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  2. Shin TORIUMI

Shin TORIUMI

  (鳥海 森)

Profile Information

Affiliation
Associate Professor, Institute of Space and Astronautical Science, Department of Solar System Science, Japan Aerospace Exploration Agency
Degree
Ph.D. (Science)(Mar, 2014, The University of Tokyo)
Contact information
toriumi.shinjaxa.jp
Researcher number
30738290
ORCID ID
 https://orcid.org/0000-0002-1276-2403
J-GLOBAL ID
201801010150385982
researchmap Member ID
B000334089

Graduated from the School of Science, the University of Tokyo (PhD in Science, March 2014), Shin Toriumi has been working on the formation of sunspots and genesis of solar flares through both numerical simulations and observational data analysis. He is also interested in stellar activity phenomena. ADS Google Scholar ORCID

  • Magnetic flux emergence and sunspot formation: Sunspots are created through emergence of magnetic fields from the solar interior, which cannot be investigated by direct optical observations. Toriumi performed large-scale numerical simulations and revealed the physical properties of emerging magnetic fields such as a rising speed and magentic structure. He also developed a new method of probing subsurface magnetic fields using helioseismology and estimated the emergence speed, which was in accordance with the numerical result.
  • Sunspot jets and explosions: Sunspots harbor a variety of activity events like jets and explosions. He analyzed the observational data from Hinode and IRIS and numerical model of sunspots, revealing that the sunspots jets are caused by magnetic reconnection, driven by turbulent convection. → NAOJ press release
  • Flare-producing sunspots: Major solar flares tend to occur in complex-shaped sunspot groups. Toriumi analyzed a number of flare-producing sunspots and revealed their statistical properties. He also succeeded in the first-ever modling of spontaneous generation of flaring sunspots via realistic simulation of magnetic flux emergence. → HMI Nuggets Web release
  • Solar-Stellar connections: To see what starspots would look like, Toriumi surveyed sun-as-a-star light curves of sunspot transit events for a variety of wavelengths and explored the ways to characterize the magnetic and thermal circumstances of starspots.→ NASA press release He also revealed that ultra-hot atmospheres of the Sun and Sun-like stars are produced by the common heating mechanisms.→ American Univ press release
  • SOLAR-C: With the target launch in FY2028, Japan's next-generation solar-observing satellite SOLAR-C is now in Phase B. Toriumi is leading the development of science operation, data handling, ground segments, etc.
  • PR: He is involved in PR activities for the ISAS/JAXA, including the host for the live-streaming of the lunar landing of the Smart Lander for Investigating Moon (SLIM).→ YouTube Live

