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The transition from lab-scale studies to pilot-scale applications is a critical step in advancing water remediation technologies. While laboratory experiments provide valuable insights into the underlying mechanisms and method effectiveness, pilot-scale studies are essential for evaluating their practical feasibility and scalability. This progression addresses challenges related to operational conditions, effectiveness and energy requirements in real-world scenarios. In this study, the potential of nanopulsed plasma bubbles, when scaled up from a lab environment, was explored by investigating critical experimental parameters, such as plasma gas, pulse voltage, and pulse repetition rate, while also analyzing plasma-treated water composition. To validate the broad effectiveness of this method, various classes of highly toxic organic pollutants were examined in terms of pollutant degradation efficiency and energy requirements. The pilot-scale plasma bubble reactor generated a high concentration of short-lived reactive species with minimal production of long-lived species. Additionally, successful degradation of all pollutants was achieved in both lab- and pilot-scale setups, with even lower electrical energy-per-order (EEO) values at the pilot scale, 2–3 orders of magnitude lower compared to other advanced oxidation processes. This study aimed to bridge the gap between lab-scale plasma bubbles and upscaled systems, supporting the rapid, effective, and energy-efficient destruction of organic pollutants in water. [ABSTRACT FROM AUTHOR]

Plasma bubbles represent notable ionospheric irregularities primarily observed in low latitudes, characterized by plasma depletions exhibiting large spatial scales, which can make a significant impact on the propagation of OTHR (over-the-horizon radar) waves. Firstly, we constructed a three-dimensional model of plasma bubbles, which is modulated by Gaussian function distribution in the horizontal direction, and then we analyzed the impact of EPBs (Equatorial Plasma Bubbles) on the ray path of OTHR shortwaves. When radio waves propagate through EPBs with different RMS ΔN/N, there is a significant difference in the propagation path of OTHR waves. For the EPB with an RMS ΔN/N of 75%, radio waves exhibit more pronounced refraction than those with lower RMS values, the focusing effect of radio waves is more obvious, and the focusing point is relatively lower. In terms of different seasons, OTHR shortwaves propagating through EPBs exhibit different degrees of refraction. In addition, radio waves show the effect of inward focusing in different seasons: the focusing effect is the most pronounced in spring, followed by autumn, then summer, and the weakest in winter. For different solar activities, the impact of EPBs on OTHR shortwaves is more significant in the high-solar-activity year. [ABSTRACT FROM AUTHOR]

In this study, the synergetic action of nanopulsed plasma bubbles (PBs) and photocatalysts for the degradation/mineralization of trimethoprim (TMP) in water was investigated. The effects of ZnO or TiO2 loading, plasma gas, and initial TMP concentration were evaluated. The physicochemical characterization of plasma-treated water, the quantification of plasma species, and the use of appropriate plasma species scavengers shed light on the plasma-catalytic mechanism. ZnO proved to be a superior catalyst compared to TiO2 when combined with plasma bubbles, mainly due to the increased production of ⋅OH and oxygen species resulting from the decomposition of O3. The air–PBs + ZnO system resulted in higher TMP degradation (i.e., 95% after 5 min of treatment) compared to the air–PBs + TiO2 system (i.e., 87%) and the PBs-alone process (83%). The plasma gas strongly influenced the process, with O2 resulting in the best performance and Ar being insufficient to drive the process. The synergy between air–PBs and ZnO was more profound (SF = 1.7), while ZnO also promoted the already high O2–plasma bubbles' performance, resulting in a high TOC removal rate (i.e., 71%). The electrical energy per order in the PBs + ZnO system was very low, ranging from 0.23 to 0.46 kWh/m3, depending on the plasma gas and initial TMP concentration. The study provides valuable insights into the rapid and cost-effective degradation of emerging contaminants like TMP and the plasma-catalytic mechanism of antibiotics. [ABSTRACT FROM AUTHOR]

In the present study, occurrences of amplitude scintillations during the ascending phase of the 25th solar cycle from November 2020 to March 2023 are studied over the equatorial anomaly region Varanasi (latitude 25.31° N, longitude 82.97° E, magnetic dip Lat. 16.2° N). Multi-frequency Global navigation satellite system (GNSS) receiver is used to study the occurrence of amplitude scintillation index S 4. Diurnal, monthly, and seasonal occurrence characteristics of the S 4 index are presented. The scintillation occurrence is observed during nighttime and daytime but is more probable during nighttime. It is observed that maximum scintillation occurred during the equinox season for the solar moderate period whereas the highest occurrence is in summer during the low solar activity period. The highest scintillation occurrences during the summer solstice for a period of low solar activity condition is rare and could be attributed to the gravity waves (GWs) generation due to the weather phenomena in the lower atmosphere. GWs could act as a seeding perturbation in electron density, affecting the growth of ionospheric irregularities through Rayleigh-Taylor instability. The solar flux index (F10.7) is compared with the percentage occurrence of scintillation for the low and moderate solar activity periods to observe the effect of solar activity on scintillation occurrences. Overall, the scintillation occurrence increases with increasing solar activity. To study the effect of geomagnetic storms on scintillations, we have considered seven moderate and intense geomagnetic storms grouped in three categories that occurred during solar cycle 25. It is observed that the occurrence of scintillations is enhanced for the storms with the recovery phase starting at post-midnight. The probability of occurrence of scintillation during the night hours is decreased when the geomagnetic storm occurs during the daytime. [ABSTRACT FROM AUTHOR]

This paper presents the novel simultaneous observations of plasma blobs, MSTIDs and plasma depletions in OI 630 nm all sky airglow images over Srinagar, India (34.1 °N, 74.8 °E) during the night of July 29, 2019, obtained using an airglow imager. Notably, the MSTID bands that followed the plasma blob interacted with a plasma depletion structure and suddenly disappeared, resulting in a reduction in the intensity of the plasma depletion. The SWARM satellite observations during the airglow observations indicated the occurrence of the plasma blob event and showed the conjugate appearance of MSTIDs in both hemispheres. The ROTI maps indicated the absence of EPBs but the occurrence of irregularities near the transition zone just before the presence of plasma blobs in airglow images and at the time of plasma irregularity detection. These observations suggest potential interactions between these phenomena, indicating that the presence of one impacts the other. This paper discusses in detail the observed ionospheric features and time evolution of the occurrences of these events, in addition to their interactions.Utilizingthe satellite observations, including SABER, INSAT-3DR and AIRS, the presence of deep convective clouds and upward propagating gravity waves near the location of the plasma blob is demonstrated, suggesting that convective-generated gravity waves could possibly trigger the formation of plasma blobs. [ABSTRACT FROM AUTHOR]

The aim of the present study was the direct comparison of two popular minerals, bauxite and palygorskite, as adsorbents for the removal of cephalexin (CPX) from aqueous solutions and the regeneration of the spent adsorbents through cold atmospheric plasma. Batch kinetics and isotherm studies were carried out to evaluate the effect of contact time, initial CPX concentration, adsorbent dosage, pH and temperature. The adsorbents were characterized by ATR-FTIR, N2 sorption, SEM and XRD, while several isotherm, kinetic and thermodynamic models were evaluated attempting to shed light on the adsorption mechanisms. CPX adsorption on both adsorbents was better described by Langmuir model, with an adsorption capacity of 112.36 mg/g for palygorskite and 11.79 mg/g for bauxite. Thermodynamics revealed the endothermic and the spontaneous character of the process, indicating chemisorption as the main adsorption mechanism for both adsorbents. The pseudo-second-order and the Elovich models fitted satisfactorily the adsorption onto bauxite, while adsorption onto palygorskite was well presented by Weber–Morris model, indicating that pore diffusion is also involved in the process. The adsorption capacity of both minerals decreased significantly after being used for several adsorption cycles and then almost completely recovered (regeneration efficiency was 99.6% and 98% for palygorskite and bauxite, respectively) inside a novel cold plasma microbubble reactor energized by high-voltage nanopulses, revealing the potential of these adsorbents to be reused. In addition to the regeneration of the adsorbents, the cold plasma completely eliminated the CPX transferred from the solid to the aqueous phase during the regeneration process. [ABSTRACT FROM AUTHOR]

Abstract The aim of the present study was the direct comparison of two popular minerals, bauxite and palygorskite, as adsorbents for the removal of cephalexin (CPX) from aqueous solutions and the regeneration of the spent adsorbents through cold atmospheric plasma. Batch kinetics and isotherm studies were carried out to evaluate the effect of contact time, initial CPX concentration, adsorbent dosage, pH and temperature. The adsorbents were characterized by ATR-FTIR, N2 sorption, SEM and XRD, while several isotherm, kinetic and thermodynamic models were evaluated attempting to shed light on the adsorption mechanisms. CPX adsorption on both adsorbents was better described by Langmuir model, with an adsorption capacity of 112.36 mg/g for palygorskite and 11.79 mg/g for bauxite. Thermodynamics revealed the endothermic and the spontaneous character of the process, indicating chemisorption as the main adsorption mechanism for both adsorbents. The pseudo-second-order and the Elovich models fitted satisfactorily the adsorption onto bauxite, while adsorption onto palygorskite was well presented by Weber–Morris model, indicating that pore diffusion is also involved in the process. The adsorption capacity of both minerals decreased significantly after being used for several adsorption cycles and then almost completely recovered (regeneration efficiency was 99.6% and 98% for palygorskite and bauxite, respectively) inside a novel cold plasma microbubble reactor energized by high-voltage nanopulses, revealing the potential of these adsorbents to be reused. In addition to the regeneration of the adsorbents, the cold plasma completely eliminated the CPX transferred from the solid to the aqueous phase during the regeneration process.

