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In this study, we have performed a detailed analysis for the correlation between electron density (Ne) and temperature (Te) at the topside ionosphere. In situ measurements from four satellites have been utilized, including the China Seismo-Electromagnetic Satellite (CSES), Swarm A and B, as well as the earlier Challenging Minisatellite Payload (CHAMP) satellite. To make a fair comparison, only simultaneous observations between CSES and Swarm A/B have been considered; while for CHAMP, as it doesn’t have overlaps with CSES period, the observations during similar low solar activity years are considered. Our study has been confined to the dayside around 14:00 local time (LT), due to the fixed LT coverage of CSES. Observations from the four satellites show generally consistent relationship between the Ne and Te at the topside ionosphere. When Ne is low, the Te is negative correlated with Ne, while the slop of negative relation becomes shallower or even reverses to a positive relation after Ne exceeds a certain threshold. The slope of Ne/Te relation shows also dependence on season and magnetic latitude (MLat), as the ionospheric Ne and Te themselves are seasonal and MLat dependent. Interestingly, we find two abnormal features of the Swarm Te measurements: 1) when Ne is lower than 1×1011 m−3, Te sometimes becomes very scatter at low and middle latitudes; 2) when Ne is larger than 1×1011 m−3, Te is grouped into two branches at the equatorial and low latitudes. Further analysis reveals that the flags used in the Swarm Level-1 B plasma density product cannot well distinguish the two abnormal features of Te, implying further efforts are needed for the Swarm Te data calibration.

Driven by the objective of earthquake disaster prevention and mitigation, China launched the Zhangheng mission to build a stereoscopic earthquake monitoring system from the lithosphere to space. This report briefly presents the possible seismic ionospheric disturbances recorded by the first probe of the Zhangheng mission, which is known as the China-Seismo-Electromagnetic Satellite (CSES). The routine data preprocessing and seismo-ionospheric information analysis methods are briefly introduced. The possible seismo-ionospheric disturbances that appeared during the strong shallow earthquakes (with a magnitude over 7 and a depth shallower than 30 km) are analyzed by using CSES and other multi-source data. Investigating seismo-ionospheric mechanisms requires multidisciplinary knowledge involving geophysics, atmosphere/ionosphere physics, geochemistry/atmospheric chemistry, etc. We state that the results from the CSES scientific application center are preliminary, calling for international scientists to contribute to the seismo-ionospheric perturbation phenomena, which is one of the most challenging scientific problems.

The Langmuir probe has been used as an effective tool for in-situ plasma parameter measurements since the past century (Bering et al., 1973;Mott-Smith & Langmuir, 1926;. In recent decades, it has been widely carried by many Low Earth Orbit (LEO) satellites, such as the Challenging Minisatellite Payload (CHAMP) (Cooke et al., 2003), the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) (Lebreton et al., 2006), the Swarm satellites (Alpha, Bravo, and Charlie) (Buchert et al., 2015), and the China Seismo-Electromagnetic Satellite (CSES) (Shen et al., 2018) whose Langmuir probe data is the subject of this paper.The Langmuir probe can provide the electron density (Ne), electron temperature (Te) and plasma potential (Vp) by collecting the plasma currents (I) after applying a specific range of bias voltage (V) to the probe (Chen & Chang, 2002;Lebreton et al., 2006;Mott-Smith & Langmuir, 1926). Ne and Te are two essential parameters for describing ionosphere physics, so their reliability and accuracy directly concern scientific research. However, due to the complicated space plasma environment and the limitations of the Langmuir probe detection methods, the adverse effects of probe contamination and interferences generated onboard the satellite always need to be carefully considered (

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.,