Dynamo action refers to energy exchange processes through which magnetic fields are generated at the expense of kinetic energy of the plasma flows. Dynamos can generate magnetic fields across scales larger or smaller than the flows themselves. Multi-scale dynamo processes underpin magnetic phenomena from planetary cores to stellar and galactic environments, while also shaping turbulent magnetic fields at smaller scales. Yet, experimental validation of dynamo action has remained largely confined to laboratories. Here we report evidence for a turbulent dynamo in the terrestrial magnetosheath. Observations reveal the predicted spatial topology of stretched and folded magnetic fields, compressive effects, and pressure anisotropy instabilities essential for magnetic field amplification. Our findings also highlight the central role of turbulent dynamos in energy conversion and structure formation within collisionless plasma turbulence. The observed energy exchange signatures indicate that the magnetosheath may serve as a natural testbed for validating dynamo theories and simulations.

Jupiter's magnetosheath is a natural yet complex laboratory for analyzing compressible plasma turbulence. Recent observations by the Juno mission provide a promising opportunity for the first time to reckon the energy cascade rate in the magnetohydrodynamic scales in the vicinity of Jupiter's space. In the present work, a two-dimensional model is constructed for a whistler wave that is nonlinearly coupled with a wave magnetic field via ion density perturbation. The dynamics of whistler wave propagating in the direction of the magnetic field are derived within the limit of the two-fluid modeling approach. The magnetic field localization along with magnetic field spectra and spectral slope variations are estimated to realize the turbulence generation and energy cascade from large to small scales in the Jovian magnetosheath region. The simulated magnetic field spectrum in the wave number (in the unit of ion inertial length rho i ) consists of turbulence in the inertial range with a spectral slope of -1.4 and a spectral knee at k rho i = 1. Subsequently, the spectral slope increases to -2.6 and the spectrum becomes steeper. The simulated magnetic field spectrum in the wave number is further translated into the frequency domain using the whistler wave dispersion relation and by considering the Taylor frozen-in condition. The analytically estimated magnetic field spectrum slopes, i.e., -1.8 and -4.2 at low and high frequencies are further compared with recent Juno mission observations. The comparison further affirms the existence of Kolmogorov scaling, a spectral knee, and steepening in the spectrum at high frequencies. Furthermore, it is found that the two-fluid model can reasonably simulate the turbulence effects in Jovian magnetosheath in terms of magnetic field spectral distribution in wave number and frequency domains.

A comparison of three types of ionosonde data from Europe during an interplanetary coronal mass ejection (ICME)- and a corotating interaction region (CIR)-driven geomagnetic storm event is detailed in this study. The selected events are 16–20 March 2015 for the ICME-driven storm and 30 May to 4 June 2013 for the CIR-driven one. Ionospheric data from three European ionosonde stations, namely Pruhonice (PQ), Sopron (SO) and Rome (RO), are investigated. The ionospheric F2-layer responses to these geomagnetic events are analyzed with the ionospheric foF2 and h’F2 parameters, the calculated deltafoF2 and deltahF2 values, the ratio of total electron content (rTEC) and Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite Global Ultraviolet Imager (GUVI) thermospheric [O]/[N2] measurement data. The storm-time and the quiet-day mean values are also compared, and it can be concluded that the quiet-day curves are similar at all the stations while the storm-time ones show the latitudinal dependence during the development of the storm. As a result of the electron density comparison, during the two events, it can be concluded that the sudden storm commencement (SSC) that characterized the ICME induced a traveling atmospheric disturbance (TAD) seen in the European stations in the main phase, while this is not seen in the CIR-driven ionospheric storm, which shows a stronger and more prolonged negative effect in all the stations, probably due to the season and the depleted O/N2 ratio.

