鳥海 森

https://ui.adsabs.harvard.edu/abs/2023BAAS...55c.160H/abstract

会議情報 主催: 一般社団法人日本物理学会 会議名: 2018年度日本物理学会第73回年次大会 開催日: 2018/03/22 - 2018/03/25

https://ui.adsabs.harvard.edu/abs/2018RNAAS...2....8W/abstract

We perform two-dimensional magnetohydrodynamic (MHD) simulations of the flux emergence from the solar convection zone to the corona. The flux sheet is initially located moderately deep (-20,000 km) in the adiabatically stratified convection zone and is perturbed to trigger the Parker instability. The flux rises through the interior, but decelerates around the strongly sub-adiabatic photosphere. As the magnetic pressure gradient increases, the flux becomes unstable to the Parker instability again so that further evolution to the corona occurs. We show the results of the simulations based on this 'two-step emergence' model and make sonic discussions in connection with the results of the thin-flux-tube simulations.

In this study, we aim to figure out the flux emergence from the interior to the atmosphere through the surface, by conducting a numerical simulation and a Hinode/SOT observation. First, we performed a three-dimensional magnetohydrodynamic (MHD) simulation on the flux tube emergence from -20,000 km of the convective layer. As a result, the rising tube expands sideways beneath the surface to create a flat structure. As time goes on, the subphotospheric field rises again into the corona due to the magnetic buoyancy instability. We newly found that the photospheric magnetogram shows multiple separation events as well as shearing motions, which reflects the Parker instability of the subphotospheric field. This situation agrees well with Strous & Zwaan (1999)'s model based on their observation. We also confirmed that the wave-length perpendicular to the separations is approximately a few times the tube's initial radius. Secondly, we analyzed SOT/FG magnetogram of AR 10926, and observed that the small-scale magnetic elements among the major sunspots make alignments with a certain orientation. The wavelength perpendicular to the alignments was found to be similar to 3,000 km. Comparing with the numerical results, we speculate that this active region observed by the SOT is created by the rising flux tube with a radius of the order of 1,000 km in the deeper convection zone.

Solar active regions including sunspots are thought to be the consequence of the emergence of a magnetic flux tube from the bottom of the convection zone (at -200,000km depth). Here we perform the two-dimensional magnetohydrodynamic (MHD) simulations to show the emergence of the flux tube from a -20,000km depth to the atmosphere through the solar surface. The simulations are done for the axial and the cross-sectional evolutions of the flux tube. As a result, both fluxes show the deceleration halfway to the surface and extend laterally near the surface. From the parameter surveys, we obtain the conditions for actual active regions: the field strength 10^4G, the total magnetic flux 10^<21>-10^<22>Mx, and the twist 5.0×10^<-4>km^<-1> at -20,000km depth.

Emerging magnetic flux tubes in the solar convection zone are thought to be responsible for formation of active regions. We performed two-dimensional MHD simulations of the flux emergence from the solar interior to the atmosphere. The flux tube is initially placed deep down at the convection zone (-20,000km) and perturbed to generate Parker instability. The tube rises through the convection zone, but stops below the surface bacause of the strong pressure gradient. After being unstable to the Parker instability, the tube emerges to the atmosphere again. We show this 'two-step emergence' model and have some discussions on the parameter survey.