Dynamik des Schweifs der Jupitermagnetosphäre

The Jupiter orbiting spacecraft Galileo has provided evidence that the Jovian magnetotail is subject to a periodic process with a typical timescale of several days by which the Jovian system is presumably releasing its excess iogenic mass. This process is analyzed using data returned from the Energetic Particles Detector (EPD), the magnetometer and plasma wave experiment on Galileo. The mass release process resembles a terrestrial substorm in the sense of a global reconfiguration of the magnetotail. During the initial "loading" phase the plasma convection is at a moderate speed in the corotational direction, and the Jovian plasma sheet appears to be in a stable configuration. In the release phase reconnection through a thinned current sheet leads to radially inward and outward plasma flows and the ejection of plasmoids. The striking difference from terrestrial substorms is the periodical appearance of the reconfiguration events. Such an intrinsic periodic behavior cannot readily be explained by a solar wind driven process. Therefore the role of the solar wind as energy source is of less importance than for terrestrial substorms. Instead, ion mass-loading from internal plasma sources and fast planetary rotation causes stretching of magnetotail field lines. The resulting magnetotail configuration favors magnetic reconnection. This leads to the formation and release of plasmoids. Continued mass-loading then again leads to stretching of tail field lines. Thus assuming that this quasi-periodical process is internally driven, a simple conceptual model to estimateMit Hilfe des Satelliten Galileo, der um Jupiter kreist, konnte nachgewiesen werden, dass periodische Prozesse mit einer Zeitskala von einigen Tagen eine wichtige Rolle für die Dynamik der Jupitermagnetosphäre spielen. Es wird angenommen, daß das System innerhalb dieses Zeitraumes überschüssige Masse auswirft. Diese Prozesse werden mit Hilfe des Energetic Particles Detector (EPD), einem Magnetometer und dem Plasmawellenexperiment auf Galileo untersucht. Der Massenauswurfprozess ähnelt einem geomagnetischem Teilsturm und führt zu einer globalen Umstrukturierung der Jupitermagnetosphäre. Während der anfänglichen Aufladephase strömt das Plasma langsam mit beinahe korotierender Geschwindigkeit und die Plasmaschicht der Jupitermagnetosphäre ist stabil. In der folgenden dynamischen Entladephase kommt es zu magnetischer Rekonnexion auf Grund der zuvor gebildeten dünnen Stromschicht, was zu in und auswärts gerichteten radialen Strömungen und dem Auswurf von Plasmoiden führt. Der wesentliche Unterschied zu einem geomagnetischem Sturm liegt in der Periodizität des Umstrukturierungsprozesses. Diese eingeprägte Periodizität kann nicht durch Sonnenwind getriebene Vorgänge erklärt werden. Daher ist der Einfluss des Sonnenwindes hier weniger wichtig als für geomagnetische Teilstürme. Wichtiger ist ionische Massenbeladung durch interne Plasmaquellen und die schnelle Planetenrotation, was zur Streckung der magnetosphärischen Feldlinien führt. Die resultierende Schweifkonfiguration begünstigt magnetische Rekonnexionsprozesse, was zur Bildung und zum Auswurf von Plasmoiden führt. Fortgesetzte Massenbeladung führt wiederum zur Streckung der Magnetfeldlinien im Magnetosphärenschweif. Unter der Annahme, dass dieser quasiperiodische Prozess durch interne Plasmaquellen getrieben wird, wurde ein einfaches, konzeptionelles Modell entwickelt um die Zeitskalen des periodischen Umstrukturierungsprozesses abzuschätzen. Das Modell zeigt, dass der vorgeschlagene, eingeprägte Mechanismus die beobachtete Periodizität von einigen Tagen für teilsturmähnliche Vorgänge in der Jupitermagnetosphäre erklären kann

Oxygen and hydrogen ion abundance in the near-Earth magnetosphere: Statistical results on the response to the geomagnetic and solar wind activity conditions

The composition of ions plays a crucial role for the fundamental plasma properties in the terrestrial magnetosphere. We investigate the oxygen-to-hydrogen ratio in the near-Earth magnetosphere from -10 RE<XGSE}< 10 RE. The results are based on seven years of ion flux measurements in the energy range ~10 keV to ~955 keV from the RAPID and CIS instruments on board the Cluster satellites. We find that (1) hydrogen ions at ~10 keV show only a slight correlation with the geomagnetic conditions and interplanetary magnetic field changes. They are best correlated with the solar wind dynamic pressure and density, which is an expected effect of the magnetospheric compression; (2) ~10 keV O+ ion intensities are more strongly affected during disturbed phase of a geomagnetic storm or substorm than >274 keV O+ ion intensities, relative to the corresponding hydrogen intensities; (3) In contrast to ~10 keV ions, the >274 keV O+ ions show the strongest acceleration during growth phase and not during the expansion phase itself. This suggests a connection between the energy input to the magnetosphere and the effective energization of energetic ions during growth phase; (4) The ratio between quiet and disturbed times for the intensities of ion ionospheric outflow is similar to those observed in the near-Earth magnetosphere at >274 keV. Therefore, the increase of the energetic ion intensity during disturbed time is more likely due to the intensification than to the more effective acceleration of the ionospheric source. In conclusion, the energization process in the near-Earth magnetosphere is mass dependent and it is more effective for the heavier ions

