Thermosphere Ionosphere Electrodynamics General Circulation Model was used to investigate the underlying physical processes of the thermospheric and ionospheric vortex-like structure over East Asia region in November 2003 superstorm. Horizontal neutral winds with a vortex configuration modulate the composition (O/N2) perturbations, forming a two-dimensional vortex-like structure. Vertical winds also have a positive contribution to the final shape of this structure in the altitude distribution. The ionospheric vortex-like structure below the ionospheric peak height (hmF2) is dominated by chemical effects (O/N2 enhancements) and neutral wind transport, while it is directly controlled by the neutral wind transport above the hmF2. Decreases in plasma density within the core region of this structure, driven by E & times; B drifts at all altitudes, also contribute to its formation. Analysis of the forcing terms driving the wind vortex in the middle thermosphere reveals the dominant role of pressure gradients, alongside the combined action from the Coriolis force and horizontal momentum advection. In the upper thermosphere, the ion drag becomes significant, but only partially offsets the substantial positive effects of pressure gradients. Furthermore, controlled numerical experiments demonstrate that the storm intensity is not the single trigger mechanism for this structure. Instead, the asymmetrical prevailing circulation is more beneficial to the formation of the vortex-like structure. The storm onset time also affects the formation and location of this structure, although it is more likely to appear near the magnetic poles, primarily in the American and East Asian sector.

Abstract The irregularities of ionospheric plasma bubbles (EPBs) sequentially generated over wide longitudes are expected to share similar lifetime under normal conditions. In this study, we report a special case where the EPB irregularity lifetime over wide longitudes showed a quasi‐wavelike undulation pattern with wavelength of ∼3,000 km, that is, the lifetime of EPB irregularities sequentially generated at different longitudes experienced several gradually decreasing/increasing cycles. Irregularities with longer (shorter) lifetime corresponded to the EPBs with larger (smaller) development in latitude/altitude. Further observations revealed that smaller‐scale (hundred‐kilometer) and larger‐scale (thousand‐kilometer) waves may coexist at the bottomside of ionosphere around sunset. The former acted as the seeding source for EPB generation, whereas the latter superimposed on PRE and modulated EPB development in altitude over different longitudes, leading to the wavelike undulation morphology in irregularity lifetime ultimately. This study provides implications on how the complex wave structures influence EPB morphology over wide longitudes.

Longitudinal structuring of the ionosphere reflects the coupled neutral and electrodynamic processes that shape regional plasma transport and space weather variability; however, its behavior at low-midlatitudes remains incompletely understood. Here we investigate longitudinal variations in ionospheric total electron content (TEC) over South America during the 2020-2021 solar minimum using ground-based Global Navigation Satellite System observations, COSMIC-2 radio occultation data, and ICON in situ measurements. We identify a previously unreported diurnal east-west differential structure extending across low- and midlatitudes during local summer (November-February). The observed pattern exhibits a three-phase evolution: enhanced daytime TEC in the western sector before local noon, a post-noon to sunset reversal with higher TEC in the eastern sector, and a subsequent return to western dominance. Simulations from the Horizontal Wind Model 14 reproduce the TEC structure near noon and after sunset but show opposite behavior in the early morning, indicating that neutral wind forcing alone cannot account for the observations. Multi-instrument analysis further reveals that longitudinal gradients in electric fields and field-aligned diffusion contribute significantly to the TEC asymmetry. These results demonstrate that low-midlatitude longitudinal TEC variations over South America arise from the interplay of multiple physical mechanisms and exhibit substantially greater complexity than their midlatitude counterparts, highlighting the need to incorporate coupled neutral and electrodynamic processes in regional ionospheric modeling and space weather prediction.

In this study, daytime F-region irregularities were observed at low latitudes during the main phase of the 12 November 2025 strong magnetic storm, causing intense very high frequency radar echoes ranging hundreds of kilometers in altitude. They were generated mainly at the F-region topside, associated with significant plasma density enhancement possibly driven by storm-time electric field polarity transition from eastward to westward, or meridional wind. The enhanced plasma density could provide favorable downward density gradient for generating the daytime irregularities via gradient drift instability at F-region topside under westward storm-time electric field. The irregularities occurred over a large zonal region spanning thousands of kilometers. The study provides new possibility of low-latitude F-region irregularities different from the major irregularity types over low latitudes, which could be the first report of its kind at this region.

