Abstract The plasmapause (PP) marks the transition from a dense and cold plasma to a tenuous and hot plasma in the inner magnetosphere. Several electrodynamic processes are taking place at this steep electron density gradient. Here we make use of the high‐resolution magnetic field recordings by the Swarm A and C spacecraft for investigating broad‐band signal bursts in the 4–10 Hz frequency range. In more than 80% of the cases, when the Swarm passes the L‐shell bounding the plasmasphere on its low‐Earth orbit, an enhanced broad‐band signal is observed in the transverse field components. The actual location of the plasmapause is derived from in situ plasma measurements of the Arase satellite in the magnetosphere. The broad‐band signals around midnight are different from those near noon. During the dark hours in ∼90% of cases, a broad‐band signal is found right outside the PP continuing far into the magnetosphere. Its characteristic agrees well with the large‐amplitude kilometer‐scale FACs described recently by Zhou and Lühr (2025), https://doi.org/10.5194/angeo‐43‐667‐2025 . Different from that, around the noon sector broad‐band bursts appear rather confined in the L range (∼0.03 Re) and about 0.5 Re inward from the PP. The bursts observed on the dayside seem to represent resonances of preexisting waves, which suffer a chaotic breakdown after running into saturation. Opposed to the nightside, daytime broad‐band signal bursts are encountered only on about 80% of the passes. This implies that the resonance does not exist everywhere along the dayside PP. On the dawn and dusk sides, both types of broad‐band signatures can be found.

This review examines ultra-low frequency (ULF) waves across different planetary environments, focusing on Earth, Mercury, and Saturn. Data from spacecraft missions (CHAMP, Swarm, and Oersted for Earth; MESSENGER for Mercury; and Cassini for Saturn) provide insights into ULF wave dynamics. At Earth, compressional ULF waves, particularly Pc3 waves, show significant power near the equator and peak around Magnetic Local Time (MLT) = 11. These waves interact complexly with Alfvén waves, impacting ionospheric responses and geomagnetic field line resonances. At Mercury, ULF waves transition from circular to linear polarization, indicating resonant interactions influenced by compressional components. MESSENGER data reveal a lower occurrence rate of ULF waves in Mercury’s foreshock compared to Earth’s, attributed to reduced backstreaming protons and lower solar wind Alfvénic Mach numbers, as ULF wave activity increases with heliocentric distance. Short Large-Amplitude Magnetic Structures (SLAMS) observed at Mercury and Saturn show distinct characteristics compared to those of Earth, including the presence of whistler precursos waves. However, due to the large differences in heliospheric distances, SLAMS (their temporal scale size correlate with the ULF wave frequency) at Mercury are significantly shorter in duration than at Earth or Saturn, since the ULF wave frequency primarily depends on the strength of the interplanetary magnetic field. This review highlights the variability of ULF waves and SLAMS across planetary environments, emphasizing Earth’s well-understood ionospheric interactions and the unique behaviours observed for Mercury and Saturn. These findings enhance our understanding of space plasma dynamics and underline the need for further research regarding planetary magnetospheres.

This paper presents the project Comprehensive spAce wEather Studies for the ASPIS prototype Realization (CAESAR), which aims to tackle the relevant aspects of Space Weather (SWE) science and develop a prototype of the scientific data centre for Space Weather of the Italian Space Agency (ASI) called ASPIS (ASI SPace Weather InfraStructure). To this end, CAESAR involves the majority of the SWE Italian community, bringing together 10 Italian institutions as partners, and a total of 92 researchers. The CAESAR approach encompasses the whole chain of phenomena from the Sun to Earth up to planetary environments in a multidisciplinary, comprehensive, and unprecedented way. Detailed and integrated studies are being performed on a number of well-observed “target SWE events”, which exhibit noticeable SWE characteristics from several SWE perspectives. CAESAR investigations synergistically exploit a great variety of different products (datasets, codes, models), both long-standing and novel, that will be made available in the ASPIS prototype: this will consist of a relational database (DB), an interface, and a wiki-like documentation structure. The DB will be accessed through both a Web graphical interface and the ASPIS.py module, i.e., a library of functions in Python, which will be available for download and installation. The ASPIS prototype will unify multiple SWE resources through a flexible and adaptable architecture, and will integrate currently available international SWE assets to foster scientific studies and advance forecasting capabilities.

Tides not only affect ocean dynamics but also influence the Earth's magnetosphere. Satellite observations have now revealed evidence of tidal effects in the Earth's plasmasphere correlated with Moon phases.