The transition from lab-scale studies to pilot-scale applications is a critical step in advancing water remediation technologies. While laboratory experiments provide valuable insights into the underlying mechanisms and method effectiveness, pilot-scale studies are essential for evaluating their practical feasibility and scalability. This progression addresses challenges related to operational conditions, effectiveness and energy requirements in real-world scenarios. In this study, the potential of nanopulsed plasma bubbles, when scaled up from a lab environment, was explored by investigating critical experimental parameters, such as plasma gas, pulse voltage, and pulse repetition rate, while also analyzing plasma-treated water composition. To validate the broad effectiveness of this method, various classes of highly toxic organic pollutants were examined in terms of pollutant degradation efficiency and energy requirements. The pilot-scale plasma bubble reactor generated a high concentration of short-lived reactive species with minimal production of long-lived species. Additionally, successful degradation of all pollutants was achieved in both lab- and pilot-scale setups, with even lower electrical energy-per-order (EEO) values at the pilot scale, 2–3 orders of magnitude lower compared to other advanced oxidation processes. This study aimed to bridge the gap between lab-scale plasma bubbles and upscaled systems, supporting the rapid, effective, and energy-efficient destruction of organic pollutants in water.

During a long-term Equatorial Plasma Bubbles (EPBs) occurrence between October 2020 and March 2021, a significant EPB suppression event was identified on November 22 and the observations from multi-instrument have been utilized to investigate this event. Global-scale Observations of the Limb and Disk (GOLD) satellite observed prominent EPBs between 23;40 UT and 23;55 UT during the long-term occurrence days. However, no dark stripes representing EPBs were observed on November 22, and the Equatorial Ionization Anomaly (EIA) structure remained intact. The Total Electron Content (TEC) maps show that these EPBs appeared in the region between 35" W and 65" W longitudes and the magnitudes of the TEC loss in EPBs regions were about 20 TECU. Except for 22 November, the S4 index was consistently greater than 0.6 throughout November, indicating significant ionospheric scintillation. The Rate Of TEC Index (ROTI) maps revealed that the spatial extent and intensity of EPBs increased after their suppression, and the EPBs were locally generated. The swarm electron density measurements indicated that the variation amplitudes of EPBs at 510 km altitude were approximately 3 to 5 times larger than that at 460 km altitude. The impact region of EPBs at 510 km was between 15"S and 20" N latitudes, while at 460 km, it was between 0° and 17"N latitudes. During the period of EPB suppression, the average h ' f at three ionosonde stations decreased by about 50 km, and the vertical drift velocity (Vf approached ~0 m/s while it was more than 20 m/s during the long-term occurrence. [ABSTRACT FROM AUTHOR]

Although energetic particle (EP) injections are commonly thought to be formed by the flow burst intrusion from the magnetotail, important details and quantitative aspects of their transport, acceleration and flow braking need further investigation and understanding. Motivated by frequent observations of short transient EP injections being not associated with substorms, we analyze high‐resolution Rice Convection Model simulations of a short (5‐min long) localized (∼3RE width) density depletion (evacuating 90% of flux tube content) initiated at the tailward simulation boundary (∼18RE) and allowed to evolve within an otherwise typical plasma sheet environment. We note that, driven by betatron‐like acceleration, the peak EP flux at fixed energy dramatically increases in a couple of minutes when the bubble head enters the inner magnetosphere at r < 8–10 RE giving rise to a localized injection of subsequently drifting EP clouds. Here the 50–200 keV electron flux reaches values as high as #105 (cm2 s sr keV)−1, and even higher energies (up to 1 MeV) may briefly appear. Surprisingly, at a later stage of bubble penetration, after termination of bubble jet from the tail, the injection boundary of high energy (HE) particles detaches from the bubble earthward boundary while the latter continues moving inward. Time History of Events and Macroscale Interactions during Substorms multi‐spacecraft mission observations of a short bubble‐like flow burst at the spacecraft cluster located near the flow stopping point, show much similarity with simulation results but also reveal important differences between responses of HE protons and electrons attributed to the finite gyroradius effect. Plain Language Summary: Large sudden increases of energetic particle (EP) fluxes in the outer radiation belts, associated with sporadic intrusions of localized fast plasma jets (plasma bubbles) from the tail plasma sheet, were studied by many authors. Still there were very few simulations of the entire process, from bubble launch till generation of energetic electron cloud drifting around the Earth in the radiation belt, which include the drift physics and self‐consistently and realistically treat the flow braking region. To fill this gap we analyze high‐resolution Rice Convection Model simulation of short (5‐min long) localized (3 RE width) density depletion starting from 18 RE, focusing on the formation of intense EP cloud during flow braking phase of elementary intrusion. Although particle acceleration acts all the way during flow burst propagation, EP energy and fluxes are significantly enhanced during last couple minutes of intrusion in the radially confined (couple RE) region near geostationary orbit, where injected accelerated particles are suddenly deflected azimuthally by the magnetic drift. While observations of Time History of Events and Macroscale Interactions during Substorms multi‐spacecraft mission spacecraft group in the flow braking region confirm close association of energetic electron flux and magnetic variations, different from simulations, proton flux increases started 1–2 min ahead of bubble arrival, which is explained by kinetic interaction with very narrow bubble front. Key Points: Energy flux of energetic particles explosively rises when bubble enter the flow braking regionSelf‐consistent dynamical sharp magnetic field gradients help form the injection boundary and assist in deeper inward penetrationofinjectionSharp appearance of high energy proton burst observed before the electron burst and dipolarization front as kinetic effect of non‐adiabatic protons [ABSTRACT FROM AUTHOR]

Plasma bubbles represent notable ionospheric irregularities primarily observed in low latitudes, characterized by plasma depletions exhibiting large spatial scales, which can make a significant impact on the propagation of OTHR (over-the-horizon radar) waves. Firstly, we constructed a three-dimensional model of plasma bubbles, which is modulated by Gaussian function distribution in the horizontal direction, and then we analyzed the impact of EPBs (Equatorial Plasma Bubbles) on the ray path of OTHR shortwaves. When radio waves propagate through EPBs with different RMS ΔN/N, there is a significant difference in the propagation path of OTHR waves. For the EPB with an RMS ΔN/N of 75%, radio waves exhibit more pronounced refraction than those with lower RMS values, the focusing effect of radio waves is more obvious, and the focusing point is relatively lower. In terms of different seasons, OTHR shortwaves propagating through EPBs exhibit different degrees of refraction. In addition, radio waves show the effect of inward focusing in different seasons: the focusing effect is the most pronounced in spring, followed by autumn, then summer, and the weakest in winter. For different solar activities, the impact of EPBs on OTHR shortwaves is more significant in the high-solar-activity year.

A very challenging task in ionospheric studies is to determine the separate contributions of penetration and disturbance dynamo processes in the generation of equatorial plasma drift during magnetic storms. In this study, we analyze the ion drift measured by the Communications/Navigation Outage Forecasting System satellite during the magnetic storm on 15–16 July 2012. A unique feature of this storm is the exceptionally long period of continuous southward interplanetary magnetic field (IMF) for 32 hr. The storm‐induced net change of the meridional/vertical ion drift, the difference drift between the storm time and the quiet time, is derived during the storm main phase and the first 20 hr of the recovery phase with southward IMF. The difference drift during the recovery phase cannot be explained by the disturbance dynamo effect alone. A new method is used to separate the drifts caused by the penetration and disturbance dynamo processes. The penetration drift is represented by an empirical pattern of penetration electric field and depends on the IMF magnitude, and the disturbance dynamo drift is obtained by subtracting the penetration drift from the measured difference drift. The derived disturbance dynamo drift is in good agreement with previous statistical pattern. This is the first effort to identify the separate contributions of the penetration and disturbance dynamo processes to the total drift from observed data. The results have important implications in identifying storm‐time penetration and disturbance dynamo electric fields and their effects on the generation and evolution of plasma bubbles. Key Points: A new method is proposed to separate the storm‐time penetration and disturbance dynamo electric fields from ion drift measurementsThe derived disturbance dynamo drifts in this storm are in reasonable agreement with previous statistical patternThe combined penetration and dynamo effects provide a good explanation of post‐midnight plasma bubbles during the storm recovery phase [ABSTRACT FROM AUTHOR]

Equatorial plasma bubbles (EPBs) are regions of depleted plasma within the ionosphere that form during post‐sunset hours near the magnetic equator. EPBs tend to align with local geomagnetic field lines, extend hundreds of kilometers along geomagnetic longitudes, and thousands of kilometers along geomagnetic latitudes. EPBs can attenuate lower frequency radio waves, such as HF radar. Smaller features, usually 10s of meters, along the EPB's wall can interfere with centimeter scale wavelengths, such as GPS, via Bragg scattering. Statistical analysis of EPBs can further understanding of their occurrence and behavior. The current study utilizes Global‐Scale Observations of the Limb and Disk (GOLD) 135.6 nm nightglow data from 5 October 2018 to 30 September 2022. GOLD has a unique perspective from geostationary orbit, allowing consistent viewing of nightglow and structures over the Americas and Atlantic. An EPB detection method is developed and used to generate a database of occurrences. Occurrences are used to calculate EPB drift speeds and separations. All data is looked at as a whole, including any possible solar or geomagnetic disturbance periods. Seasonality in occurrence rate is evident. Occurrences peak during December solstice and minimize during June solstice for longitudes seen by GOLD. Within GOLD's view, higher occurrences are seen to the west during December solstice and to the east during June solstice. EPB drift speeds and separations show consistent distributions regardless of magnetic latitude region, geographic region, or season. This suggests EPBs behave consistently and regularly once formed, at least on spatial scales observed by GOLD. Plain Language Summary: Equatorial plasma bubbles (EPBs) are large regions of the upper atmosphere and tend to drift eastward after formation. These structures can form when smaller amplitude perturbations in the F‐region ionosphere grow in both amplitude and scale as they expand outwards, forming a void or bubble in the plasma. Equatorial plasma bubbles can be thousands of kilometers north to south, hundreds of kilometers east to west, and thousands of kilometers in altitude. The composition and irregularities along the outer extremities of EPBs can interfere with radio waves such as GPS. The current work develops a method, analyzes 4 years of GOLD data, and generates a database of all EPBs in GOLD's purview. Seasonal variations in occurrence of EPBs is verified: highest during December solstice and lowest during June solstice. A slight increase in EPB occurrence from year to year coincides with increases in solar activity. Little variation can be seen for EPB drifts or inter‐bubble separations by season and/or region. Key Points: Equatorial plasma bubbles (EPBs) are automatically detected, tracked, and analyzed with a new algorithmFour years of GOLD airglow observations are used to generate a database of EPB characteristicsEPB occurrence rate varies with region and season but characteristics like drift speed are similar [ABSTRACT FROM AUTHOR]

