Tetsuya Magara

We present a detailed investigation of the dynamical behavior of emerging magnetic flux using three-dimensional MHD numerical simulation. A magnetic flux tube with a left-handed twist, initially placed below the photosphere, emerges into the solar atmosphere. This leads to a dynamical expansion of emerging field lines as well as an injection of magnetic energy and magnetic helicity into the atmosphere. The field-aligned distributions of forces and plasma flows show that emerging field lines can

We present the results from three-dimensional MHD simulations of a magnetic flux tube emerging through the solar photosphere. The simulation is initialized with a straight tube of twisted magnetic field located in the upper convection zone. Buoyancy effects drive an arched segment of the tube upward through the photospheric layer and into the corona. Matter drains from the coronal field, which thereafter undergoes a rapid expansion. The coronal magnetic field formed in this manner exhibits outer

This paper is intended to study the evolution of a magnetic flux tube that rises from the upper convection zone to the solar atmosphere by means of a 2.5-dimensional MHD simulation with the focus on the cross section of the flux tube. A cylindrical flux tube placed horizontally in the convection zone starts rising by magnetic buoyancy. When the top of the tube reaches the photosphere, the cross section of the tube changes from the circular shape to horizontally extended shape, forming a magnetic

We study the emergence of magnetic fields in the solar atmosphere with a focus on photospheric and coronal activities produced by flux emergence. These activities are examined using a three-dimensional MHD simulation of an emerging flux tube. The simulation has been performed for a highly twisted flux tube (highly twisted case) and a weakly twisted one (weakly twisted case). The emerging flux tube globally forms a bipolar region associated with a flow in the photosphere. We decompose the flow in

Prompted by the Yohkoh observations of solar flares, which have established the essential role of magnetic reconnection in the release of energy, we have studied the evolution of eruptive flares in some detail based on the reconnection model by means of the two-dimensional magnetohydrodynamic (MHD) simulations. We are interested in what factor affects the time evolution of solar flares and how the related phenomena, particularly observed loop-top source and plasmoid eruption, can be explained by

In this paper we study the dynamic evolution of emerging magnetic fields in the solar atmosphere by deriving a model based on a three-dimensional MHD simulation. The simulation shows that magnetic field lines initially forming a twisted flux tube below the solar surface emerge into the atmosphere by magnetic buoyancy. Outer field lines of the flux tube are almost free to expand in a wide fan shape without strong confinement by surrounding field lines. On the other hand, inner field lines are sub

We investigate the resistive processes of plasmoid dynamics in eruptive flares by performing 2.5-dimensional resistive MHD numerical simulations. We start with a linear force-free field arcade and impose the localized resistive perturbation on the symmetry axis of the arcade. Then the magnetic fields begin to dissipate, producing inflows toward this region. These inflows make the magnetic fields convex to the symmetry axis and hence a neutral point is formed on this axis, leading to a formation

This paper is intended to present key features of the evolution toward the onset of a solar flare, using Hinode's observations on the photospheric magnetic field. Hinode can provide the temporal development of the photospheric field as a vector quantity, which shows that magnetic shear is initially developed in a flare-productive active region (AR 10930), and then decreases toward the onset of an X-class flare. The magnetic helicity in this active region first increases rapidly, while it become

In order to understand the configuration of magnetic field producing a solar penumbral microjet that was recently discovered by Hinode, we performed a magnetohydrodynamic simulation reproducing a dynamic process of how that configuration is formed in a modeled solar penumbral region. A horizontal magnetic flux tube representing a penumbral filament is placed in a stratified atmosphere containing the background magnetic field that is directed in a relatively vertical direction. Between the flux t

In this paper we study resistive processes in the preflare phase of eruptive flares by means of the 2.5-dimensional MHD numerical simulation. According to many detailed observations of solar flares, their evolution is characterized by several phases, each of which has a distinct nature. In the first phase, some kinds of radiation begin to be enhanced gradually, which implies the occurrence of the preflare heating. Then, at a certain time, that gradual energy-release phase is replaced by the viol

We present a theoretical model for the shock formation that is related to coronal and interplanetary type II radio bursts associated with coronal mass ejections on the basis of the magnetic reconnection model of eruptive solar flares. Coronal type II bursts are usually observed in the metric wavelength range (metric type II bursts), and interplanetary bursts are usually observed in the decametric-hectometric wavelength range (decametric-hectometric bursts). Our research shows that the decametric

Abstract We report a result, that the emergence of a subsurface magnetic field naturally reproduces the feature of the global magnetic configuration observed in solar filaments. This was obtained by performing a three-dimensional simulation of a twisted flux tube that emerges in the shape of a multi-$\Omega$-loop in a highly stratified solar atmosphere, extending from the subsurface layer to the corona. One of the key findings is that a kinking of the twisted flux tube occurs at the site of a li

The emergence process of the magnetic field into the solar atmosphere plays an essential role in determining the configuration of the magnetic field and its activity on the Sun. This paper focuses on how much the magnetic flux contained by a flux tube emerges into the solar atmosphere, which is the key to understanding the physical mechanism of solar eruptions. By comparing a kinematic model of an emerging flux tube to a series of magnetohydrodynamic simulations, we derive the characteristics of

In this Letter we report a result of investigating the structure of subsurface magnetic field in an emerging flux region on the Sun, which was observed by Hinode. The data obtained by Hinode captured well the structure end evolution of the emerging flux region, showing the appearance of small magnetic features that lead to a well-developed bipolar structure. We derived several statistical quantities characterizing the spatial distribution of surface magnetic field. These quantities were then use

In this paper, we investigate how photospheric material moves below a dark filament, and we study chromospheric gas motions inside the filament. In the photosphere we trace granular motions by means of a local correlation tracking (LCT) technique to derive horizontal velocity field, while inside the filament we obtain the line-of-sight velocity field by subtracting a blueshifted Hα image from a redshifted Hα image. We find that a typical value of horizontal photospheric velocity is 1 km s-1, and