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The accuracy of BDS triple-frequency cycle slip detection and repair is influenced by the observation environment. Three linear independence geometry-free and ionosphere-free combinations (GIF) have been widely applied detect and then to repair the GNSS cycle-slip, but for some special cycle-slip combinations or when observations with bad observation environment, the cycle-slip repair may be invalidated. For this, we further introduce the STPIR combination to the GIF model to detect and repair the cycle-slip, and use the second-order time-difference of the STPIR to further reduce the influence of the observational noise. The proposed method was applied to detect cycle slips in BDS observations during a magnetic storm. It shows that the proposed method can be used to detect and repair all possible cycle-slip combinations of BDS un-differenced observations.

子午工程二期计划在漠河、北京、武汉、深圳四地分别建设由一个发射站和三个接收站构成的电离层高频多普勒监测台阵. 本文介绍了为此研制的电离层高频多普勒监测仪的进展和试观测期间取得的一些观测结果. 通过与电离层测高仪进行交叉对比，设备的性能和探测能力得到了验证. 目前该设备已部署7个站点进行试观测，本文报告了该设备探测到的太阳耀斑导致的电离层扰动、电离层行进式扰动、大尺度电场导致的多站同时扰动等多种现象. 未来子午工程二期建成后，该设备将具备我国上空北至漠河、南至广东的电离层扰动监测能力，并与其它探测手段融合发挥空间天气综合监测网络的最大效能.

We investigate how the Martian dayside ionospheric structure is modified by crustal magnetic field (CMF) strength and upstream solar wind pressure by analyzing electron density data from the Langmuir Probe and Waves instrument onboard the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft. We find that the electron density above the exobase is anticorrelated with the ratio of solar wind's normal dynamic pressure (PSW⊥${P}_{\\text{SW}\\perp }$ ) to CMF magnetic pressure (PCMF${P}_{\\text{CMF}}$ ). We also analyze the electron density behavior across different magnetic topologies as a function of PSW⊥/PCMF${P}_{\\text{SW}\\perp }/{P}_{\\text{CMF}}$ . The extremely low electron density in the draped topology relates to ionopause‐like structures. The lower electron density in the closed and open topology under higher PSW⊥/PCMF${P}_{\\text{SW}\\perp }/{P}_{\\text{CMF}}$may be attributed to a downward force, potentially the J × B force in the case of closed topology. This study highlights the complex interplay between solar wind and CMF in influencing the Martian dayside upper ionosphere. Plain Language Summary Mars is unique in the solar system because it lacks a global dipole field like Earth and instead has crustal magnetic fields (CMF, i.e., pockets of magnetic fields unevenly distributed on its surface). Such a magnetic scenario yields a very special picture of the interaction between solar wind (a stream of charged particles from the Sun) and the Martian upper atmosphere. For decades, people have found that the structure of the Martian ionosphere (an ionized layer in its upper atmosphere) can be heavily influenced by solar wind dynamic pressure (ram pressure of the stream of charged particles) and CMF strength, but the physics behind this is unclear. Our results indicate that the competition between the solar wind dynamic pressure and CMF strength can induce electromagnetic force, which affects the electron density in the Martian ionosphere. This study sheds light on the detailed physics of the interaction between solar wind and CMF and its implication for the behaviors of the Martian ionosphere. Key Points The electron density in the Martian dayside upper ionosphere is anticorrelated with pressure ratio of solar wind to crustal magnetic field The electron density in closed, open, and draped topology behaves differently as a function of this ratio The J × B force may play an important role in the effect of crustal magnetic field and solar wind conditions on the Martian upper ionosphere