A multi-instrumental analysis of the meridional ionospheric response is presented over Europe during the two largest ICME-driven geomagnetic storms of solar cycle #24 maximum. Data from 5 European digisonde stations, ground-based Global Navigation Satellite System, Total Electron Content (GNSS TEC), the ratio of the TEC difference (rTEC), as well as Swarm and Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite observations have been used for the investigation of selected intervals (11–17 November, 2012, and 16–25 March, 2015). The storm evolution is monitored by digisonde foF2 critical frequency (related to the maximum electron density of F2-layer) and GNSS TEC data. Moreover, Global Ultraviolet Imager (GUVI) measurements from the TIMED satellite are used to investigate the changes in the thermospheric O/N 2 ratio. Our main focus was on the main phase of the geomagnetic storms, when during the nighttime hours extremely depleted plasma was detected. The extreme depletion is observed in foF2, TEC and rTEC, which is found to be directly connected to the equatorward motion of the midlatitude ionospheric trough (MIT) on the nightside. We demonstrate a method (beside the existing ones) which allows the monitoring of the storm-time evolution of the disturbances (e.g., MIT, SAPS, SED) in the thermosphere-ionosphere-plasmasphere system by the combined analysis of the worldwide digisonde system data (with the drift measurements and the ionospheric layer parameters with 5–15 min cadence), with rTEC and GNSS TEC data, and with the satellite data like Swarm, TIMED/GUVI.

<p>The almost one decade of operation of ESAs Swarm mission provides an unprecedented opportunity to investigate the appearance of small-scale nonlinear magnetic field irregularities in the topside ionosphere in terms of various climatological and solar-cycle conditions. Within the framework of the EPHEMERIS project supported by ESA we have developed an index for the characterization of the intermittent status of the compressional and tangential (i.e., parallel and perpendicular to the mean background field, respectively) magnetic field fluctuations along the orbits of the Swarm spacecraft triplet. The index is called intermittency index, in short IMI. IMIs are computed for consecutive overlapping segments of Swarm’s magnetic field records by evaluating the deviation of their statistical distribution from the Gaussian distribution. By portraying the global spatial distribution of IMIs, it turns out that the most intensive intermittent fluctuations appear in the polar and equatorial regions, due to auroral field-aligned currents (FAC) and equatorial spread F and plasma bubble phenomena, respectively. Making use of the Adjusted Spherical Cap Harmonic (ASHA) expansion of IMIs, we model the distribution of the intermittent transverse magnetic fluctuations in the polar region in terms of geomagnetic latitude and magnetic local time (MLT), for different geomagnetic activities. We show that the most intermittent fluctuations at high latitudes are distributed about two oval regions that adjoin in the night sector. The ovals expand towards the equator with increasing geomagnetic activity. We argue that the boundaries of the poleward oval coincide with the locations of FACs, while the equatorward oval of intermittent fluctuations (separating from the poleward oval in the noon sector) corresponds to the ionosphere footprint of the plasmasphere boundary, i.e. the plasmapause. These findings are reinforced by independent aurora oval and plasmapause models.</p>

On 4 November 2021 it was detected the most intense geomagnetic storm that occurred so far during the rising phase of solar cycle 25 (Kp=8-). This work summarizes the state of the solar wind before and during the geomagnetic storm, the response of the plasmasphere-ionosphere-thermosphere system in the European sector and, for a comparison, the ionosphere-thermosphere response of the American sector. The plasmasphere dynamics was investigated through field line resonances detected at the European quasi-Meridional Magnetometer Array. The ionosphere was investigated through the combined use of ionospheric parameters (foF2, hmF2) from ionosondes and Total Electron Content (TEC) obtained from Global Navigation Satellite System receivers at four locations in the European sector and three locations in the American sectors. Aeronomic parameters were retrieved by using an original method based on the observed electron concentration in the ionospheric F region. The behavior of foF2 and TEC data is also discussed, speculating about the possible interconnection between the topside ionosphere and the plasmasphere at the investigated European sites. Experimental results can be summarized as it follows: a) The plasmasphere, originally in a state of saturation, was eroded up to two Earth’s radii, and only partially recovered after the main phase of the storm, and a possible formation of a drainage plume is also observed; b) The ionospheric parameters showed phases characterized by negative and positive variations, with longitudinal and latitudinal dependence of storm features in the European sector; c) Negative storm signature in electron concentration at the F2 region is also observed in the American sector. This result is mainly attributable to the neutral composition and temperature variations.