Research Interests

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Research Areas

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Research History

 4

Education

 3

Committee Memberships

 7
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Awards

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Papers

 58
  • S. Toriumi, T. Yokoyama
    Astronomy and Astrophysics, 553 A55, 2013  Peer-reviewedLead authorCorresponding author
    Context. Solar active regions are formed through the emergence of magnetic flux from the deeper convection zone. Recent satellite observations have shown that a horizontal divergent flow (HDF) stretches out over the solar surface just before the magnetic flux appearance. Aims. The aims of this study are to investigate the driver of the HDF and to see the dependency of the HDF on the parameters of the magnetic flux in the convection zone. Methods. We conducted three-dimensional magnetohydrodynamic (3D MHD) numerical simulations of the magnetic flux emergence and varied the parameters in the initial conditions. An analytical approach was also taken to explain the dependency. Results. The horizontal gas pressure gradient is found to be the main driver of the HDF. The maximum HDF speed shows positive correlations with the field strength and twist intensity. The HDF duration has a weak relation with the twist, while it shows negative dependency on the field strength only in the case of the stronger field regime. Conclusions. Parametric dependencies analyzed in this study may allow us to probe the structure of the subsurface magnetic flux by observing properties of the HDF. © 2013 ESO.
  • K. Kusano, Y. Bamba, T. T. Yamamoto, Y. Iida, S. Toriumi, A. Asai
    ASTROPHYSICAL JOURNAL, 760(1) 31, Nov, 2012  Peer-reviewed
    Solar flares and coronal mass ejections, the most catastrophic eruptions in our solar system, have been known to affect terrestrial environments and infrastructure. However, because their triggering mechanism is still not sufficiently understood, our capacity to predict the occurrence of solar eruptions and to forecast space weather is substantially hindered. Even though various models have been proposed to determine the onset of solar eruptions, the types of magnetic structures capable of triggering these eruptions are still unclear. In this study, we solved this problem by systematically surveying the nonlinear dynamics caused by a wide variety of magnetic structures in terms of three-dimensional magnetohydrodynamic simulations. As a result, we determined that two different types of small magnetic structures favor the onset of solar eruptions. These structures, which should appear near the magnetic polarity inversion line (PIL), include magnetic fluxes reversed to the potential component or the nonpotential component of major field on the PIL. In addition, we analyzed two large flares, the X-class flare on 2006 December 13 and the M-class flare on 2011 February 13, using imaging data provided by the Hinode satellite, and we demonstrated that they conform to the simulation predictions. These results suggest that forecasting of solar eruptions is possible with sophisticated observation of a solar magnetic field, although the lead time must be limited by the timescale of changes in the small magnetic structures.
  • S. Toriumi, K. Hayashi, T. Yokoyama
    ASTROPHYSICAL JOURNAL, 751(2) 154, Jun, 2012  Peer-reviewedLead authorCorresponding author
    It is widely accepted that solar active regions including sunspots are formed by the emerging magnetic flux from the deep convection zone. In previous numerical simulations, we found that the horizontal divergent flow (HDF) occurs before the flux emergence at the photospheric height. This paper reports the HDF detection prior to the flux emergence of NOAA AR 11081, which is located away from the disk center. We use SDO/HMI data to study the temporal changes of the Doppler and magnetic patterns from those of the reference quiet Sun. As a result, the HDF appearance is found to come before the flux emergence by about 100 minutes. Also, the horizontal speed of the HDF during this time gap is estimated to be 0.6-1.5 km s(-1), up to 2.3 km s(-1). The HDF is caused by the plasma escaping horizontally from the rising magnetic flux. And the interval between the HDF and the flux emergence may reflect the latency during which the magnetic flux beneath the solar surface is waiting for the instability onset to the further emergence. Moreover, SMART H alpha images show that the chromospheric plages appear about 14 minutes later, located cospatial with the photospheric pores. This indicates that the plages are caused by plasma flowing down along the magnetic fields that connect the pores at their footpoints. One important result of observing the HDF may be the possibility of predicting the sunspot appearances that occur in several hours.
  • S. Toriumi, T. Yokoyama
    ASTRONOMY & ASTROPHYSICS, 539 A22, Mar, 2012  Peer-reviewedLead authorCorresponding author
    We have performed a three-dimensional magnetohydrodynamic simulation to study the emergence of a twisted magnetic flux tube from - 20 000 km of the solar convection zone to the corona through the photosphere and the chromosphere. The middle part of the initial tube is endowed with a density deficit to instigate a buoyant emergence. As the tube approaches the surface, it extends horizontally and makes a flat magnetic structure due to the photosphere ahead of the tube. Further emergence to the corona breaks out via the interchange-mode instability of the photospheric fields, and eventually several magnetic domes build up above the surface. What is new in this three-dimensional experiment is multiple separation events of the vertical magnetic elements are observed in the photospheric magnetogram, and they reflect the interchange instability. Separated elements are found to gather at the edges of the active region. These gathered elements then show shearing motions. These characteristics are highly reminiscent of active region observations. On the basis of the simulation results above, we propose a theoretical picture of the flux emergence and the formation of an active region that explains the observational features, such as multiple separations of faculae and the shearing motion.
  • S. Toriumi, T. Yokoyama
    ASTROPHYSICAL JOURNAL, 735(2) 126, Jul, 2011  Peer-reviewedLead authorCorresponding author