This study analyzes extensive ground-based and space-borne ionospheric data over East Asia during the geomagnetic storm of 1-2 October 2002, focusing on regional differences during the main and recovery phases. During the main phase, strong negative disturbances propagated from high to mid-latitudes, affecting Northeast Asia near sunset, while prolonged southward interplanetary magnetic field Bz drove sustained prompt penetration electric fields (PPEFs) into mid- and low latitudes, producing local time (LT)-dependent positive storm effects over China and Japan. However, PPEF did not consistently uplift hmF2 at magnetic latitudes 15-25 degrees N. Rapid universal time (UT)-and latitude-dependent changes in downward diffusion led to complex responses: hmF2 at 15-20 degrees N rose slightly and then declined nearly synchronously before recovering, whereas uplift occurred near 25 degrees N. During the recovery phase, mid-latitude Japan exhibited a strong negative storm effect, in contrast to a weak positive response at comparable latitudes in central and western China. ROCSAT-1 observations show that the disturbance dynamo electric field displayed distinct UT-LT evolution, with a stronger westward component over the Japanese sector and an eastward component over eastern China. Simulations using the Thermosphere Ionosphere Electrodynamics General Circulation Model reproduced the longitudinal gradient in electron density across East Asia. Diagnostic analysis indicates that the pronounced zonal gradient in total electron content is mainly controlled by longitudinal variations in the electric field, while chemical processes, neutral wind transport, and ambipolar diffusion play secondary roles. These results demonstrate marked regional variability in the East Asian ionosphere even under non-extreme geomagnetic activity.

Abstract Intense Global Navigation Satellite System (GNSS) amplitude scintillations usually occur in nighttime at low latitudes due to ionospheric plasma bubble irregularities. During daytime at middle latitudes, previous studies found that the sporadic E (Es) layer could lead to GNSS amplitude scintillations, which however, is relatively weak, for example, S4 generally below 0.3. In this study, relatively intense daytime GNSS amplitude scintillations with S4 up to ∼0.5 were observed linked with strong Es with a top frequency up to 20 MHz. The strong Es layer, manifested as pulse‐like disturbances in total electron content time series and narrow‐band‐like structures elongating ∼2,000 km in the horizontal plane, caused short‐duration signal fading up to ∼3 dB in the raw GNSS data, thus resulting in the relatively intense scintillations. Further analysis found that the strong Es was possibly multi‐layered in the vertical direction, which may complicate radio‐wave propagation between multiple layers and further enhance signal fading and scintillation.

Deep learning has become a central focus in space weather research, especially for accurately predicting ionospheric parameters such as Total Electron Content (TEC). This paper devised three prediction methods: the Global Data-Driven Method, the Regional Data-Driven Method, and the Single-Station Data-Driven Method, evaluating their performance extensively. These methods employ deep learning algorithms to analyze historical observational data and predict future variations in the TEC. Comparative analysis revealed that the Single-Station Data-Driven Method surpasses the Global Data-Driven Method and Regional Data-Driven Method in predictive accuracy. The Single-Station Data-Driven Method is a technique that utilizes data from a single observation station, thereby enhancing prediction accuracy through the construction of models comprising a substantial number of parameters. This indicates that complex models may not have better predictive performance than multiple simple models. However, predictions from the Single-Station Data-Driven Method may show discontinuities and instability. The Regional Data-Driven Method exhibits superior accuracy in short-term predictions compared to the Global Data-Driven Method. Conversely, within the context of medium to long-term predictions, the Global Data-Driven Method demonstrates improved accuracy. This phenomenon can be attributed to the Regional Data-Driven Method, which excels in short-term predictions due to its strong correlation with local TEC data. In contrast, the Global Data-Driven Method is more accurate for long-term predictions as it captures global ionospheric evolution and uses a solar-geographical reference frame. (c) 2025 Published by Elsevier B.V. on behalf of COSPAR.