On 3 November 2021, an interplanetary coronal mass ejection impacted the Earth’s magnetosphere leading to a relevant geomagnetic storm (Kp = 8-), the most intense event that occurred so far during the rising phase of solar cycle 25. This work presents the state of the solar wind before and during the geomagnetic storm, as well as the response of the plasmasphere–ionosphere–thermosphere system in the European sector. To investigate the longitudinal differences, the ionosphere–thermosphere response of the American sector was also analyzed. The plasmasphere dynamics was investigated through field line resonances detected at the European quasi-Meridional Magnetometer Array, while the ionosphere was investigated through the combined use of ionospheric parameters (mainly the critical frequency of the F2 layer, foF2) from ionosondes and Total Electron Content (TEC) obtained from Global Navigation Satellite System receivers at four locations in the European sector, and at three locations in the American one. An original method was used to retrieve aeronomic parameters from observed electron concentration in the ionospheric F region. During the analyzed interval, the plasmasphere, originally in a state of saturation, was eroded up to two Earth’s radii, and only partially recovered after the main phase of the storm. The possible formation of a drainage plume is also observed. We observed variations in the ionospheric parameters with negative and positive phase and reported longitudinal and latitudinal dependence of storm features in the European sector. The relative behavior between foF2 and TEC data is also discussed in order to speculate about the possible role of the topside ionosphere and plasmasphere response at the investigated European site. The American sector analysis revealed negative storm signatures in electron concentration at the F2 region. Neutral composition and temperature changes are shown to be the main reason for the observed decrease of electron concentration in the American sector.

The complex analysis of the largest geomagnetic storms of solar cycle #24 maximum is our main aim in this study. Our focus is on the ionosphere, more precisely on the ionospheric F2-layer. The selected storm intervals are: 11-17 November 2012 (Kpmax=6.33, Dstmin=-108 nT ), 16-23 March 2013 (Kpmax= 6.67, Dstmin=-132 nT ), and 16-25 March 2015 (Kpmax=7.67, Dstmin=-228 nT). Data from 6 digisonde (DPS4D) stations, ground GNSS TEC and Swarm satellite constellation have been used for the investigation. This study is the next step to validate our previous results discussed in Berényi et al. (2018). We analyse the meridional behaviour of the geomagnetic disturbance caused ionospheric storms to understand and interpret the evolution of the caused effects. The storm from 2012 is a no-positive phase (NPP) storm, but the 2013 and 2015 storms show the pattern of the regular positive phase (RPP) storm type (after the categorization by Mendillo and Narvaez, 2010). In all three cases a significant increase in electron density of the F2-layer can be observed at dawn/early morning (around 6:00 UT, 07:00 LT). We compared also the digisonde foF2 parameter with the GNSS TEC data. Besides, we observed the fade-out of the ionospheric layers at night during the geomagnetically disturbed time periods of storm 2012 and 2015. In order to determine whether this fade-out is connected to the L-shell location of the plasmapause we analysed the Swarm observations (for the storm 2015), too. Berényi, K. A., Barta, V., & Kis. (2018). Midlatitude ionospheric F2-layer response to eruptive solar events-caused geomagnetic disturbances over Hungary during the maximum of the solar cycle 24: A case study. Advances in Space Research, 61(5), 1230–1243. https://doi.org/10.1016/j.asr.2017.12.021 Mendillo, M., & Narvaez, C. (2010). Ionospheric storms at geophysically-equivalent sites - Part 2: Local time storm patterns for sub-auroral ionospheres. Annales Geophysicae, 28(7), 1449–1462. https://doi.org/10.5194/angeo-28-1449-2010

The investigation of heavy ions dynamics and properties in the Earth's magnetosphere is still an important field of research as they play an important role in several space weather aspects. We present a statistical survey of the average ion mass in the dayside magnetosphere made comparing plasma mass density with electron number density measurements and focusing on both spatial and geomagnetic activity dependence. Field line resonance frequency observations across the European quasi‐Meridional Magnetometer Array, are used to infer the equatorial plasma mass density in the range of magnetic L‐shells 1.6–6.2. The electron number density is derived from local electric field measurements made on Van Allen Probes using the Neural‐network‐based Upper‐hybrid Resonance Determination algorithm. The analysis is conducted separately for the plasmasphere and the plasmatrough during favorable periods for which both the plasma parameters are observed simultaneously. We found that throughout the plasmasphere the average ion mass is ≃1 amu for a wide range of geomagnetic activity conditions, suggesting that the plasma mainly consist of hydrogen ions, without regard to the level of geomagnetic activity. Conversely, the plasmatrough is characterized by a variable composition, highlighting a heavy ion mass loading that increases with increasing levels of geomagnetic disturbance. During the most disturbed conditions, the average radial structure shows a broad maximum around 3–4 Earth radii, probably correlated with the accumulation of oxygen ions near the plasmapause. Those ions are mostly observed in the post‐dawn and pre‐dusk longitudinal sectors.

