Author name code: toriumi
ADS astronomy entries on 2022-09-14
author:"Toriumi, Shin"
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Title: Flux emergence and generation of flare-productive active
regions
Authors: Toriumi, Shin
Bibcode: 2022AdSpR..70.1549T
Altcode: 2021arXiv210509961T
Solar flares and coronal mass ejections are among the most prominent
manifestations of the magnetic activity of the Sun. The strongest
events of them tend to occur in active regions (ARs) that are large,
complex, and dynamically evolving. However, it is not clear what the
key observational features of such ARs are, and how these features
are produced. This article answers these fundamental questions based
on morphological and magnetic characteristics of flare-productive ARs
and their evolutionary processes, i.e., large-scale flux emergence and
subsequent AR formation, which have been revealed in observational
and theoretical studies. We also present the latest modeling of
flare-productive ARs achieved using the most realistic flux emergence
simulations in a very deep computational domain. Finally, this review
discusses the future perspective pertaining to relationships of flaring
solar ARs with the global-scale dynamo and stellar superflares.
Title: Universal Scaling Laws for Solar and Stellar Atmospheric
Heating: Catalog of Power-law Index between Solar Activity Proxies
and Various Spectral Irradiances
Authors: Toriumi, Shin; Airapetian, Vladimir S.; Namekata, Kosuke;
Notsu, Yuta
Bibcode: 2022arXiv220810511T
Altcode:
The formation of extremely hot outer atmospheres is one of the most
prominent manifestations of magnetic activity common to the late-type
dwarf stars, including the Sun. It is widely believed that these
atmospheric layers, the corona, transition region, and chromosphere,
are heated by the dissipation of energy transported upwards from
the stellar surface by the magnetic field. This is signified by the
spectral line fluxes at various wavelengths, scaled with power-law
relationships against the surface magnetic flux over a wide range of
formation temperatures, which are universal to the Sun and Sun-like
stars of different ages and activity levels. This study describes a
catalog of power-law indices between solar activity proxies and various
spectral line fluxes. Compared to previous studies, we expanded the
number of proxies, which now includes the total magnetic flux, total
sunspot number, total sunspot area, and the F10.7 cm radio flux,
and further enhances the number of spectral lines by a factor of
two. This provides the data to study in detail the flux-flux scaling
laws from the regions specified by the temperatures of the corona
(log(T/K)=6-7) to those of the chromosphere (log(T/K)~4), as well as
the reconstruction of various spectral line fluxes of the Sun in the
past, F-, G-, and K-type dwarfs, and the modeled stars.
Title: Response of solar and stellar atmospheric heating to the
surface magnetic flux
Authors: Toriumi, Shin; Airapetian, Vladimir
Bibcode: 2022cosp...44.2475T
Altcode:
Atmospheres of the Sun and stars, i.e., the coronae, transition
regions, and chromospheres, are heated up and brightened in
response to the appearance of active regions, the home to flares
and coronal mass ejections (CMEs). Therefore, in order to understand
the transient radiations and impacts associated with solar/stellar
flares and CMEs, it is crucial to clarify the quasi-stationary
radiations caused by the active regions. In this study, we analyze
the Sun-as-a-star multi-wavelength observations over 10 years to
investigate proportionalities between the surface magnetic flux and
the irradiances of various wavelengths from X-ray to radio bands. As a
result, the irradiances of X-ray, EUV, and radio fluxes corresponding
to the coronal temperatures (logT=6-7) show power-law relationships
with exponents of 1.1 to 1.4 with respect to the magnetic flux, while
the power-law exponents are less than unity for NUV and visible lines
corresponding to the chromospheric temperatures (logT=4). Moreover,
in any wavelengths, i.e., in any temperature ranges, these scaling
laws can be extended to G-type dwarf stars. By expanding the present
analysis, we may empirically derive the XUV spectrum for a given
stellar magnetic flux (see the presentation by Namekata et al.). Our
study shows that the response of the atmospheres to the photospheric
magnetic flux is universal among the Sun and sun-like stars, regardless
of age or activity.
Title: XUV Spectra of Active Solar-like Stars: Extension of Empirical
Laws from Solar Observations
Authors: Namekata, Kosuke; Watanabe, Kyoko; Toriumi, Shin; Shoda,
Munehito; Notsu, Yuta; Airapetian, Vladimir
Bibcode: 2022cosp...44.2480N
Altcode:
The X-ray and Extreme Ultraviolet (XUV) emissions from stars are
essential for understanding the atmospheric heating of stellar active
regions (ARs) and their impact on (exo)planetary atmospheres. However,
characterization of a full stellar XUV spectrum is a difficult task,
especially in the extreme-ultraviolet (EUV) regime. Understanding
the relation between solar ARs and XUV spectra could be useful
not only for extrapolating the stellar XUV spectra, but also for
understanding the nature of stellar ARs. Recent studies characterized
the empirical solar-stellar relationship between XUV radiation flux
($F$) and surface magnetic field fluxes ($\Phi$) in the formula of
$F\propto\Phi^{\alpha}$ (e.g., Toriumi and Airapetian 2022). However,
their analyses were limited to the selected wavebands or spectral lines
of interest. Here we investigate the response of the full XUV spectrum
($F_{\lambda}$; from X-ray to far-ultraviolet (FUV)) as a function of
the total unsigned magnetic flux ($\Phi_{\rm tot}$) for the full-disk
Sun. By analyzing 10-years data of solar XUV spectra obtained by
SDO/EVE and SORCE/XPS&SOLSTICE, we derive the power-law relation
$F_{\lambda}\propto (\Phi_{\rm tot})^{\alpha_{\lambda}}$ for each
wavelength with a spectral resolution of 1-10 {\AA}. The power-law
indices decrease from above-unity to sub-unity as the wavelength
increases from X-ray to FUV, similar to previous studies (see the
presentation by Toriumi & Airapetian). We applied the scaling
relations to nearby active solar-like stars, such as EK Dra (G1.5V),
$\pi$1 Uma (G1.5V), and $\kappa$1 Ceti (G5V). These stars represent the
limited number of objects for which total unsigned magnetic fluxes and
XUV spectra (except for EUV ranges) are currently available. We found
that the XUV spectra of these stars estimated from $\Phi_{\rm tot}$
obtained from the empirical relation are roughly consistent with the
observed spectra with an order-of-magnitude error, for large part of
wavebands and emission lines. This result suggests that the solar
power-law relations may be helpful in estimating a full set of XUV
spectrum for other stars with measured surface magnetic fluxes. In
this presentation, we will discuss the possibilities and limitations
of this empirical method for applications to other solar-like stars.
Title: Integrated simulation study on the formation of
flare-productive regions and the onset of solar flares
Authors: Kusano, Kanya; Toriumi, Shin; Hotta, Hideyuki; Kaneko,
Takafumi
Bibcode: 2022cosp...44.2466K
Altcode:
What is the condition for forming flare-productive regions and what
determines the onset of large solar flares are crucial issues for solar
flare study and space weather forecast. However, although various
studies have been published so far from the different aspects, they
are not yet well elucidated, hindering the predictability of large
flares. In this study, we have developed three numerical models and
conducted an integrated study to holistically understand the process
from the formation of active regions to the onset of solar flares. The
first model is the realistic magnetic flux emergence simulation
using the radiative magnetohydrodynamics (MHD) code R2D2 (Hotta et
al. 2019). We surveyed the interaction between the convection and the
magnetic flux emergence through an ensemble simulation and derived a
condition for producing a flare-productive delta-spot region. The second
model is the physics-based flare prediction model, called kappa-scheme
(Kusano et al. 2020). We evaluated the MHD stability of active regions
synthesized by the first model and predicted a possible flare using
it. The third model is the data-driven simulation (Kaneko et al. 2021),
and we simulated the nonlinear dynamics of solar flares which may
occur in the synthesized active region. Finally, we discuss the causal
relationship between the flux emergence, the formation and stability
of active regions, and solar flares through the comparative analyses
of the integrated simulation and the variety of observations. The
result suggests the possibility of a new type of prediction for the
formation of the flare-productive region and the onset of solar flares.
