Magnetospheric Current Systems Research Articles

Two distinct current systems in the ionosphere of Mars

When the solar wind interacts with the ionosphere of an unmagnetized planet, it induces currents that form an induced magnetosphere. These currents and their associated magnetic fields play a pivotal role in controlling the movement of charged particles, which is essential for understanding the escape of planetary ions. Unlike the well-documented magnetospheric current systems, the ionospheric current systems driven by solar wind and atmospheric neutral winds have not been quantitatively observed, which constrains the quantification of energy transfer from stars to these planets. Here, utilizing eight years of data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we investigate the global distribution of ionospheric currents on Mars. We identify two distinct current systems in the ionosphere: one aligns with the solar wind electric field but exhibits hemispheric asymmetry perpendicular to the solar wind electric field direction; the other corresponds to the flow pattern of annually averaged neutral winds. We propose that these two current systems are driven by the solar wind and atmospheric neutral winds, respectively. Our findings reveal that Martian ionospheric dynamics are influenced by the neutral winds from below and the solar wind from above, highlighting the complex and intriguing nature of current systems on unmagnetized planets.

Monitoring of magnetospheric parameters based on cosmic ray effects in August

Using data (uncorrected for the temperature effect) from the global network of neutron monitors (GNNM), along with data from the Yakutsk muon telescope complex and the muon hodoscope URAGAN (Moscow), we have applied a modified spectrographic global survey (SGS) method to the 2018 August event in order to split cosmic ray variations into components of primary, magnetospheric, and atmospheric origin. We obtained time variations in the 4 GV-rigidity primary particle isotropic flux and pitch-angle anisotropy, as well as in the interplanetary magnetic field (IMF) orientation. We also showed variations in the geomagnetic cutoff rigidity (GCR) in Irkutsk.
 Using the obtained data on the changes in the planetary system of GCR within a simple model of a bounded magnetosphere, we have calculated some parameters of magnetospheric current systems, namely, the ring current radius, the magnetopause current radius, and the Dst index.

Мониторинг параметров магнитосферы по эффектам в космических лучах в августе 2018 г.

Using data (uncorrected for the temperature effect) from the global network of neutron monitors (GNNM), along with data from the Yakutsk muon telescope complex and the muon hodoscope URAGAN (Moscow), we have applied a modified spectrographic global survey (SGS) method to the 2018 August event in order to split cosmic ray variations into components of primary, magnetospheric, and atmospheric origin. We obtained time variations in the 4 GV-rigidity primary particle isotropic flux and pitch-angle anisotropy, as well as in the interplanetary magnetic field (IMF) orientation. We also showed variations in the geomagnetic cutoff rigidity (GCR) in Irkutsk.
 Using the obtained data on the changes in the planetary system of GCR within a simple model of a bounded magnetosphere, we have calculated some parameters of magnetospheric current systems, namely, the ring current radius, the magnetopause current radius, and the Dst index.

Prediction of Proton Pressure in the Outer Part of the Inner Magnetosphere Using Machine Learning

AbstractThe information on plasma pressure in the outer part of the inner magnetosphere is important for simulations of the inner magnetosphere and a better understanding of its dynamics. Based on 17‐year observations from both Cluster Ion Spectrometry and Research with Adaptive Particle Imaging Detector instruments onboard the Cluster mission, we used machine‐learning‐based models to predict proton plasma pressure at energies from ∼40 eV to 4 MeV in the outer part of the inner magnetosphere ( = 5–9). Proton pressure distributions are assumed to be isotropic. The location in the magnetosphere, the property of stably trapped particles, and parameters of solar, solar wind, and geomagnetic activity from the OMNI database are used as predictors. We trained several different machine‐learning‐based models and compared their performances with observations. The results demonstrate that the Extra‐Trees Regressor has the best predicting performance. The Spearman correlation between the observations and predictions by the model is about 70%. The most important parameter for predicting proton pressure in our model is the value, which relates to the property of stably trapped particles. The most important predictor of solar and geomagnetic activity is F10.7 index. Based on the observations and predictions by our model, we find that no matter under quiet or disturbed geomagnetic conditions, both the dusk‐dawn asymmetry at the dayside with higher pressure at the duskside and the day‐night asymmetry with higher pressure at the nightside occur. Our results have direct practical applications, for instance, inputs for simulations of the inner magnetosphere or the reconstruction of the 3‐D magnetospheric electric current system based on the magnetostatic equilibrium.