In this study, the synergetic action of nanopulsed plasma bubbles (PBs) and photocatalysts for the degradation/mineralization of trimethoprim (TMP) in water was investigated. The effects of ZnO or TiO2 loading, plasma gas, and initial TMP concentration were evaluated. The physicochemical characterization of plasma-treated water, the quantification of plasma species, and the use of appropriate plasma species scavengers shed light on the plasma-catalytic mechanism. ZnO proved to be a superior catalyst compared to TiO2 when combined with plasma bubbles, mainly due to the increased production of ⋅OH and oxygen species resulting from the decomposition of O3. The air–PBs + ZnO system resulted in higher TMP degradation (i.e., 95% after 5 min of treatment) compared to the air–PBs + TiO2 system (i.e., 87%) and the PBs-alone process (83%). The plasma gas strongly influenced the process, with O2 resulting in the best performance and Ar being insufficient to drive the process. The synergy between air–PBs and ZnO was more profound (SF = 1.7), while ZnO also promoted the already high O2–plasma bubbles’ performance, resulting in a high TOC removal rate (i.e., 71%). The electrical energy per order in the PBs + ZnO system was very low, ranging from 0.23 to 0.46 kWh/m3, depending on the plasma gas and initial TMP concentration. The study provides valuable insights into the rapid and cost-effective degradation of emerging contaminants like TMP and the plasma-catalytic mechanism of antibiotics.

Abstract Equatorial plasma bubbles (EPBs) are regions of depleted plasma within the ionosphere that form during post‐sunset hours near the magnetic equator. EPBs tend to align with local geomagnetic field lines, extend hundreds of kilometers along geomagnetic longitudes, and thousands of kilometers along geomagnetic latitudes. EPBs can attenuate lower frequency radio waves, such as HF radar. Smaller features, usually 10s of meters, along the EPB's wall can interfere with centimeter scale wavelengths, such as GPS, via Bragg scattering. Statistical analysis of EPBs can further understanding of their occurrence and behavior. The current study utilizes Global‐Scale Observations of the Limb and Disk (GOLD) 135.6 nm nightglow data from 5 October 2018 to 30 September 2022. GOLD has a unique perspective from geostationary orbit, allowing consistent viewing of nightglow and structures over the Americas and Atlantic. An EPB detection method is developed and used to generate a database of occurrences. Occurrences are used to calculate EPB drift speeds and separations. All data is looked at as a whole, including any possible solar or geomagnetic disturbance periods. Seasonality in occurrence rate is evident. Occurrences peak during December solstice and minimize during June solstice for longitudes seen by GOLD. Within GOLD's view, higher occurrences are seen to the west during December solstice and to the east during June solstice. EPB drift speeds and separations show consistent distributions regardless of magnetic latitude region, geographic region, or season. This suggests EPBs behave consistently and regularly once formed, at least on spatial scales observed by GOLD.

Our investigation aims to answer if it is possible to detect plasma bubbles using single-frequency measurements of the Global Navigation Satellite System (GNSS). In this regard, we show a methodology based on a regional model to calibrate GNSS single-frequency measurements and derive ionospheric maps showing plasma bubbles in one of the most challenging conditions, the Brazilian region. Simultaneous observations of all-sky images at Cachoeira Paulista (22.7°S, 45.0°W), São João do Cariri (7.4°S, 36.5°W) and Boa Vista (2.8°N, 60.7°W) were used to compare the plasma bubbles structures. The results were validated by the comparison between airglow and total electron content (TEC) single-frequency maps in terms of keograms and drift velocities of the ionospheric plasma bubbles. Plasma bubbles were successfully observed by mapping TEC single-frequency. The rate of success in detecting the plasma bubbles with single-frequency TEC data was 65% when using keograms. In addition, in regions with good GNSS coverage, such as Cachoeira Paulista and São João do Cariri, it was easier to detect the plasma bubbles. The velocities of plasma bubbles were also obtained with good agreement in comparison with the velocities estimated using airglow data. For São João do Cariri, the mean drift velocities estimated with airglow data were 117.10 m/s whereas with TEC data were 117.94 m/s. Therefore, the results revealed the proposed method as an efficient tool for mapping the ionospheric plasma bubbles and computing their drift velocities. This technique provides new opportunities, in particular for ionospheric sounding, since the number of low-cost GNSS receivers continues growing. [ABSTRACT FROM AUTHOR]

Dramatic irregularities in the plasma density of the ionosphere, first discovered by their effects on radio wave propagation in 1938, despite decades of investigation, still remain puzzling. Their deleterious effects on radio wave communication, satellite command and control, and GPS navigation strongly motivate better understanding of their nature. Many aspects of such irregularities are now understood, but the mechanism(s) of their formation and their detailed nature remain a topic of great interest. In this work, detailed time resolved measurements of lightning generated waves sometimes show dispersionless, strongly attenuated propagation with substantial propagation delays. These characteristics of the electromagnetic wave propagation in the hypothetical two‐phase bubble/non‐bubble lower ionosphere parallel the characteristics of acoustic wave propagation through two‐phase liquid/vapor foams. This motivates the suggestion that the bottomside layer of the ionosphere may sometimes be foamy. Plain Language Summary: Just as ocean waves breaking at the interface between sea and land produce copious bubbles and foam, recent satellite data suggests a similar phenomenon at the interface between neutral atmosphere and the charged plasma of the ionosphere. Lightning generated electromagnetic waves passing through the lower ionosphere observed by low altitude satellites are found to have the same characteristics as acoustic waves passing through foamy water. This hypothetical foam in the lower ionosphere apparently strongly absorbs some radio wave frequencies and seems to prevent most such waves from escaping the foam to pass through to the upper ionosphere. Key Points: Dispersionless, highly attenuated, lightning generated electromagnetic waves are observed in the lower ionosphereThe propagation of these electromagnetic waves has characteristics of acoustic wave propagation through two‐phase foamsSuch foamy plasma bubbles may cover approximately 85% of the bottomside of the equatorial nightside ionosphere [ABSTRACT FROM AUTHOR]

The occurrence probability of equatorial plasma bubbles and the associated spread F (ESF) irregularities have been derived from ground-based and space-borne measurements. In general, ESF occurrence depends on season and longitude and is high in equinoctial months and low around June solstice. In the West Pacific sector, previous statistical results show that the ESF occurrence probability increases gradually and continuously from March to August. In this study, we use trans-ionospheric VHF data received at Kwajalein Atoll in 2012 to derive the occurrence characteristics of scintillation. It is found that the occurrence probability of strong scintillation had two maxima in June and September and a minimum in July in the evening and midnight sector but only one maximum in June in the post-midnight sector. The monthly variations of scintillation occurrence at Kwajalein are different from almost all previous studies on ESF and scintillation at or near this longitude. To identify the cause for the June peak and the July minimum of scintillation, the ion density and velocity data measured by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite in 2011–2012 are used to derive the ESF occurrence and the post-sunset vertical ion drift near Kwajalein. The ESF occurrence probability and the ion drift measured by the C/NOFS satellite showed two maxima in May/June and August/September and a minimum in July, verifying that the June peak and the July minimum of the VHF scintillation are realistic and caused by the similar variations in the ionospheric ion drift and density. [ABSTRACT FROM AUTHOR]

Plasma blobs are night-time ionospheric irregularities whose generation mechanism is still under investigation. A large number of observations highlighted several aspects of their morphology and dynamics. However, the plasma blobs have not been attributed convincingly to a known mechanism. We analyzed the OI 630.0 nm emission images during March and October of 2019 and 2020 (minimum solar activity) using the ground-based all-sky imager at ZF-2 (2.58° S, 60.22° W) in the Amazon region of Brazil. The novelties of the present study are the rarely reported observation of both plasma blob merging and bifurcation. We studied the evolutional dynamics of plasma blobs and observed that blobs are distinct phenomena with unique properties. We attribute the merging of plasma blobs to the "wind reversion effect" (WRE) mechanism caused by a change in the direction of the zonal thermospheric wind from east to west. In some cases, the slower-drifting plasma blobs may merge with the faster ones. Moreover, blobs were observed initially bifurcating at the topside and later divided into two. The activity of the polarized electric field inside the plasma bubble mapping along the magnetic field lines is possibly responsible for the blob's bifurcation. Subjecting the two features of ionospheric plasma blobs to simulation may reveal further the physics of blobs' merging and bifurcation. [ABSTRACT FROM AUTHOR]