The comparison of three types of ionosonde data from Europe during an Interplanetary Coronal Mass Ejection (ICME) and a Stream Interaction Regions (SIRs) / Corotating Interaction Regions (CIRs) -driven geomagnetic storm event is detailed in this study. The selected events are 16-20 March 2015 for the ICME-driven and 30 May to 04 June 2013 for the SIR/CIR-driven one. Ionospheric data from three European ionosonde stations, namely Pruhonice (PQ), Sopron (SO) and Rome (RO), are investigated. The ionospheric F2-layer responses to these geomagnetic events are analyzed with the ionospheric foF2 and h’F2 parameter, the calculated deltafoF2 and deltahF2 values, ratio of Total Electron Content (rTEC) and Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite Global Ultraviolet Imager (GUVI) thermospheric [O]/[N2] measurement data. The storm-time and the quiet day mean values are also compared, and it can be concluded that the quiet day curves are similar at all stations while the storm-time ones showed the latitudinal dependence during the development of the storm. As a result of the electron density comparison, during the two events it can be concluded that SSC that characterized the ICME induced a Travelling Atmospheric Disturbance (TAD) seen in the European stations, while this is not in the SIR/CIR-driven ionospheric storm, which showed a stronger and more prolonged negative effect in all stations probably due to the season.

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.

Solar wind (SW) quantities, referred to as coupling parameters (CPs), are often used in statistical studies devoted to the analysis of SW–magnetosphere–ionosphere couplings. Here, the CPs and their limitations in describing the magnetospheric response are reviewed. We argue that a better understanding of SW magnetospheric interactions could be achieved through estimations of the energy budget in the magnetosheath (MS), which is the interface region between the SW and magnetosphere. The energy budget involves the energy transfer between scales, energy transport between locations, and energy conversions between electromagnetic, kinetic, and thermal energy channels. To achieve consistency with the known multi-scale complexity in the MS, the energy terms have to be complemented with kinetic measures describing some aspects of ion–electron scale physics.

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.

We investigate the differences between the effects of geomagnetic storms due to Interplanetary Coronal Mass Ejections (ICME) and due to Stream Interaction Regions or Corotating Interaction Regions (SIR/CIR) on the ionospheric F2-layer during the maximum of solar cycle 24. We have created a unique list of the ICME- and SIR/CIR-driven geomagnetic storm events for the time interval between November 2012 and October 2014. Finally, 42 clear ICME and 34 clear SIR/CIR events were selected for this analysis. The individual geomagnetic storm periods were grouped by seasons, time of day, and local time of Dstmin and were analyzed using three different methods: linear correlation analysis using 4-h averages of foF2 parameters and the geomagnetic indices (1st), daily variation of deltafoF2 (2nd), and 3D plotting: geomagnetic indices vs. time vs. deltafoF2 (3rd). The main phase day of the ICME- and SIR/CIR-induced geomagnetic storms was our main focus. We used manually evaluated ionospheric foF2 parameters measured at the Sopron ionosonde station and the geomagnetic indices (Kp, Dst, and AE) for this analysis. We have found that in most cases, the variation of the Dst index is the best indicator of the impact caused in the F2 layer. We conclude as well that the representation of the data by the third method gives a better description of the ICME and SIR/CIR-triggered storm behavior. In addition, our investigation shows that the SIR/CIR-related perturbations can be predicted with greater accuracy with the second method.

A tanulmány részletesen bemutatja a geomágneses vihar keletkezési folyamatát és fő fázisait. A szerző ismerteti a skálázási lehetőséget – amely az „enyhe” (G1) fokozattól a „rendkívüli” (G5) fokozatig terjed –, illetve a geomágneses vihar lehetséges következményeit. Vizsgálja a geomágneses vihar esetén kialakuló kéregáramok keletkezési mechanizmusát, és a jelenség általokozott veszélyeket. Végül áttekintést ad néhány történelmi jelentőségű geomágneses viharról, és bemutatja az azok kapcsán megfigyelt jelenségeket.

Az űridőjárás kutatása az űrkutatás tudományágainak viszonylag új területe. Az űridőjárás hatásaival napjainkban egyre gyakrabbankell számolnunk, a modern technológiai eszközök és a kritikus infrastruktúra ugyanis fokozottan sérülékenyek az űridőjárás hatásaira. A szerző tanulmányában áttekinti az űridőjárás forrásait és folyamatait, összefoglalja a modern technológiára gyakorolt fontosabb hatásokat és következményeket, valamint kitér a védekezés lehetőségére is.