Magnetospheric current system parameters during the geomagnetic disturbances in May 1998

Based on the data from the global network of neutron monitors, by using the spectrographic global survey, we obtained the parameters of magnetospheric current systems in the 1998 May events. Within the axisymmetric model for the bounded Earth magnetosphere, we determined the DR (ring current) and DCF (magnetopause currents) parameters for the current systems, as well as their contribution to variations in the rigidity of the geomagnetic cutoff and to the Dst-index over the addressed period.

Parameters of Magnetospheric Current Systems during Geomagnetic Disturbances of May, 1998

Parameters of Magnetospheric Current Systems during Geomagnetic Disturbances of May, 1998

The Ionospheric Dynamics of the African Sector Responding to a Severe Geomagnetic Storm; the Storm of 3–5 November 2021

AbstractThe sudden storm commencement (SSC) of 3 November 2021, a severe storm was detected through disturbances in magnetospheric and ring current systems at around 1942 UT. We used a daily variation of total electron content (TEC) from ground‐based GNSS stations, ionosonde parameters and modeled zonal and meridional wind velocities to study the ionospheric response over the African region by comparing storm and quiet time variations. The equatorial GNSS station of NKLG recorded initial positive storm effects around the time of SSC, of which these effects spread over the whole African region during the main phase with positive and negative storm effects during the main and recovery phases respectively. The two disturbances at the SSC and the main phase were caused by the penetrating electric field and traveling atmospheric disturbances respectively. The analysis of TIMED Global UltraViolet Imager images revealed storm time‐induced changes in thermospheric composition during the main phase which resulted in a differential ionospheric response with intense, moderate, and weak positive storm effects in northern, equatorial, and southern regions respectively. The horizontal magnetic field components show two signatures of prompt penetration electric field that suppressed the formation of the equatorial anomaly at SSC and enhanced positive storm effects in the equatorial region at the main phase, Therefore, the ionospheric response was due to the relative contributions of prompt penetration electric field effects and equatorward traveling disturbances which depended on storm onset time, past ionospheric state, and storm phase.

A Plasma Pressure Plateau in the Night Sector of the Earth’s Magnetosphere and Its Stability

In this paper, we consider the behavior of the radial distribution of the plasma pressure, magneticfield, and plasma parameter in the night sector of the Earth’s magnetosphere at geocentric distances from 7to 12 RE that are obtained using the THEMIS mission measurements. The results of measurements on theTHEMIS-D and THEMIS-A satellites on February 2009 when the satellites were near the equatorial planewere analyzed. Time intervals are identified when the plasma pressure actually did not change with a changein the distance from the Earth. It is shown that profiles with a pressure plateau can exist stably during the dayare destroyed during the period of disturbance and are restored after destruction. The role of the pressure plateauin the formation of the structure of magnetospheric current systems is discussed

Power-law dependence of the wavelet spectrum of ground magnetic variations during magnetic storms

We show that time variations in the ring current and auroral electrojets in 2015, during which three major magnetic storms (MSs) occurred, are recorded in several specific ways by ground magnetometers. Specifically, we show that the time variations in magnetic field intensity have power-law wavelet spectra. The variations in ring current intensity are detected in geomagnetic field measurements of ground stations at magnetic mid-latitudes between λ=-50° and +50°. We confirmed the results of Balasis et al. (2006), who had shown that the Dst index wavelet spectrum follows a power law of the form f-β, where f is the frequency, and β is the exponent of the power law, by applying the same wavelet analysis to the SYM-H index version of the Dst index, and also to ground magnetic field measurements. Balasis et al. (2006) also showed that the critical exponent β of the power law, obtains values greater than 2 (or equivalently that the Hurst exponent H>0.5), shortly before the onset and during the main phase of the storms. Here, using wavelet transforms on the Earth’s magnetic field as measured at different magnetic latitudes (MLAT), we showed that at mid-geomagnetic latitudes, where the Earth’s magnetic field is determined mainly by the ring current, the resulting Hurst exponent is greater than 0.5 several hours before and during magnetic storms. Geomagnetic field variation at higher magnetic latitudes between λ=+50° and +73°, also show power-law wavelet spectra. However, here we find a more complex dependence with two power-law exponents. We interpret this double power law as the effect of both the ring current and the auroral electrojets. Finally, for polar latitudes, between λ=+73° and +85°, we find the same complex dependence with two power-law exponents. Our results show that the geomagnetic field at auroral latitudes has much lower power and very different wavelet spectra compared to the geomagnetic field at ranges of lower magnetic latitude. Our results show how wavelet-based measures of ground geomagnetic variations reflect the time evolution of several magnetospheric current systems.

