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The role a geospace plume in influencing the efficiency of magnetopause reconnection is an open question with two contrasting theories being debated. A local-control theory suggests that a plume decreases both local and global reconnection rates, whereas a global-control theory argues that the global reconnection rate is controlled by the solar wind rather than local physics. Observationally, limited numbers of point measurements from spacecraft cannot reveal whether a local change affects the global reconnection. A distributed observatory is hence needed to assess the validity of the two theories. We use THEMIS and Los Alamos National Laboratory spacecraft to identify the occurrence of a geospace plume and its contact with the magnetopause. Global evolution and morphology of the plume is traced using GPS measurements. SuperDARN is then used to monitor the distribution and the strength of dayside reconnection. Two storm-time geospace plume events are examined and show that as the plume contacts the magnetopause, the efficiency of reconnection decreases at the contact longitude. The amount of local decrease is 81% and 68% for the two events, and both values are consistent with the mass loading effect of the plume if the plume's atomic mass is ∼4 amu. Reconnection in the surrounding is enhanced, and when the solar wind driving is stable, little variation is seen in the cross polar cap potential. This study illuminates a pathway to resolve the role of cold dense plasma on solar wind-magnetosphere coupling, and the observations suggest that plumes redistribute magnetopause reconnection activity without changing the global strength substantially.

A multi‐instrument study is conducted at the dayside polar ionosphere to investigate the spatio‐temporal evolution of scintillation in Global Navigation Satellite System (GNSS) signals during non‐storm conditions. Bursts of intense amplitude and phase scintillation started to occur at ∼ ${\sim} $ 9 MLT and persisted for more than 1 hour implying the simultaneous existence of Fresnel and large‐scale sized irregularities of significant strength in the pre‐noon sector. Measurements from the EISCAT radar in Svalbard (ESR) revealed the presence of dense plasma structures with significant gradients in regions of strong Joule heating/fast flows and soft precipitation when scintillation was enhanced. Plasma structuring down to Fresnel scales were observed both in the auroral oval as well as inside the polar cap with the associated amplitude scintillation exhibiting similar strengths regardless of whether the density structures were in regions of active auroral dynamics or not. The observations are placed within the context of different sources of free energy, providing insights into the important mechanisms that generate irregularities capable of perturbing GNSS signal properties in the dayside ionosphere. Furthermore, a strong negative excursion in the interplanetary magnetic field (IMF) By ${B}_{y}$ component during the northward turning of Bz ${B}_{z}$ led to the transport of a depleted region of plasma density into the post‐noon sector that significantly weakened both amplitude and phase scintillation. Plain Language Summary: Ionospheric scintillation is a disturbance imposed by the ionosphere on radio signals of satellites in the form of rapid fluctuations in amplitude and phase. They are caused by electron density structures of varying sizes as they move across the path between a satellite signal and a ground based receiver. During strong scintillation, tracking signals become difficult thereby affecting technologies dependent on positioning, navigation and timing (PNT) services. It is therefore important to understand dynamics of the ionosphere that would result in enhanced scintillation in order to develop prediction or mitigation strategies for products using PNT information. In this study, we present evidence for the occurrence of intense amplitude and phase scintillation during quite geomagnetic conditions in the high latitude ionosphere. Our analysis revealed that large density structures propagating from lower latitudes can be modulated by different ionospheric processes such as fast flows and/or soft precipitation generating irregularities of varying scale‐sizes which are associated with scintillation. Additionally, we also observed the depletion of irregularities in relation to the variation of interplanetary magnetic field components which, from a practical viewpoint, are beneficial for the users of satellites technologies and services due to the reduced impact of scintillation during such periods. Key Points: Intense amplitude and phase scintillation in the pre‐noon sector during non‐storm conditionsStructuring down to Fresnel scales in both the auroral oval and inside the polar capDepletion of Fresnel structures due to IMF Bz and By reversal in the post‐noon sector [ABSTRACT FROM AUTHOR]

