We summarize the recent studies on the nature of plasma sheet turbulence within Earth's magnetosphere using data from the Magnetospheric Multiscale Mission (MMS), focusing on the role of this turbulence in driving magnetospheric processes. Our analysis reveals a radial dependence of the eddy diffusion coefficient, which governs the transport of energy and momentum within the plasma sheet. We also analyze the limits of the applicability of the frozen-in condition for magnetic fields in plasmas with high Reynolds numbers, and provide the arguments highlighting the role of pressure balance in low-velocity plasma regimes for understanding the causes of the development of geomagnetic disturbances. We also analyze the processes leading to the Interplanetary Magnetic Field (IMF) penetration into the magnetosphere. We show that understanding of the interconnection between the magnetospheric turbulence, pressure balance and IMF penetration into the magnetosphere allows us to offer novel self-consistent explanations for a number of phenomena, including the dynamics of an isolated substorm.

In the present study, the influence of the solar wind dynamic pressure on the plasma and magnetic pressures of the magnetosphere is studied. We use 11-year Time History of Events and Macroscale Interactions during Substorms (THEMIS) instruments for plasma and magnetic field measurements in the magnetosphere and the OMNI database for solar wind dynamic pressure and IMF data. We focus on the effects of the solar wind dynamic pressure (PSW) and consider only times in which the interplanetary magnetic field (IMF) components are within +/- 5 nT. We find that the plasma pressure inside the magnetosphere follows the solar wind dynamic pressure and that an increase in PSW also influence the day-night pressure asymmetry. Our analysis also reveals the existence of ion and electron drifts from midnight toward the dusk and dawn sectors, respectively. We observe a local magnetic pressure minimum located near a plasma pressure maximum at around 11 RE on the nightside. Comparing the effect of PSW on both plasma and magnetic pressures, we observe trends which are consistent with the diamagnetic properties of plasmas. In general, the distribution of plasma pressure within the Earth's magnetosphere is an important criterion for evaluating the magnetostatic equilibrium and electric current system. The outcome of this study should provide additional methodologies for the characterization of key plasma characteristics within the magnetosphere. Magnetospheric activity and space weather are driven by the interaction of the solar wind and the Earth's magnetic field. The solar wind dynamic pressure and interplanetary magnetic field (IMF) are two important factors that affect the behavior of the Earth's magnetosphere. The interaction between these two factors are complex and can have significant effects on our planet. Based on 11-year plasma and magnetic field measurements, obtained from THEMIS satellites, we investigated the effect of solar wind dynamic pressure on the plasma and magnetic pressures within the Earth magnetosphere. In this study, we show that changes in the plasma pressure within the magnetosphere are linked to variations in the solar wind dynamic pressure. Our findings confirm that the plasma pressure inside the magnetosphere is mainly controlled by the solar wind dynamic pressure, which can be attributed to pressure balance. Overall, the distribution of plasma pressure within the Earth's magnetosphere is a key parameter for evaluating the magnetostatic equilibrium and electric current system. Our results are expected to offer scientists additional methodologies for characterizing main plasma parameters in the magnetosphere. Increase in solar wind dynamic pressure leads to increase in plasma and magnetic pressures in the magnetosphere Larger solar wind dynamic pressure make the plasma pressure more symmetric around the Earth Observations reveal a local magnetic pressure minimum located near a plasma pressure maximum around 11RE on the nightside

The Earth's magnetosphere is filled with a collisionless plasma that exhibits non-Maxwellian particle distributions which are well described by Kappa functions. In contrast to the Maxwellian, the Kappa contains not only density and temperature but also the kappa index that allows us to characterize the energetic tails. In this study, we analyze the response of the ion and electron Kappa distributions, obtained by fitting ion and electron fluxes measured by the five THEMIS satellites, to changes of the solar wind dynamic pressure. It was found that the solar wind dynamic pressure strongly affects the values of the kappa index, and that its impact depends on the magnetic local time (MLT). In particular, there is a significant dawn-dusk asymmetry for low PSW values which is enhanced in the night side. Further, we observe a narrow partial ring-shaped structure at different azimuthal extension that divides the plasma into two clearly defined domains. The results obtained reflect the global reconfiguration of the magnetosphere caused by variations of the solar wind dynamic pressure. Kappa distribution parameters and their average values for different ranges of PSW and MLT are provided, which we believe will contribute as realistic inputs to the modeling of the magnetosphere. The Kappa distribution function, which combines the Maxwellian-type and the power-law distributions, has been widely used in literature to describe particle populations in space and astrophysical plasmas. In such environments, ions and electrons rarely experience collisions and they are out of thermal equilibrium, which allows us to get insights into the mechanism of energy transfer in these plasmas. The goal is to investigate the roles of non-thermal particle distributions, and their response to solar wind dynamic pressure in poorly collisional plasma environments such as the Earth magnetosphere. The availability of high cadence Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite data have enabled us to conduct this statistical analysis using THEMIS and OMNI database. Our findings confirm that the ion and electron kappa parameters exhibit distinct behaviors when subjected to the dynamic pressure exerted by the solar wind. Moreover, we find an interesting narrow partial ring shaped structure at different azimuthal extension exhibiting a local minimum for ion kappa parameters, and a local maximum for electron kappa parameters. The behavior of Kappa distribution parameters in the Earth magnetosphere in response to the variation of the solar wind dynamic pressure is studied The solar wind dynamic pressure strongly influence ion and electron kappa indices The core energy (Ec) exhibits a significant dawn-dusk asymmetry for ions and much weaker for electrons in various range of PSW