On the Magnetosphere‐Ionosphere Coupling During the May 2021 Geomagnetic Storm

AbstractOn 12 May 2021 the interplanetary doppelgänger of the 9 May 2021 coronal mass ejection impacted the Earth's magnetosphere, giving rise to a strong geomagnetic storm. This paper discusses the evolution of the various events linking the solar activity to the Earth's ionosphere with special focus on the effects observed in the circumterrestrial environment. We investigate the propagation of the interplanetary coronal mass ejection and its interaction with the magnetosphere—ionosphere system in terms of both magnetospheric current systems and particle redistribution, by jointly analyzing data from interplanetary, magnetospheric, and low Earth orbiting satellites. The principal magnetospheric current system activated during the different phases of the geomagnetic storm was correctly identified through the direct comparison between geosynchronous orbit observations and model predictions. From the particle point of view, we have found that the primary impact of the storm development is a net and rapid loss of relativistic electrons from the entire outer radiation belt. Our analysis shows no evidence for any short‐term recovery to pre‐storm levels during the days following the main phase. Storm effects also included a small Forbush decrease driven by the interplay between the interplanetary shock and subsequent magnetic cloud arrival.

An Eastward Current Encircling Mercury

AbstractMercury has a terrestrial‐like magnetosphere which is usually taken as a scaled‐down‐version of Earth's magnetosphere with a similar current system. We examine Mercury's magnetospheric current system based on a survey of Mercury's magnetic field measured by the Mercury Surface, Space Environment, Geochemistry, and Ranging spacecraft as well as computer simulations. We show that there is no significant Earth‐like ring current flowing westward around Mercury, instead, we find, for the first time, an eastward current (EC) encircling the planet near the night‐side magnetic equator with an altitude of ∼500–1,000 km. The EC is closed with the dayside magnetopause current and could be driven by the gradient of plasma pressure as a diamagnetic current. Thus, Mercury's magnetosphere is not a scaled‐down Earth magnetosphere, but a unique natural space plasma laboratory. Our findings offer fresh insights to analyze data from the BepiColombo mission, which is expected to orbit Mercury in 2025.

Modeling of Magnetospheres of Terrestrial Exoplanets in the Habitable Zone around G-Type Stars

Using a paraboloid model of an Earth-like exoplanetary magnetospheric magnetic field, developed from a model of the Earth, we investigate the magnetospheric structure of planets located in the habitable zone around G-type stars. Different directions of the stellar wind magnetic field are considered and the corresponding variations in the magnetospheric structure are obtained. It is shown that the exoplanetary environment significantly depends on stellar wind magnetic field orientation and that the parameters of magnetospheric current systems depend on the distance to the stand-off magnetopause point.

Time‐Domain Modeling of Three‐Dimensional Earth's and Planetary Electromagnetic Induction Effect in Ground and Satellite Observations

AbstractElectric currents induced in conductive planetary interiors by time‐varying magnetospheric and ionospheric current systems have a significant effect on electromagnetic (EM) field observations. Complete characterization of EM induction effects is difficult owing to nonlinear interactions between the three‐dimensional electrical structure of a planet and spatial complexity of inducing current systems. We present, a general framework for time‐domain modeling of three‐dimensional EM induction effects in heterogeneous conducting planets. Our approach does not assume that the magnetic field is potential, allows for an arbitrary distribution of electrical conductivity within a planet, and can deal with spatially complex time‐varying current systems. The method is applicable to both data measured at stationary observation sites and satellite platforms, and enables the calculation of three‐dimensional EM induction effects in near real‐time settings.

A Long‐Lasting Auroral Spiral Rotating Around Saturn's Pole

AbstractThe main ultraviolet auroral emission at Saturn consists of multiple structures forming a discontinuous ring of emission around the poles, occasionally organized in a global spiral. We present continuous observation of an auroral spiral rotating at ∼85% of rigid corotation during several hours. Simultaneously, energetic neutral atom (ENA) emissions revealed a hot magnetospheric plasma population located in the same local time sector as the ends of the rotating spiral. Following plasma theory, we propose that pressure gradients induced by the energized plasma distorted the magnetospheric current system, resulting in the spiral morphology of the aurora. The rotating hot plasma was several times reenergized in the dusk sector during at least 2 days, generating a long‐lasting auroral spiral. The ultraviolet spiral, the ENA emissions, and the ions revealed by this multi‐instrument data set are three signatures of a magnetosphere‐ionosphere coupling current system and of the associated hot plasma population rotating around Saturn.

