The CMEs are sometimes associated with solar flares however, the detailed understanding of the relationship between these two phenomena remains elusive ( Chen 2011 Schmieder et al. These field lines are extrapolated using the nonlinear force-free field (NLFFF) approximation this is one of the main topics of this paper.įurthermore, this causes a huge amount of coronal gas (a typical mass is 10 15 g) with a velocity of 100–2000 kms −1 to be released into interplanetary space this is called a coronal mass ejection (CME e.g., Forbes (2000)). 2 b here, the field lines are responsible for the current density accumulation, which initiates the flare. Figure 2 c is an enlarged view of the region that is marked by an arrow in Fig. In addition, because the solar corona satisfies the low- β plasma condition ( β= 0.01–0.1) ( Gary 2001) in which the magnetic energy dominates that of the coronal plasma, solar flares are widely considered to be a manifestation of the conversion of the magnetic energy of the solar corona into kinetic and thermal energy, culminating in the release of high-energy particles and electromagnetic radiation. Solar flares often occur above the sunspots corresponding to a cross section of strong magnetic flux. Figure 2 b shows the three-dimensional (3D) magnetic field lines traced from the positive to the negative polarities these have been extrapolated under the assumption of the potential field approximation (this will be discussed below). Figure 2 a shows the line-of-sight component of the magnetic field, and the positive and negative polarities cover the whole sun. The Sun is known to be a magnetized star. The scale is classified as soft X-rays, using the 1–8 Å band obtained by the GOES-5 satellite (one of the Geostationary Orbiting Environment Satellites), as shown in Fig. These events are observed as sudden bursts of electromagnetic radiation, such as extreme ultraviolet radiation (EUV), X-rays, and even white light some examples are shown in Fig. Solar flares are explosive phenomena observed in the atmosphere of the Sun (the solar corona). Herein, we review the results obtained by state-of-the-art MHD modeling combined with the NLFFF. Although MHD simulations play a vital role in explaining a number of observed phenomena, there still remains much to be understood. These results have begun to reveal complex dynamics, some of which have not been inferred from previous simulations of hypothetical situations, and they have also successfully reproduced some observed phenomena. Recently, MHD simulations using the NLFFF as an initial condition have been proposed for understanding these dynamics in a more realistic scenario. On the other hand, because in the force-free approximation the NLFFF is reconstructed for equilibrium states, the onset and dynamics of solar flares and CMEs cannot be obtained from these calculations. Specifically, we focus on the nonlinear force-free field (NLFFF) approximation extrapolated from the three components of the photospheric magnetic field.
We first review the 3D extrapolation of the coronal magnetic fields from measurements of the photospheric field. Unfortunately, even with the existing state-of-the-art solar physics satellites, only the photospheric magnetic field can be measured.
In this paper, we summarize current progress on using the observed magnetic fields for magnetohydrodynamics (MHD) modeling of the coronal magnetic field and of solar eruptions, including solar flares and coronal mass ejections (CMEs).
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