Title: Various Activities above Sunspot Light Bridges in IRIS
Observations: Classification and Comparison
Authors: Hou, Yijun; Li, Ting; Yang, Shuhong; Toriumi, Shin; Guo,
Yilin; Zhang, Jun
Bibcode: 2022ApJ...929...12H
Altcode: 2022arXiv220210159H
Light bridges (LBs) are among the most striking substructures in
sunspots, where various activities have been revealed by recent
high-resolution observations from the Interface Region Imaging
Spectrograph (IRIS). Based on the variety of their physical properties,
we classified these activities into four distinct categories:
transient brightening (TB), intermittent jet (IJ), type-I light
wall (LW-I), and type-II light wall (LW-II). In IRIS 1400/1330 Å
observations, TBs are characterized by abrupt emission enhancements,
and IJs appear as collimated plasma ejections with a width of 1-2 Mm
at some LB sites. Most observed TBs are associated with IJs and show
superpositions of some chromosphere absorption lines on enhanced and
broadened wings of C II and Si IV lines, which could be driven by
intermittent magnetic reconnection in the lower atmosphere. LW-I and
LW-II are wall-shaped structures with bright fronts above the whole
LB. An LW-I has a continuous oscillating front with a typical height
of several Mm and an almost stationary period of 4-5 minutes. On the
contrary, an LW-II has an indented front with a height of over 10
Mm, which has no stable period and is accompanied by recurrent TBs
in the entire LB. These results support that LW-IIs are driven by
frequent reconnection occurring along the entire LB due to large-scale
magnetic flux emergence or intrusion, rather than the leakage of waves
producing LW-Is. Our observations reveal a highly dynamical scenario
of activities above LBs driven by different basic physical processes,
including magnetoconvection, magnetic reconnection, and wave leakage.
Title: Solar Flares and Magnetic Helicity
Authors: Toriumi, Shin; Park, Sung-Hong
Bibcode: 2022arXiv220406010T
Altcode:
Solar flares and coronal mass ejections are the largest energy release
phenomena in the current solar system. They cause drastic enhancements
of electromagnetic waves of various wavelengths and sometimes eject
coronal material into the interplanetary space, disturbing the magnetic
surroundings of orbiting planets including the Earth. It is generally
accepted that solar flares are a phenomenon in which magnetic energy
stored in the solar atmosphere above an active region is suddenly
released through magnetic reconnection. Therefore, to elucidate the
nature of solar flares, it is critical to estimate the complexity
of the magnetic field and track its evolution. Magnetic helicity,
a measure of the twist of coronal magnetic structures, is thus used
to quantify and characterize the complexity of flare-productive active
regions. This chapter provides an overview of solar flares and discusses
how the different concepts of magnetic helicity are used to understand
and predict solar flares.
Title: Universal Scaling Laws for Solar and Stellar Atmospheric
Heating
Authors: Toriumi, Shin; Airapetian, Vladimir S.
Bibcode: 2022ApJ...927..179T
Altcode: 2022arXiv220201232T
The Sun and Sun-like stars commonly host multimillion-kelvin coronae
and 10,000 K chromospheres. These extremely hot gases generate X-ray
and extreme ultraviolet emissions that may impact the erosion and
chemistry of (exo)planetary atmospheres, influencing the climate and
conditions for habitability. However, the mechanism of coronal and
chromospheric heating is still poorly understood. While the magnetic
field most probably plays a key role in driving and transporting
energy from the stellar surface upwards, it is not clear whether the
atmospheric heating mechanisms of the Sun and active Sun-like stars can
be described in a unified manner. To this end, we report on a systematic
survey of the responses of solar and stellar atmospheres to surface
magnetic flux over a wide range of temperatures. By analyzing 10 years
of multiwavelength synoptic observations of the Sun, we reveal that the
irradiance and magnetic flux show power-law relations with an exponent
decreasing from above unity to below as the temperature decreases from
the corona to the chromosphere. Moreover, this trend indicating the
efficiency of atmospheric heating can be extended to Sun-like stars. We
also discover that the power-law exponent depends on the solar cycle,
becoming smallest at maximum activity, probably due to the saturation
of atmospheric heating. Our study provides observational evidence that
the mechanism of atmospheric heating is universal among the Sun and
Sun-like stars, regardless of age or activity.
Title: Sun-as-a-star Spectral Irradiance Observations of Transiting
Active Regions: a Milestone for Characterization of Stellar Active
Regions
Authors: Toriumi, Shin; Airapetian, Vladimir; Hudson, Hugh; Schrijver,
Karel; Cheung, Chun Ming Mark; DeRosa, Marc
Bibcode: 2021AGUFM.U43B..05T
Altcode:
Recent observations have revealed that solar-type stars can produce
massive "superflares". The strongest flares on the Sun are almost
always associated with large, complex, rapidly-evolving active regions
(ARs) including sunspots. Therefore, to understand why and how stellar
flares and coronal eruptions occur, which may directly determine
the circumstances of exoplanets, it is critically important to gain
information on stellar ARs. One possible way to do so is to monitor the
star in multiple wavelengths. In this study, we perform multi-wavelength
irradiance monitoring of transiting solar ARs by using full-disk
observational (i.e. Sun-as-a-star) data from four satellites. We find
that the near UV light curves show strong correlations with photospheric
total magnetic flux and that there are time lags between the coronal
and photospheric light curves when ARs are close to the limb. Such time
lags result from high-arching, bright coronal loops above stellar ARs
being visible even when the AR is behind the limb. It is also found
that the EUV light curves sensitive to transition-region temperatures
are sometimes dimmed because of a reduction in the emission measure of
0.60.8 MK due to the plasma being heated to higher temperatures over a
wide area around the AR. These results indicate that, by measuring the
stellar light curves in multiple wavelengths, we may obtain information
on the structures and evolution of stellar ARs.
Title: PSTEP: project for solar-terrestrial environment prediction
Authors: Kusano, Kanya; Ichimoto, Kiyoshi; Ishii, Mamoru; Miyoshi,
Yoshizumi; Yoden, Shigeo; Akiyoshi, Hideharu; Asai, Ayumi; Ebihara,
Yusuke; Fujiwara, Hitoshi; Goto, Tada-Nori; Hanaoka, Yoichiro;
Hayakawa, Hisashi; Hosokawa, Keisuke; Hotta, Hideyuki; Hozumi,
Kornyanat; Imada, Shinsuke; Iwai, Kazumasa; Iyemori, Toshihiko; Jin,
Hidekatsu; Kataoka, Ryuho; Katoh, Yuto; Kikuchi, Takashi; Kubo, Yûki;
Kurita, Satoshi; Matsumoto, Haruhisa; Mitani, Takefumi; Miyahara,
Hiroko; Miyoshi, Yasunobu; Nagatsuma, Tsutomu; Nakamizo, Aoi; Nakamura,
Satoko; Nakata, Hiroyuki; Nishizuka, Naoto; Otsuka, Yuichi; Saito,
Shinji; Saito, Susumu; Sakurai, Takashi; Sato, Tatsuhiko; Shimizu,
Toshifumi; Shinagawa, Hiroyuki; Shiokawa, Kazuo; Shiota, Daikou;
Takashima, Takeshi; Tao, Chihiro; Toriumi, Shin; Ueno, Satoru;
Watanabe, Kyoko; Watari, Shinichi; Yashiro, Seiji; Yoshida, Kohei;
Yoshikawa, Akimasa
Bibcode: 2021EP&S...73..159K
Altcode:
Although solar activity may significantly impact the global environment
and socioeconomic systems, the mechanisms for solar eruptions and
the subsequent processes have not yet been fully understood. Thus,
modern society supported by advanced information systems is at risk
from severe space weather disturbances. Project for solar-terrestrial
environment prediction (PSTEP) was launched to improve this situation
through synergy between basic science research and operational
forecast. The PSTEP is a nationwide research collaboration in Japan
and was conducted from April 2015 to March 2020, supported by a
Grant-in-Aid for Scientific Research on Innovative Areas from the
Ministry of Education, Culture, Sports, Science and Technology of
Japan. By this project, we sought to answer the fundamental questions
concerning the solar-terrestrial environment and aimed to build a
next-generation space weather forecast system to prepare for severe
space weather disasters. The PSTEP consists of four research groups and
proposal-based research units. It has made a significant progress in
space weather research and operational forecasts, publishing over 500
refereed journal papers and organizing four international symposiums,
various workshops and seminars, and summer school for graduate students
at Rikubetsu in 2017. This paper is a summary report of the PSTEP and
describes the major research achievements it produced.