In this study, we analyze a discontinuous negative storm evolution process in the ionosphere over the East Asian region during the recovery phase of the geomagnetic storms on 20 and 21 November 2003, using data from the Global Ultraviolet Imager (GUVI) for [O] and [N 2 ] column density ratio (Σ[O]/[N 2 ]), Total Electron Content (TEC), as well as ionospheric parameters, namely, the ionospheric peak height (hmF2) and peak electron density (NmF2), supplemented by Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulations. The event lasted 3–4 hr and may represent the first simultaneous observation of vortex‐like structures in both the thermosphere and ionosphere since Solar Cycle 23. Our research findings suggest that this structure is most probably related to the vortex‐like structure of thermospheric composition caused by thermospheric winds blowing from the Southern Hemisphere under the influence of pressure gradient force and Coriolis force.

F‐region bottom‐type scattering layers (BSLs) occurring over equatorial and low latitudes may act as the precursor of plasma bubbles, usually observed by narrow‐beam very high frequency radars. However, their spatial features remain unknown due to the radar narrow field‐of‐view. Here we report a case of localized BSL not accompanying plasma bubbles firstly observed by an all‐sky radar at low latitude. Based on radar interferometry over a large field‐of‐view, the BSL was revealed to occur over a limited area northeastward of the radar and did not cause scintillation when Global Navigation Satellite System satellites passed through. The BSL vertical displacement precisely followed the F‐layer bottom fluctuation, without obvious horizontal movement. Interestingly, the localized BSL caused weak spread‐F traces in the ionograms indicating irregularities from specific directions, which are distinct from the satellite traces or range spread F related to plasma bubble development thus could serve as a new signature of BSL in future studies.

Ionospheric plasma bubbles refer to density depletion structures in the ionosphere, which are usually seen in the electron density profiles observed by radar, and have never been observed in the density profiles of metallic ions. In this letter, we report the first observation of plasma bubble signatures captured by lidar, manifested as depletion and bifurcation structures in the density profile of a Ca + patch appearing at F‐region height over low latitude. Different from majority of plasma bubbles observed by radar mainly seen in F‐region altitude, the bubble depletion signatures visualized by lidar at low latitude could be down to below the F layer bottom, that is, valley‐region altitude ∼150 km. The results highlight the possibility of plasma bubbles to create depletion structures in metallic ion profiles appearing at F region, and provide a new method to investigate plasma bubbles by lidar.

Valley region irregularities (VRIs) have been previously investigated using radar, ionosonde, and rocket‐borne in situ observations. In this paper, based on a joint observational experiment by lidar and radars performed in Hainan, China, we report a case of low‐latitude VRIs generated in association with uplifted metallic ions for the first time, which was observed during the 2025 New Year magnetic storm. The uplifted ions accumulated at valley region altitudes ∼150 km where VRIs were generated. It is suggested that the metallic ion uplifting could be driven by storm‐time eastward penetration electric fields and/or polarization electric fields associated with equatorial plasma bubbles. It is hypothesized that the observed ion layer was formed by ion convergence produced by the joint action of electric field and meridional neutral wind and became unstable by the gradient drift instability generating the VRIs.

While most equatorial plasma bubbles (EPBs) dissipate before or around sunrise, some can persist into the daytime in the topside ionosphere. Using measurements from a phased array radar of the Meteor and ionospheric Irregularity Observation System (MIOS) and ground-based Global Navigation Satellite System (GNSS) receivers, this paper presents cases of daytime ionospheric topside irregularities observed by the MIOS radar at low latitudes in China under both geomagnetic storm and quiet conditions. By using the rate of change of total electron content index from GNSS receivers combined with plasma zonal drifts from a model, the origins of these daytime ionospheric topside irregularities were successfully identified. The results show that the daytime ionospheric topside irregularities observed by the MIOS radar were the remnants of EPBs generated during post-midnight or post-sunset hours on the previous night. The daytime ionospheric topside irregularities originated from the nighttime EPBs initially generated at the same, western, or eastern longitudes of the radar site. One interesting finding is that EPBs were first detected by the MIOS radar during nighttime, and their remnants returned to the radar site during the daytime and were detected once again on some occasions.