To elucidate the effect of solar wind dynamic pressure on the activities of ionospheric plasma irregularities in both high‐latitude and equatorial regions, we analyzed the long‐term global navigation satellite system (GNSS) total electron content (TEC) data from 2000 to 2018 and performed a superposed epoch analysis of the GNSS rate of the TEC index (ROTI), solar wind, interplanetary magnetic field (IMF), and geomagnetic index. We found that during the main phase of geomagnetic storms, the activities of ionospheric plasma irregularities were considerably enhanced in both high‐latitude and equatorial regions under high‐pressure conditions, and the equatorward edge of the auroral oval moved to lower latitudes. The poleward edge of the enhanced low‐latitude ROTI region (occurrence region of the plasma bubbles) in the evening sector extended to higher latitudes under high‐pressure conditions. During the recovery phase of geomagnetic storms, the plasma bubble occurrence in the dusk sector was suppressed under high‐pressure conditions. Our results suggest that the high‐latitude convection electric field and the penetration and disturbance dynamo electric fields at low latitudes become stronger during geomagnetic storms when the solar wind dynamic pressure is enhanced. This is because the conversion from solar wind energy to electromagnetic energy in the magnetosphere is enhanced by the formation of a high plasma pressure area in the high‐latitude cusp and mantle region. Therefore, not only the southward IMF but also solar wind dynamic pressure are important factors for varying global ionospheric responses during geomagnetic storms. Key Points: Dependence of storm‐time ionospheric density irregularities on solar wind dynamic pressure was studied using global navigation satellite system‐rate of the total electron content index (ROTI)Low‐latitude ROTI enhancements extended to higher latitudes under high solar wind dynamic pressure during the main storm phaseHigh‐latitude ROTI enhancements extended equatorward under high solar wind dynamic pressure during the main storm phase [ABSTRACT FROM AUTHOR]

Abstract This study, for the first time, reports the geomagnetically conjugate structure of a plasma bubble extending to the mid-latitudes and the asymmetrical structure of the decay of the plasma bubble during a geomagnetic storm. We investigated the temporal and spatial variations of plasma bubbles in the Asian sector during a geomagnetic storm on March 1, 2013, using Global Navigation Satellite System-total electron content data with high spatiotemporal resolutions. The first important point of our data analysis results is that the plasma bubble extended from the equator to the mid-latitudes with geomagnetic conjugacy along the magnetic field lines. The total electron content data showed that the plasma bubbles appeared in the equatorial regions near 150° E after sunset during the main phase of the geomagnetic storm. From ionosonde data over both Japan and Australia, they suggest that a large eastward electric field existed in the Asian sector. Finally, the plasma bubbles extended up to the mid-latitudes (~ 43° geomagnetic latitude) in both hemispheres, maintaining geomagnetic conjugacy. The second point is that the mid-latitude plasma bubble disappeared 1–2 h earlier in the northern hemisphere than in the southern hemisphere at close to midnight. In the northern hemisphere, the ionospheric virtual height decreased near midnight, followed by a rapid decrease in the total electron content and a rapid increase in the ionospheric virtual height. These results imply that the mid-latitude plasma bubble disappeared as the background plasma density decreased after midnight due to the recombination resulting from the descent of the F layer. Therefore, we can conclude that mid-latitude plasma bubbles can be asymmetric between the northern and southern hemispheres because of the rapid decay of plasma bubbles in one of the hemispheres. Graphical Abstract

Introduction: Accurate characterization of the plasma sheet source population in the ring current region and its outer boundary at geosynchronous orbit is crucial for understanding the dynamics of the Earth’s magnetosphere. The interaction between the ring current and plasma populations from the ionosphere is a focus of extensive research.Methods: We used the Rice Convection Model (RCM) to simulate the transient meso-scale injections of fast flows or plasma sheet bubbles from the outer boundary into the inner magnetosphere and the associated impacts on the ionosphere. We compared our simulation results of the average properties of bulk plasma access to geosynchronous orbit to a number of empirical models. We also examined the role of plasma sheet bubbles in forming field-aligned currents (FACs).Results: Our modeling results show that impulsive plasma sheet injections dramatically alter the average distribution of FACs in the ionosphere. We found both quantitative and qualitative agreements and disagreements when comparing our simulation results to empirical models. Furthermore, we demonstrated that several discrete auroral structures can be identified in the nightside ionosphere in accordance with theupward FACs.Discussion: The significance of plasma sheet bubbles in modifying the averageplasma properties at geosynchronous orbit and FACs in the ionosphere is highlighted by oursimulation findings, offering novel understandings into the dynamics of Earth's magnetosphere,and emphasizing the necessity for further research in this field.

Airglow observation is a very effective method to investigate plasma bubbles, and can obtain their horizontal structure. In this study, the image processing method was used to process airglow data, including image enhancement, azimuth correction, and image projection, and the clear image products of equatorial plasma bubbles (EPBs) were obtained. Based on the optical data of the airglow imager in Hainan, we investigated the main optical features of EPBs, and statistically analyzed the occurrence of EPBs from September 2014 to August 2015. The observation results show that EPB exhibits plume-shaped structures, usually tilting westward, and EPB extends to a long distance along the geomagnetic field lines. It is found that the west wall of EPB is relatively stable, while there are some bifurcations on the east wall of EPB, and the bifurcation of EPB becomes more pronounced with time. Moreover, the spatial scale of EPB gradually increases with time, which is about several hundred kilometers, and the drift velocity of EPB is in the range of 40–130 m/s (+/−20 m/s). The statistical results show that EPBs mainly occur in the months of September to November and February to April, with a higher occurrence rate. In terms of seasonal occurrence, EPBs tend to appear more frequently in spring and autumn, and the occurrence rate of EPBs is relatively low in winter and summer. [ABSTRACT FROM AUTHOR]

Plasma bubbles are large‐scale irregular structures that often occur at equatorial latitudes, equatorial plasma bubbles (EPBs) affect the propagation of high‐frequency (HF) radio waves. Based on their main observational characteristics, a three‐dimensional (3D) model of EPBs was established, and a preliminary simulation of EPBs was performed. Three‐dimensional ray tracing can be used to simulate HF radio wave propagation. In this study, we consider EPBs at different scales, appearing at different times and different heights, and investigate the influence of EPBs on the propagation path of radio waves at low latitudes. The simulation results show that when they propagate through EPBs of different scales, the propagation paths of radio waves are completely different. Radio waves at 6, 8, and 10 MHz show obvious refraction; With an increase in EPB scale, the focusing effect of radio waves will diminish, and the focusing height will increase. The propagation of HF radio waves through EPB change with time as follows: partial penetration, partial reflection, and total penetration, the refraction effect of EPB on radio waves gradually decreases over time. When radio waves propagate through EPB at different heights, the simulation results show that EPB at an altitude of 200 km makes little impact on the radio waves. As the height of EPB increases, the radio waves will exhibit significant refraction, showing an obvious focusing effect. Key Points: The influence of plasma bubbles on radio wave propagation can be simulated by three‐dimensional ray tracingRadio waves propagating through plasma bubbles exhibit significant refraction, showing an obvious focusing effectWith the increase in radio frequency, the focusing effect of radio waves will diminish, and the focusing height will increase [ABSTRACT FROM AUTHOR]

Total electron content (TEC) and L‐band scintillations measured by several networks of GPS and GNSS receivers that operate in South and Central America and the Caribbean region are used to observe the morphology of the equatorial ionization anomaly (EIA), examine the evolution of plasma bubbles, and investigate the enhancement of L‐band scintillations that occurred on February 12 and 13, 2016. A few weak and short magnetic storms developed these days, and a minor sudden stratospheric warming (SSW) event was initiated a few days before. During these unusual conditions, TEC maps reported a split of the otherwise continuous crests of the EIA and the formation of a large‐scale (thousands of kilometers) almost‐circular structure. The western part of the southern crest faded, and a north‐south aligned segment developed near the center of the South American continent, joining the north and south crests of the EIA, forming an anomaly that resembled a closed loop on the eastern side of the continent. Concurrently with the anomaly events, several GPS stations reported increases in the L‐band scintillation index from 0.4 to values greater than 1. We analyzed TEC values from receivers between ±6° from the magnetic equator to identify and follow TEC depletions associated with plasma bubbles when they reach different stations. Although the magnetic activity was moderate (Kp = 3°), we believe that the anomaly redistribution and the scintillation enhancements are not related to a prompt penetration electric field but to enhancing the semidiurnal lunar tide propitiated by the onset of the minor SSW event. We found that depending on the lunar tide phase cycle, the neutral wind's meridional component can augment sub‐km scale irregularities and enhance L‐band scintillations through the wind gradient instability when U·∇ $\nabla $n < 0 or the action of wind gradients (∇ $\nabla $U) within the bubbles. Our observations imply that the SSW event enables prominent changes in the thermosphere wind system at F‐region altitudes. Plain Language Summary: GPS receivers can measure the total electron content (TEC) between the satellite and the ground receivers. We have used TEC data collected with several networks of GPS receivers in South America to construct maps of TEC over the continent. These maps are used to examine the variability of the low latitude ionosphere during a special event that originates in the northern polar stratosphere called sudden stratospheric warming (SSW), consisting of an increase in the local temperature. In February 2016, a minor SSW produced prominent changes in the equatorial ionization anomaly. The anomaly consists of a pattern of two regions of enhanced densities on both sides of the magnetic equator that develops during the daytime and early evening. A few days after the initiation of the SSW event, the low‐latitude ionosphere dynamics changed, forming a large‐scale structure resembling a closed loop on the continent's eastern side. Concurrently with the anomaly events, several GPS stations reported increases in the level of fadings of the GPS signal‐to‐noise ratio, a process called scintillation. It is indicated that the neutral wind meridional component developed shears and a reversal increasing the level of plasma irregularities at km and sub‐km‐scale lengths, originating a scintillation enhancement. Key Points: Sudden increases in L‐band scintillations coincide with changes in the geometry of the equatorial ionization anomalyThese events occurred on February 12 and 13, 2016, a few days after a minor sudden stratospheric warming eventThe analysis suggests that a meridional neutral wind associated with an increased lunar tide is responsible for anomaly variability [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrified BSG pretreatment with plasma bubbles led to efficient refining. • Improved BSG enzymatic hydrolysis (73% conversion yield) using plasma bubbles. • Poly(3-hydroxybutyrate) production at 74.4 g PHB /L and 2.64 g/L/h productivity. • Low global warming potential (0.59 kg CO2-eq per kg PHB) and abiotic depletion potential fossil (11.12 MJ per kg PHB) • 1 kg BSG could be converted into 147.6 g PHB, 137.4 g protein and 98.4 g lignin. Biorefinery electrification could be implemented for sustainable refining of crude renewable resources eliminating the use of high temperatures and pressures, alkaline and acidic solutions and conventional solvents. A plasma bubble reactor using air as the feed gas was employed to enhance poly(3-hydroxybutyrate) (PHB) production from brewers' spent grains (BSG) facilitating the fractionation of protein and lignin as value-added co-products. Plasma factors (voltage, pretreatment duration, duty cycle, initial solids concentration) were evaluated with the highest overall conversion yield of glucan and hemicellulose (73 %, 0.494 g sugars/g BSG) achieved for initial solids concentration of 150 g/L. The produced BSG hydrolysate led to higher PHB production efficiency (130 g/L total dry weight, 74.4 g PHB /L, 0.32 g/g yield, 2.64 g/L/h productivity) than conventional hydrolysates produced by enzymatic hydrolysis alone and enzymatic hydrolysis combined with hydrothermal treatment. The protein and lignin losses in the remaining BSG solids were 24.1 % and 29.2 % respectively. When renewable electricity is employed, the global warming potential was estimated at 0.59 kg CO 2 -eq per kg PHB and the abiotic depletion potential fossil at 11.12 MJ per kg PHB for PHB production based on plasma treated BSG. In the proposed biorefinery concept, 1 kg BSG could be converted into 147.6 g PHB with a solid fraction containing 137.4 g protein and 98.4 g lignin that could be subsequently fractionated as value-added co-products. The rationale of this study is to demonstrate that BSG plasma treatment can be used for the exploitation of the full potential of BSG for the production of PHB with improved environmental impact and minimal losses of protein and lignin. [ABSTRACT FROM AUTHOR]