Title: Sun-as-a-star Spectral Irradiance Observations: Milestone
For Characterizing The Stellar Active Regions
Authors: Toriumi, S.; Airapetian, V.; Hudson, H.; Schrijver, C.;
Cheung, M.; DeRosa, M.
Bibcode: 2021AAS...23820503T
Altcode:
For understanding the physical mechanism behind the solar flares, it
is crucial to measure the magnetic fields of active regions (ARs) from
the photosphere to the corona and investigate their scale, complexity,
and evolution. This is true for the stellar flares. However, it is
still difficult to spatially resolve the starspots, and one possible
way to probe their evolution and structure is to monitor the star in
multiple wavelengths. To test this possibility with the solar data,
we perform multi-wavelength irradiance monitoring of transiting solar
ARs by using full-disk observation data from SDO, Hinode, GOES, and
SORCE. As a result, we find, for instance, that the near UV light
curves show strong correlations with photospheric total magnetic flux
and that there are time lags between the coronal and photospheric light
curves when ARs are close to the limb, which together may enable one
to discern how high bright coronal loops extend above stellar ARs. It
is also revealed that the sub-MK (i.e. transition-region temperature)
EUV light curves are sometimes dimmed because the emission measure
is reduced owing to the heating over a wide area around the AR. These
results indicate that, by measuring the stellar light curves in multiple
wavelengths, we may obtain information on the structure and evolution
of stellar ARs.
Title: Sun-as-a-star Multi-wavelength Observations: A Milestone for
Characterization of Stellar Active Regions
Authors: Toriumi, Shin; Airapetian, Vladimir S.; Hudson, Hugh S.;
Schrijver, Carolus J.; Cheung, Mark C. M.; DeRosa, Marc L.
Bibcode: 2021csss.confE..46T
Altcode:
It has been revealed that "superflares" can occur on solar-type
stars. The magnetic energy of the flares is likely to be stored in
active-region atmospheres. Therefore, to explain the energy storage and
occurrence of the flares, it is important to monitor the evolutions of
the active regions, not only in visible light but also in ultraviolet
(UV) and X-rays. To demonstrate this, we perform multi-wavelength
irradiance monitoring of transiting solar active regions by using
full-disk observation data. As a result of this sun-as-a-star spectral
irradiance analysis, we confirm that the visible continuum that
corresponds to the photosphere becomes darkened when the spot is at the
central meridian, whereas most of the UV, EUV and X-rays, which are
sensitive to chromospheric to coronal temperatures, are brightened,
reflecting the bright magnetic features above the starspots. The
time lags between the coronal and photospheric light curves have
the potential to probe the extent of coronal magnetic fields above
the starspots. These results indicate that, by measuring the stellar
light curves in multiple wavelengths, we may obtain information on
the structures and evolution of stellar active regions.
Title: Flux Emergence and Generation of Flare-productive Active
Regions
Authors: Toriumi, Shin
Bibcode: 2021cosp...43E1731T
Altcode:
Observations revealed that the delta-sunspots, in which opposite
polarities are closely neighboring that they share a common penumbra,
produce the strongest solar flares in history. Within the delta-spots,
magnetic flux ropes are sometimes observed above the sheared polarity
inversion lines before the flare onset. In this talk, we review the
generation mechanisms of delta-spots and such magnetic structures
from both observational and theoretical points of view, based on
the recently published Living Reviews article (Toriumi & Wang
2019). We show that the advances of observational capabilities in
the past decades significantly improved our understanding, whereas
state-of-the-art radiative MHD simulations can now reproduce the flux
emergence and spontaneous generation of delta-spots, sheared polarity
inversion lines, and magnetic flux ropes.
Title: Delta-sunspot Formation in Realistic Magnetic Flux Emergence
Simulations
Authors: Toriumi, S.; Hotta, H.
Bibcode: 2020AGUFMSH006..04T
Altcode:
Observations revealed that the strongest solar flares tend to occur in
complex-shaped active regions called delta-sunspots, often associated
with sheared polarity inversion lines (PILs) in between. The formation
of delta-spots is, however, not understood well because we cannot probe
the subsurface layer with direct optical observations. To this end, we
perform a series of flux emergence simulations with using the radiative
magnetohydrodynamics code R2D2. This code solves thermal convection
of various scales from 100 Mm sized cells to surface granules at the
same time. We set a computational box that stretches down to -140 Mm,
which is deeper than any previous simulations of this kind, and place
a magnetic flux tube at -17 Mm without any artificial triggering
of buoyant emergence. It is found that the flux tube is elevated
by large-scale convective upflows at two segments and, as a result,
a pair of emerging bipolar spots appear on the photosphere. As the
emergence continues, the spots of opposite polarities collide against
each other and eventually form strongly-packed delta-spots. Each
spot shows rotating motion that is driven by the Lorentz force, and
between the positive and negative polarities, strongly sheared PILs
are created. Above the PIL, a helical flux rope is produced. All
these structures are the key elements of flare-productive active
regions. Moreover, around the PILs, we detect super-equipartition
magnetic fields (exceeding 6000 G), which are produced by the shear
motion between the delta-spots. These results indicate that the strong
coupling between emerging magnetic flux and background turbulence is
a key to generate active regions that are prone to major flares.
Title: The Solar-C (EUVST) mission: the latest status
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko; Suematsu,
Yoshinori; Hara, Hirohisa; Tsuzuki, Toshihiro; Katsukawa, Yukio; Kubo,
Masahito; Ishikawa, Ryoko; Watanabe, Tetsuya; Toriumi, Shin; Ichimoto,
Kiyoshi; Nagata, Shin'ichi; Hasegawa, Takahiro; Yokoyama, Takaaki;
Watanabe, Kyoko; Tsuno, Katsuhiko; Korendyke, Clarence M.; Warren,
Harry; De Pontieu, Bart; Boerner, Paul; Solanki, Sami K.; Teriaca,
Luca; Schuehle, Udo; Matthews, Sarah; Long, David; Thomas, William;
Hancock, Barry; Reid, Hamish; Fludra, Andrzej; Auchère, Frederic;
Andretta, Vincenzo; Naletto, Giampiero; Poletto, Luca; Harra, Louise
Bibcode: 2020SPIE11444E..0NS
Altcode:
Solar-C (EUVST) is the next Japanese solar physics mission to
be developed with significant contributions from US and European
countries. The mission carries an EUV imaging spectrometer with
slit-jaw imaging system called EUVST (EUV High-Throughput Spectroscopic
Telescope) as the mission payload, to take a fundamental step towards
answering how the plasma universe is created and evolves and how the
Sun influences the Earth and other planets in our solar system. In
April 2020, ISAS (Institute of Space and Astronautical Science) of JAXA
(Japan Aerospace Exploration Agency) has made the final down-selection
for this mission as the 4th in the series of competitively chosen
M-class mission to be launched with an Epsilon launch vehicle in mid
2020s. NASA (National Aeronautics and Space Administration) has selected
this mission concept for Phase A concept study in September 2019 and
is in the process leading to final selection. For European countries,
the team has (or is in the process of confirming) confirmed endorsement
for hardware contributions to the EUVST from the national agencies. A
recent update to the mission instrumentation is to add a UV spectral
irradiance monitor capability for EUVST calibration and scientific
purpose. This presentation provides the latest status of the mission
with an overall description of the mission concept emphasizing on key
roles of the mission in heliophysics research from mid 2020s.