Dayside transients, such as hot flow anomalies, foreshock bubbles, magnetosheath jets, flux transfer events, and surface waves, are frequently observed upstream from the bow shock, in the magnetosheath, and at the magnetopause. They play a significant role in the solar wind-magnetosphere-ionosphere coupling. Foreshock transient phenomena, associated with variations in the solar wind dynamic pressure, deform the magnetopause, and in turn generates field-aligned currents (FACs) connected to the auroral ionosphere. Solar wind dynamic pressure variations and transient phenomena at the dayside magnetopause drive magnetospheric ultra low frequency (ULF) waves, which can play an important role in the dynamics of Earth’s radiation belts. These transient phenomena and their geoeffects have been investigated using coordinated in-situ spacecraft observations, spacecraft-borne imagers, ground-based observations, and numerical simulations. Cluster, THEMIS, Geotail, and MMS multi-mission observations allow us to track the motion and time evolution of transient phenomena at different spatial and temporal scales in detail, whereas ground-based experiments can observe the ionospheric projections of transient magnetopause phenomena such as waves on the magnetopause driven by hot flow anomalies or flux transfer events produced by bursty reconnection across their full longitudinal and latitudinal extent. Magnetohydrodynamics (MHD), hybrid, and particle-in-cell (PIC) simulations are powerful tools to simulate the dayside transient phenomena. This paper provides a comprehensive review of the present understanding of dayside transient phenomena at Earth and other planets, their geoeffects, and outstanding questions.

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

A Széchenyi István Geofizikai Obszervatóriumban (SZIGO) már több, mint hat évtizede folyik a felszíni geoelektromos és geomágneses tér megfigyelése. Az Obszervatórium a geomágneses megfigyelő állomásokat tömörítő nemzetközi hálózat, az INTERMAGNET egyik legjobb minősítéssel kitüntetett tagja, melyet a folyamatos és nagy pontosságú adatszolgáltatás révén érdemelt ki (https://www.intermagnet.org/). A geomágneses megfigyelő rendszer nemrégiben újult meg, illetve egészült ki egy redundáns digitalizáló-adatgyűjtő-szerver lánccal, melynek révén a fluxgate magnetométer analóg jelét két független rendszer digitalizálja, rendezi ASCII fájlokba, valamint továbbítja egy-egy adatszerveren telepített SQL adatbázisba. A geomágneses indukció révén az előbbihez szervesen kapcsolódó fizikai mennyiség, a geoelektromos tér mérésére szolgáló rendszer a közeljövőben szintén megújul, melynek eredményeképpen egy nagyobb dinamikatartományt, jobb felbontásban leképező rendszer kerül beüzemelésre. Az alábbiakban az újonnan telepített geomágneses mérőrendszer kerül bemutatásra, valamint néhány, az új rendszerrel, az elmúlt 12 hónapban regisztrált SSC esemény.

Summary Electromagnetic variation’s amplitude decreases exponentially in conducting media. Higher conductance results higher attenuation of the electromagnetic variations vs. depth. In this presentation an investigation is introduced which aims to estimate the electromagnetic attenuation coefficient and mean resistivity of the near surface rocky layers of the Mátra mountains, Hungary. The whole investigation consists of a confirmation, based on high frequency magnetotelluric sounding, too. The direct estimation of the attenuation coefficient is performed by means of a signal excited by the global thunderstorm activity in the ground-ionosphere cavity, the so called Schumann resonance. The method basis on the direct determination of the ELF signal’s amplitude decay between a surface and the corresponding subsurface site. In case of parallel recording at the two sites, the attenuation could basically be computed from the rate of the variation’s spectral amplitude at certain frequencies. As the surface and the subsurface observation could not be performed at the same time due technical reasons, an ELF reference observation site had been involved in the investigation. The attenuation can then be estimated by comparison of the transfer functions related to the ‘subsurface station - reference site’ and the ‘reference site – surface station’ relation.