Influence of Mercury's Exosphere on the Structure of the Magnetosphere

AbstractMercury is embedded in a tenuous and highly anisotropic sodium exosphere, generated mainly by plasma‐surface interactions. The absolute values of the sodium ion density are still under debate. Observations by MESSENGER's Fast Imaging Plasma Spectrometer (FIPS) instrument suggest the density of exospheric ions to be several orders of magnitude lower than the upstream solar wind density, indicating that the sodium exosphere has no substantial influence on the magnetospheric current systems. However, MESSENGER magnetic field observations of field line resonances revealed sodium ion densities comparable to the upstream solar wind density. To investigate how a dense exosphere would affect the current systems within Mercury's magnetosphere, we apply an established hybrid (kinetic ions, fluid electrons) model and conduct multiple model runs with gradually increasing exospheric density, ranging from no sodium ions at all to comet‐like configurations. We demonstrate how a sufficiently dense exosphere leads to self‐shielding of the sodium ion population from the ambient electric field and a significant inflation and symmetrization of Mercury's magnetosphere, which is decreasingly affected by the dipole offset. Once the sodium ion density is sufficiently high, Region 2 field‐aligned currents emerge close to the planet. The modeled Region 2 currents are located below the orbit of MESSENGER, thereby providing a possible explanation for the absence of these currents in observations. The sodium exosphere also closes a significant fraction of the Region 1 currents through Pedersen and Hall currents before the “guiding” magnetic field lines even reach the planetary surface. The modeled sodium ion and solar wind densities agree well with observations.

Linear Versus Nonlinear Methods for Detecting Magnetospheric and Ionospheric Current Systems Patterns

AbstractThere is a growing interest in the development of models and methods of analysis aimed to recognize in the geomagnetic field signals the different contributions coming from the various sources both internal and external to the Earth. Many models describing the geomagnetic field of internal and external origin have been developed. Here, we investigate the possibility to recognize in the magnetic field of external origin the different contributions coming from external sources. We consider the measurements of the vertical component of the geomagnetic field recorded by the European Space Agency (ESA) Swarm A and B satellites at low and mid latitudes during a geomagnetically quiet period. We apply two different methods of analysis: a linear method, that is, the empirical orthogonal function (EOF), and a nonlinear one, that is, the multivariate empirical mode decomposition (MEMD). Due to the high nonlinear behavior of the different external contributions to the magnetic signal the MEMD seems to recognize better than EOF the main intrinsic modes capable of describing the different magnetic spatial structures embedded in the analyzed signal. By applying the MEMD only five modes and a residue are necessary to recognize the different contributions coming from the external sources in the magnetic signal against the 26 modes that are necessary in the case of the EOF. This study is an example of the potential of the MEMD to give new insights into the analysis of the geomagnetic field of external origin and to separate the ionospheric signal from the magnetospheric one in a simple and rapid way.

From the Sun to Earth: effects of the 25 August 2018 geomagnetic storm

Abstract. On 25 August 2018 the interplanetary counterpart of the 20 August 2018 coronal mass ejection (CME) hit Earth, giving rise to a strong G3 geomagnetic storm. We present a description of the whole sequence of events from the Sun to the ground as well as a detailed analysis of the observed effects on Earth's environment by using a multi-instrumental approach. We studied the ICME (interplanetary-CME) propagation in interplanetary space up to the analysis of its effects in the magnetosphere, ionosphere and at ground level. To accomplish this task, we used ground- and space-collected data, including data from CSES (China Seismo-Electric Satellite), launched on 11 February 2018. We found a direct connection between the ICME impact point on the magnetopause and the pattern of Earth's auroral electrojets. Using the Tsyganenko TS04 model prevision, we were able to correctly identify the principal magnetospheric current system activating during the different phases of the geomagnetic storm. Moreover, we analysed the space weather effects associated with the 25 August 2018 solar event in terms of the evaluation of geomagnetically induced currents (GICs) and identification of possible GPS (Global Positioning System) losses of lock. We found that, despite the strong geomagnetic storm, no loss of lock had been detected. On the contrary, the GIC hazard was found to be potentially more dangerous than other past, more powerful solar events, such as the 2015 St Patrick's Day geomagnetic storm, especially at latitudes higher than 60∘ in the European sector.