Title: Current Status of the Solar-C_EUVST Mission
Authors: Imada, S.; Shimizu, T.; Kawate, T.; Toriumi, S.; Katsukawa,
Y.; Kubo, M.; Hara, H.; Suematsu, Y.; Ichimoto, K.; Watanabe, T.;
Watanabe, K.; Yokoyama, T.; Warren, H.; Long, D.; Harra, L. K.;
Teriaca, L.
Bibcode: 2020AGUFMSH056..05I
Altcode:
Solar-C_EUVST (EUV High-Throughput Spectroscopic Telescope) is designed
to comprehensively understand the energy and mass transfer from the
solar surface to the solar corona and interplanetary space, and to
investigate the elementary processes that take place universally
in cosmic plasmas. As a fundamental step towards answering how the
plasma universe is created and evolves, and how the Sun influences
the Earth and other planets in our solar system, the proposed mission
is designed to comprehensively understand how mass and energy are
transferred throughout the solar atmosphere. Understanding the solar
atmosphere, which connects to the heliosphere via radiation, the solar
wind and coronal mass ejections, and energetic particles is pivotal
for establishing the conditions for life and habitability in the solar
system. The two primary science objectives for Solar-C_EUVST are :
I) Understand how fundamental processes lead to the formation of the
solar atmosphere and the solar wind, II) Understand how the solar
atmosphere becomes unstable, releasing the energy that drives solar
flares and eruptions. Solar-C_EUVST will, A) seamlessly observe all
the temperature regimes of the solar atmosphere from the chromosphere
to the corona at the same time, B) resolve elemental structures of the
solar atmosphere with high spatial resolution and cadence to track their
evolution, and C) obtain spectroscopic information on the dynamics of
elementary processes taking place in the solar atmosphere. In this
talk, we will first discuss the science target of the Solar-C_EUVST,
and then discuss the current status of the Solar-C_EUVST mission.
Title: Testing a Data-driven Active Region Evolution Model with
Boundary Data at Different Heights from a Solar Magnetic Flux
Emergence Simulation
Authors: Jiang, Chaowei; Toriumi, Shin
Bibcode: 2020ApJ...903...11J
Altcode: 2020arXiv201002497J
A data-driven active region evolution (DARE) model has been developed
to study the complex structures and dynamics of solar coronal magnetic
fields. The model is configured with a typical coronal environment
of tenuous gas governed by strong magnetic field, and thus its lower
boundary is set at the base of the corona, but driven by magnetic
fields observed in the photosphere. A previous assessment of the
model using data from a flux emergence simulation (FES) showed that
the DARE failed to reproduce the coronal magnetic field in the FES,
which is attributed to the fact that the photospheric data in the
FES has a very strong Lorentz force and therefore spurious flows
are generated in the DARE model. Here we further test the DARE by
using three sets of data from the FES sliced at incremental heights,
which correspond to the photosphere, the chromosphere, and the base of
the corona. It is found that the key difference in the three sets of
data is the extent of the Lorentz force, which makes the data-driven
model perform very differently. At the two higher levels above the
photosphere, the Lorentz force decreases substantially, and the
DARE model attains results in much better agreement with the FES,
confirming that the Lorentz force in the boundary data is a key issue
affecting the results of the DARE model. However, unlike the FES data,
the photospheric field from SDO/HMI observations has recently been found
to be very close to force-free. Therefore, we suggest that it is still
reasonable to use the photospheric magnetic field as an approximation
of the field at the coronal base to drive the DARE model.
Title: Sun-as-a-star Spectral Irradiance Observations of Transiting
Active Regions
Authors: Toriumi, Shin; Airapetian, Vladimir S.; Hudson, Hugh S.;
Schrijver, Carolus J.; Cheung, Mark C. M.; DeRosa, Marc L.
Bibcode: 2020ApJ...902...36T
Altcode: 2020arXiv200804319T
Major solar flares are prone to occur in active-region (AR) atmospheres
associated with large, complex, dynamically evolving sunspots. This
points to the importance of monitoring the evolution of starspots,
not only in visible but also in ultraviolet (UV) and X-rays, in
understanding the origin and occurrence of stellar flares. To this end,
we perform spectral irradiance analysis on different types of transiting
solar ARs by using a variety of full-disk synoptic observations. The
target events are an isolated sunspot, spotless plage, and emerging flux
in prolonged quiet-Sun conditions selected from the past decade. We find
that the visible continuum and total solar irradiance become darkened
when the spot is at the central meridian, whereas it is bright near
the solar limb; UV bands sensitive to the chromosphere correlate well
with the variation of total unsigned magnetic flux in the photosphere;
amplitudes of extreme ultraviolet (EUV) and soft X-ray increase with
the characteristic temperature, whose light curves are flat-topped
due to their sensitivity to the optically thin corona; the transiting
spotless plage does not show the darkening in the visible irradiance,
while the emerging flux produces an asymmetry in all light curves about
the central meridian. The multiwavelength Sun-as-a-star study described
here indicates that the time lags between the coronal and photospheric
light curves have the potential to probe the extent of coronal magnetic
fields above the starspots. In addition, EUV wavelengths that are
sensitive to temperatures just below 1 MK sometimes show antiphased
variations, which may be used for diagnosing plasmas around starspots.
Title: Formation of superstrong horizontal magnetic field in
delta-type sunspot in radiation magnetohydrodynamic simulations
Authors: Hotta, H.; Toriumi, S.
Bibcode: 2020MNRAS.498.2925H
Altcode: 2020MNRAS.tmp.2450H; 2020arXiv200807741H
We perform a series of radiative magnetohydrodynamic simulations to
understand the amplification mechanism of the exceptionally strong
horizontal magnetic field in delta-type sunspots. In the simulations,
we succeed in reproducing the delta-type sunspot and resulting strong
magnetic field exceeding 6000 G in a light bridge between the positive
and negative polarities. Our conclusions in this study are summarized
as follows: (1) The essential amplification mechanism of the strong
horizontal magnetic field is the shear motion caused by the rotation
of two spots. (2) The strong horizontal magnetic field remains
the force-free state. (3) The peak strength of the magnetic fields
does not depend on the spatial resolution, top boundary condition,
or Alfvén speed limit. The origin of the rotating motion is rooted
in the deep convection zone. Therefore, the magnetic field in the
delta-spot light bridge can be amplified to the superequipartition
values in the photosphere.