The twisted local magnetic field at the front or rear regions of the magnetic clouds (MCs) associated with interplanetary coronal mass ejections (ICMEs) is often nearly opposite to the direction of the ambient interplanetary magnetic field. There is also observational evidence for magnetic reconnection (MR) outflows occurring within the boundary layers of MCs. In this study, a MR event located at the western flank of the MC occurring on October 3, 2000 is studied in detail. Both the large‐scale geometry of the helical MC and the MR outflow structure are scrutinized in a detailed multipoint study. The ICME sheath is of hybrid propagation‐expansion type. Here, the freshly reconnected open field lines are expected to slip slowly over the MC resulting in plasma mixing at the same time. As for MR, the current sheet geometry and the vertical motion of the outflow channel between ACE‐Geotail‐WIND spacecraft were carefully studied and tested. The main findings on MR include (a) first‐time observation of non‐Petschek‐type slow‐shock‐like discontinuities in the inflow regions; (b) observation of turbulent Hall magnetic field associated with a Lorentz‐force‐deflected electron jet; (c) acceleration of protons by reconnection electric field and their back‐scatter from the slow‐shock‐like discontinuity; (d) observation of relativistic electron near the MC inflow boundary/separatrix; these electron populations can presumably appear as a result of nonadiabatic acceleration, gradient B drift, and via acceleration in the electrostatic potential well associated with the Hall current system; and (e) observation of Doppler‐shifted ion‐acoustic and Langmuir waves in the MC inflow region.

We compare the predictions of the GUMICS$-$4 global magnetohydrodynamic model for the interaction of the solar wind with the Earth's magnetosphere with Cluster~SC3 measurements for over one year, from January 29, 2002, to February 2, 2003. In particular, we compare model predictions with the north/south component of the magnetic field ($B_{z}$) seen by the magnetometer, the component of the velocity along the Sun-Earth line ($V_{x}$), and the plasma density as determined from a top hat plasma spectrometer and the spacecraft's potential from the electric field instrument. We select intervals in the solar wind, the magnetosheath, and the magnetosphere where these instruments provided good-quality data, and the model correctly predicted the region in which the spacecraft is located. We determine the location of the bow shock, the magnetopause, and the neutral sheet from the spacecraft measurements and compare these locations to those predicted by the simulation. The GUMICS$-$4 model agrees well with the measurements in the solar wind however its accuracy is worse in the magnetosheath. The simulation results are not realistic in the magnetosphere. The bow shock location is predicted well, however, the magnetopause location is less accurate. The neutral sheet positions are located quite accurately thanks to the special solar wind conditions when the $B_{y}$ component of the interplanetary magnetic field is small.

Geomagnetic and geoelectric registration has been continuously executed in SZIGO for more than six decades. The Observatory is a member of the global network of the geomagnetic observatories, the so-called INTERMAGNET (https://www.intermagnet.org). The geomagnetic observation system has recently been renewed in all of its components and the organically related geoelectric measurement system is going to be upgraded and improved, too. Present paper provides a short summary of the new geomagnetic observation system and introduces a few SSC events registered in the SZIGO from the last 12 months via the new observation station.

The paper reviews the interaction of collisionless interplanetary (IP) shocks with the turbulent solar wind. The coexistence of shocks and turbulence plays an important role in understanding the acceleration of particles via Fermi acceleration mechanisms, the geoeffectiveness of highly disturbed sheaths following IP shocks and, among others, the nature of the fluctuations themselves. Although our knowledge of physics of upstream and downstream shock regions has been greatly improved in recent years, many aspects of the IP-shock/turbulence interaction are still poorly known, for example, the nature of turbulence, its characteristics on spatial and temporal scales, how it decays, its relation to shock passage and others. We discuss properties of fluctuations ahead (upstream) and behind (downstream) of IP shock fronts with the focus on observations. Some of the key characteristics of the upstream/downstream transition are 1) enhancement of the power in the inertial range fluctuations of the velocity, magnetic field and density is roughly one order of magnitude, 2) downstream fluctuations are always more compressible than the upstream fluctuations, and 3) energy in the inertial range fluctuations is kept constant for a significant time after the passage of the shock. In this paper, we emphasize that–for one point measurements–the downstream region should be viewed as an evolutionary record of the IP shock propagation through the plasma. Simultaneous measurements of the recently launched spacecraft probing inner parts of the Solar System will hopefully shed light on some of these questions.