arXiv subjects

Tsugunobu Nagai

Publications and source records attributed to Tsugunobu Nagai.

5 recordsLinked to original sources

arXiv2022

Space Plasma Physics: A Review

Owing to the ever-present solar wind, our vast solar system is full of plasmas. The turbulent solar wind, together with sporadic solar eruptions, introduces various space plasma processes and phenomena in the solar atmosphere all the way to the Earth's ionosphere and atmosphere and outward to interact with the interstellar media to form the heliopause and termination shock. Remarkable progress has been made in space plasma physics in the last 65 years, mainly due to sophisticated in-situ measurements of plasmas, plasma waves, neutral particles, energetic particles, and dust via space-borne satellite instrumentation. Additionally high technology ground-based instrumentation has led to new and greater knowledge of solar and auroral features. As a result, a new branch of space physics, i.e., space weather, has emerged since many of the space physics processes have a direct or indirect influence on humankind. After briefly reviewing the major space physics discoveries before rockets and satellites, we aim to review all our updated understanding on coronal holes, solar flares and coronal mass ejections, which are central to space weather events at Earth, solar wind, storms and substorms, magnetotail and substorms, emphasizing the role of the magnetotail in substorm dynamics, radiation belts/energetic magnetospheric particles, structures and space weather dynamics in the ionosphere, plasma waves, instabilities, and wave-particle interactions, long-period geomagnetic pulsations, auroras, geomagnetically induced currents (GICs), planetary magnetospheres and solar/stellar wind interactions with comets, moons and asteroids, interplanetary discontinuities, shocks and waves, interplanetary dust, space dusty plasmas and solar energetic particles and shocks, including the heliospheric termination shock. This paper is aimed to provide a panoramic view of space physics and space weather.

physics.space-ph↗

arXiv2017

Electron dynamics surrounding the X-line in asymmetric magnetic reconnection

Electron dynamics surrounding the X-line in magnetopause-type asymmetric reconnection is investigated using a two-dimensional particle-in-cell simulation. We study electron properties of three characteristic regions in the vicinity of the X-line. The fluid properties, velocity distribution functions (VDFs), and orbits are studied and cross-compared. On the magnetospheric side of the X-line, the normal electric field enhances the electron meandering motion from the magnetosheath side. The motion leads to a crescent-shaped component in the electron VDF, in agreement with recent studies. On the magnetosheath side of the X-line, the magnetic field line is so stretched in the third dimension that its curvature radius is comparable with typical electron Larmor radius. The electron motion becomes nonadiabatic, and therefore the electron idealness is no longer expected to hold. Around the middle of the outflow regions, the electron nonidealness is coincident with the region of the nonadiabatic motion. Finally, we introduce a finite-time mixing fraction (FTMF) to evaluate electron mixing. The FTMF marks the magnetospheric side of the X-line, where the nonideal energy dissipation occurs.

physics.plasm-ph↗

arXiv2016

Particle dynamics in the electron current layer in collisionless magnetic reconnection

Particle dynamics in the electron current layer in collisionless magnetic reconnection is investigated by using a particle-in-cell simulation. Electron motion and velocity distribution functions are studied by tracking self-consistent trajectories. New classes of electron orbits are discovered: figure-eight-shaped regular orbits inside the electron jet, noncrossing regular orbits on the jet flanks, noncrossing Speiser orbits, and nongyrotropic electrons in the downstream of the jet termination region. Properties of a super-Alfvénic outflow jet are attributed to an ensemble of electrons traveling through Speiser orbits. Noncrossing orbits are mediated by the polarization electric field near the electron current layer. The noncrossing electrons are found to be non-negligible in number density. The impact of these new orbits to electron mixing, spatial distribution of energetic electrons, and observational signatures, is presented.

astro-ph.SR↗

arXiv2014

Kinetic aspects of the ion current layer in a reconnection outflow exhaust

Kinetic aspects of the ion current layer at the center of a reconnection outflow exhaust near the X-type region are investigated by a two-dimensional particle-in-cell (PIC) simulation. The layer consists of magnetized electrons and unmagnetized ions that carry a perpendicular electric current. The ion fluid appears to be nonideal, sub-Alfvenic, and nondissipative. The ion velocity distribution functions contain multiple populations such as global Speiser ions, local Speiser ions, and trapped ions. The particle motion of the local Speiser ions in an appropriately rotated coordinate system explains the ion fluid properties very well. The trapped ions are the first demonstration of the regular orbits in the chaotic particle dynamics [Chen and Palmadesso, J. Geophys. Res., 91, 1499 (1986)] in self-consistent PIC simulations. They would be observational signatures in the ion current layer near reconnection sites.

astro-ph.SR↗

arXiv2012

Evidence for the dissipation region in magnetotail reconnection

Signatures of the dissipation region of collisionless magnetic reconnection are investigated by the Geotail spacecraft for the 15 May 2003 event. The energy dissipation in the rest frame of the electron's bulk flow is considered in an approximate form D*_e, which is validated by a particle-in-cell simulation. The dissipation measure is directly evaluated from the {plasma moments}, the electric field, and the magnetic field. Using D*_e, a compact dissipation region is successfully detected in the vicinity of the possible X-point in Geotail data. The dissipation rate is 45 pWm**{-3}. The length of the dissipation region is estimated to 1--2 local ion inertial length. The Lorentz work W, the work rate by Lorentz force to plasmas, is also introduced. It is positive over the reconnection region and it has a peak around the pileup region away from the X-point. These new measures D*_e and W provide useful information to understand the reconnection structure.

astro-ph.EP↗