Acceleration of protons and heavy ions to suprathermal energies during dipolarizations in the near-Earth magnetotail

In this work we present an analysis of the dynamics of suprathermal ions of different masses (H+, He+, O+) during prolonged dipolarizations in the near-Earth magnetotail (X > -17 R-E/according to Cluster/RAPID observations in 2001- 2005. All dipolarizations from our database were associated with fast flow braking and consisted of multiple dipolarization fronts (DFs). We found statistically that fluxes of suprathermal ions started to increase similar to 1 min before the dipolarization onset and continued to grow for similar to 1 min after the onset. The start of flux growth coincided with the beginning of a decrease in the spectral index . The decrease in gamma was observed for protons for similar to 1 min after the dipolarization onset, and for He+ and O+ ions for similar to 3 and similar to 5 min after the onset respectively. The negative variations of gamma for O+ ions were similar to 2.5 times larger than for light ions. This demonstrates more efficient acceleration for heavy ions. The strong negative variations of gamma were observed in finite energy ranges for all ion components. This indicates the possibility of nonadiabatic resonant acceleration of ions in the course of their interaction with multiple DFs during dipolarizations. Our analysis showed that some fraction of light ions can be accelerated up to energies >= 600 keV and some fraction of oxygen ions can be accelerated up to similar to 1.2 MeV. Such strong energy gains cannot be explained by acceleration at a single propagating DF and suggest the possibility of multistage ion acceleration in the course of their interaction with multiple DFs during the prolonged dipolarizations

Turbulent processes in the Earth's magnetotail: spectral and statistical research

We use the magnetic field measurements from four spacecraft of the Cluster-II mission (three events from 2005 to 2015) for the analysis of turbulent processes in the Earth's magnetotail. For this study we conduct the spectral, wavelet and statistical analysis. In the framework of statistical examination, we determine the kurtosis for selected events and conduct extended self-similarity evaluation (analysis of distribution function moments of magnetic field fluctuations on different scales). We compare the high-order structure function of magnetic fluctuations during dipolarization with the isotropic Kolmogorov model and three-dimensional log-Poisson model with She-Leveque parameters. We obtain power-law scaling of the generalized diffusion coefficient (the power index that varies within the range of 0.2-0.7). The obtained results show the presence of super-diffusion processes. We find the significant difference of the spectral indices for the intervals before and during the dipolarization. Before dipolarization the spectral index lies in the range from - 1.68 +/- 0.05 to -2.08 +/- 0.05 (similar to 5/3 according to the Kolmogorov model). During dipolarization the type of turbulent motion changes: on large timescales the turbulent flow is close to the homogeneous models of Kolmogorov and Iroshnikov-Kraichnan (the spectral index lies in the range from -2.20 to -1.53), and at smaller timescales the spectral index is in the range from -2.89 to -2.35 (the Hall-MHD model). The kink frequency is less than or close to the average value of the proton gyrofrequency. The wavelet analysis shows the presence of both direct and inverse cascade processes, which indicates the possibility of self-organization processes, as well as the presence of Pc pulsations

Contrasting dynamics of electrons and protons in the near-Earth plasma sheet during dipolarization

The fortunate location of Cluster and the THEMIS P3 probe in the near-Earth plasma sheet (PS) (at X similar to -7-9- R-E) allowed for the multipoint analysis of properties and spectra of electron and proton injections. The injections were observed during dipolarization and substorm current wedge formation associated with braking of multiple bursty bulk flows (BBFs). In the course of dipolarization, a gradual growth of the B-Z magnetic field lasted similar to 13 min and it was comprised of several B-Z pulses or dipolarization fronts (DFs) with duration 50 keV) electron fluxes - the injection boundary - was observed in the PS simultaneously with the dipolarization onset and it propagated dawnward along with the onset-related DF. The subsequent dynamics of the energetic electron flux was similar to the dynamics of the magnetic field during the dipolarization. Namely, a gradual linear growth of the electron flux occurred simultaneously with the gradual growth of the B-Z field, and it was comprised of multiple short (similar to few minutes) electron injections associated with the B-Z pulses. This behavior can be explained by the combined action of local betatron acceleration at the B-Z pulses and subsequent gradient drifts of electrons in the flux pile up region through the numerous braking and diverting DFs. The nonadiabatic features occasionally observed in the electron spectra during the injections can be due to the electron interactions with high-frequency electromagnetic or electrostatic fluctuations transiently observed in the course of dipolarization. On the contrary, proton injections were detected only in the vicinity of the strongest B-Z pulses. The front thickness of these pulses was less than a gyroradius of thermal protons that ensured the nonadiabatic acceleration of protons. Indeed, during the injections in the energy spectra of protons the pronounced bulge was clearly observed in a finite energy range similar to 70-90 keV. This feature can be explained by the nonadiabatic resonant acceleration of protons by the bursts of the dawn-dusk electric field associated with the B-Z pulses