Title: On the Lorentz Force and Torque of Solar Photospheric Emerging
Magnetic Fields
Authors: Duan, Aiying; Jiang, Chaowei; Toriumi, Shin; Syntelis, Petros
Bibcode: 2020ApJ...896L...9D
Altcode: 2020arXiv200510532D
Magnetic flux generated and intensified by the solar dynamo emerges
into the solar atmosphere, forming active regions (ARs) including
sunspots. Existing theories of flux emergence suggest that the
magnetic flux can rise buoyantly through the convection zone but
is trapped at the photosphere, while its further rising into the
atmosphere resorts to the Parker buoyancy instability. To trigger such
an instability, the Lorentz force in the photosphere needs to be as
large as the gas pressure gradient to hold up an extra amount of mass
against gravity. This naturally results in a strongly non-force-free
photosphere, which is indeed shown in typical idealized numerical
simulations of flux tube buoyancy from below the photosphere into
the corona. Here we conduct a statistical study of the extents of
normalized Lorentz forces and torques in the emerging photospheric
magnetic field with a substantially large sample of Solar Dynamics
Observatory/Helioseismic and Magnetic Imager vector magnetograms. We
found that the photospheric field has a rather small Lorentz force and
torque on average, and thus is very close to a force-free state, which
is not consistent with theories as well as idealized simulations of flux
emergence. Furthermore, the small extents of forces and torques seem not
to be influenced by the emerging AR's size, the emergence rate, or the
nonpotentiality of the field. This result puts an important constraint
on future development of theories and simulations of flux emergence.
Title: Temporal and Spatial Scales in Coronal Rain Revealed by UV
Imaging and Spectroscopic Observations
Authors: Ishikawa, Ryohtaroh T.; Katsukawa, Yukio; Antolin, Patrick;
Toriumi, Shin
Bibcode: 2020SoPh..295...53I
Altcode: 2020arXiv200313214I
Coronal rain corresponds to cool and dense clumps in the corona
accreting towards the solar surface; it is often observed above solar
active regions. These clumps are generally thought to be produced by
a thermal instability in the corona and their lifetime is limited by
the time they take to reach the chromosphere. Although the rain usually
fragments into smaller clumps while falling down, their specific spatial
and temporal scales remain unclear. In addition, the observational
signatures of the impact of the rain with the chromosphere have not been
clarified yet. In this study, we investigate the time evolution of the
velocity and intensity of coronal rain above a sunspot by analyzing
coronal images obtained by the Atmospheric Imaging Assembly (AIA)
onboard the Solar Dynamics Observatory (SDO) as well as the slit-jaw
images (SJIs) and spectral data taken by the Interface Region Imaging
Spectrograph (IRIS) satellite. We identify dark and bright threads
moving towards the umbra in AIA images and in SJIs, respectively,
and co-spatial chromospheric intensity enhancements and redshifts in
three IRIS spectral lines, Mg II k 2796 Å, Si IV 1394 Å, and C II
1336 Å. The intensity enhancements and coronal rain redshifts occur
almost concurrently in all the three lines, which clearly demonstrates
the causal relationship with coronal rain. Furthermore, we detect bursty
intensity variation with a time scale shorter than 1 minute in Mg II k,
Si IV, and C II, indicating that a length scale of rain clumps is about
2.7 Mm if we multiply the typical time scale of the busty intensity
variation at 30 sec by the rain velocity at 90 kms−1. Such
rapid enhancements in the IRIS lines are excited within a time lag
of 5.6 sec limited by the temporal resolution. These temporal and
spatial scales may reflect the physical processes responsible for
the rain morphology, and are suggestive of instabilities such as the
Kelvin-Helmholtz instability.
Title: VizieR Online Data Catalog: Spot parameters on KIC solar-type
stars (Namekata+, 2019)
Authors: Namekata, K.; Maehara, H.; Notsu, Y.; Toriumi, S.; Hayakawa,
H.; Ikuta, K.; Notsu, S.; Honda, S.; Nogami, D.; Shibata, K.
Bibcode: 2020yCat..18710187N
Altcode:
In order to assess the diversity and similarity of the star spots by
comparing them with the sunspots, we selected solar-type stars as target
stars from the Kepler data set on the basis of the stellar effective
temperature (Teff) and surface gravity (logg) listed in the Kepler
Input Catalog (see DR25; Mathur+, 2017, J/ApJS/229/30). In this study,
we defined solar-type stars with a criterion of 5000K<Teff<6000K
and logg>4.0. For each star, we used all of the available Kepler
pre-search data conditioning long-cadence (30min) data in which
instrumental effects are removed. (1 data file).
Title: Temporal Evolution of Spatially Resolved Individual Star
Spots on a Planet-hosting Solar-type Star: Kepler-17
Authors: Namekata, Kosuke; Davenport, James R. A.; Morris, Brett M.;
Hawley, Suzanne L.; Maehara, Hiroyuki; Notsu, Yuta; Toriumi, Shin;
Ikuta, Kai; Notsu, Shota; Honda, Satoshi; Nogami, Daisaku; Shibata,
Kazunari
Bibcode: 2020ApJ...891..103N
Altcode: 2020arXiv200201086N
Star spot evolution is visible evidence of the emergence/decay of the
magnetic field on a stellar surface, and it is therefore important for
the understanding of the underlying stellar dynamo and consequential
stellar flares. In this paper, we report the temporal evolution
of individual star spot areas on the hot-Jupiter-hosting, active
solar-type star Kepler-17, whose transits occur every 1.5 days. The
spot longitude and area evolution are estimated (1) from the stellar
rotational modulations of Kepler data and (2) from the brightness
enhancements during the exoplanet transits caused by existence of
large star spots. As a result of the comparison, the number of spots,
spot locations, and the temporal evolution derived from the rotational
modulations are largely different from those of in-transit spots. We
confirm that, although only two light-curve minima appear per rotation,
there are clearly many spots present on the star. We find that the
observed differential intensity changes are sometimes consistent with
the spot pattern detected by transits, but at other times they do not
match with each other. Although the temporal evolution derived from
the rotational modulation differs from those of in-transit spots to
a certain degree, the emergence/decay rates of in-transit spots are
within an order of magnitude of those derived for sunspots as well
as our previous research based only on rotational modulations. This
supports the hypothesis that the emergence/decay of sunspots and
extremely large star spots on solar-type stars occur through the same
underlying processes.
Title: Comparative Study of Data-driven Solar Coronal Field Models
Using a Flux Emergence Simulation as a Ground-truth Data Set
Authors: Toriumi, Shin; Takasao, Shinsuke; Cheung, Mark C. M.; Jiang,
Chaowei; Guo, Yang; Hayashi, Keiji; Inoue, Satoshi
Bibcode: 2020ApJ...890..103T
Altcode: 2020arXiv200103721T
For a better understanding of the magnetic field in the solar corona
and dynamic activities such as flares and coronal mass ejections, it
is crucial to measure the time-evolving coronal field and accurately
estimate the magnetic energy. Recently, a new modeling technique called
the data-driven coronal field model, in which the time evolution of
magnetic field is driven by a sequence of photospheric magnetic and
velocity field maps, has been developed and revealed the dynamics
of flare-productive active regions. Here we report on the first
qualitative and quantitative assessment of different data-driven
models using a magnetic flux emergence simulation as a ground-truth
(GT) data set. We compare the GT field with those reconstructed from
the GT photospheric field by four data-driven algorithms. It is found
that, at minimum, the flux rope structure is reproduced in all coronal
field models. Quantitatively, however, the results show a certain
degree of model dependence. In most cases, the magnetic energies and
relative magnetic helicity are comparable to or at most twice of the GT
values. The reproduced flux ropes have a sigmoidal shape (consistent
with GT) of various sizes, a vertically standing magnetic torus, or
a packed structure. The observed discrepancies can be attributed to
the highly non-force-free input photospheric field, from which the
coronal field is reconstructed, and to the modeling constraints such
as the treatment of background atmosphere, the bottom boundary setting,
and the spatial resolution.
Title: Lifetimes and emergence/decay rates of star spots on solar-type
stars estimated by Kepler data in comparison with those of sunspots
Authors: Namekata, K.; Shibata, K.; Maehara, H.; Notsu, Y.; Nogami,
D.; Toriumi, S.; Davenport, J.; Hawley, S.; Morris, B.