The radial distribution of the magnetospheric plasma pressure frequently shows the existence of definite features such as local increases and decreases. Regions with near to constant radial plasma pressure distribution were observed using INTERBALL/Tail probe and THEMIS mission satellites. Such regions were named the plasma pressure plateaus. In spite of the simultaneous observations near the same plateau pressure distribution by two satellites at near the same orbits with time delay ~30 min, it is essential to precisely separate purely temporal pressure changes from spatial variations. We compare the results of THEMIS observations with the predictions of Tsyganenko and Mukai [2003] model of magnetotail plasma pressure distribution using observed IMF and solar wind conditions from the OMNI data base. We also determine the projection of the observed pressure plateau to Iijima and Potemra [1978] picture of field-aligned currents using TS01, TA16 models. We show that observed plasma pressure profile cannot be the result of the temporal pressure changes.

In this work, we discuss the problems associated with the formation of the outer radiation belt (ORB) taking into account previous results, including the recent ones. In our opinion, the traditional approaches to the dynamics of the ORB have the following problems: • inconsistency between the times provided by the popular “quasilinear” approach to the ORB description and the observed electron acceleration times; • impossibility to describe ORB dynamics during magnetospheric storms using the “quasilinear” approach when the particle fluxes after storm restore to their pre-storm values, i.e., belong to the storms of the third type according to Reeves et al. (2003, https://doi.org/10.1029/2002GL016513 ) classification; • impossibility of explaining the Tverskaya’s relation, which connects the position of the maximum of the relativistic flux formed after storm with the minimum value of the Dst/SYM-H variation, as well as the acceleration of relativistic electrons during magnetospheric substorms even in the absence of storms. We show that such difficulties do not appear if we take into account the large- scale magnetospheric dynamics, including auroral oval shift toward low latitudes during storms, substorm injections into the region of depressed magnetic field during storm recovery phase and the action of the adiabatic mechanism of electron deceleration and acceleration. The action of stochastic mechanisms of ORB acceleration is also discussed.

The results of observations of low-altitude spacecraft crossing the daytime sector of the auroral zone and of high-apogee spacecraft in the equatorial plane of the magnetosphere were analyzed in order to identify the main processes leading to the formation of dayside polar cusps. Observations from the DMSP F7 spacecraft were used to analyze the latitudinal characteristics of ion precipitation in the cusp region and to study the latitudinal profile of ion pressure in the cusp depending on the IMF parameters. A significant difference was found in identifying the cusp boundaries using an automated data processing system and direct analysis of spacecraft observations. It is shown that for small negative values of the Bz-component of the IMF (〈Bz〉 = –3.0 nT), an ordinary feature of the cusp is the latitudinal profile of the ion pressure (Pi) with a width of 1° of latitude with two maxima, one of which is located in the equatorward and the other in the poleward of the cusp. For large negative Bz values (–6, –8 nT), the polar maximum in the latitudinal profile Pi disappears; only the equatorial maximum remains, the Pi level at the maximum increases, and the width of the cusp decreases to 0.7°. For Bz IMF > 0, the most characteristic is the Pi profile with a maximum ion pressure in the polar part of the cusp. The cusp for Bz > 0 is located at higher latitudes than for Bz < 0, and its average latitudinal width increase to 1.4° of latitude. In the prenoon sector MLT, the most typical for periods with a large negative By-component of the IMF (〈By〉 = –6.3 nT, 〈Bz〉 = –1.7 nT) is a cusp with a width of 1.4° of latitude with a flat top in the latitudinal Pi profile. Comparison of the pressure distributions observed at low heights with data from high-apogee satellites confirmed the possibility of describing the formation of the cusp as a diamagnetic cavity and using observations in the cusp to determine the ion pressure in the magnetosheath.