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Using NASA's Global‐scale Observations of the Limb and Disk (GOLD) imager, we report nightside ionospheric changes during the G5 super geomagnetic storm of 10 and 11 May 2024. Specifically, the nightside southern crest of the Equatorial Ionization Anomaly (EIA) was observed to merge with the aurora near the southern tip of South America. During the storm, the EIA southern crest was seen moving poleward as fast as 450 m/s. Furthermore, the aurora extended to mid‐latitudes reaching the southern tips of Africa and South America. The poleward shift of the equatorial ionospheric structure and equatorward motion of the aurora means there was no mid‐latitude ionosphere in this region. These observations offer unique insights into the ionospheric response to extreme geomagnetic disturbances, highlighting the complex interplay between solar activity and Earth's upper atmosphere. Plain Language Summary On Earth's nightside during the super geomagnetic storm that occurred on 10 May 2024, NASA's GOLD imager saw something new: a part of Earth's ionosphere, the southern peak of what typically appears as a double‐peaked structure in the ionospheric density at equatorial and low latitudes, merged with the aurora near the southern tip of South America. This has never been reported before. Additionally, the boundary of the aurora expanded further equatorward than usual. These observations of what happened in the Earth's ionosphere during this super storm are reported for the first time in this study. Key Points EIA crests between ∼70° and 35°W moved poleward, with northern and southern crest reaching ∼38°N and ∼35°S Mlat in the American sector Southern EIA crest moved poleward with a speed of ∼450 m/s near ∼55°W Glon during strong IMF Bz and d(Dst)/dt First observation of the merging of an EIA crest with the aurora indicating no mid‐latitude ionosphere

A new observational phenomenon, named Simultaneous Global Ionospheric Density Disturbance (SGD), is identified in GNSS total electron content (TEC) data during periods of three typical geospace disturbances: a Coronal Mass Ejection‐driven severe disturbance event, a high‐speed stream event, and a minor disturbance day with a maximum Kp of 4. SGDs occur frequently on dayside and dawn sectors, with a ∼1% TEC increase. Notably, SGDs can occur under minor solar‐geomagnetic disturbances. SGDs are likely caused by penetration electric fields (PEFs) of solar‐geomagnetic origin, as they are associated with Bz southward, increased auroral AL/AU, and solar wind pressure enhancements. These findings offer new insights into the nature of PEFs and their ionospheric impact while confirming some key earlier results obtained through alternative methods. Importantly, the accessibility of extensive GNSS networks, with at least 6,000 globally distributed receivers for ionospheric research, means that rich PEF information can be acquired, offering researchers numerous opportunities to investigate geospace electrodynamics. Plain Language Summary Electric fields of solar wind and geomagnetic disturbance origin can penetrate into the low latitude upper atmosphere, influencing the ionospheric dynamics and electron density variations. This study employs a new method that utilizes global and continuous GNSS total electron content (TEC) observations to investigate the electric field effects. The analysis focuses on three geospace disturbance events of different intensities and solar‐terrestrial conditions. The study identifies a novel phenomenon named Simultaneous Global Ionospheric Density Disturbance (SGD), primarily occurring on the sunlit portion of the Earth's ionosphere and also near dawn hours with 1% or larger amplitudes of the background TEC, or a few tenths of a TEC unit (1016 m3). The remarkable global extent of ionospheric responses to minor solar‐geomagnetic conditions is noteworthy. The solar wind magnetic field directed southward is highly correlated with most SGDs, lasting for up to 30 min. The findings present an effective approach for continuously monitoring electric field penetration and ionospheric impacts, leading to an improved understanding of space weather and its technological implications. Key Points Simultaneous global ionospheric disturbances (SGDs) are often observed even during minor solar and geomagnetic disturbances SGDs occur predominately on dayside and are related to penetration electric fields (PEFs) of solar wind and geomagnetic disturbance origin Global GNSS networks offer a novel and effective technique for continuous PEF monitoring, providing rich data sets for further study

Increasing CO2 concentration is known to cause global‐scale changes throughout the atmosphere and ionosphere. However, how the global change affects smaller‐scale ionospheric phenomena remains unclear. This study investigates for the first time the impact of increasing CO2 on the formation of sporadic‐E layer, a key space weather element links to HF/VHF communications. Using the Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy (GAIA), simulations were conducted for normal (315 ppm) and doubled CO2 (667 ppm) levels to evaluate changes in the vertical ion convergence (VIC). Simulation results reveal that the VIC is enhanced in the 100–120 km altitude range globally. Furthermore, VIC hotspots shift downward by approximately 5 km and exhibit changes in their diurnal pattern. The reduction of the ion‐neutral collision frequency alongside changes in the zonal wind shear contributes significantly to these changes. Our study suggests that, as CO2 concentrations continue to rise, future Es layers may become more intense, last longer, and form at lower altitudes compared to present‐day conditions. These changes could potentially challenge the reliability of HF communication systems in the future.

