The High Precision Magnetometer (HPM) on board the China Seismo-Electromagnetic Satellite (CSES) allows highly accurate measurement of the geomagnetic field; it includes FGM (Fluxgate Magnetometer) and CDSM (Coupled Dark State Magnetometer) probes. This article introduces the main processing method, algorithm, and processing procedure of the HPM data. First, the FGM and CDSM probes are calibrated according to ground sensor data. Then the FGM linear parameters can be corrected in orbit, by applying the absolute vector magnetic field correction algorithm from CDSM data. At the same time, the magnetic interference of the satellite is eliminated according to ground-satellite magnetic test results. Finally, according to the characteristics of the magnetic field direction in the low latitude region, the transformation matrix between FGM probe and star sensor is calibrated in orbit to determine the correct direction of the magnetic field. Comparing the magnetic field data of CSES and SWARM satellites in five continuous geomagnetic quiet days, the difference in measurements of the vector magnetic field is about 10 nT, which is within the uncertainty interval of geomagnetic disturbance.

The High Precision Magnetometer (HPM) is one of the main payloads onboard the China Seismo-Electromagnetic Satellite (CSES). The HPM consists of two Fluxgate Magnetometers (FGM) and the Coupled Dark State Magnetometer (CDSM), and measures the magnetic field from DC to 15 Hz. The FGMs measure the vector components of the magnetic field; while the CDSM detects the magnitude of the magnetic field with higher accuracy, which can be used to calibrate the linear parameters of the FGM. In this paper, brief descriptions of measurement principles and performances of the HPM, ground, and in-orbit calibration results of the FGMs are presented, including the thermal drift and magnetic interferences from the satellite. The HPM in-orbit vector data calibration includes two steps: sensor non-linearity corrections based on on-ground calibration and fluxgate linear parameter calibration based on the CDSM measurements. The calibration results show a reasonably good stability of the linear parameters over time. The difference between the field magnitude calculated from the calibrated FGM components and the magnitude directly measured by the CDSM is just 0.5 nT (1σ) when the linear parameters are fitted separately for the day- and the night-side. Satellite disturbances have been analyzed including soft and hard remanence as well as magnetization of the magnetic torquer, radiation from the Tri-Band Beacon, and interferences from the rotation of the solar wing. A comparison shows consistency between the HPM and SWARM magnetic field data. Observation examples are introduced in the paper, which show that HPM data can be used to survey the global geomagnetic field and monitor the magnetic field disturbances in the ionosphere.

Lunar horizon glows observed by the Apollo missions suggested a dense dust exosphere near the lunar terminator. But later missions failed to see such a high‐density dust exosphere. Why the Apollo missions could observe so large number of dust grains remains a mystery. For the first time, we report five dust enhancement events observed by the Lunar Dust Experiment on board Lunar Atmosphere and Dust Environment Explorer mission, which happen near a twilight crater with dust densities comparable to the Apollo measurements. Moreover, the dust densities are larger on the downstream side of the crater and favor a higher solar wind temperature, consistent with an electrostatic dust lofting from the negatively charged crater floor. We also check the Apollo observations and find similar twilight craters, suggesting that the so‐called dust exosphere is not a global phenomenon but just a local electrified dust fountain near twilight craters.

Due to lack of in situ observations, people still know little about the formation conditions and the internal structure of lunar mini‐magnetosphere. Here we present the first energetic neutral atom (ENA) measurement on lunar surface by the Chang'E‐4 mission. It is found that when downstream from the Imbrium antipode magnetic anomalies, the measured ENA fluxes are generally decreased, suggesting a mini‐magnetosphere that can shield the lunar surface from the solar wind. Further studies show that the shielding effect can only be found when the ion inertia length is small (<120 km) and some solar wind ions can penetrate into the mini‐magnetosphere with a penetrating efficiency positively correlated with the solar wind dynamic pressure. When the ion inertia length is large, no shielding effect can be found. With the help of Hall MHD simulations, we confirm the existence of a mini‐magnetosphere and the shielding effect anti‐correlated with ion inertia length.

During the storm recovery phase on 27 August 2018, the China Seismo-Electromagnetic Satellite (CSES) detected Pc1 wave activities in both the Northern Hemisphere and Southern Hemisphere in the high-latitude, post-midnight ionosphere with a central frequency of about 2 Hz. Meanwhile, the typical Pc1 waves were simultaneously observed for several hours by the Sodankylä Geophysical Observatory (SGO) stations on the ground. In this paper, we study the propagation characteristics and possible source regions of those waves. Firstly, we find that the Pc1 waves observed by the satellites exhibited mixed polarisation, and the wave normal is almost parallel with the background magnetic field. The field-aligned Poynting fluxes point downwards in both hemispheres, implying that the satellites are close to the wave injection regions in the ionosphere at about L=3. Furthermore, we also find that the estimated position of the plasmapause calculated by models is almost at L=3. Therefore, we suggest that the possible sources of waves are near the plasmapause, which is consistent with previous studies in that the outward expansion of the plasmasphere into the ring current during the recovery phase of geomagnetic storms may generate electromagnetic ion cyclotron (EMIC) waves, and these EMIC waves propagate northwards and southwards along the background magnetic field to the ionosphere at about L=3. Additionally, the ground station data show that Pc1 wave power attenuates with increasing distance from L=3, supporting the idea that the CSES observes the wave activities near the injection region. The observations are unique in that the Pc1 waves are observed in the ionosphere in nearly conjugate regions where transverse Alfvén waves propagate down into the ionosphere.