Bibcode: 2020AAS...23514805N
Altcode:
Active solar-type stars show large quasi-periodic brightness variations
caused by stellar rotations with large star spots, and the amplitude
changes as the spots emerge and decay. Temporal evolution of star spots
has been hardly measured because of its difficulty in measurement,
especially on solar-type stars. The Kepler's long-term data are suitable
for investigations on the emergence and decay processes of star spots,
which are important to understand underlying stellar dynamo. In this
talk, we report the measurements of temporal evolution of individual
star-spot area on solar-type stars by using Kepler data. We estimated
it (i) by tracing local minima of the Kepler light curves (Namekata et
al. 2019) and (ii) by modeling the small brightness variation during
exoplanet transit (c.f. Morris et al. 2017, Namekata et al. submitted
to ApJ). We successfully obtained temporal evolution of individual star
spots showing clear emergence and decay, and derived the statistical
values of the lifetimes and emergence/decay rates of star spots. As
a result, we found that lifetimes (T) of star spots are ranging
from 10 to 350 days when spot areas (A) are 0.1-2.3% of a solar
hemisphere (SH). The lifetimes of star spots are much shorter than
those extrapolated from an empirical relation of sunspots, while being
consistent with other researches on star spot lifetimes. The emerging
and decay rates of star spots are typically 5×1020 Mx/h
(8 MSH/h) with the area of 0.1-2.3% of SH and are mostly consistent
with those expected from sunspots observations (Petrovay et al. 1997,
Norton et al. 2017). This strongly supports a possibility that the
emergence/decay mechanism of extremely large star spots (0.1-2.3%
of SH) is same as that of smaller sunspots (< 0.5% of SH), which
can constrain the stellar dynamo theory.
Title: Comparative Study of Data-driven Coronal Field Models with
a Ground-truth Flux Emergence Simulation
Authors: Toriumi, S.; Takasao, S.; Cheung, C. M. M.; Jiang, C.; Guo,
Y.; Hayashi, K.; Inoue, S.
Bibcode: 2019AGUFMSH34B..04T
Altcode:
To better understand the dynamic activities in the so lar corona, it is
desirable to follow the temporal evolution of coronal magnetic field and
accurately measure the stored free magnetic energy. Data-driven coronal
field models, in which the coronal field evolves in response to the
sequentially updated photospheric field, have recently been developed
and revealed the dynamics of flare-producing active regions. Here
we report on the first attempt to qualitatively and quantitatively
compare different data-driven models by using a magnetic flux emergence
simulation as a ground-truth data set. We find that, at least, all
models succeed in reproducing the twisted flux rope structure in the
atmosphere. However, they show a certain degree of model dependence in,
for instance, the structure of the flux rope, the rising speed, and
the estimation of magnetic energy and helicity. In the presentation,
we discuss the possible causes of the discrepancies, attributing them
to the highly non-force-free input photospheric field, from which the
coronal field is reconstructed, and the constraints in the data-driven
models.
Title: Revisiting Carrington event with archival materials:
Spatiotemporal Evolutions of a Large Sunspot Group and Great Auroral
Storms
Authors: Oliveira, D. M.; Hayakawa, H.; Ebihara, Y.; Willis, D. M.;
Toriumi, S.; Iju, T.; Hattori, K.; Wild, M.; Ribeiro, J.; Ermolli,
I.; Correia, A. P.; Ribeiro, A. I.; Knipp, D. J.; Zesta, E.
Bibcode: 2019AGUFMSM13E3353O
Altcode:
T he Carrington event (1/2 September 1859) is arguably considered
one of the most extreme space weather events in observational history
within a series of magnetic storms caused by extreme interplanetary
coronal mass ejections (ICMEs) from a large and complex active region
(AR) emerged on the solar disk, which hosted probably the earliest and
the brightest flare in the observational history. In this presentation,
we study the temporal and spatial evolutions of this source sunspot AR
and the subsequent visual aurorae, and compare this storm with other
extreme space weather events with respect to their their auroral spatial
evolution, on the basis of Hayakawa et al. (2019). Original sunspot
drawings by multiple contemporary observers including Carrington are
analyzed to describe the position and morphology of the source AR at
that time. Visual auroral reports from the Russian Empire, Iberia,
Ireland, Oceania, and Japan fill the existing spatial gap of auroral
visibility and revise the time series of auroral visibility in mid
to low magnetic latitudes. The revised time series is compared with
magnetic measurements and shows their fair correspondences. The spatial
evolution of the auroral oval is compared with those of other extreme
space weather events in February 1872, September 1909, May 1921,
and March 1989 as well as their storm intensity. This comparison
contextualizes the Carrington event certainly within one of the most
extreme space weather events, but likely not unique.
Title: Temporal and Spatial Evolutions of a Large Sunspot Group and
Great Auroral Storms Around the Carrington Event in 1859
Authors: Hayakawa, Hisashi; Ebihara, Yusuke; Willis, David M.;
Toriumi, Shin; Iju, Tomoya; Hattori, Kentaro; Wild, Matthew N.;
Oliveira, Denny M.; Ermolli, Ilaria; Ribeiro, José R.; Correia,
Ana P.; Ribeiro, Ana I.; Knipp, Delores J.
Bibcode: 2019SpWea..17.1553H
Altcode: 2019arXiv190810326H
The Carrington event is considered to be one of the most extreme space
weather events in observational history within a series of magnetic
storms caused by extreme interplanetary coronal mass ejections from
a large and complex active region that emerged on the solar disk. In
this article, we study the temporal and spatial evolutions of the
source sunspot active region and visual aurorae and compare this
storm with other extreme space weather events on the basis of their
auroral spatial evolution. Sunspot drawings by Schwabe, Secchi, and
Carrington describe the position and morphology of the source active
region at that time. Visual auroral reports from the Russian Empire,
Iberia, Ireland, Oceania, and Japan fill the spatial gap of auroral
visibility and revise the time series of auroral visibility in middle to
low magnetic latitudes. The reconstructed time series is compared with
magnetic measurements and shows the correspondence between low-latitude
to mid-latitude aurorae and the phase of magnetic storms. The spatial
evolution of the auroral oval is compared with those of other extreme
space weather events in 1872, 1909, 1921, and 1989 as well as their
storm intensity and contextualizes the Carrington event, as one of
the most extreme space weather events, but likely not unique.
Title: Spontaneous Generation of δ-sunspots in Convective
Magnetohydrodynamic Simulation of Magnetic Flux Emergence
Authors: Toriumi, Shin; Hotta, Hideyuki
Bibcode: 2019ApJ...886L..21T
Altcode: 2019arXiv191103909T
Observations reveal that strong solar flares and coronal mass ejections
tend to occur in complex active regions characterized by δ-sunspots,
spot rotation, sheared polarity inversion lines (PILs), and magnetic
flux ropes. Here we report on the first modeling of spontaneous δ-spot
generation as a result of flux emergence from the turbulent convection
zone. Utilizing state-of-the-art radiative magnetohydrodynamics
code R2D2, we simulate the emergence of a force-free flux tube in the
convection zone that stretches down to -140 Mm. Elevated by large-scale
convective upflows, the tube appears on the photosphere as two emerging
bipoles. The opposite polarities collide against each other due to
the subsurface connectivity, and they develop into a pair of closely
packed δ-spots. The Lorentz force drives the spot rotation and a strong
counter-streaming flow of 10 km s-1 at the PIL in δ-spots,
which, in tandem with local convection, strengthens the horizontal field
to 4 kG and builds up a highly sheared PIL. In the atmosphere above
the PIL, a flux rope structure is created. All these processes follow
the multi-buoyant segment theory of the δ-spot formation, and they
occur as a natural consequence of interaction between magnetic flux and
turbulent convection, suggesting that the generation of δ-spots and the
resultant flare eruptions may be a stochastically determined process.
