He Huang

The F2-layer peak electron density (NmF2), the F2-layer peak height (hmF2), and the α-Chapman scale height (H) are key parameters for characterizing the vertical structure of ionospheric electron density, and of great significance for space environment monitoring and space weather applications. Using Global Navigation Satellite System (GNSS) radio occultation (GRO) observations from the CSES-01 satellite, this study proposes the CSES-NET model. A reliable sample data set is first constructed through sample screening, α-Chapman fitting, and physical constraints. On this basis, a multitask model integrating convolutional neural network (CNN), long short-term memory (LSTM) network, and an attention mechanism is developed to simulate the three parameters. The results show that the proposed model reproduces the spatiotemporal characteristics of NmF2, hmF2, and H well and effectively improves the reconstruction accuracy of electron density profiles (EDP). Baseline and ablation experiments are also carried out to ascertain the optimal modeling scheme. This study may provide a reference for reconstructing ionospheric profiles from the key parameters of the Chapman profile under quiet geomagnetic conditions.

This paper presents the second generation of the China Seismo-Electromagnetic Satellite (CSES) Global Geomagnetic Field Model (CGGM-2), specifically designed to derive candidate models for the fourteenth generation of the International Geomagnetic Reference Field (IGRF-14). To build this CGGM-2 model, we utilize more than six years of geomagnetic field data collected by the high-precision magnetometer (HPM) onboard CSES. The model is parametrized by expanding the internal field to spherical harmonic degree and order 45, now incorporating lithospheric contributions. This was not the case for the first generation CGGM model, which was limited to spherical harmonic degrees up to 15. We now also implement order six B-splines in time with one year knot spacing for degrees 1 to 13 to capture non-linear temporal variations in the core field, superseding the linear approximation used in CGGM. Despite a number of challenges, such as boom deformation on which the HPM is located (away from the star imager that provides attitude information) and high-latitude magnetic field platform disturbances, the CGGM-2 model succeeds at capturing the non-linear temporal variations of the geomagnetic field. In particular, the SV-2025-2030 candidate model derived from CGGM-2 performs particularly well among all 18 candidate models for IGRF-14. Candidate models derived from the CGGM-2 are also the only IGRF-14 candidate models using CSES data only and not directly relying on any ESA’s Swarm satellite data, thus providing useful candidate models to compare against all other IGRF candidate models. Our findings underscore the potential of CSES data for geomagnetic field modeling and the likely benefits of CSES’s revisiting capability for accurately capturing the main field's variations. It is expected that future data from the forthcoming companion CSES-02 mission will help improve the temporal–spatial resolution of the model and mitigate high-latitude magnetic platform disturbances. Graphical Abstract

This study statistically investigates the distribution of the coseismic ionospheric disturbances (CIDs) in the north and south directions and the feature of the north‐south asymmetry of the CID amplitude using total electron content measurements for 13 earthquakes with magnitude 6.7–8.8 in the Chile subduction zone. The relative CID amplitude in the south direction is generally smaller than that in the north direction, but the propagation range of the CID in the south direction is basically consistent with that in the north direction. The north‐south amplitude ratio increases with decreasing epicentral distance. The larger CID amplitude in the north direction and the dependence of the north‐south amplitude ratio on the epicentral distance are found to be mainly associated with the effect of the geomagnetic field. Furthermore, the empirical relationship between the relative CID amplitude and the earthquake magnitude is suggested to consider geomagnetic field‐neutral orientation factor (GNF) for improved accuracy. It is also found that the north‐south amplitude ratio increases with the earthquake magnitude, which cannot be fully explained by the combined effect of GNF, north‐south asymmetry of the seismic energy release, and satellite observation geometry.

This study investigates the four‐peak electron density structure in the Equatorial Ionization Anomaly (EIA) during the intense geomagnetic storms of 10–20 May 2024, utilizing dayside data at ∼500 km from the China Seismo‐Electromagnetic Satellite (CSES‐01). Observations revealed distinct four peaks in latitudinal profiles of electron density, symmetrically distributed across both hemispheres. Particularly, the poleward crests can expand beyond ±30° quasi‐dipole latitude during the 10 May superstorm. To reveal the potential driver of such unique EIA structure, statistical analysis is conducted on 35 CSES‐01 orbits which identified the four‐peak phenomenon. The enhanced equatorial electrojet activity, inferred from the scalar magnetic field residuals, indicates that the four‐peak morphology is likely related to the prompt penetration electric field (PPEF). Superposed epoch analysis also highlighted that intensification of the mean SuperMAG |SML| index preceded the onset of four‐peak structures by ∼20 min, whereas the mean eastward equatorial electric field, derived from an empirical model of the interplanetary electric field driven penetration, exhibits no statistically significant enhancement, implying that substorm‐associated PPEF may be the primary driver of this type of EIA structure. This study advances understanding of EIA variability under extreme space weather conditions and the findings underscore the critical role of magnetosphere‐ionosphere coupling via substorm‐driven electric fields in reshaping storm‐time ionospheric plasma distribution.

The typical equatorial ionization anomaly (EIA) exhibits two crests around the magnetic equator. Here we reported evidence for a double‐peak superposition at the EIA crest of each hemisphere, forming a four‐peak structure, with the additional peaks located ∼10° poleward of normal crests, as observed by CSES at 500 km altitudes on dayside, during the 23 April 2023 geomagnetic storm. Such a unique structure occurred when the eastward prompt penetration electric field (PPEF) was developed. Interestingly, distinctive large‐scale traveling ionospheric disturbances derived from GNSS‐TEC data propagated equatorward but not coincidently interacted with the EIA poleward peaks. The short‐duration intense PPEF may be the most plausible mechanism, which could cause the “fountain” plasma highly elevated into the topside which gradually fell into CSES altitudes on poleward sides of regular EIA crests, causing the superposition of crest in addition to nominal crest generated by the regular wind dynamo.

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 (V_z) 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 V_z significantly increased along the ground-to-space direction. The relative variation of No⁺ and V_z before the strong EQs is more prominent, and the V_z 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.

China Seismo‐Electromagnetic Satellite (CSES) was successfully launched in February 2018. About 280 thousand ionospheric radio occultation (RO) electron density profiles (EDP) have been accumulated till the end of 2020. The CSES is a Sun‐synchronous orbit satellite with descending and ascending nodes around 14:00 and 02:00 LT, respectively, at the height of 507 km. Thus, most of the RO EDP concentrate on these two local time bins. First, we constructed empirical NmF2, hmF2, and Hm models at two local time windows 14:00 and 02:00 LT, respectively. The three models describe that NmF2, hmF2, and Hm vary with solar activity, season, longitude, and latitude. Through the comparison with CSES observations, the NmF2, hmF2, and Hm models could reproduce the physical characteristics rather well. Then, according to Chapman profile function, a EDP model was reconstructed based on the NmF2, hmF2, and Hm models, named CSES_Ne‐Profile Model. To evaluate the model performance, we simulated the COSMIC‐2 observations by CSES_Ne‐Profile Model and international reference ionosphere (IRI) model respectively. The results show that CSES_Ne‐Profile Model precedes the IRI model. Additionally, our model captures the merging phenomenon of the two peaks of equatorial ionospheric anomaly, which is missed by IRI. Further, CSES_NePrf model is a useful tool to provide the quiet background for case studies and joint studies with other payloads onboard CSES.