Abstract Since the discovery of the large‐scale field‐aligned currents it is widely acknowledged that gaps exist between the Region 1 (R1) and Region 2 (R2) currents in which the current values are relatively small as compared to neighboring regions. Assuming that the field‐aligned currents are generated by plasma pressure gradients, we analyzed data collected by the THEMIS satellites between 2007 and 2011 to identify regions with very low plasma pressure gradients (pressure plateaus), which could be responsible for the appearance of these gaps. It was found that the pressure profiles with low radial gradients are typically located between 8 and 10 Radii around the Earth. Projections of pressure plateau regions onto ionospheric altitudes, for both individual events and on a statistical basis, coincide with the locations of gaps between Iijima and Potemra field‐aligned currents. The role played by identified pressure plateaus in shaping the pattern of large‐scale field‐aligned currents is discussed.

We analyzed the applicability of a hydrodynamic approach to the analysis of large-scale magnetospheric dynamics in the conditions of quiet geomagnetic activity. The main parameter, determining the applicability of the ideal MHD, is the ratio between the Alfvén and plasma velocities. We obtained the 2D distribution of this parameter using data of the THEMIS mission at geocentric distances <20 RE, and showed that not only the ring current region can be described suggesting full pressure balance. The external part of the ring current, which is localized in the surrounding the Earth plasma ring and earlier considered as a plasma sheet continuation, can be regarded as a stress balance region as well. Azimuthal plasma pressure gradients in this region create a system of large-scale field-aligned currents. Their closing in the ionosphere generates a large-scale convection in the ionosphere and magnetosphere. The mechanism of the large-scale convection control due to "penetration" of large-scale solar wind magnetic field is discussed. We discuss the role of turbulent transport in the analysis of magnetospheric regions, in which high level of turbulence is observed simultaneously with large-scale stress balance.

The most recent findings on the dynamics of the outer radiation belt (ORB) and the physics of magnetospheric substorms are examined. Specifically, we investigate the relationship between storm time substorms and the energetic electron population that forms the ORB. Traditionally, storm time substorms have been considered as the primary source of energetic electrons, which are further accelerated during storms to contribute to the formation of the ORB. However, several observations have demonstrated that large magnetospheric substorms can generate high-energy electrons even in the absence of magnetic storms. Substorms introduce dispersionless injections of energetic electrons deep into the magnetosphere from the geosynchronous orbit during storm times. The injected electrons undergo additional acceleration via the betatron mechanism during the storm recovery phase, thus increasing the ORB population. To gain a better understanding of this process, it is crucial to study plasma sheet turbulence, substorm onset processes, and the brightening of auroral arcs. By analyzing the aforementioned findings, this study aims to highlight the need for reanalyzing of the role of auroral processes in the formation of the ORB.

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

The data from the DMSP spacecraft were used to study the characteristics of ion and electron precipitation in the nightside sector of the auroral zone during magnetically quiet periods at extreme values of the solar wind dynamic pressure ( Psw ). It was shown that the ion pressure at the isotropy boundary (IB) increases with Psw and can reach a level of 4–6 nPa at Psw = 20–22 nPa. The latitude profiles of the ion pressure obtained at different levels of Psw indicate that the increase in Psw is accompanied by an expansion of the ion precipitation region and a shift of the IB to lower latitudes. At 〈 Psw 〉 = 0.5 nPa, the IB latitude is ~70.4° CGL, while at 〈 Psw 〉 = 16.3 nPa, it shifts toward the equator to ~64.6° CGL. As the Psw level decreases, the energy fluxes of precipitating electrons decrease significantly. At Psw < ~ 2.0 nPa, auroras in the region of the auroral oval can be considered subvisual. At extremely low values of dynamic pressure, Psw = ~ 0.2 nPa, it becomes very problematic to identify the zone of electron and ion precipitation.

We analyzed the problems of formation of the outer radiation belt (ORB) taking into consideration the latest changes in our understanding of the high-latitude magnetospheric topology. This includes strong evidence that the auroral oval maps to the outer part of the ring current, meanwhile the ORB polar boundary maps inside the auroral oval. Our analysis also includes the variation of the plasma pressure distribution and the time of the acceleration of relativistic electrons during geomagnetic storm. It is shown that the maximum of ORB is formed after the geomagnetic storm in the region of plasma pressure maximum. The position of this maximum agrees with the prediction of the ORB formation theory based on the analysis of ring current development during storm. We emphasize the role of adiabatic processes in the ORB dynamics and the importance of the substorm injections during storm recovery phase for the formation of enhanced fluxes of ORB electrons after the storm.