This study, for the first time, reports the geomagnetically conjugate structure of a plasma bubble extending to the mid-latitudes and the asymmetrical structure of the decay of the plasma bubble during a geomagnetic storm. We investigated the temporal and spatial variations of plasma bubbles in the Asian sector during a geomagnetic storm on March 1, 2013, using Global Navigation Satellite System-total electron content data with high spatiotemporal resolutions. The first important point of our data analysis results is that the plasma bubble extended from the equator to the mid-latitudes with geomagnetic conjugacy along the magnetic field lines. The total electron content data showed that the plasma bubbles appeared in the equatorial regions near 150° E after sunset during the main phase of the geomagnetic storm. From ionosonde data over both Japan and Australia, they suggest that a large eastward electric field existed in the Asian sector. Finally, the plasma bubbles extended up to the mid-latitudes (~ 43° geomagnetic latitude) in both hemispheres, maintaining geomagnetic conjugacy. The second point is that the mid-latitude plasma bubble disappeared 1–2 h earlier in the northern hemisphere than in the southern hemisphere at close to midnight. In the northern hemisphere, the ionospheric virtual height decreased near midnight, followed by a rapid decrease in the total electron content and a rapid increase in the ionospheric virtual height. These results imply that the mid-latitude plasma bubble disappeared as the background plasma density decreased after midnight due to the recombination resulting from the descent of the F layer. Therefore, we can conclude that mid-latitude plasma bubbles can be asymmetric between the northern and southern hemispheres because of the rapid decay of plasma bubbles in one of the hemispheres. [ABSTRACT FROM AUTHOR]

The occurrence probability of equatorial plasma bubbles and the associated spread F (ESF) irregularities have been derived from ground-based and space-borne measurements. In general, ESF occurrence depends on season and longitude and is high in equinoctial months and low around June solstice. In the West Pacific sector, previous statistical results show that the ESF occurrence probability increases gradually and continuously from March to August. In this study, we use trans-ionospheric VHF data received at Kwajalein Atoll in 2012 to derive the occurrence characteristics of scintillation. It is found that the occurrence probability of strong scintillation had two maxima in June and September and a minimum in July in the evening and midnight sector but only one maximum in June in the post-midnight sector. The monthly variations of scintillation occurrence at Kwajalein are different from almost all previous studies on ESF and scintillation at or near this longitude. To identify the cause for the June peak and the July minimum of scintillation, the ion density and velocity data measured by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite in 2011–2012 are used to derive the ESF occurrence and the post-sunset vertical ion drift near Kwajalein. The ESF occurrence probability and the ion drift measured by the C/NOFS satellite showed two maxima in May/June and August/September and a minimum in July, verifying that the June peak and the July minimum of the VHF scintillation are realistic and caused by the similar variations in the ionospheric ion drift and density.

Spectral analysis is a technique largely used to study scale size regime of ionospheric plasma irregularities based on in situ measurements, notwithstanding the visual representation of power spectral density (PSD) of a signal is often a source of ambiguity during fitting routines and identification of breakpoints. In this work, a method is proposed in order to mitigate the uncertainties inherent to this process. Here, the spectral behavior of time series fluctuations is alternatively investigated using Detrended Fluctuation Analysis (DFA). The DFA algorithm is a scaling analysis procedure widely applied to estimate the detection of long-range correlation without considering apparent short-range ones. Furthermore, the DFA technique is able to remove trends implicit to the signal and to be applied to non-stationary time series. Using in situ measurements of both ionospheric electron density and electric field fluctuations, it was able to analyze plasma bubbles with scales ranging from 1.66 km to 12.4 m. The results show that DFA and PSD routines provide quite similar spectra, but different spectral indices. On the other hand, the spectra revealed steep slopes wrapping the medium scales, a characteristic also detected in other studies. Besides that, the DFA is less noisy than Fourier spectra, which allows a more precise identification of spectral breakpoints. [ABSTRACT FROM AUTHOR]

Plasma blobs are night-time ionospheric irregularities whose generation mechanism is still under investigation. A large number of observations highlighted several aspects of their morphology and dynamics. However, the plasma blobs have not been attributed convincingly to a known mechanism. We analyzed the OI 630.0 nm emission images during March and October of 2019 and 2020 (minimum solar activity) using the ground-based all-sky imager at ZF-2 (2.58° S, 60.22° W) in the Amazon region of Brazil. The novelties of the present study are the rarely reported observation of both plasma blob merging and bifurcation. We studied the evolutional dynamics of plasma blobs and observed that blobs are distinct phenomena with unique properties. We attribute the merging of plasma blobs to the “wind reversion effect” (WRE) mechanism caused by a change in the direction of the zonal thermospheric wind from east to west. In some cases, the slower-drifting plasma blobs may merge with the faster ones. Moreover, blobs were observed initially bifurcating at the topside and later divided into two. The activity of the polarized electric field inside the plasma bubble mapping along the magnetic field lines is possibly responsible for the blob’s bifurcation. Subjecting the two features of ionospheric plasma blobs to simulation may reveal further the physics of blobs’ merging and bifurcation.

Ionospheric F-region irregularities can acutely affect navigation and communication systems. To develop predictive capabilities on their occurrence, it is key to understand their variabilities in a wide range of time scales. Previous studies at low latitudes in South America have been performed mostly in the eastern region. However, there are still few reports on the spread-F over Argentina owing to a lack of ionosonde data. This work presents the analysis of the spread-F (range spread-F and frequency spread-F) and plasma bubble occurrence characteristics near the southern crest of the Equatorial Ionization Anomaly in Argentina (Tucumán, 26.8°S, 65.2°W; magnetic latitude 15.5°S). We used ionosonde and Global Positioning System (GPS) data from November 2014 to December 2019 for different solar and geomagnetic conditions. The data show that spread-F and plasma bubble occurrence rates peak in local summer and are minimum in equinox and winter, respectively. There is a negative correlation between each type of spread-F and solar activity, whereas the opposite happens for plasma bubbles. Geomagnetic activity suppresses the generation of spread-F in equinox and summer and enhances it in winter. Plasma bubble occurrence is higher during disturbed days than during quiet days, but under medium solar activity, summer months register more plasma bubbles in quiet conditions. Range spread-F observed in winter under low solar activity is not associated with plasma bubbles originated at the magnetic equator. These results contribute to the knowledge necessary to improve the prediction of the spatial and temporal distribution of the night-time ionospheric irregularities. [ABSTRACT FROM AUTHOR]