    We present the new results of the two-dimensional numerical experiments on the cross-sectional evolution of a twisted magnetic flux tube rising from the deeper solar convection zone (-20,000 km) to the corona through the surface. The initial depth is 10 times deeper than most of the previous calculations focusing on the flux emergence from the uppermost convection zone. We find that the evolution is illustrated by the following two-step process. The initial tube rises due to its buoyancy, subject to aerodynamic drag due to the external flow. Because of the azimuthal component of the magnetic field, the tube maintains its coherency and does not deform to become a vortex roll pair. When the flux tube approaches the photosphere and expands sufficiently, the plasma on the rising tube accumulates to suppress the tube's emergence. Therefore, the flux decelerates and extends horizontally beneath the surface. This new finding owes to our large-scale simulation, which simultaneously calculates the dynamics within the interior as well as above the surface. As the magnetic pressure gradient increases around the surface, magnetic buoyancy instability is triggered locally and, as a result, the flux rises further into the solar corona. We also find that the deceleration occurs at a higher altitude than assumed in our previous experiment using magnetic flux sheets. By conducting parametric studies, we investigate the conditions for the two-step emergence of the rising flux tube: field strength greater than or similar to 1.5 x 10(4) G and the twist greater than or similar to 5.0 x 10(-4) km(-1) at -20,000 km depth.
  • Shin Toriumi, Takehiro Miyagoshi, Takaaki Yokoyama, Hiroaki Isobe, Kazunari Shibata
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 63(2) 407-415, Apr, 2011  Peer-reviewedLead authorCorresponding author
    We present a series of numerical experiments that model the evolution of magnetic flux tubes with a different amount of initial twist. As a result of calculations, tightly twisted tubes reveal a rapid two-step emergence to the atmosphere with a slight slowdown at the surface, while weakly twisted tubes show a slow two-step emergence waiting longer the secondary instability to be triggered. This picture of the two-step emergence is highly consistent with recent observations. These tubes show multiple magnetic domes above the surface, indicating that the secondary emergence is caused by an interchange mode of magnetic buoyancy instability. In the case of the weakest twist, the tube exhibits an elongated photospheric structure, and never rises into the corona. The formation of the photospheric structure is due to an inward magnetic tension force of the azimuthal field component of the rising flux tube (i.e., tube's twist). When the twist is weak, the azimuthal field cannot hold the tube's coherency, and the tube extends laterally at the subadiabatic surface. In addition, we newly found that the total magnetic energy measured above the surface depends on the initial twist. Strong twist tubes follow the initial relation between the twist and the magnetic energy, while weak twist tubes deviate from this relation, because these tubes store their magnetic energy in the photospheric structure.
  • Shin Toriumi
    The University of Tokyo, Mar, 2011  Peer-reviewedLead authorCorresponding author
    Master thesis
  • S. Toriumi, T. Yokoyama
    ASTROPHYSICAL JOURNAL, 714(1) 505-516, May, 2010  Peer-reviewedLead authorCorresponding author
    We perform two-dimensional magnetodydrodynamic simulations of the flux emergence from the solar convection zone to the corona. The flux sheet is initially located moderately deep in the adiabatically stratified convection zone (-20,000 km) and is perturbed to trigger the Parker instability. The flux rises through the solar interior due to the magnetic buoyancy, but suffers a gradual deceleration and a flattening in the middle of the way to the surface since the plasma piled on the emerging loop cannot pass through the convectively stable photosphere. As the magnetic pressure gradient enhances, the flux becomes locally unstable to the Parker instability so that the further evolution to the corona occurs. The second-step nonlinear emergence is well described by the expansion law by Shibata et al. To investigate the condition for this "two-step emergence" model, we vary the initial field strength and the total flux. When the initial field is too strong, the flux exhibits the emergence to the corona without a deceleration at the surface and reveals an unrealistically strong flux density at each footpoint of the coronal loop, while the flux either fragments within the convection zone or cannot pass through the surface when the initial field is too weak. The condition for the "two-step emergence" is found to be 10(21)-10(22) Mx with 10(4) G at z = -20,000 km. We present some discussions in connection with recent observations and the results of the thin-flux-tube model.

Major Misc.

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Books and Other Publications

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Teaching Experience

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Professional Memberships

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Major Research Projects

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Academic Activities

 15
  • Planning, Management, etc., Panel moderator, Session chair, etc.
    Japan Geoscience Union (Makuhari Messe / Virtual), May 30, 2024 - May 30, 2024
  • Planning, Management, etc.
    (Niigata, Japan), Sep 25, 2023 - Sep 29, 2023
    Served as the chair of the Scientific Organizing Committee (SOC) for the 6th NAOJ Symposium Hinode-16/IRIS-13
  • Planning, Management, etc.
    Japan Geoscience Union (Makuhari Messe / Virtual), May 21, 2023 - May 26, 2023
  • Planning, Management, etc.
    Committee on Space Research (COSPAR) (Athens / Online), Aug 21, 2022 - Aug 23, 2022
    Session title: Connecting Solar and Stellar Coronal Mass Ejections: Lessons Learned, Challenges and Perspectives
  • Planning, Management, etc., Panel moderator, Session chair, etc.
    Japan Geoscience Union (Makuhari Messe / Virtual), May 24, 2022 - Jun 1, 2022
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Social Activities

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