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From August to October 2018, a series of strong earthquake (EQ) events occurred in southeast Asia and northern Oceania (22°S to 0°N, 115°E to 170°E) within 50 days. In this paper, we analyze the features of ionospheric plasma perturbations, recorded by the Plasma Analyzer Package (PAP) and Langmuir probe (LAP) onboard the China Seismo-Electromagnetic Satellite (CSES-01), before four EQs with magnitudes of Ms 6.9 to Ms 7.4. The ion parameters such as the oxygen ion density (No+), the ion drift velocity in the vertical direction (Vz) under the conditions of geomagnetic storms, and strong EQs are compared. The results show that within 1 to 15 days before the strong EQs, the No+ and the electron density (Ne) increased while the electron temperature (Te) decreased synchronously. Meanwhile, the Vz significantly increased along the ground-to-space direction. The relative variation of No+ and Vz before the strong EQs is more prominent, and the Vz is not easily influenced by the geomagnetic storm but is susceptible to the seismic activities. Our results suggest that the anomaly of ionospheric plasma perturbations occurring in this area is possibly related to the pre-EQ signatures. [ABSTRACT FROM AUTHOR]

The China Seismo-Electromagnetic Satellite (CSES) was successfully launched on February 2, 2018, with a plasma analyzer package (PAP) onboard to in-situ detect the ionospheric ion parameters. In this paper, the availability of PAP data is investigated for the first time through analyzing three typical ionospheric disturbance events. Firstly, the ionospheric radio and plasma disturbances caused by two high-power terrestrial very low frequency (VLF) transmitters over American NAA station and Australian NWC station are investigated. Furthermore, several possible anomaly observations before the 22 August 2018 Ms7.3 Venezuela earthquake are analyzed. In the southwest of the epicenter, the oxygen ion density increased significantly, and the ion drift velocity in vertical direction reversed synchronously from space-to-ground direction to ground-to-space direction. Finally, during a global intense geomagnetic storm event which started from August 25, 2018, the oxygen ion density well reflected the geomagnetic storm event's temporal evolution process. The results show that the PAP onboard CSES has ability to discern the relative variations and features of ionospheric disturbances. [ABSTRACT FROM AUTHOR]