State Transition of the Solar Magnetic Field: Probing the Trigger for the Solar Activity Grand Minimum through MHD Simulations

2023 Fiscal Year Final Research Report

• Project/Area Number: 18K03700
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 16010:Astronomy-related
• Research Institution: Fukuoka University (2022-2023); Aichi University of Education (2018-2021)
• Principal Investigator: Yohei MASADA 福岡大学, 理学部, 准教授 (30590608)
• Project Period (FY): 2018-04-01 – 2024-03-31
• Keywords: プラズマ / 太陽・恒星 / 天体ダイナモ / 乱流 / 乱流輸送

Outline of Final Research Achievements

The thermal convection, which is the origin of the solar magnetic field, is not fully understood even in terms of its driving mechanisms. There are two candidate driving mechanisms for solar thermal convection: cooling-driven (CD) and entropy gradient-driven (ED). The results of this study have revealed that (i) the CD type better reproduces the characteristic patterns of solar convection, (ii) in the CD type, non-linear and non-equilibrium downward plumes significantly contribute to the transport, and (iii) the presence of downward plumes causes a significant deviation from a Gaussian distribution in the frequency distribution of the convection (Yokoi et al. 22; Masada et al. 24 in prep.). Furthermore, the knowledge gained from this study has been applied to other astrophysical thermal convection phenomena, leading to several pioneering results.

Free Research Field

天体物理学

Academic Significance and Societal Importance of the Research Achievements

太陽の内部熱対流は太陽磁場（黒点）の成因だと考えられており、本研究で得た成果は、太陽磁気活動に対する我々の理解の深化につながる。太陽磁気活動に対する理解が深まることで、地球の気候変動予測や宇宙天気予報の精度が向上し、通信や電力網の障害対策に寄与できる（社会的意義）。また、太陽は究極の高レイノルズ数・高磁気レイノルズ数・高レイリー数流体であり、地上の実験室では実現不可能なパラメータレンジでの熱対流のメカニズムに関する本研究の成果は、他の天体現象の背後にある物理の解明につながるだけでなく、流体力学やプラズマ物理学など基礎物理の分野にも大きなインパクトを与える（学術的意義）。