An unusual case of a large ionospheric longitudinal gradient in East Asia on 11 May 2021 occurred during a geomagnetically‐quiet period. It shows the largest east‐west difference in electron density at Yamagawa and Wuhan stations when Kp < 2 for 13:00–17:00 LT in 2021. Ground‐ and satellite‐based observations consistently confirm that there was a decrease in the west and an increase in the east of ∼125°E, with hemispherical symmetric with respect to the geomagnetic equator. The potential mechanism is further investigated through multi‐observations of plasma drifts and neutral winds, provided by the Ionospheric Connections Explorer satellite and newly‐established Sanya Incoherent Scatter Radar. The prominent longitudinal gradient in plasma drifts, electro‐dynamically coupled with E‐region winds, is suggested as the contributor for the east‐west differences, together with the strong gradient of F‐region winds in phase. This study provides direct evidence linking atmosphere perturbations to unusual longitudinal structure of terrestrial space plasma environment.

A coupled thermosphere-ionosphere tongue-like structure was observed in the daytime at middle latitudes by ground-based Global Navigation Satellite System (GNSS) and Global-scale Observations of the Limb and Disk (GOLD) observations during the storm recovery phase on 12 May 2021. The storm-induced variations in total electron content (TEC) and the column density ratio of O to N2 (& sum;O/N2) both showed a relatively narrow region of enhancement in latitude, originating from low latitudes and surrounded by depleted regions. The concurrent neutral temperature observations also showed a tongue-like decrease surrounded by temperature enhancements. The Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) qualitatively reproduced the observed thermosphere-ionosphere structure. The simulations indicate that the formation of the TEC tongue-like structure was dominated by the enhanced Sigma O/N2. Unlike the previously reported tongue of ionization (TOI) driven by E x B drifts, the tongue-like structure occurred at relatively lower geomagnetic latitudes (similar to 30 degrees $\mathit{{}<^>{\circ}}$-similar to 65 degrees $\mathit{{}<^>{\circ}}$) and had a smaller magnitude of enhancement. This is the first time that the concurrent tongue-like structures in thermospheric composition, temperature and electron density are observed, which advances the understanding of thermosphere-ionosphere coupling.

In this study, multiple instrumental observations including Global Navigation Satellite System total electron content (TEC), plasma drift velocity measured by Sanya (18.3 degrees N, 109.6 degrees E, dip latitude 12.6 degrees N) Incoherent Scatter Radar (SYISR) and F2-layer peak electron density (NmF2) and peak height (hmF2) from ionosonde and SYISR have been used to investigate ionospheric responses during a minor yet highly geo-effective geomagnetic storm on 26-27 May 2021. Our findings revealed a significant time delay in the post-sunset plasma density enhancement peak across different latitudes over East Asia, that is, the lower the geographic latitude, the earlier the peak appeared. The plasma density enhancement was accompanied by a decrease in hmF2 prior to NmF2 peak around sunset. The newly built SYISR measurements around sunset verified that the field-aligned drift decreased the ionosphere with a notable time delay at latitude, beneficial to electron density enhancements at lower altitudes within the 16-30 degrees N latitudinal band but a small TEC change. While at 30-50 degrees N, it is possible that the competition between storm-induced equatorward winds and downward field-aligned drift depressed hmF2 decline and the buildup increased both NmF2 and TEC. The ICON observations suggested that the meridional wind during this minor storm event modulated the direction of plasma transport near sunset, playing a dominant role in post-sunset plasma density enhancement from low to middle latitudes. These results provide fresh insight into the electrodynamic mechanisms of post-sunset enhancements at middle and low latitudes over East Asia, and also enhance our understanding of the intricate behaviors within the ionosphere-thermosphere system in response to a minor storm. The local time of post-sunset plasma density enhancement peak had a notable time delay with increasing latitude during a minor storm The plasma drift during postsunset hours observed by Sanya incoherent scatter radar exhibited strong response to the minor geomagnetic storm The meridional winds changing from equatorward to poleward explained the post-sunset enhancement from low to middle latitudes