Данные спутников серии DMSP использованы для исследования ионного давления в ночном секторе авроральной зоны в магнитоспокойные периоды при экстремальных значениях динамического давления солнечного ветра (Psw). Показано, что при экстремально высоких уровнях динамического давления солнечного ветра давление ионов на границе изотропизации (ГИ) увеличивается с ростом Psw и может достигать уровня 4-6 нПа при Psw = 20-22 нПа. Получены широтные профили ионного давления при средних уровнях динамического давления равных 0.5 нПа, 2.1 нПа и 16.3 нПа, указывающие на то, что увеличение Psw сопровождается не только ростом давления плазмы в авроральной зоне, но и расширением области авроральных высыпаний, главным образом за счет смещения ГИ в более низкие широты. Проведено проецирование широтного профиля ионного давления на экваториальную плоскость магнитосферы при Psw~2.0 нПа.

The Earth's magnetosphere is mainly a collisionless plasma system with non-Maxwellian particle distributions, which are often fitted by the kappa function. While the Maxwell distribution function is described by two parameters (density and temperature), the kappa distribution function has three parameters: density, core energy, and the kappa index that characterizes the slope at high energies. In this study, we fitted an ion flux measured by the five Time History of Events and Macroscale Interactions during Substorms satellites in the Earth's magnetosphere during quiet geomagnetic conditions by a single kappa distribution function. The data were constrained to the following regions: from seven Earth Radii (7 RE) to the Earth's magnetopause at the dayside, and up to 20 RE for other magnetic local time sectors. The two-dimensional spatial distribution of the fitted parameters and their radial dependencies were analyzed. Regions of high and low kappa-parameter are selected and their formation is discussed.

The possible influence of MHD turbulence on the energy distributions of ions in the Earth's plasma sheet was studied using data taken by the THEMIS satellites. Turbulence levels were traced using eddy diffusion coefficients ( D ), of which we measured one for each Geocentric Solar Magnetospheric (GSM) coordinates every 12 min. Ion fluxes between 1.75 and 210.5 keV during the same time windows that correspond to mainly suprathermal populations were fitted to Kappa distribution functions, which approximate a Maxwellian distribution when the κ -index ( κ ) is large. We found that the distribution of the eddy diffusion coefficients is bimodal, independently of both the eddy diffusion component and the plasma beta ( β ) parameter, which is defined as the ratio between plasma and magnetic pressures. The main peak corresponds to turbulent plasma flows with D > 10 3 km 2 s −1 . In such cases, the impact of turbulence on the κ index depends on the value of β and also on the direction of the turbulent transport. For eddy diffusion perpendicular to the neutral sheet, the values of κ decrease as D zz increases for β < 2; while for higher values of β , κ increases with D zz . For the other two directions, the values of κ decrease as D increases. This last tendency is stronger for β ~ 1 but almost null for β ~ 10. The secondary peak in the distribution of D values might represent quasi-laminar flows forming part of very large vortices, correct detection and description of which is beyond the scope of this study.

Formation of kappa distribution functions and their relaxation to Maxwellian distributions are the main feature of astrophysical and space collisionless plasmas. In this work, we use the magnetosphere of the Earth as a giant plasma laboratory to study the properties of ion kappa distribution functions. Four years of measurements, performed by the multi-satellite Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission during quiet geomagnetic conditions, at geocentric distances from three Earth radii (R-E) to the magnetopause at daytime (of the order of 10R(E)), and up to 20R(E) at night time are used for the analyses. We find a dependence of the k parameter on the core energy E-0 of a single kappa distribution inside the magnetospheric ring current and in the plasma sheet, for different values of the plasma parameter (the ratio between the plasma and magnetic pressures). We show that k increases with E-0 for all values of plasma parameter, which supports earlier results obtained for the magnetospheres of the Earth, Jupiter, and Saturn, but using lower statistics. However, contrary to previous results, our studies show that the relation between k and E-0 is nonlinear, and most probably is a power law with a nearly constant index. The results obtained are relevant to solve the problem of thermalization of kappa distributions.

Variations in the radial profile of the pressure and distortions of the magnetic field of the magnetosphere in the dark sector near the equatorial plane during the storm of May 29, 2010, are analyzed based on THEMIS data. The position of the pressure maximum during the main phase of the storm is determined. The time dynamics of the pressure maximum is traced during the recovery phase. The time of pressure relaxation to initial values (before the main phase) during the recovery phase are assessed. The coincidence of the positions of the pressure peak maximum and of maximal deviation of the magnetic field from the dipole one is ascertained.