A key element of magnetosphere‐ionosphere coupling is the precipitation of electrons, which transfers energy from the collisionless, rarefied magnetospheric plasma into the dense, collisional ionosphere. Two distinct types of such precipitation are: auroral electrons, which carry field‐aligned currents and are responsible for auroral arc formation, and energetic electrons, which contribute to ionization in the lower ionosphere. Although these two electron populations are well separated in energy, this study reveals a close connection between them, likely due to the collocation of their equatorial drivers. Using low‐Earth orbit satellite measurements from Electron Losses and Fields Investigation of energetic (50–1,000 keV) electron precipitation and ground‐based all‐sky imager observations of auroral arcs, we demonstrate how the auroral arc structures and locations strongly correlate with the boundaries or gradients of >50 ${ >} 50$ keV precipitation. We identify three typical correlation patterns and discuss their implications for the physics of magnetosphere‐ionosphere coupling.

The weakly ionized plasma in the Earth's ionosphere is controlled by a complex interplay between solar and magnetospheric inputs from above, atmospheric processes from below, and plasma electrodynamics from within. This interaction results in ionosphere structuring and variability that pose major challenges for accurate ionosphere prediction for global navigation satellite system (GNSS) related applications and space weather research. The ionospheric structuring and variability are often probed using the total electron content (TEC) and its relative perturbations (dTEC). Among dTEC variations observed at high latitudes, a unique modulation pattern has been linked to magnetospheric ultra‐low‐frequency (ULF) waves, yet its underlying mechanisms remain unclear. Here using magnetically conjugate observations from the THEMIS spacecraft and a ground‐based GPS receiver at Fairbanks, Alaska, we provide direct evidence that these dTEC modulations are driven by magnetospheric electron precipitation induced by ULF‐modulated whistler‐mode waves. We observed peak‐to‐peak dTEC amplitudes reaching ∼${\\sim} $0.5 TECU (1 TECU is equal to 106${10}^{6}$electrons/m2${\\mathrm{m}}^{2}$ ) with modulations spanning scales of ∼${\\sim} $5–100 km. The cross‐correlation between our modeled and observed dTEC reached ∼${\\sim} $0.8 during the conjugacy period but decreased outside of it. The spectra of whistler‐mode waves and dTEC also matched closely at ULF frequencies during the conjugacy period but diverged outside of it. Our findings elucidate the high‐latitude dTEC generation from magnetospheric wave‐induced precipitation, addressing a significant gap in current physics‐based dTEC modeling. Theses results thus improve ionospheric dTEC prediction and enhance our understanding of magnetosphere‐ionosphere coupling via ULF waves. Plain Language Summary Radio signals are refracted or diffracted as they traverse the ionosphere filled with free electrons. The ionosphere TEC, which is the total number of electrons along the raypath from the satellite to a receiver, helps to correct refractive errors in the signal, while its relative perturbations dTEC can be used to probe diffractive fluctuations known as ionosphere scintillation. Refractive error degrades GNSS positioning service accuracy while scintillation leads to signal reception failures and disrupts navigation and communication. Thus, an accurate understanding and modeling of TEC and dTEC is vital for space weather monitoring and GNSS‐related applications. This study analyzes conjugate observations of ionospheric dTEC from a ground‐based GPS receiver and magnetospheric whistler‐mode waves (a distinct type of very‐low‐frequency electromagnetic waves) from the THEMIS spacecraft, which were well‐aligned both in time and space. We find a good cross‐correlation (∼${\\sim} $0.8) between observed and modeled dTEC, driven by whistler‐induced magnetospheric electron precipitation. These results point to whistler‐mode waves as the driver of the observed dTEC. Both dTEC and whistler‐mode wave amplitudes were modulated by ULF waves. These findings enhance physics‐based ionospheric TEC prediction and our understanding of magnetosphere‐ionosphere coupling. Key Points Space‐ground conjugate observations point to magnetospheric whistler‐mode waves as the driver of ionospheric TEC perturbations (dTEC) The amplitude spectra of dTEC and whistlers are consistent and the cross‐correlation between modeled and observed dTEC reaches 0.8 Whistler‐mode wave amplitudes and dTEC are modulated by ULF waves, which exhibit concurrent compressional and poloidal mode variations