This study investigates midlatitude ionospheric variations during the super geomagnetic storm on 10–11 May 2024, utilizing multi‐instrument data from ground‐based sources (Global Navigation Satellite Systems receivers and a Fabry–Perot Interferometer) and space‐based measurements (Swarm and DMSP). We observed several distinct density gradient structures in the midlatitude ionosphere, with the main findings summarized as follows: (a) Significant zonal plasma density enhancements developed continuously in local dusk across the American‐Pacific‐Asian longitude sectors around ±40° $\pm 40{}^{\circ}$ geomagnetic latitude. These midlatitude peaks exhibited a wide longitudinal extension exceeding 150° ${}^{\circ}$ and a prolonged duration of 12–15 hr during the late main phase and early recovery phase of the storm. (b) Strong storm‐enhanced density (SED) was observed in both hemispheres yet with different longitudinal and universal time preferences. In the Northern Hemisphere, significant SED occurred over the American longitude sector during 20:30–22:30 UT on May 10. In the Southern Hemisphere, pronounced SED was observed not only in the American longitudes during 20:30–22:30 UT on May 10 but also in the Australian longitude sector during 02:00–04:00 UT on May 11. Plain Language Summary: The super geomagnetic storm on 10–12 May 2024, known as the Mother's Day Storm, was one of the strongest storms recorded in the Space Age era. This storm induced a series of significant disturbances in the global midlatitude ionosphere, revealing unexpected plasma density gradient structures. Notably, distinct midlatitude plasma density peaks were observed on the poleward side of the equatorial ionization anomaly crests during local dusk. These zonal plasma density enhancements extended across the wide American‐Pacific‐Asian longitude sectors, covering more than 150° ${}^{\circ}$, and persisted for 12–15 hr. Furthermore, strong storm‐enhanced density plume appeared in both hemispheres though with considerable asymmetry. In the Northern Hemisphere, the plume enhancement was more pronounced in the American longitude sector, while in the Southern Hemisphere, the plume intensity was more significant in the Australian longitude sector. These salient and dynamic density gradient structures highlight the complex nature of magnetosphere‐ionosphere‐thermosphere coupling processes during super geomagnetic storms. Key Points: Distinct midlatitude plasma density peaks continuously developed in local dusk across American‐Pacific‐Asian sector around ±40° MLATMidlatitude plasma density enhancements showed a wide zonal extension exceeding 150° in longitude and a prolonged duration of 12–15 hrStrong storm‐enhanced density occurred in both hemispheres, with the Northern (Southern) one being more significant over American (Australian) longitudes [ABSTRACT FROM AUTHOR]

The mid‐latitude ionospheric trough (MLIT), an anomaly in the ionosphere's F layer caused by various mechanisms, affects radio wave propagation. In this study, we investigated the morphology and oscillations of the MLIT using global Global Positioning System total electron content map data between 1 January 2018, and 31 December 2020. The MLIT position varies longitudinally, reaching its farthest equatorward at 60° ${}^{\circ}$W and its farthest poleward at 30° ${}^{\circ}$E. The MLIT occurrence rates peak during the winter and equinoxes and dip in summer, while seasonal variations in MLIT position vary across longitude bands. Heightened geomagnetic activities, quantified by the SME6 index, promote MLIT occurrence, especially during pre‐midnight hours in summer and equinoxes, and shift the MLIT equatorward, particularly during midnight and post‐midnight hours. The MLIT position shows clear local time variation, with a gradual decrease before midnight, stabilization afterward, and a minor resurgence around dawn. Wavelet analysis reveals three distinct periodic components in the MLIT position: 27, 13.5, and 9, with the 27‐day period being the most persistent. Cross‐wavelet and wavelet coherence analyses suggest that solar wind (SW) velocity variations precede changes in the MLIT position. The main factors responsible for the equatorward movement of MLIT are the electric fields in high‐speed SW that enhance the ionospheric convection pattern, and the intensified geomagnetic activities induced by interplanetary shocks. Key Points: The minimum position of mid‐latitude ionospheric trough shows discernible longitudinal variationThree distinct periodic components were observed in the trough's minimum position: 27, 13.5, and 9 daysHigh latitude ionospheric plasma convection plays an important role in controlling the trough's minimum position [ABSTRACT FROM AUTHOR]