What are the fundamental modes of energy transfer and partitioning in the coupled Magnetosphere-Ionosphere system?

The fundamental processes responsible for energy exchange between large-scale electromagnetic fields and plasma are well understood theoretically, but in practice these theories have not been tested. These processes are ubiquitous in all plasmas, especially at the interface between high and low beta plasmas in planetary magnetospheres and other magnetic environments. Although such boundaries pervade the plasma Universe, the processes responsible for the release of the stored magnetic and thermal plasma energy have not been fully identified and the importance of the relative impact of each process is unknown. Despite advances in understanding energy release through the conversion of magnetic to kinetic energy in magnetic reconnection, how the extreme pressures in the regions between stretched and more relaxed field lines in the transition region are balanced and released through adiabatic convection of plasma and fields is still a mystery. Recent theoretical advances and the predictions of large-scale instabilities must be tested. In essence, the processes responsible remain poorly understood and the problem unresolved. The aim of the White Paper submitted to ESA's Voyage 2050 call, and the contents of this paper, is to highlight three outstanding open science questions that are of clear international interest: (i) the interplay of local and global plasma physics processes: (ii) the partitioning during energy conversion between electromagnetic and plasma energy: and (iii) what processes drive the coupling between low and high beta plasmas. We present a discussion of the new measurements and technological advances required from current state-of-the-art, and several candidate mission profiles with which these international high-priority science goals could be significantly advanced.Peer reviewe

Distribution of energetic oxygen and hydrogen in the near-Earth plasma sheet

The spatial distributions of different ion species are useful indicators for plasma sheet dynamics. In this statistical study based on 7 years of Cluster observations, we establish the spatial distributions of oxygen ions and protons at energies from 274 to 955 keV, depending on geomagnetic and solar wind (SW) conditions. Compared with protons, the distribution of energetic oxygen has stronger dawn-dusk asymmetry in response to changes in the geomagnetic activity. When the interplanetary magnetic field (IMF) is directed southward, the oxygen ions show significant acceleration in the tail plasma sheet. Changes in the SW dynamic pressure (Pdyn) affect the oxygen and proton intensities in the same way. The energetic protons show significant intensity increases at the near-Earth duskside during disturbed geomagnetic conditions, enhanced SW Pdyn, and southward IMF, implying there location of effective inductive acceleration mechanisms and a strong duskward drift due to the increase of the magnetic field gradient in the near-Earth tail. Higher losses of energetic ions are observed in the dayside plasma sheet under disturbed geomagnetic conditions and enhanced SW Pdyn. These observations are in agreement with theoretical models

Quasi-parallel Whistler Waves and Their Interaction with Resonant Electrons during High-velocity Bulk Flows in the Earth’s Magnetotail

In collisionless space, plasma waves are important channels of energy conversion, affecting the local particle velocity distribution functions through wave–particle interactions. In this paper we present a comparative statistical analysis of the characteristics of quasi-parallel narrowband whistler waves and the properties of resonant electrons interacting with these waves during the intervals of earthward and tailward high-velocity bulk flows produced by the near-Earth X-line and observed by Magnetospheric Multiscale Mission spacecraft. We found that on both sides of the X-line, the suprathermal electrons (≥1 keV) having large pitch angles make the major contribution to the maximal growth rate ( γ ) of these waves. The whistler waves were observed almost simultaneously with strong enhancements of perpendicular magnetic gradients localized at electron scales near dipolarization fronts associated with the earthward bulk flows, and near flux ropes/magnetic islands embedded into the tailward bulk flows. Betatron energization of electrons due to the appearance of such gradients increases the perpendicular anisotropy of electron distribution, which could be responsible for the whistler wave generation. We found that in the course of electron interactions with the whistler waves the lower-energy resonant electrons can transfer a part of their kinetic energy to the higher-energy electrons, especially in the Central Plasma Sheet. This results in formation/enhancement of energy-dependent perpendicular anisotropy and power-law tails in the high-energy range of electron velocity distribution. We conclude that despite the differences in the magnetic structure of the earthward and tailward bulk flows, the mechanisms of the quasi-parallel whistler wave generation and the properties of resonant electrons are quite similar