Title: Achievements of Hinode in the first eleven years
Authors: Hinode Review Team; Al-Janabi, Khalid; Antolin, Patrick;
Baker, Deborah; Bellot Rubio, Luis R.; Bradley, Louisa; Brooks,
David H.; Centeno, Rebecca; Culhane, J. Leonard; Del Zanna, Giulio;
Doschek, George A.; Fletcher, Lyndsay; Hara, Hirohisa; Harra,
Louise K.; Hillier, Andrew S.; Imada, Shinsuke; Klimchuk, James A.;
Mariska, John T.; Pereira, Tiago M. D.; Reeves, Katharine K.; Sakao,
Taro; Sakurai, Takashi; Shimizu, Toshifumi; Shimojo, Masumi; Shiota,
Daikou; Solanki, Sami K.; Sterling, Alphonse C.; Su, Yingna; Suematsu,
Yoshinori; Tarbell, Theodore D.; Tiwari, Sanjiv K.; Toriumi, Shin;
Ugarte-Urra, Ignacio; Warren, Harry P.; Watanabe, Tetsuya; Young,
Peter R.
Bibcode: 2019PASJ...71R...1H
Altcode:
Hinode is Japan's third solar mission following Hinotori (1981-1982)
and Yohkoh (1991-2001): it was launched on 2006 September 22 and is in
operation currently. Hinode carries three instruments: the Solar Optical
Telescope, the X-Ray Telescope, and the EUV Imaging Spectrometer. These
instruments were built under international collaboration with the
National Aeronautics and Space Administration and the UK Science and
Technology Facilities Council, and its operation has been contributed
to by the European Space Agency and the Norwegian Space Center. After
describing the satellite operations and giving a performance evaluation
of the three instruments, reviews are presented on major scientific
discoveries by Hinode in the first eleven years (one solar cycle long)
of its operation. This review article concludes with future prospects
for solar physics research based on the achievements of Hinode.
Title: The Solar-C_EUVST mission
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko;
Ichimoto, Kiyoshi; Suematsu, Yoshinori; Hara, Hirohisa; Katsukawa,
Yukio; Kubo, Masahito; Toriumi, Shin; Watanabe, Tetsuya; Yokoyama,
Takaaki; Korendyke, Clarence M.; Warren, Harry P.; Tarbell, Ted; De
Pontieu, Bart; Teriaca, Luca; Schühle, Udo H.; Solanki, Sami; Harra,
Louise K.; Matthews, Sarah; Fludra, A.; Auchère, F.; Andretta, V.;
Naletto, G.; Zhukov, A.
Bibcode: 2019SPIE11118E..07S
Altcode:
Solar-C EUVST (EUV High-Throughput Spectroscopic Telescope) is a
solar physics mission concept that was selected as a candidate for
JAXA competitive M-class missions in July 2018. The onboard science
instrument, EUVST, is an EUV spectrometer with slit-jaw imaging
system that will simultaneously observe the solar atmosphere from the
photosphere/chromosphere up to the corona with seamless temperature
coverage, high spatial resolution, and high throughput for the first
time. The mission is designed to provide a conclusive answer to the
most fundamental questions in solar physics: how fundamental processes
lead to the formation of the solar atmosphere and the solar wind, and
how the solar atmosphere becomes unstable, releasing the energy that
drives solar flares and eruptions. The entire instrument structure
and the primary mirror assembly with scanning and tip-tilt fine
pointing capability for the EUVST are being developed in Japan, with
spectrograph and slit-jaw imaging hardware and science contributions
from US and European countries. The mission will be launched and
installed in a sun-synchronous polar orbit by a JAXA Epsilon vehicle in
2025. ISAS/JAXA coordinates the conceptual study activities during the
current mission definition phase in collaboration with NAOJ and other
universities. The team is currently working towards the JAXA final
down-selection expected at the end of 2019, with strong support from
US and European colleagues. The paper provides an overall description
of the mission concept, key technologies, and the latest status.
Title: Multi-wavelength Multi-height Study of Super Strong Surface
and Coronal Magnetic Fields in Active Region 12673
Authors: Wang, Haimin; Chen, Bin; Jing, Ju; Yu, Sijie; Liu, Chang;
Yurchyshyn, Vasyl B.; Ahn, Kwangsu; Okamoto, Takenori; Toriumi, Shin;
Cao, Wenda; Gary, Dale E.
Bibcode: 2019AAS...23440205W
Altcode:
Using the joint observations of Goode Solar telescope (GST), Expanded
Owens Valley Solar Array (EOVSA), Solar Dynamics Observatory (SDO)
and Hinode, we study the Solar Active Region (AR) 12673 in September
2017, which is the most flare productive AR in the solar cycle 24. GST
observations show the strong photospheric magnetic fields (nearly
6000 G) in polarity inversion line (PIL) and apparent photospheric
twist. Consistent upward flows are also observed in Dopplergrams
of Hinode, HMI and GST at the center part of that section of PIL,
while the down flows are observed in two ends, indicating that the
structure was rising from subsurface. Combining Non-Linear Force Free
Extrapolation and EOVSA microwave imaging spectroscopy, we also look
into the coronal structure of magnetic fields in this unusual AR,
including the evolution before and after the X9.3 flare on September
6, 2017. Coronal fields between 1000 and 2000 gauss are found above
the flaring PIL at the height range between 8 and 4Mm, outlining the
structure of a fluxrope or sheared arcade.
Title: Lifetimes and emergence/decay rates of star spots on solar-type
stars estimated by Kepler data in comparison with those of sunspots
Authors: Namekata, Kosuke; Maehara, H.; Davenport, J.; Morris, B.;
Hawley, S.; Notsu, Y.; Toriumi, S.; Hayakawa, H.; Honda, S.; Notsu,
S.; Ikuta, K.; Nogami, D.; Shibata, K.
Bibcode: 2019shin.confE..42N
Altcode:
Active solar-type stars show large quasi-periodic brightness variations
caused by stellar rotations with large star spots, and the amplitude
change as the spots emerge and decay. Temporal evolution of star spots
has been hardly measured because of its difficulty in measurement,
especially on solar-type stars. The Kepler’s long-term data is
suitable for investigations on the emergence and decay processes
of star spots, which are important to understand underlying stellar
dynamo. In this talk, we report the measurements of temporal evolution
of individual star-spot area on solar-type stars by using Kepler
data. We estimated it (i) by tracing local minima of the Kepler
light curves (Namekata et al. 2019) and (ii) by modeling the small
brightness variation during exoplanet transit (c.f. Morris et al. 2017,
Namekata et al. in prep). We successfully obtained temporal evolution
of individual star spots showing clear emergence and decay, and derived
the statistical values of the lifetimes and emergence/decay rates of
star spots. As a result, we found that lifetimes (T) of star spots
are ranging from 10 to 350 days when spot areas (A) are 0.1-2.3% of
a solar hemisphere (SH). The lifetimes of star spots are much shorter
than those extrapolated from an empirical relation of sunspots, while
being consistent with other researches on star spot lifetimes. The
emerging and decay rates of star spots are typically 5×10^20 Mx/h
(8 MSH/h) with the area of 0.1-2.3% of SH and are mostly consistent
with those expected from sunspots observations (Petrovay et al. 1997,
Norton et al. 2017). This strongly supports a possibility that the
emergence/decay mechanism of extremely large star spots (0.1-2.3%
of SH) is same as that of smaller sunspots (<0.5% of SH), which
can constrain the stellar dynamo theory.
