi‐linear diffusion theory. This new finding will help to deeply understand the electron precipitation dynamics in radiation belt physics. The rising‐tone quasi‐periodic (QP) whistler waves are observed by CSES satellite in the inner radiation belt100 ∼ 400 keV electrons within 30° equatorial pitch angles in the conjugate region was periodically precipitatedQP whistler waves can efficiently diffuse relativistic electrons near the bounce loss cone in extremely low L−shells (L= 2 ∼ 3.5) The rising‐tone quasi‐periodic (QP) whistler waves are observed by CSES satellite in the inner radiation belt 100 ∼ 400 keV electrons within 30° equatorial pitch angles in the conjugate region was periodically precipitated QP whistler waves can efficiently diffuse relativistic electrons near the bounce loss cone in extremely low L−shells (L= 2 ∼ 3.5)

This paper reports a large‐scale magnetospheric line radiation (MLR) event during a moderate geomagnetic storm on 11 September 2018, which was well recorded by the China‐Seismo‐Electromagnetic Satellite (CSES) in the upper ionosphere. The event shows a symmetrical propagation feature at the conjugated locations between the two hemispheres, exhibiting a large spatial extension roughly from the latitudes 54°N to 53°S. The parallel structures are visible both in the electric and magnetic fields at a frequency band ranging from the local proton cyclotron frequency to ∼1.6 kHz. The wave intensity of parallel spectral lines was primarily enhanced in high latitude regions, gradually weakening at mid‐low latitudes, and then got absorbed in the equatorial region, presenting a distinct V‐shaped structure. The frequency spacings between neighboring spectral lines roughly vary from ∼80 to 110 Hz at the high latitudes and ∼80–130 Hz at the low latitudes, suggesting a slight variation feature with latitude. The parallel spectral structures of MLR drift between ∼0.39 and 0.57 Hz/s at high latitudes and ∼0.18–0.19 Hz/s at low latitudes. The wave vector analysis shows that the MLR waves are right‐hand polarized, obliquely propagating toward the Earth and in the azimuthal direction, where the Poynting flux is primarily oriented perpendicular to the ambient magnetic field. The other large‐scale MLR events all exhibit similar parallel structures and polarization characteristics, suggesting the universality of such a phenomenon. However, the azimuthal angles differ among different events, showing complex features. Magnetospheric line radiation (MLR) is a unique electromagnetic wave distinguished by parallel spectral lines. This study reports a large‐scale MLR event that occurred in the dayside ionosphere. The event shows a symmetrical propagation feature, with a large spatial extension between latitudes 54°N and 53°S. The parallel structures are visible both in the electric and magnetic spectrogram, ranging from the local proton cyclotron frequency to ∼1.6 kHz. The MLR structures were primarily enhanced in high latitude regions, gradually weakening at mid‐low latitudes, and then got absorbed in the equatorial region, presenting a distinct V‐shaped structure. The frequency spacings of MLR roughly vary from ∼80 to 110 Hz in the high latitudes and from ∼80 to 130 Hz in the mid‐low latitude region, slightly varying with latitude. The MLR structures drift between ∼0.39 and 0.57 Hz/s at high latitudes and ∼0.18–0.19 Hz/s at low latitudes. This MLR event is right‐hand polarized, obliquely propagating toward the Earth and in the azimuthal direction, and the Poynting flux is primarily oriented perpendicular to the ambient magnetic field. However, the azimuthal angles differ among different events, indicating the complexity of the wave propagation feature. A large‐scale magnetospheric line radiation (MLR) event shows a symmetrical propagation feature in two hemispheres, presenting a distinct V‐shaped structureBoth the frequencies of the parallel spectral lines and their frequency spacings slightly drift with latitudesThe MLR waves are right‐hand polarized, obliquely propagating toward the Earth and azimuthal direction A large‐scale magnetospheric line radiation (MLR) event shows a symmetrical propagation feature in two hemispheres, presenting a distinct V‐shaped structure Both the frequencies of the parallel spectral lines and their frequency spacings slightly drift with latitudes The MLR waves are right‐hand polarized, obliquely propagating toward the Earth and azimuthal direction