This paper conducts a multi‐instrument and data assimilation analysis of the three‐dimensional ionospheric electron density responses to the total solar eclipse on 08 April 2024. The altitude‐resolved electron density variations over the continental US and adjacent regions are analyzed using the Millstone Hill incoherent scatter radar data, ionosonde observations, Swarm in situ measurements, and a novel TEC‐based ionospheric data assimilation system (TIDAS) with SAMI3 model as the background. The principal findings are summarized as follows: (a) The ionospheric hmF2 exhibited a slight enhancement in the initial phase of the eclipse, followed by a distinct reduction of 20–30 km in the recovery phase of the eclipse. The hmF2 in the umbra region showed a post‐eclipse fluctuation, characterized by wavelike perturbations of 10–25 km in magnitude and a period of ∼ ${\sim} $30 min. (b) There was a substantial reduction in ionospheric electron density of 20%–50% during the eclipse, with the maximum depletion observed in the F‐region around 200–250 km. The ionospheric electron density variation exhibited a significant altitude‐dependent feature, wherein the response time gradually delayed with increasing altitude. (c) The bottomside ionospheric electron density displayed an immediate reduction after local eclipse began, reaching maximum depletion 5–10 min after the maximum obscuration. In contrast, the topside ionospheric electron density showed a significantly delayed response, with maximum depletion occurring 1–2.5 hr after the peak obscuration. Plain Language Summary: On 8 April 2024, a total solar eclipse traversed across North America with a dense network of observational equipment in place, providing a great opportunity for analyzing ionospheric effects during the eclipse. This paper presents a multi‐instrument and data assimilation analysis of the three‐dimensional ionospheric electron density response to this solar eclipse, utilizing Millstone Hill incoherent scatter radar data, ionosonde observations, Swarm satellite in situ measurements, and a new TEC‐based ionospheric data assimilation system (TIDAS) over continental US and adjacent regions with the SAMI3 as the background model. The observations and SAMI3‐TIDAS data assimilation reveals the time‐evolving 3‐D spatial distribution of the ionospheric electron density during the eclipse, highlighting key features of altitude‐dependent ionospheric variation with significant discrepancies and time delays between the bottomside and topside ionosphere. Key Points: The altitude‐resolved Ne response to the solar eclipse in the 3‐D domain was effectively reconstructed by TIDAS‐SAMI3 data assimilationThe eclipse led to a substantial ionospheric Ne reduction of 20%–50%, with the maximum depletion occurring in the F region of 200–250 kmThe Ne showed a time‐delayed variation with increasing altitude, from 5 to 10 min in the bottomside to 1–2.5 hr in the topside ionosphere [ABSTRACT FROM AUTHOR]

This paper investigates the midlatitude ionospheric disturbances over the American/Atlantic longitude sector during an intense geomagnetic storm on 23 April 2023. The study utilized a combination of ground‐based observations (Global Navigation Satellite System total electron content and ionosonde) along with measurements from multiple satellite missions (GOLD, Swarm, Defense Meteorological Satellite Program, and TIMED/GUVI) to analyze storm‐time electrodynamics and neutral dynamics. We found that the storm main phase was characterized by distinct midlatitude ionospheric density gradient structures as follows: (a) In the European‐Atlantic longitude sector, a significant midlatitude bubble‐like ionospheric super‐depletion structure (BLISS) was observed after sunset. This BLISS appeared as a low‐density channel extending poleward/westward and reached ∼40° geomagnetic latitude, corresponding to an APEX height of ∼5,000 km. (b) Coincident with the BLISS, a dynamic storm‐enhanced density plume