The relation between the plasmapause (PP) and various ionospheric phenomena, such as the midlatitude ionospheric trough (MIT) has been studied for decades. More recently, it was found that the equatorward boundary of small‐scale field‐aligned currents (SSB) and the PP are also closely coupled. In spite of prolonged efforts many details of these relationships, as well as the mechanisms responsible for them remain poorly understood. ESA's Swarm mission in conjunction with magnetospheric missions (RBSP, Arase, and THEMIS) provides an unprecedented opportunity to study these relationships on a global scale and over an extended period. Swarm delivers observations of MIT, the associated sub‐auroral electron temperature enhancement (SETE), as well as SSB, while PP crossings can be inferred from in‐situ magnetospheric electron density measurements. In this study, we use 7 years of Swarm observations and PP positions from 2014 to 2017 to address some of the open questions. We confirm that MIT/SETE and PP are directly coupled, however only in the nighttime. Their correlation remains high after post‐dawn, however, with an increasing, MLT‐dependent time lag. Afternoon MIT observations were found conjugated with a plasmaspheric plume. The correlation between SSB and PP is also high and they intersect each other near MLT midnight. Our results confirm the scenario that the PP is formed on the night side, and propagates to the dayside by co‐rotating with the Earth and suggest that the plasma is transported from the depleted ionospheric/dense plasmaspheric stagnation region also westward/sunward forming the afternoon MIT/narrow plumes, respectively.

The Compact Linear Collider (CLIC) targets a nanometer beam size at the collision point. Realizing this beam size requires the generation and transport of ultralow emittance beams. Dynamic imperfections can deflect the colliding beams, leading to a collision with a relative offset. They can also degrade the emittance of each beam. Both of these effects can significantly impact the luminosity of CLIC. In this paper, we examine a newly considered dynamic imperfection: stray magnetic fields. Measurements of stray magnetic fields in the Large Hadron Collider tunnel are presented and used to develop a statistical model that can be used to realistically generate stray magnetic fields in simulations. The model is used in integrated simulations of CLIC at 380 GeV including mitigation systems for stray magnetic fields to evaluate their impact on luminosity.

The magnetic and plasma observations of Low-Earth orbit (LEO) space missions represent not only the dynamical state of the ionosphere but also the physical variations of its electromagnetically connected surroundings, i.e. of the plasmasphere and magnetosphere, as well as of their driver, the solar wind. The monitoring of the ionosphere plasma variables is therefore a big asset for the study of our space environment in broad spatial region. Within the framework of the EPHEMERIS project supported by ESA, we aim at investigating two ionosphere phenomena that exhibit close relationship to global physical processes and space weather activity. We use the magnetic and plasma records of the LEO Swarm mission. First, we investigate the temporal and spatial occurrences of the mid-latitude ionosphere trough (MIT), a typical feature of the topside sub-auroral ionosphere appearing as a few degree wide depleted zone, where electron density (Ne) drops by orders of magnitude. It is shown that the locations of MITs are excellent proxies for the detection of the plasmapause position as well as of the equatorward edge of the auroral oval. Secondly, we monitor the irregular fluctuations of the magnetic field along the Swarm orbits via their intermittent behaviour. A new index called intermittency index (IMI) is introduced for the quantitative exemplification of the spatial and temporal distribution of irregular variations at the Swarm spacecraft altitudes. The paper focuses on the introduction of the methodology of IMI time-series compilation. Since IMIs are deduced via a statistical approach, we use the 50 Hz sampling frequency magnetic field records of the mission. We show that most frequently, the ionosphere magnetic field irregularities occur at low-latitudes, about the dip equator and at high latitudes, around the auroral region. It is conjectured that the equatorial events are the results of equatorial spread F (ESF) or equatorial plasma bubble (EPB) phenomena, while the auroral irregularities are related to field-aligned currents (FAC). The ionosphere plasma irregularities may result in the distortion or loss of GPS signals. Therefore our analysis also concerns the investigation of the correlation between observed intermittent events in the ionosphere and contemporary GPS signal loss events and scintillations detected both by on-board Swarm GPS receivers and ground GNSS stations.