AbstractLow latitude ionosphere experiences complex dynamical and electrodynamical processes, which make the spatiotemporal variations of the corresponding electron density complicated and therefore influence trans‐ionosphere radio communications. The monitoring of low latitude dynamical drivers, such as neutral wind and ionospheric electric field, is essential for both dynamic mechanism investigations and applications. The Sanya Incoherent Scatter Radar Tristatic System (SYISR‐TS) was proposed with the main objective of low latitude ionospheric monitoring and investigation and has been successfully developed over the past decade. The system consists of the Sanya (18.3°N, 109.6°E) trans‐receiving main station with key parameters of ∼1,600 m2 antenna aperture, >4 MW peak power, <120 K system noise temperature, and ∼46 dBi normal gain, and Danzhou (19.5°N, 109.1°E) and Wenchang (19.6°N, 110.8°E) receiving only stations with key parameters of ∼790 m2 antenna aperture, <130 K system noise temperature, and ∼43 dBi normal gain. Three stations form a quasi‐equilateral triangle at Hainan Island and use Global Navigation Satellite System satellite common view technique to achieve the time synchronization with the uncertainty of the timing and time synchronization less than 50 and 10 ns, respectively. Initial collaborative satellite tracking and ionospheric common volume experiments among three stations have confirmed the detection ability of SYISR‐TS and the feasibility of achieving its scientific goals in the future.

In this study, we offer an extensive examination of the F-region ionospheric disturbances during the May 2024 superstorm, focusing primarily on the middle-low latitude regions of East Asia. Our analysis is grounded in a wealth of data sources including Total Electron Content (TEC), ionospheric parameters NmF2 and hmF2, Electron Density Profile (EDP) retrieved from Radio Occultation (RO) data, and & sum;[O]/[N2] from the Global Ultraviolet Imager (GUVI), among others, complemented by model simulations. The observed negative ionospheric storm effect, characterized by a significant and long-lasting reduction in electron density across the entire China, commenced immediately following the sudden storm commencement (SSC) on 10 May and continued through the main and early recovery phase of the storm on 11 May. On 11-12 May, positive ionospheric storm impacts were initially observed in a restricted geographical area from the post-midnight to sunrise, first manifesting over the eastern regions of China and then shifting to the central regions. Subsequently, a pronounced negative storm effect persisted throughout the later stages of recovery phase. In contrast, the western regions of China experienced a positive storm effect on 12 May followed by a comparatively mild negative storm phase. This persistent extensive zonal gradient in electron density across the East Asian region resembles the scenarios depicted in prior superstorms attributed to the thermospheric circulation patterns. The disparity in the ionospheric response from east to west in this area is probably a common feature during superstorms, potentially resulting from an arch-shaped structure of elevated & sum;[O]/[N2]. The superstorm in May 2024 led to a significant and persistent decrease in electron density at middle-low latitude over Eastern China Positive ionospheric effects spread from post-midnight eastern China to central China, with western China seeing a weaker positive storm The disparity in ionospheric response from east to west mainly arose from an arch-shaped structure of elevated & sum;[O]/[N2]