rapidly formed and decayed at local afternoon in the North American sector, with the plume intensity being doubled and halved in just a few hours. (c) The simultaneous occurrence of these strong yet opposite midlatitude gradient structures could be mainly attributed to common key drivers of prompt penetration electric fields and subauroral polarization stream electric fields. This shed light on the important role of storm‐time electrodynamic processes in shaping global ionospheric disturbances. Plain Language Summary: The storm‐time midlatitude ionosphere is a highly dynamic region that can exhibit much more pronounced electron density gradients and disturbances than expected. The combined data from ground‐based and satellite measurements provided valuable insights into the intricate behavior of the midlatitude ionosphere during an intense geomagnetic storm on 23 April 2023. The midlatitude ionosphere was characterized by significant electron density gradient structures, comprising both phenomenal density depletion and exceptional enhancements. Notably, a remarkable band‐like ionospheric super‐depletion structure was observed in local dusk, which extended to ∼40° geomagnetic latitude, corresponding to an altitude of ∼5,000 km above the geomagnetic equator. In contrast, a significant midlatitude ionospheric density enhancement plume appeared simultaneously in local afternoon, which exhibited a dynamic variation with its intensity being quickly doubled and halved in just a few hours. The synchronous occurrence of these striking yet opposing density gradients highlights the importance of electrodynamic effect driven by common key drivers of storm‐time perturbed electric fields. This underscores the complex and interconnected nature of the ionospheric response during intense geomagnetic storms. Key Points: The storm main phase was characterized by coincident nightside bubble‐like ionospheric super‐depletion structure (BLISS) and dayside storm‐enhanced density (SED)The BLISS manifested as a poleward/westward‐streaming channel and extended to ∼40 MLAT, corresponding to an APEX height of ∼5,000 kmThe SED plume experienced a dynamic variation with the plume intensity being quickly doubled and halved in just a few hours [ABSTRACT FROM AUTHOR]

This work investigates mid‐ and low‐latitude ionospheric disturbances over the American sector during a moderate but geo‐effective geomagnetic storm on 13–14 March 2022 (π‐Day storm), using ground‐based Global Navigation Satellite System total electron content data, ionosonde observations, and space‐borne measurements from the Global‐scale Observations of Limb and Disk (GOLD), Swarm, the Defense Meteorological Satellite Program (DMSP), and the Ionospheric Connection Explorer (ICON) satellites. Our results show that this modest but geo‐effective storm created a number of large ionospheric disturbances, especially the dynamic multi‐scale electron density gradient features in the storm main phase as follows: (a) The low‐latitude equatorial ionization anomaly (EIA) exhibited a dramatic storm‐time deformation and reformation, where the EIA crests evolved into a bright equatorial band for 1–2 hr and then quickly separated back into the typical double‐crest structure with a broad crest width and deep equatorial trough. (b) Strong equatorial plasma bubbles (EPBs) occurred with an abnormally high latitude/altitude extension, reaching the geomagnetic latitude of ∼30°, corresponding to an Apex height of 2,600 km above the dip equator. (c) The midlatitude ionosphere experienced a conspicuous storm‐enhanced density (SED) plume structure associated with the subauroral polarization stream (SAPS). This SED/SAPS feature showed an unusual temporal variation that intensified and diminished twice. These distinct mid‐ and low‐latitude ionospheric disturbances could be attributed to the storm‐time electrodynamic effect of electric field perturbation, along with contributions from neutral dynamics and thermospheric composition change. Key Points: A common key driver of storm‐time electric field generated three dynamic ionospheric changes simultaneously from low to subauroral latitudesEquatorial ionization anomaly crests showed merging and separation during interplanetary magnetic field Bz oscillation, and strong equatorial plasma bubbles reached 30° MLAT corresponding to 2,600 km Apex heightSalient storm‐enhanced density associated with subauroral polarization stream occurred in midlatitudes, showing a dynamic temporal variation that intensified and diminished twice [ABSTRACT FROM AUTHOR]