In the past decades researchers have revealed links between a series of sub-auroral ionospheric phenomena and the plasmapause (PP) dynamics, such as the mid-latitude ionospheric trough (MIT) and the associated sub-auroral temperature enhancement (SETE), the light-ion trough (LIT), the sub-auroral ion drift (SAID) or the more intense sub-auroral polarisation stream (SAPS), and most recently, the inner boundary of small-scale field-aligned currents (SSFACs). Most of these phenomena can be directly observed by the Swarm constellation of ESA at LEO. Thus, Swarm presents a unique opportunity to study the relations between them and also their relation to the PP dynamics.In a recent Swarm DISC project, PRISM (Plasmapause Related boundaries in the topside Ionosphere as derived from Swarm Measurements), three new products have been developed. Two products characterise the MIT (and the associated SETE). The MITx_LP utilises the Langmuir probe measurements of electron density and temperature, while the MITxTEC product derives the MIT properties from GPS TEC observations. The third product, PPIxFAC provides information on the location and the main characteristics of the equatorial boundary of SSFACs, and it also includes a proxy for the location of the PP at MLT midnight.In this presentation we introduce the above Swarm L2 products, present the results of a comparative study aiming at revealing their mutual relations and also their dynamic coupling to the PP. Then we demonstrate how the observations of all these ionospheric phenomena combined can be used to develop an improved proxy for monitoring the PP dynamics at LEO as one of the goals of our new ESA-funded project PLASMA.

We present a comparison of magnetospheric plasma mass/electron density observations during an 11‐day interval which includes the geomagnetic storm of June 22, 2015. For this study we used: Equatorial plasma mass density derived from geomagnetic field line resonances (FLRs) detected by Van Allen Probes and at the ground‐based magnetometer networks EMMA and CARISMA; in situ electron density inferred by the Neural‐network‐based Upper hybrid Resonance Determination algorithm applied to plasma wave Van Allen Probes measurements. The combined observations at L ∼ 4, MLT ∼ 16 of the two longitudinally separated magnetometer networks show a temporal pattern very similar to that of the in situ observations: A density decrease by an order of magnitude about 1 day after the Dst minimum, a partial recovery a few hours later, and a new strong decrease soon after. The observations are consistent with the position of the measurement points with respect to the plasmasphere boundary as derived by a plasmapause test particle simulation. A comparison between plasma mass densities derived from ground and in situ FLR observations during favorable conjunctions shows a good agreement. We find however, for L < ∼3, the spacecraft measurements to be higher than the corresponding ground observations with increasing deviation with decreasing L, which might be related to the rapid outbound spacecraft motion in that region. A statistical analysis of the average ion mass using simultaneous spacecraft measurements of mass and electron density indicates values close to 1 amu in plasmasphere and higher values (∼2–3 amu) in plasmatrough.

A local time dependent empirical model of the equatorial plasma mass density in the inner magnetosphere is derived from field line resonance (FLR) observations at the European quasi‐Meridional Magnetometer Array (EMMA). Models of the plasmasphere, plasmatrough, and plasmapause are derived separately and then combined. The whole model is limited to the local time (LT) sector 06:00‐18:00 and to the range of equatorial distances 2.3RE

This presentation illustrates the recent results obtained in the context of scientific ESA Swarm projects. The project “Swarm data quality Investigation of Field-Aligned Current products, Ionosphere, and Thermosphere system” (SIFACIT) has been recently extended in order to achieve two additional objectives: To provide to users an open-source program package to estimate Field Aligned Current (FAC) density and quality indicators, using single- and multi-s/c methods from Swarm data; To study the Joule heating of the ionosphere–thermosphere system on multiple scales, using Swarm data, together with conjugate ground information and simulations. The other project illustrated here is EPHEMERIS (nEw sPace weatHER inforMation Exploited from the SwaRm observatIonS). This project is investigating the Midlatitude Ionospheric Trough (MIT) with Swarm data, and will also develop a new MIT Swarm data product based on Swarm L1b Langmuir Probe (LP) data. The second part of the project will develop a quasi-real-time intermittency index (IMI) for the detection of ionosphere plasma irregularities along the Swarm orbit, which can be responsible for errors and loss of lock in GPS signals. A statistical comparison of the IMI index with GPS signal from ground based receivers will be performed, in order to identify the ionospheric irregularities at Swarm altitude responsible for scintillations in GPS signals.