The G-condition (NmF2 <= NmF1) was observed by ground-based ionosondes at Mohe and Beijing during the geomagnetic storm occurred on 23 and 24 April 2023. We studied exospheric temperature (Tex) responses during the G-condition. Tex was derived from electron density (Ne) profiles (similar to 150-200 km) by the method proposed by Li et al. (2023, ). The retrieved Tex showed obvious enhancements, with relative deviation of similar to 10%-35% and similar to 3%-20% at Mohe and Beijing, respectively. Additionally, chemical reaction rate increased by similar to 15%-100% and similar to 13%-30%, and O/N2 decreased by similar to 17%-35% and similar to 23%-30% at Mohe and Beijing, respectively. Under photochemical equilibrium assumption, peak Ne is inversely proportional to chemical reaction rate and proportional to O/N2. Increased chemical reaction rate and decreased O/N2 indicate a decrease in peak Ne. Compared to the increased Tex, the relative enhancement in Tex is more significantly associated with the G-condition, with relative deviation above similar to 10% during the G-condition. Normally, the peak Ne in the F2 layer (NmF2) is the largest in the full Ne profile. G-conditions are special events in ionospheric observations, when NmF2 is smaller than or equal to NmF1 (i.e., NmF2 <= NmF1). Due to shielding effect of the F1 layer, no information above hmF1 can be obtained from ground-based ionosondes, and Ne peak height is typically below 200 km. In previous works, incoherent scatter radar (ISR) observations are usually used to extract thermospheric parameters (Tex, neutral composition and thermospheric wind). In this paper, ground-based ionosonde observations (similar to 150-200 km) at Mohe and Beijing prior to, during and after the G-condition (from 22 to 26 April 2023) were selected to derive Tex using the method proposed by Li et al. (2023, ). Furthermore, corresponding neutral temperature (Tn) and densities were further calculated by replacing the Tex module in the NRLMSISE-00 model with the retrieved Tex. In our analysis, the retrieved Tex and chemical reaction rate showed significant enhancements and O/N2 showed obvious decrease compared to quiet reference days. This is consistent with the analysis of the mechanism of G-conditions formation in previous studies. The G-condition (NmF2 <= NmF1) was observed by ground-based ionosondes at Mohe and Beijing during the G4 storm on 24 April 2023 Relative enhancements in Tex during the G-condition were greater than that in other periods, with relative deviation above similar to 10% Enhanced Tex with corresponding increased chemical reaction rate and decreased O/N2 collectively contributed to a decrease in Ne

This study investigated the latitudinal variations of post-sunset enhancements in the ionospheric electron density during the geomagnetic quiet period in May 2021 with a combination of high-precision ionospheric parameters obtained from four ionosondes, Beidou geostationary satellite (BD-GEO) receiver network and Sanya incoherent scatter radar (SYISR). We identified four categories of post-sunset enhancement phenomena (Types 1-4), each with unique spatial and temporal evolutions, yet uniformly accompanied by a decrease in hmF2. Measurements of plasma drift vector velocities from SYISR and hmF2 gradients across various latitudes provided pivotal insights, confirming that the ionospheric post-sunset enhancements can result from downward plasma motion due to westward electric field, downward field-aligned drift, or a combination of both. For Type 1, dominated by field-aligned drift, plasma density enhancements not only intensify at low latitudes but may also extend to mid-latitudes, exhibiting a distinct temporal delay with increasing latitude. In contrast, Type 4, primarily driven by the westward electric field, is characterized by modest increases in plasma density confined to localized low-latitude regions, with no observable latitudinal time delay in the peak of enhancements. Types 2 and 3, which are subject to the combined influence of the westward electric field and field-aligned drift, exhibit plasma density increases at certain low-latitude areas, with Type 2 presenting a delayed pattern and Type 3 showing none with rising latitude. Meanwhile, neutral winds can partially account for the observed post-sunset enhancement from low to middle latitudes. These findings offer new insights into the factors influencing ionospheric behavior after sunset. Four types of distinctive latitudinal variations of post-sunset enhancements were identified with multiple data sets during the quiet period Accompanying the increase in the electron density at sunset, the decrease in hmF2 is favorable for the formation of post-sunset enhancement Downward field-aligned drift and westward electric field govern the spatial scale of post-sunset enhancements at low and middle latitudes

AbstractPlasma blob is generally a low‐latitude phenomenon occurring at the poleward edge of equatorial plasma bubble (EPB) during post‐sunset periods. Here we report a case of midlatitude ionospheric plasma blob‐like structures occurring along with super EPBs over East Asia around sunrise during the May 2024 great geomagnetic storm. Interestingly, the blob‐like structures appeared at both the poleward and westward edges of EPBs, reached up to 40°N magnetic latitudes, and migrated westward several thousand kilometers together with the bubble. The total electron content (TEC) inside the blob‐like structures was enhanced by ∼50 TEC units relative to the ambient ionosphere. The blob‐like structure at the EPB poleward edge could be partly linked with field‐aligned plasma accumulation due to poleward development of bubble. For the blob‐like structure at the EPB west side, one possible mechanism is that it was formed and enhanced accompanying the bubble evolution and westward drift.