Current Sheets, Magnetic Islands, and Associated Particle Acceleration in the Solar Wind as Observed by Ulysses near the Ecliptic Plane

Recent studies of particle acceleration in the heliosphere have revealed a new mechanism that can locally energize particles up to several MeV nucleon–1. Stream–stream interactions, as well as the heliospheric current sheet (CS)—stream interactions, lead to formation of large magnetic cavities, bordered by strong CSs, which in turn produce secondary CSs and dynamical small-scale magnetic islands (SMIs) of ~0.01 au or less owing to magnetic reconnection. It has been shown that particle acceleration or reacceleration occurs via stochastic magnetic reconnection in dynamical SMIs confined inside magnetic cavities observed at 1 au. The study links the occurrence of CSs and SMIs with characteristics of intermittent turbulence and observations of energetic particles of keV–MeV nucleon–1 energies at ~5.3 au. We analyze selected samples of different plasmas observed by Ulysses during a widely discussed event, which was characterized by a series of high-speed streams of various origins that interacted beyond Earth's orbit in 2005 January. The interactions formed complex conglomerates of merged interplanetary coronal mass ejections, stream/corotating interaction regions, and magnetic cavities. We study properties of turbulence and associated structures of various scales. We confirm the importance of intermittent turbulence and magnetic reconnection in modulating solar energetic particle flux and even local particle acceleration. Coherent structures, including CSs and SMIs, play a significant role in the development of secondary stochastic particle acceleration, which changes the observed energetic particle flux time–intensity profiles and increases the final energy level to which energetic particles can be accelerated in the solar win

Comparison of current sheets in solar wind and planetary magnetospheres

International audienceCurrent sheets are structures that can be formed at the boundaries of different plasmas, magnetic fluxes and in areas with strong field gradients. When current sheets thicknesses become comparable with proton gyroradii they can play a key role of reservoirs of a free magnetic energy that can be released due to development of different current sheet instabilities. Such comparatively thin current sheets were relatively recently discovered by space missions in the magnetospheres of the Earth and planets, as well as in the solar wind. The development of a self-consistent current sheet theory in collisionless plasma has relatively long and dramatic history. The solution of the problem of thin current sheet structure and stability become possible in a frame of a kinetic quasi-adiabatic approach explaining multiscale embedded structure of thin current sheets and their metastability. We showed that the structure and stability of current structures are completely determined by the nonlinear dynamics of plasma particles within them. The similarity and difference of the current sheets in the solar wind and planetary magnetospheres are presented. Development of theoretical approaches to investigation of different current systems in space are discussed

Symmetries of Magnetic Fields Driven by Spherical Dynamos of Exoplanets and Their Host Stars

Observations of exoplanets open a new area of scientific activity and the structure of exoplanet magnetospheres is an important part of this area. Here we use symmetry arguments and experiences in spherical dynamo modeling to obtain the set of possible magnetic configurations for exoplanets and their corresponding host stars. The main part of our results is that the possible choice is much richer than the basic dipole magnetic field of both exoplanets and stars. Other options, for example, are quadrupole configurations or mixed parity solutions. Expected configurations of current sheets for the above mentioned exoplanet host star systems are presented as well

Comparison of current sheets in solar wind and planetary magnetospheres

International audienceCurrent sheets are structures that can be formed at the boundaries of different plasmas, magnetic fluxes and in areas with strong field gradients. When current sheets thicknesses become comparable with proton gyroradii they can play a key role of reservoirs of a free magnetic energy that can be released due to development of different current sheet instabilities. Such comparatively thin current sheets were relatively recently discovered by space missions in the magnetospheres of the Earth and planets, as well as in the solar wind. The development of a self-consistent current sheet theory in collisionless plasma has relatively long and dramatic history. The solution of the problem of thin current sheet structure and stability become possible in a frame of a kinetic quasi-adiabatic approach explaining multiscale embedded structure of thin current sheets and their metastability. We showed that the structure and stability of current structures are completely determined by the nonlinear dynamics of plasma particles within them. The similarity and difference of the current sheets in the solar wind and planetary magnetospheres are presented. Development of theoretical approaches to investigation of different current systems in space are discussed

Acceleration of plasma in current sheet during substorm dipolarizations in the Earth’s magnetotail : Comparison of different mechanisms

International audienc

Acceleration of plasma in current sheet during substorm dipolarizations in the Earth’s magnetotail : Comparison of different mechanisms

International audienc

On the response of quasi-adiabatic particles to magnetotail reconfigurations

International audienceWe investigate the response of quasi-adiabatic particles to dynamical reconfigurations of the magnetotail field lines. Although they travel through a sharp field reversal with a characteristic length scale smaller than their Larmor radii, these quasi-adiabatic particles experience a negligible net change in magnetic moment. We examine the robust-ness of such a quasi-adiabatic behavior in the presence of a large surging electric field induced by magnetic field line reconfiguration as observed during the expansion phase of substorms. We demonstrate that, although such a short-lived electric field can lead to substantial nonadiabatic heating, quasi-adiabaticity is conserved for particles with velocities larger than the peak ExB drift speed. Because of the time-varying character of the magnetic field, it is not possible to use the adiabaticity parameter κ in a straightforward manner to characterize the particle behavior. We rather consider a κ parameter that is averaged over equatorial crossings. We demonstrate that particles intercepting the field reversal in the early stage of the magnetic transition may experience significant energization and enhanced oscillating motion in the direction normal to the midplane. In contrast, particles interacting with the field reversal in the late stage of the magnetic transition experience weaker energization and slower oscillations about the midplane. We show that quasi-adiabatic particles accelerated during such events can lead to energy–time dispersion signatures at low altitudes as is observed in the plasma sheet boundary layer

Ulysses Flyby in the Heliosphere: Comparison of the Solar Wind Model with Observational Data

A model capable of reproducing a set of solar wind parameters along the virtual spacecraft orbit out of an ecliptic plane has been developed. In the framework of a quasi-stationary axisymmetric self-consistent MHD model the spatial distributions of magnetic field and plasma characteristics at distances from 20 to 1200 Solar radii at almost all solar latitudes could be obtained and analyzed. This model takes into account the Sun’s magnetic field evolution during the solar cycle, when the dominant dipole magnetic field is replaced by the quadrupole one. Self-consistent solutions for solar wind characteristics were obtained, depending on the phase of the solar cycle. To verify the model, its results are compared with the observed characteristics of solar wind along the Ulysses trajectory during its flyby around the Sun from 1990 to 2009. It is shown that the results of numerical simulation are generally consistent with the observational data obtained by the Ulysses spacecraft. A comparison of the model and experimental data confirms that the model can adequately describe the solar wind parameters and can be used for heliospheric studies at different phases of the solar activity cycle, as well as in a wide range of latitudinal angles and distances to the Sun

Atmospheric escape from the Earth during geomagnetic reversal

We considered basic mechanisms of atmospheric particle acceleration and estimated the escape rates of ionospheric ions (H+ and O+) during the geomagnetic field reversal. It is assumed that during the reversal the Earth's magnetic field deviates from the current dipole configuration, and the quadrupole component dominates. The standoff distance of the quadrupole magnetosphere is about of 3 Earth's radii and therefore a magnetic shielding protects the atmosphere from sputtering and ion pickup but not from the polar and auroral winds