Fluid Dynamics in Earth and Planetary Sciences (FDEPS)
25th FDEPS workshop, Dec. 2 - Dec. 5, 2025 at Kansai Seminar House

[English page is here]

第 25 回ワークショップ「地球惑星科学における流体力学」

日程:
2025 年 12 月 2 日(火)〜12 月 5 日(金)

共催:
  • Research Institute for Mathematical Sciences (RIMS), Kyoto University (京都大学 数理解析研究所)
  • Center for Planetary Science (CPS), Kobe University (神戸大学 惑星科学研究センター)
場所:
関西セミナーハウス
京都市左京区一乗寺竹ノ内町23
TEL:075-711-2115, FAX:075-701-5256

登録が必要です. 詳しい情報は「こちら」.

プログラム

講師: Dr. (HDR) Allan Sacha BRUN (Director of Research CEA, CEA Paris-Saclay, 名古屋大学宇宙地球環境研究所 客員教授)

  • 連続講義と自由討論 : 恒星天体物理流体力学と恒星ー惑星相互作用
    Why do stars shine? How do they evolve? How are their rotational and magnetic properties changing with time? How is the solar wind operating? What is the origin of their intense magnetism and surface activity? What is the impact of solar activity on planets and our technological society? This course will look at stellar evolution from birth to death, with particular emphasis on the nonlinear dynamics, rotation and magnetism operating within and on the surface of stars, and their interaction with their surrounding (exo-)planets, touching on concepts such as space weather and habitability. We'll cover both the theoretical and observational aspects of these astrophysical concepts, starting with basic physical concepts and illustrating them with the latest theoretical and observational advances in the field. One of the special features of this course is that it covers a wide range of physics topics (nuclear physics, turbulence, gravitation, magnetohydrodynamics, the dynamo effect, star-planet interaction). The Sun and solar system will serve as our reference stars/systems, enabling us to distinguish between what is specific and what is generic to these celestial objects, and to generalize our notions to the case of exo-systems.
    • 12/2(火)
      • 9:00 - 12:00
        Lecture 1. Introduction
        • What a star is: cohesion and stability of a star
        • 1D model of stellar structure,
          • Hydrostatic equilibrium and energy balance
          • Mass limits and degenerate stars (white dwarf, neutron star).
          • Hertzsprung-Russell diagram and stellar evolution
      • 14:00 - 17:00
        Lecture 2. Convective turbulence, rotation and magnetism in stars
        • Dynamo effect and magnetic field variability in stars
        • Convection scales and associated large scale mean flows
        • Turbulence and scaling law regimes
      • 夜間:<自由討論>
    • 12/3(水)
      • 9:00 - 12:00
        Lecture 3. Seismology of the Sun and stars
        • Modes of vibration
        • Observations and seismic inversions of the internal flows of stars
      • 午後:<自由討論>
      • 夜間:<自由討論>
    • 12/4(木)
      • 9:00 - 12:00
        Lecture 4. Stellar wind, magneto-rotation evolution of stars
        • Skumanich' law and gyrochronology
        • Solar wind models and wind braking torque mechanism
      • 14:00 - 17:00
        Lecture 5. Structuring the environment of stars -the astrosphere-
        • Transient and eruptive phenomena in the atmosphere of solar-type stars
        • Space Weather and consequences of solar activity on our technological society
          • Radio and gpsblackout
          • Ionospehric effects
          • Power grids/networks
          • Satellites shutdown
        • Joint secular evolution of a star and its environment
        • Habitability: notion of 'habitable' planet as a function of distance from the host star and the age of the system
      • 夜間:<自由討論>
    • 12/5(金) 研究セミナー
      • 09:30 - 11:30
        Research Seminar : Magnetochronology of solar-type stars and the convective conundrum
        We present a large numerical survey of 3-D MHD numerical simulations that allow us to study the magnetism and dynamo mechanism of solar-type stars along their secular evolution. We propose a magneto-rotational scenario that makes a direct link between stellar age and rotational and magnetic properties of stars, known as magnetochronology. We find a good agreement between our results and observations of stellar magnetism B(t) ~ Ro^-1.4 in a range in Rossby number Ro between ~ [0.1,1], and advocate for a change of behavior at slow rotation rate (Ro > 1), with lost of stellar magnetic cycle. When positioning our simulation for the Sun in that scenario, we find that it is however slightly misplaced. This shift is likely due to the so-called Convective Conundrum, e.g. a disagreement between helioseismic inversions of large scales convective power and that obtained in 3-D global simulations of solar convection. To this end, we have developed a new series of global convective dynamo models at fixed Rossby number but increasing Reynolds number by following a theoretical path in parameters space that better controls key identified forces balance. The new set of simulations present very interesting dynamical behavior, including a better match with observations of convection power and the development of intense magnetic concentrations that feedback into the convection. We discuss the properties of these new models and the way forward to paint a coherent picture of solar-type stars magnetism.