In this paper, we study the onset conditions and features of equatorial F region irregularities linked with equatorial plasma bubbles (EPBs) using observations made simultaneously by using a DPS‐4D digisonde and the Gadanki Ionospheric Radar Interferometer (GIRI), both collocated at Gadanki. Importantly, we have employed specific analysis tools on DPS‐4D observations, providing range‐time displays of radio frequency and signal‐to‐noise ratio (SNR) of the reflected/backscattered echoes and the angle‐of‐arrival of the echoes, to characterize the echoes and to study the ambient and disturbed states of the ionosphere. Observations clearly show noticeably different background conditions, in terms of the height of the F layer base, electron density gradient and vertical drift, for the freshly generated and drifting EPBs. The zonal wavelengths of the pre‐sunset large‐scale wave structures (LSWS) observed using the DPS‐4D, however, are found to show a close connection with EPB spacings for freshly generated and drifting EPBs, consistent with earlier findings. The satellite traces were observed just prior to the equatorial spread F (ESF) and were found to be associated with the bottomside upwellings. Comparison of the range‐time displays of radio frequency and SNR of the DPS‐4D observations and the height‐time variations of SNR of the GIRI observations demonstrates that the relatively weak echoes in the DPS‐4D observations, which represent the ESF echoes, correlate fairly well temporally with the plume structures observed by the GIRI. The GIRI observations also reproduce the bottomside upwellings observed by the DPS‐4D. We propose that the bottomside upwellings are due to the growth of the LSWS and these bottomside upwellings are instrumental for the growth of the Rayleigh‐Taylor instability generating EPBs. Finally, the new aspects of the digisonde observations are discussed with regard to their usefulness in understanding and forecasting EPBs/ESF. Plain Language Summary: Equatorial plasma bubbles (EPBs) and associated irregularities are the important constituents of the near‐earth space weather. They are highly detrimental for satellite‐based communication/navigation applications. In this paper, we investigate the onset conditions and features of equatorial F region irregularities linked with EPBs using observations made simultaneously by a DPS‐4D digisonde and the Gadanki Ionospheric Radar Interferometer (GIRI), both collocated at Gadanki. We have employed specific analysis tools on DPS‐4D observations, providing range‐time displays of radio frequency and signal‐to‐noise ratio (SNR) of the reflected/backscattered echoes and the angle‐of‐arrival of the echoes, to characterize the echoes and to study the ambient and disturbed states of the ionosphere. Observations clearly show noticeably different background conditions for the freshly generated and drifting EPBs. The zonal wavelengths of the pre‐sunset large‐scale wave structures (LSWS) observed by the DPS‐4D, however, are found to show a close connection with EPB spacings for freshly generated and drifting EPBs, consistent with earlier findings. The satellite traces were observed just prior to the ESF and were found to be associated with the bottomside upwellings. Comparison of the range‐time displays of radio frequency and SNR of the DPS‐4D observations and the height‐time variations of SNR of the GIRI observations demonstrates that the relatively weak echoes in the DPS‐4D observations, which represent the ESF echoes, correlate fairly well temporally with the plume structures observed by the GIRI. The GIRI observations also reproduce the bottomside upwellings observed by the DPS‐4D. We propose that the bottomside upwellings are due to the growth of the LSWS and these bottomside upwellings are instrumental for the growth of the Rayleigh‐Taylor (RT) instability generating EPBs. The usefulness of the new aspects of the digisonde observations are discussed in understanding and forecasting EPBs/ESF. Key Points: Untapped potentials of a digisonde in studying the ambient and disturbed states of the equatorial ionosphere are demonstratedUse of digisonde observations for predicting overhead equatorial plasma bubbles (EPBs) has been demonstratedResults indicate that bottomside upwellings are due to growth of LSWS and are responsible for the satellite trace and subsequent growth of the Rayleigh‐Taylor instability generating EPBs [ABSTRACT FROM AUTHOR]

Plasma density depletions at midlatitudes during geomagnetic storms are often understood in terms of equatorial plasma bubbles (EPBs) due to their morphological similarity. However, our study reports the observations that reveal the generation of plasma depletions at midlatitudes by local sources. During the geomagnetic storm on 26 August 2018, the Defense Meteorological Satellite Program and Swarm satellites detected plasma depletions at midlatitudes in the Asian sector in the absence of EPBs in the equatorial region. This observation and the total electron content (TEC) maps over Japan demonstrate that traveling ionospheric disturbances (TIDs) are the sources of midlatitude plasma depletions in the Asian sector. Near the west coast of the United States, the development of a narrow TEC depletion band was identified from TEC maps. The TEC depletion band, which is elongated in the northwest–southeast direction, moves toward the west with a velocity of approximately 240 m/s. The TEC at the TEC depletion band is about 5 TEC units (1016 m−2) smaller than the ambient TEC. As this band is confined to the midlatitudes, this phenomenon is not associated with an EPB. The characteristics of the TEC depletion band are consistent with those of medium‐scale TIDs. Observations in the Asian sector and the TEC depletion band over the United States demonstrate that plasma depletions can develop at midlatitudes by local sources. Therefore, the morphological similarity between midlatitude irregularities and EPBs or their coincident occurrence does not provide corroborating evidence of their connection. Key Points: Different forms of plasma depletions develop at midlatitudes in the absence of plasma bubbles in the equatorial regionPlasma depletions develop locally in midlatitudes in association with traveling ionospheric disturbancesCoincident occurrence of plasma depletions in midlatitudes and equatorial regions does not warrant their connection [ABSTRACT FROM AUTHOR]

The strong influence of equatorial plasma bubbles (EPBs) appears to mask co‐seismic ionospheric disturbances (CIDs) for the earthquakes occurring in the equatorial low‐latitudes during the post‐sunset time. Based on GPS‐TEC data, we attempted to unveil the CIDs for the two great seismic events that are the 2005 M 8.6 Nias and 2017 M 8.2 Mexico earthquakes. In the case of the Nias earthquake, the CIDs have been identified in the bandpass filtered vertical total electron content data obtained from selective GPS satellite‐receiver pairs. For the Mexico earthquake, the EPB anomalies are dominant, making the appearance of CIDs hazy. However, the N‐shaped vertical total electron content anomalies masked by the plasma bubble anomalies in the bandpass filtered data are clear after applying the frequency domain singular spectrum analysis (SSA). Furthermore, the frequency domain SSA indicates the acoustic and surface waves of CIDs for both earthquakes. It also shows the signature of propagating gravity waves for the Mexico earthquake that has generated a moderate tsunami. Thus, the present study illustrates that the CIDs concealed by the non‐stationary EPB anomalies for earthquakes occurring in low latitude equatorial regions during post‐sunset become visible. Plain Language Summary: The studies carried out so far indicate that the equatorial plasma bubble (EPB) activity masks the co‐seismic ionospheric disturbances (CIDs) detected in GPS data in the low equatorial latitudes. However, EPB activity and generation of CIDs are linearly independent processes. Thus, EPBs may mask but cannot conceal the propagation of CID to the ionospheric heights. Furthermore, previous studies indicated that even a specially designed bandpass filter fails to separate the CIDs from background EPBs. But, the singular spectrum analysis (SSA) method is known for its robustness in separating such linearly independent components. In the present study, we reanalyze the GPS‐TEC data for the great 2005 Nias and 2017 Mexico earthquakes for plausible detection and separation of CIDs using the frequency domain SSA method. The CIDs emerged in the bandpass filtered VTEC data for some combinations of satellite and station pairs in the case of the Nias earthquake. But for the Mexico earthquake, EPB anomalies are dominant, and CIDs are not visible clearly. Interestingly, the CIDs corresponding to acoustic and surface waves for both earthquakes are visible after applying frequency domain SSA. Additionally, we have even determined the signatures of propagating gravity waves in the case of the Mexico earthquake, as it has generated a moderate tsunami. Thus, the present study demonstrates the first evidence for detecting CIDs or rules out the masking of CIDs associated with the earthquakes by the EPBs prevalent during the post‐sunset time and hence valuable for early earthquake warning systems. Key Points: Unveiled co‐seismic ionospheric disturbances (CIDs) hitherto claimed to be masked by intense plasma bubbles in low equatorial latitudesDiscussed the physical mechanism for the detection of CIDs from plasma bubble induced substantial ionospheric irregularitiesThe detection of CIDs marked by equatorial plasma bubbles helps the early detection of post sunset equatorial earthquakes using GPS networks [ABSTRACT FROM AUTHOR]

Plasma bubble, a low-entropy flux tube, is usually regarded as the bearer of plasma flux transport in the magnetotail. In this study, we perform a complete analysis of electron dynamics in a plasma bubble in the Earth's magnetotail based on the high time-resolution data from the Magnetospheric Multiscale (MMS) mission. An electron jet is observed at the center of this plasma bubble. Simultaneously, intense electric field and significant current density, as well as the strong energy dissipation are detected associated with this electron jet. The pitch angle distributions (PADs) of high-energy electrons exhibit different features at different substructures in this plasma bubble. In Region-1 and Region-3, pancake-type PAD is formed; the PAD becomes isotropic type in Region-2. The electrons pitch angle changes to field-aligned distribution in Region-4. All these changes of electron PADs in substructures can be interpreted mainly by the capture of magnetic mirror and betatron cooling. High-frequency waves, including whistler waves and electrostatic waves, are detected in several parts of the plasma bubble. The observations of abundant electron-scale phenomena or processes reveal that the electrons are very dynamic in the large-scale plasma bubble. [ABSTRACT FROM AUTHOR]

Diverse studies about equatorial plasma bubble structures and their relation with ionospheric scintillation have been performed in the last decades. Among many findings, the investigations usually reported dominant plasma bubble eastward velocity with a magnitude of few tens of m/s and larger amplitude scintillation for transionospheric signals aligned with these depleted structures. However, an uncommon long-lasting event with negligible average zonal drift prevailing for hundreds of minutes was registered over the Brazilian region, allowing a case study of the scintillation pattern under this particular condition. Data from ionosondes, all-sky imager (6300 Å filter), geostationary satellites and Global Navigation Satellite System were used here, covering the eastern portion of the Brazilian ionosphere. The results show that the scintillation was less intense than in other nights around the event, suggesting that larger plasma density gradients and sequential bubble structures seem to cause more severe scintillation scenario than the alignment condition alone, even though the last also contributes to worsen the scintillation effects. Regarding the stagnant bubble pattern, the results suggest prevailing E region Hall conductivity and equatorward wind as potential agents. [ABSTRACT FROM AUTHOR]

Previous studies show equatorial plasma bubbles (EPBs) mainly occur after sunset and usually drift from west to east. In this work, two EPBs occurred after midnight and lasted to sunrise, and were observed by multi‐instruments (two all‐sky imagers (ASIs), global positioning system, Swarm satellite, and a digisonde) during a geomagnetically quiet night of December 18–19, 2018. Our observations also show that plasma depletion structure (PDS) also occurred at that night. EPBs occurred in the region of PDS and showed a special evolution process during the night. Those PDS gradually disappeared with time, but strip‐like EPBs remained clearly in airglow images. Near sunrise, new PDS appeared to merge with those EPBs to form large PDS. Meanwhile, EPBs showed different zonal drifts within a very narrow longitudinal zone (∼2°). One EPB remained stationary while the other showed a small eastward drift. These results are different from post‐sunset EPBs in previous studies. During the lifetime of those ionospheric plasma irregularities, upward and downward motion of the peak height and virtual height of the ionospheric F region was observed by a digisonde, which indicates that the evolution of EPBs should be related to the vertical drift of ionospheric plasma. Besides, based Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) simulations, we suggest the different zonal drifts of those EPBs might related to plasma zonal drifts caused by zonal winds. Key Points: The evolution of equatorial plasma bubbles (EPBs) occurring in the region of plasma depletion structure, from post‐midnight to sunrise, were observed during a geomagnetically quiet nightEPBs showed different zonal drifts in the observations: one remained stationary and the other drifted eastwardVertical drifts of ionospheric plasma are the driver of EPB evolution and different zonal drifts may be related to zonal wind variations [ABSTRACT FROM AUTHOR]

