Takashi Tanaka 교수

Mechanisms that generate the field‐aligned current (FAC) systems in the magnetosphere‐ionosphere coupling scheme by virtue of the solar wind‐magnetosphere interaction are investigated with a three‐dimensional magnetohydrodynamic (MHD) simulation. As a simulation scheme, the finite volume total variation diminishing (TVD) scheme on an unstructured grid system is employed for precise calculations of the ionospheric region. In the ionosphere, the divergence of the Pedersen and Hall currents is matc

A new MHD simulation scheme is developed on an unstructured grid system using the finite volume total variation diminishing scheme and applied to the problem of solar wind‐planet interaction, assuming a perfect‐conducting ionosphere around the planet. It is shown that the scheme presented here enables one to calculate effectively the configuration of three‐dimensional MHD flow near planets, together with the draping process of magnetic field. Results of the calculation give a general confirmatio

The substorm mechanism is investigated by analyzing the numerical results obtained through the use of the recently refined magnetohydrodynamic model. After showing the growth phase features, the numerical solution reproduces the observed signatures of a substorm onset, including the formation of a near‐Earth neutral line (NENL), earthward directed flow in the plasma sheet, a dipolarization, a geosynchronous D deflection, the development of the nightside field aligned currents (FACs), and electro

The large‐scale solar wind interaction with the Venusian ionosphere is numerically simulated in the framework of two‐component, three‐dimensional magnetohydrodynamics (MHD). The finite volume total variation diminishing scheme is used to solve this problem. The impinging solar wind is represented by H + ions, and the ionosphere is assumed to consist of O + ions produced by photoionization of atomic oxygen in the Venusian upper atmosphere and by charge exchange of CO 2 + ions. The O + ions are lo

Convection is the most fundamental process in understanding the structure of geospace and disturbances observed in the magnetosphere–ionosphere (M–I) system. In this paper, a self-consistent configuration of the global convection system is considered under the real topology as a compound system. Investigations are made based on the M–I coupling scheme by analyzing numerical results obtained from magnetohydrodynamic (MHD) simulations which guarantee the self-consistency in the whole system under

The substorm mechanism is investigated from a resistive magnetohydrodynamic simulation under the assumption that the magnetotail becomes more diffusive as it goes further downtail. The simulation uses the finite volume total‐variation diminishing scheme on an unstructured grid system to evaluate the magnetosphere‐ionosphere coupling effect more precisely and to reduce the numerical viscosity in the near‐Earth plasma sheet. The calculation started from a stationary solution under a northward inte

The configuration of the magnetosphere‐ionosphere convection system is investigated by analyzing outputs of a global magnetohydrodynamic (MHD) model for the solar wind‐magnetosphere‐ionosphere (S‐M‐I) coupling process. The input interplanetary magnetic field (IMF) to the model is inclined 45° from the due‐northward direction with downward IMF. The results clearly show that the round cell and crescent cell are formed in the polar ionosphere and that the lobe cell and merging cell in the magnetosp

With more recent advances in global magnetosphere-ionosphere (M-I) coupling simulation, the major observed signatures of the substorm have become reproducible. By using more than 1000 central processing units, the present large-scale high-speed simulation reproduces detailed signatures of the substorm in both the magnetosphere and the ionosphere as realistic as the observation. This chapter shows that almost all substorm observations can be reproduced from the global M-I coupling simulation (the

The dependence of the ionospheric electric potential (convection) on the interplanetary magnetic field (IMF) and the ionospheric conductivity is investigated to understand the generation of convection patterns in the framework of the solar wind‐magnetosphere‐ionosphere (S‐M‐I) coupling scheme and the merging concept. A numerical magnetohydrodynamic (MHD) simulation is adopted for the study of the present problem. To achieve a high resolution in the ionosphere, the MHD calculation employs the fin

The global structure of the solar wind/very local interstellar medium interaction is studied from a fully three‐dimensional time‐dependent magnetohydrodynamic model, in which the solar wind speed increases from 400 to 800 km/s in going from the ecliptic to pole and the heliolatitude of the low‐high‐speed boundary changes from 30° to 80° in going from the solar minimum to solar maximum. In addition, the interplanetary magnetic field (IMF) changes its polarity at the solar maximum. As a whole, the

Formation of the theta aurora, which appears under the conditions of northward interplanetary magnetic field (IMF) and greater IMF magnitude, is investigated from the analysis of solutions obtained from a magnetohydrodynamic (MHD) simulation. The theta aurora formation is caused by a transient convection after a sign change of IMF B y . This transient convection must include a replacement of lobe field lines from old IMF originating fields to new IMF originating fields, a rotation of plasma shee

Configurations of the field-aligned-current (FAC) systems in the magnetosphere-ionosphere (M-I) coupling system are investigated through the analysis of the solutions obtained from a three-dimensional (3-D) magnetohydrodynamic (MHD) simulation. The results of calculation reproduce the region- 1 and region-2 FAC systems for the southward interplanetary magnetic field (IMF) case, and additionally the NBZ FAC system for the northward IMF case. The energy budget associated with the generation of the

The large-scale solar wind interaction with the ionosphere of non-magnetized planets is numerically simulated in the framework of three-dimensional (3-D) magnetohydrodynamics (MHD) with a two-component plasma. The finite-volume total variation diminishing (TVD) scheme is used to solve this problem. Numerical results are given for two cases of different solar extreme ultraviolet (EUV) flux values. In case 1, solar EUV ionization is set so the peak ionospheric plasma pressure is below the incident

Based on the magnetosphere‐ionosphere (M‐I) coupling scheme, convection as a compound system is considered including the generation of plasma population regimes in the magnetosphere. In these considerations, primary elements that must be set to a self‐consistent configuration are convection flows in the magnetosphere and the ionosphere, field‐aligned current (FAC) systems, ionospheric currents, energy conversion processes, and plasma population regimes. The convection in the M‐I coupling system