Correlation of the Cosmic-Ray Cutoff Rigidity with Heliospheric and Geomagnetic-Activity Parameters at Different Phases of a Magnetic Storm in November 2004

The correlation of the variations in geomagnetic cutoff rigidity of cosmic rays ΔR with the interplanetary medium parameters and geomagnetic activity indices Dst and Kp was calculated for different phases of the superstorm on November 7–8, 2004. The strongest correlation was observed between the cutoff rigidity and Dst at all stages of storm development (correlation coefficients k ≈ 0.70–0.98); some stable influence of the solar wind (SW) density N (k ≈ 0.50–0.80) should also be noted. The dependence of the cutoff-rigidity variation on all of the dynamic parameters of the SW is observed in the main storm phase and is especially strong for the density N and pressure P. The correlation between ΔR and V is negative in all phases, while the correlation of ΔR with N and P is positive during the main phase and negative in the recovery phase. The cutoff-rigidity variations showed no sensitivity to the Bz component of the interplanetary magnetic field (IMF), the azimuthal component By, or the IMF absolute value B before the storm or in its main phase. A significant correlation or anticorrelation of ΔR with B and all the IMF components is observed only in the recovery period. The specific response of the geomagnetic cutoff rigidity to the heliospheric and magnetospheric parameters at different phases of the magnetic storm is apparently determined by the different relative contributions of the magnetospheric global current systems during these periods.

Magnetic Field Variations and Dynamics of the Outer Electron Radiation Belt of the Earth’s Magnetosphere in February 2014

The paper presents the results of a comparative analysis of the dynamics of relativistic electron fluxes of the Earth’s outer radiation belt and correspondent ring current and magnetospheric magnetic field variations for February 15–22, 2014, based on experimental data obtained in the radiation belt core aboard Van Allen Probes satellites and in geostationary orbit aboard the GOES-15 satellite. The A2000 paraboloid model of the magnetosphere is used to calculate the contributions of main magnetospheric current systems to the Dst variation. The influence of external factors—solar wind and interplanetary magnetic field—is considered. Comparison of the dynamics of electron fluxes in different orbits and the geomagnetic field variations for February 15‒22, 2014 indicate that the main mechanisms of the evolution of outer electron radiation belt are global processes: (i) outward and inward shifts of the trapped electron population inside the Earth’s magnetosphere due to large-scale variations of the magnetospheric magnetic field during geomagnetic disturbances and (ii) ExB drift of electrons from the magnetotail under the influence of electric and magnetic fields. Local particle acceleration is auxiliary process in the dynamics of radiation belts. The southward orientation of the interplanetary magnetic field is the necessary condition for an increase in the intensity of electron fluxes of the Earth’s outer radiation belt, while the function (–BzVsw) is the key external factor.

ExPRES: an Exoplanetary and Planetary Radio Emissions Simulator

Context. Earth and outer planets are known to produce intense non-thermal radio emissions through a mechanism known as cyclotron maser instability (CMI), requiring the presence of accelerated electrons generally arising from magnetospheric current systems. In return, radio emissions are a good probe of these current systems and acceleration processes. The CMI generates highly anisotropic emissions and leads to important visibility effects, which have to be taken into account when interpreting the data. Several studies have shown that modelling the radio source anisotropic beaming pattern can reveal a wealth of physical information about the planetary or exoplanetary magnetospheres that produce these emissions. Aims. We present a numerical tool, called ExPRES (Exoplanetary and Planetary Radio Emission Simulator), which is able to reproduce the occurrence in a time-frequency plane of R−X CMI-generated radio emissions from planetary magnetospheres, exoplanets, or star–planet interacting systems. Special attention is given to the computation of the radio emission beaming at and near its source. Methods. We explain what physical information about the system can be drawn from such radio observations, and how it is obtained. This information may include the location and dynamics of the radio sources, the type of current system leading to electron acceleration and their energy, and, for exoplanetary systems, the orbital period of the emitting body and the strength, rotation period, tilt, and the offset of the planetary magnetic field. Most of these parameters can only be remotely measured via radio observations. Results. The ExPRES code provides the proper framework of analysis and interpretation for past, current, and future observations of planetary radio emissions, as well as for future detection of radio emissions from exoplanetary systems (or magnetic, white dwarf–planet or white dwarf–brown dwarf systems). Our methodology can be easily adapted to simulate specific observations once effective detection is achieved.