Airglow observation is a very effective method to investigate plasma bubbles, and can obtain their horizontal structure. In this study, the image processing method was used to process airglow data, including image enhancement, azimuth correction, and image projection, and the clear image products of equatorial plasma bubbles (EPBs) were obtained. Based on the optical data of the airglow imager in Hainan, we investigated the main optical features of EPBs, and statistically analyzed the occurrence of EPBs from September 2014 to August 2015. The observation results show that EPB exhibits plume-shaped structures, usually tilting westward, and EPB extends to a long distance along the geomagnetic field lines. It is found that the west wall of EPB is relatively stable, while there are some bifurcations on the east wall of EPB, and the bifurcation of EPB becomes more pronounced with time. Moreover, the spatial scale of EPB gradually increases with time, which is about several hundred kilometers, and the drift velocity of EPB is in the range of 40–130 m/s (+/−20 m/s). The statistical results show that EPBs mainly occur in the months of September to November and February to April, with a higher occurrence rate. In terms of seasonal occurrence, EPBs tend to appear more frequently in spring and autumn, and the occurrence rate of EPBs is relatively low in winter and summer.

A new type of terrestrial line spectra found by the Arase satellite was reported in 2018. These spectra are called "hectometric line spectra (HLS)". They primarily consist of constant frequency narrowband components at frequencies between 525 kHz and 1,700 kHz, which originate and are sometimes amplified from AM broadcasting waves. In addition to these, other generated emissions are observed. Entrances and the mode conversion of the AM broadcasting waves into the equatorial and low‐latitude ionosphere with plasma density depletion called plasma bubbles are observed. Electron density profiles and equatorial plasma bubbles are examined through Global Positioning System (GPS)‐Total electron content (TEC) analyses. As a result, the Arase satellite which observed the HLS passed through the TEC depression region near the equatorial ionosphere associated with plasma bubbles. The scenario based on the mode conversion of the L‐O mode to the Z mode and vice versa was confirmed with observations and GPS‐TEC analyses. Another entrance when foF2 estimated from TEC is lower than 1,000 kHz instead of a plasma bubble is also found. No mode conversion is necessary, then. Plain Language Summary: A new type of terrestrial line spectra found by the Arase (ERG) satellite was reported. They primarily consist of constant frequency narrowband emissions at frequencies between 525 kHz and 1,700 kHz (hectometric wavelength) and additional emissions with changing frequencies. The former emissions originate and are amplified from AM broadcasting waves in the frequency band. The latter ones are emissions stimulated by broadcasting waves. This frequency range includes frequencies lower than foF2 (the maximum ordinary mode frequency capable of vertical reflection from the F2 region of the ionosphere). If low‐density region and steep density gradients like plasma bubbles exist in the ionosphere, L‐O mode (the free‐space mode) broadcasting waves can penetrate the higher density region in the Z mode at the plasma frequency. Then, they can be amplified or generated by instability while in the Z mode. They need to be mode‐converted to the L‐O mode to be received by satellite because waves in the Z mode are trapped in regions where their frequency is lower than the local upper hybrid resonance frequency. This scenario is confirmed through wave and ionospheric observations. Additionally, another entrance when foF2 < 1,000 kHz instead of a plasma bubble is also shown and explained. Key Points: Medium wave broadcasting waves whose frequencies are less than 1,700 kHz are observed above the ionosphere by the Arase satelliteThey propagated through the ionosphere via various steep density gradients like plasma bubblesSometimes stimulated emissions are observed additionally [ABSTRACT FROM AUTHOR]

INSPIRESat-1 (IS-1) is a small scientific satellite being developed jointly by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado at Boulder in the United States, the Indian Institute of Space Science and Technology (IIST) in India, the National Central University (NCU) in Taiwan and the Nanyang Technological University (NTU) in Singapore. This paper describes the science objectives of the IS-1 mission, the engineering and current development status. The IS-1 has completed all functional and performance tests as well as all environmental tests. The spacecraft is manifested on the Indian Space Research Organization's (ISRO) Polar Satellite Launch Vehicle (PSLV) C-52 mission in 2021. The IS-1 carries two scientific instruments: the Compact Ionospheric Probe (CIP) developed at NCU for studying Earth's dynamic ionosphere and the Dual-zone Aperture X-ray Solar Spectrometer (DAXSS) developed at LASP for studying the highly-variable solar X-ray radiation. It also carries a Command and Data Handling board developed by IIST. The primary science objectives of the INSPIRESat-1 are twofold. First, using CIP to characterize the temporal and spatial distributions of small-scale plasma irregularities like plasma bubbles in the ionosphere. Secondly, IS-1 aims to provide a greater understanding of why the Sun's corona is orders of magnitude hotter than the photosphere, why there is an abundance of elements change during different solar events, and how these events (observed with greater soft x-ray fidelity) affect the earth's ionosphere. The International Satellite Program in Research and Education (INSPIRE) is a consortium of universities with active space programs, formed to advance space science and engineering. [ABSTRACT FROM AUTHOR]

A large density irregularity structure in latitudinal extent was observed by the sun‐synchronous orbiting FORMOSAT‐5 satellite at 720 km topside ionosphere in the South American sector on November 24, 2018 during a magnetically quiet time. The observed density irregularity structure has a latitudinal extent of ∼30° across the dip equator, and a longitudinal width of ∼6°. Unlike previously studied equatorial plasma bubble structures with the airglow images that indicate hemispheric magnetic conjugate similarity, the gross feature of this large density irregularity structure indicates a north‐south hemispheric asymmetry in density variation. We use the Hilbert‐Huang Transform analysis to study the irregularity structure in different scales of density variations. It is found that the amplitude of density variations in the scale sizes from 22.5 to 450 km all indicate the hemispheric asymmetry. However, the spectral property of density variations in the two hemispheres is almost identical to each other. This implies that the density irregularity structure which originates from the same Rayleigh‐Taylor (RT) instability process has preserved the spectral characteristics inside the magnetic flux tube. Therefore, the cause that fails to preserve the magnetic conjugate property in the density irregularity structure comes from the fact that the background ionospheric density distribution has a north‐south hemispherical asymmetry in the beginning of the RT instability process. This hemispheric asymmetrical density distribution is caused by the seasonal variation of density distributions in the two hemispheres and the prevailing inter‐hemispheric neutral wind during solstices in the South American sector. Key Points: A density irregularity structure of large latitudinal extent was observed at 720 km height without preserving magnetic conjugate propertyA Hilbert‐Huang Transform analysis found the dominant irregularity sizes from 22.5 to 450 km, and they all indicated hemispheric asymmetryThe hemispheric asymmetry of irregularity structure comes from the hemispheric asymmetrical density distribution in the solstice ionosphere [ABSTRACT FROM AUTHOR]

Although magnetotail bursty bulk flows (BBFs)/plasma bubbles are widely recognized as major plasma transport structures that provide particle acceleration and injection, their ionospheric signatures in energetic particles have not been established. In this study, we combine the ionospheric energetic proton flux (as a proxy to the equatorial pressure) and energetic electron loss‐cone filling rate (as a marker of the equatorial magnetic field) to detect a rapid traversal from stretched to dipolarized field lines across the BBF channel. During a nonsubstorm episode when multiple flow bursts were observed in the plasma sheet, we show remarkable step‐like increases of energetic proton flux (approaching 103 in some events) observed in the middle of nightside auroral zone. We also conduct a high‐resolution Rice Convection Model (RCM) simulation of a plasma‐sheet bubble intrusion into the inner magnetosphere. Besides confirmation of the observed signatures, the simulation illustrates variability of the ionospheric signatures of bubbles and provides guidance in future studies of flow burst interactions. Plain Language Summary: Flow bursts (also known as fast flow channels, or BBFs/bubbles) are sporadic transient narrow structures in the magnetotail which transport energy, and accelerate and inject energetic particles into the outer radiation belt and the ring current in the inner magnetosphere. Sparse spacecraft coverage severely limits experimental studies of such complicated structures and their flow braking process. For this purpose, an image of related precipitation on the ionospheric screen can be of great help if we could specify its magnetospheric context. In this study, we demonstrate a combination of two specific energetic particle signatures in the ionosphere to identify the border of BBFs. Sharp transition from isotropic to depleted loss‐cone distributions of energetic electrons suggests the passage from stretched magnetic field lines outside the BBF to dipolarized lines inside the BBF. Sharp increase of energetic proton flux indicates the change of the equatorial pressure between stretched and dipolarized field lines. Observed together, these two signatures robustly indicate a sharp change in the magnetotail connectivity, a characteristic of BBFs. We also use the self‐consistent numerical simulation of a plasma‐sheet bubble injection to demonstrate these signatures on a physics‐based model as well as to discuss the inherent variability of the signatures. Key Points: Strong step‐like increases of energetic proton flux in the nightside auroral zone accompanied by depleted loss‐cone of energetic electronsSuch low‐altitude spacecraft signatures were observed 12–14 min after flow burst passage over MMS in the near‐conjugate plasma sheetRCM bubble simulation confirms such signature of azimuthal crossing of plasma bubble ionospheric projection and predicts its variability [ABSTRACT FROM AUTHOR]

Equatorial plasma bubble (EPB) irregularities are large‐scale plasma depleted structures that exist in the equatorial and low‐latitude ionosphere. Thus, particularly in these regions, much attention must be given to the effects of the EPBs in the life critical applications based on global navigation satellite systems (GNSS). The study on the dynamics of plasma bubbles, particularly in the determination of their drift velocities, and their impact on ground‐based augmentation system is of fundamental importance for civilian aviation. In this regard, we proposed a methodology to estimate the zonal drift velocities of the plasma bubble irregularities using slant total electron content (TEC) measurements derived from two spaced ground‐based GNSS receivers. The experiments were performed with the purpose to evaluate if the drift velocities obtained using the methodology proposed in this study agree with the velocities deduced from all‐sky imaging systems. The results revealed that the TEC‐estimated mean eastward drift velocities were comparable with the values deduced from the airglow techniques, and with the results obtained from previous studies. Therefore, the methodology proposed in this work to infer the plasma bubble drift velocities seem to have the potential in future investigations to provide a new data source in this field. Key Points: Global navigation satellite systems observations to infer plasma bubbles velocitiesAirglow images to confirm the plasma bubbles velocities [ABSTRACT FROM AUTHOR]

Ionospheric irregularities as plasma bubbles occur in the ionosphere, and generally, they are characterized by the low plasma density regions. The Rate Of TEC Index (ROTI) was defined in terms of the Total Electron Content (TEC) variation and is used to characterize these plasma bubbles. It is essential to evaluate the ROTI behavior since the ionospheric irregularities can cause fluctuations in the radio signal, interfering in the ionospheric data analysis. Therefore, we performed in this work a comparative study of five different methods available to calculate the ROTI to evaluate the most suitable over the Brazilian region. The ROTI was calculated over three GNSS stations at different latitudes: São Luís (SALU, 2°31′S, 44°16′W; dip: −3.8°), Cachoeira Paulista (CHPI, 22°40'S, 44°59'W; dip: −36.4°), and Santa Maria (SMAR, 29°41′S, 53°48′W, dip: −37°). The results show that the most viable method for calculating ROTI in the Brazilian region is based on the Slant TEC equation as defined by Cherniak et al. (2018), https://doi.org/10.1007/s10291‐018‐0730‐1. Our results are supported by the comparison between the ROTI with TEC maps, ionograms collected at Fortaleza (FZA0M, 3°43'S, 38°32'W, dip: −15.8°), SALU, and CHPI and All‐Sky imagers collected at the São João do Cariri (SJCA, 7°23'S, 36°31'W, dip: −11°) and CHPI. Additionally, we observe Equatorial Plasma Bubbles (EPBs) in the Brazilian region using the ROTI index map. Key Points: We have compared five Rate Of TEC Index (ROTI) methods to evaluate the most suitable one for analyzing the equatorial ionospheric irregularitiesROTI index maps are a very effective resource for observing and characterizing plasma bubbles in the Brazilian sectorThe irregularities observed in the ROTI index maps are more evident than in the total electron content maps [ABSTRACT FROM AUTHOR]

Few observations investigated the interaction between an electrical medium‐scale traveling ionospheric disturbance (EMSTID) and an equatorial plasma bubble (EPB). This paper presents another interaction between a southwestward propagating EMSTID and an eastward drifting EPB in the equatorial ionization anomaly (EIA) crest region of China. When the EMSTID and the EPB touched each other, several depletions of the EMSTID (EPB) showed the eastward (westward) velocity disturbances of the EPB (EMSTID) depletions. Besides, phase elongations of the EPB depletions contrarotated as the EMSTID propagated southwestward. However, of important finding is that the interaction of the EMSTID and the EPB could have polarized one depletion of the postmidnight EPB that should have become a fossilized bubble. Inside that polarized EPB depletion were meter‐scale irregularities that caused activated radar echoes and enhanced ranged spread F (RSF). The interaction occurred in descending ionosphere and the lower density regions got filled up with an enhanced density plasma. We propose that the EMSTID and the EPB could have electrically coupled with each other, causing an enhanced polarization electric field (PEF) that polarized that EPB depletion; the E × B gradient drift instability (Kelley, 1989) could have caused the meter‐scale irregularities when that enhanced PEF was imposed on that reactivated EPB depletion surrounded by that enhanced density plasma. This study provides observational evidence that how an electrical couple of EMSTID and EPB events can activate a postmidnight EPB depletion that should become a fossilized structure. Plain Language Summary: Otsuka et al. (2012, https://doi.org/10.1029/2012GL052286) provided the first report indicating the disappearance of an equatorial plasma bubble (EPB) airglow depletion after interaction with an electrical medium‐scale traveling ionospheric disturbance (EMSTID) airglow enhancement. For comparison, the current study reports a postmidnight airglow event in which an electrical coupling of an EMSTID and an EPB could have polarized one EPB airglow depletion that caused the activated radar echoes of very high frequency (VHF) radar and the enhanced ranged spread F (RSF) in descending ionosphere filled with an enhanced density plasma. Key Points: Interaction between an electrical medium‐scale traveling ionospheric disturbance (EMSTID) and an equatorial plasma bubble (EPB) in the equatorial ionization anomaly (EIA) crest region over ChinaElectrical coupling of the EMSTID and the EPB polarized one EPB depletion that caused activated radar echoes and enhanced ranged spread F (RSF)The interaction occurred in descending ionosphere and the lower density regions got filled up with an enhanced density plasma [ABSTRACT FROM AUTHOR]

Ionospheric plasma density data from the Planar Langmuir Probe onboard the CHAllenging Minisatellite Payload (CHAMP) are used to investigate the latitudinal profile of the ionospheric plasma density. Along with the well‐known profiles with features of the equatorial ionization anomaly and equatorial plasma bubbles, a third type is observed as smooth profiles with large‐scale deep equatorial trough (DET) where the plasma density is extremely low. A global survey focusing on magnetically quiet conditions reveals that the DET profiles are generally a post‐sunset phenomenon, and their appearance depends on longitude and season. During equinoxes in active solar years, the strong pre‐reversal enhancement electric field is believed to uplift the ionosphere and produce the DET profiles. While around June solstice, the DET profiles are clustered at 45°W–0° E longitude, where the zonal electric field is weak but the magnetic meridional component of the neutral wind is most significant. The SAMI2 model is then employed to simulate the ionospheric plasma distribution in the magnetic meridional plane with enhanced neutral wind, which successfully reproduced the main features of the observed DET profile. The results indicate that the neutral wind can obviously affect the equatorial ionosphere by transporting plasma in the magnetic flux tube through neutral‐ion interaction. The neutral wind is previously known to work with the inclined magnetic field at mid‐latitude, while this study emphasizes its effect around the magnetic equator especially when the electric field forcing (E×B) is weak or absent. Key Points: Deep equatorial trough (DET) occurs at night under weak upward plasma drift as well as under strong prereversal enhancementThe DET profiles is accompanied by higher equatorial hmF2, when either the E × B drift or strong magnetic meridional wind is presentModel simulation verifies that field‐aligned plasma transport driven by the neutral wind leads to the extremely low density at the equator [ABSTRACT FROM AUTHOR]

The production of ammonia, powered by renewable energy, in a decentralized manner is of key importance in the transition to a more sustainable future. Recent research has explored the integration of non-thermal plasma and electrochemical processes to achieve this goal. However, the success of this hybrid process is contingent on the energy efficiency of the plasma-generated species. Herein, we developed a plasma bubble reactor, driven by nanosecond pulses interfacing plasma directly with water. This reactor can comprehensively probe gas ionization processes, different energy channels, corresponding plasma catalytic reaction mechanisms, and reactive species in gas and liquid phases. By using on-and-off plasma ignition with rapid pulses, we could regulate energy consumption in cycles and achieved the lowest reported energy consumption of 2.7 ± 0.1 kWh mol-1 NO 3 − and 3.2 ± 0.1 kWh mol-1 NH 4 + after electrocatalytic nitrate reduction. This provides a promising pathway to producing green, renewable ammonia from air and water. [Display omitted] • Nanosecond pulsed plasma bubbles coupled with electrocatalysis for sustainable ammonia production. • Energy mapping and reaction pathways compared for DBD and SD modes. • SD achieves higher energy density and efficiency of 2.7 ± 0.1 kWh mol-1 NO 3 − (aq). • SD mode in a bubble interface with water generates high-density NO x(aq). [ABSTRACT FROM AUTHOR]

We report an interesting Equatorial Plasma Bubbles (EPBs) event during the night of March 22–23, 2017. To investigate the dynamics of observed EPBs, we utilize multi‐instrument data obtained with all‐sky imager (ASI) from Panhala (16.48°N, 74.6°E, 11.1°N Dip. Lat.), Canadian Advanced Digital Ionosonde (CADI) from Tirunelveli (8.73°N, 77.7°E, 1.6°N Dip. Lat.) and ionospheric backscatter echoes data of Gadanki Ionospheric Radar Interferometer (GIRI) radar from Gadanki (13.5°N, 79.2°E, 6.5°N Dip. Lat.) over Indian regions. The optical observations from Panhala reveal clear signatures of EPBs from ∼1600 UT onwards and corresponding ESF occurrence is noted in CADI at Tirunelveli as well. Backscatter echoes are also recorded in Range time intensity map obtained by GIRI after ∼17:45 UT. On this night, two EPBs (EPB1 and EPB2) are observed with inter‐depletion distance of ∼600 km. The EPB1 drifts eastward throughout the night and evolves with time as bifurcated structures while the trailing EPB2 drifts eastward initially and eventually drifts westward. We believe that this is the first evidence of differential drifts of EPBs imaged through ASI over a narrow longitudinal zone over the Indian region. Key Points: One Equatorial Plasma Bubble (EPB) moves eastward while trailing EPB moves westward indicating unusual bidirectional drift patternLarge eastward drift values toward dip equatorial region as compared to low latitude regionThe diminishing of EPBs is observed due to interaction with enhanced intensity region [ABSTRACT FROM AUTHOR]