Title: Flare-productive active regions
Authors: Toriumi, Shin; Wang, Haimin
Bibcode: 2019LRSP...16....3T
Altcode: 2019arXiv190412027T
Strong solar flares and coronal mass ejections, here defined not only
as the bursts of electromagnetic radiation but as the entire process
in which magnetic energy is released through magnetic reconnection and
plasma instability, emanate from active regions (ARs) in which high
magnetic non-potentiality resides in a wide variety of forms. This
review focuses on the formation and evolution of flare-productive
ARs from both observational and theoretical points of view. Starting
from a general introduction of the genesis of ARs and solar flares,
we give an overview of the key observational features during the
long-term evolution in the pre-flare state, the rapid changes in the
magnetic field associated with the flare occurrence, and the physical
mechanisms behind these phenomena. Our picture of flare-productive
ARs is summarized as follows: subject to the turbulent convection, the
rising magnetic flux in the interior deforms into a complex structure
and gains high non-potentiality; as the flux appears on the surface,
an AR with large free magnetic energy and helicity is built, which is
represented by δ -sunspots, sheared polarity inversion lines, magnetic
flux ropes, etc; the flare occurs when sufficient magnetic energy has
accumulated, and the drastic coronal evolution affects magnetic fields
even in the photosphere. We show that the improvement of observational
instruments and modeling capabilities has significantly advanced our
understanding in the last decades. Finally, we discuss the outstanding
issues and future perspective and further broaden our scope to the
possible applications of our knowledge to space-weather forecasting,
extreme events in history, and corresponding stellar activities.
Title: Revisiting Kunitomo's Sunspot Drawings During 1835 - 1836
in Japan
Authors: Fujiyama, Masashi; Hayakawa, Hisashi; Iju, Tomoya; Kawai,
Toshiki; Toriumi, Shin; Otsuji, Kenichi; Kondo, Katsuya; Watanabe,
Yusaku; Nozawa, Satoshi; Imada, Shinsuke
Bibcode: 2019SoPh..294...43F
Altcode: 2019arXiv190303092F
We revisit the sunspot drawings made by the Japanese astronomer Kunitomo
Toubei during 1835 - 1836 and recount the sunspot group number for each
image. There are two series of drawings, preliminary (P , containing
17 days with observations) and summary (S , covering 156 days with
observations), all made using brush and ink. S is a compilation of
drawings for the period from February 1835, to March 1836. Presently,
the P drawings are available only for one month, September 1835;
those of other periods have presumably been lost. Another drawing
(I ) lets us recover the raw group count (RGC) for 25 September 1836,
on which the RGC has not been registered in the existing catalogs. We
also revise the RGCs from P and S using the Zürich classification and
determine that Kunitomo's results tend to yield smaller RGCs than those
of other contemporary observers. In addition, we find that Kunitomo's
RGCs and spot areas have a correlation (0.71) that is not very different
from the contemporary observer Schwabe (0.82). Although Kunitomo's spot
areas are much larger than those determined by Schwabe due to skill and
instrument limitations, Kunitomo at least captured the growing trend
of the spot activity in the early phase of Solar Cycle 8. We also
determine the solar rotation axis to estimate the accurate position
(latitude and longitude) of the sunspot groups in Kunitomo's drawings.
Title: The extreme space weather event in September 1909
Authors: Hayakawa, Hisashi; Ebihara, Yusuke; Cliver, Edward W.;
Hattori, Kentaro; Toriumi, Shin; Love, Jeffrey J.; Umemura, Norio;
Namekata, Kosuke; Sakaue, Takahito; Takahashi, Takuya; Shibata,
Kazunari
Bibcode: 2019MNRAS.484.4083H
Altcode: 2018MNRAS.tmp.3046H
We evaluate worldwide low-latitude auroral activity associated with the
great magnetic storm of September 1909 for which a minimum Dst value
of -595 nT has recently been determined. From auroral observations,
we calculate that the equatorward boundary of the auroral oval in
the 1909 event was in the range from 31°-35° invariant latitude
(assuming auroral height of 400 km) to 37°-38° (800 km). These
locations compare with satellite-based observations of precipitating
auroral electrons down to 40° magnetic latitude for the March 1989
storm with its comparable minimum Dst value of -589 nT. According
to Japanese auroral records, bluish colour started to appear first,
followed by reddish colour. The colour change can be attributed to
the transition from sunlit aurora to the usual low-latitude reddish
aurora. Telegraph communications were disrupted at mid/low latitudes,
coincidently with the storm main phase and the early recovery
phase. The telegraphic disturbances were caused by geomagnetically
induced currents associated with the storm-time ring current and
substorm current wedge. From the calculated CME energy - based on the
24.75 hr separation between the flare-associated magnetic crochet
and the geomagnetic storm sudden commencement and interplanetary
conditions inferred from geomagnetic data - and consideration of the
∼-40 nT crochet amplitude, we estimated that the soft X-ray class
of the 24 September 1909 flare was ≥X10. As is the case for other
extreme storms, strong/sharp excursions in the horizontal component
of the magnetic field observed at low-latitude magnetic stations were
coincident with the observation of low-latitude aurora.
Title: Lifetimes and Emergence/Decay Rates of Star Spots on Solar-type
Stars Estimated by Kepler Data in Comparison with Those of Sunspots
Authors: Namekata, Kosuke; Maehara, Hiroyuki; Notsu, Yuta; Toriumi,
Shin; Hayakawa, Hisashi; Ikuta, Kai; Notsu, Shota; Honda, Satoshi;
Nogami, Daisaku; Shibata, Kazunari
Bibcode: 2019ApJ...871..187N
Altcode: 2018arXiv181110782N
Active solar-type stars show large quasi-periodic brightness variations
caused by stellar rotation with star spots, and the amplitude changes
as the spots emerge and decay. The Kepler data are suitable for
investigations of the emergence and decay processes of star spots,
which are important to understand the underlying stellar dynamo and
stellar flares. In this study, we measured the temporal evolution of
the star-spot area with Kepler data by tracing the local minima of the
light curves. In this analysis, we extracted the temporal evolution of
star spots showing clear emergence and decay without being disturbed
by stellar differential rotation. We applied this method to 5356
active solar-type stars observed by Kepler and obtained temporal
evolution of 56 individual star spots. We calculated the lifetimes
and emergence/decay rates of the star spots from the obtained temporal
evolution of the spot area. As a result, we found that the lifetimes
(T) of star spots range from 10 to 350 days when the spot areas (A)
are 0.1%-2.3% of the solar hemisphere. We also compared them with
sunspot lifetimes and found that the lifetimes of star spots are much
shorter than those extrapolated from an empirical relation of sunspots
(T ∝ A), while being consistent with other research on star-spot
lifetimes. The emergence and decay rates of star spots are typically 5
× 1020 Mx hr-1 (8 MSH hr-1) with an
area of 0.1%-2.3% of the solar hemisphere and mostly consistent with
those expected from sunspots, which may indicate the same underlying
processes.
Title: Solar Ultraviolet Bursts
Authors: Young, Peter R.; Tian, Hui; Peter, Hardi; Rutten, Robert J.;
Nelson, Chris J.; Huang, Zhenghua; Schmieder, Brigitte; Vissers, Gregal
J. M.; Toriumi, Shin; Rouppe van der Voort, Luc H. M.; Madjarska, Maria
S.; Danilovic, Sanja; Berlicki, Arkadiusz; Chitta, L. P.; Cheung, Mark
C. M.; Madsen, Chad; Reardon, Kevin P.; Katsukawa, Yukio; Heinzel, Petr
Bibcode: 2018SSRv..214..120Y
Altcode: 2018arXiv180505850Y
The term "ultraviolet (UV) burst" is introduced to describe small,
intense, transient brightenings in ultraviolet images of solar active
regions. We inventorize their properties and provide a definition
based on image sequences in transition-region lines. Coronal signatures
are rare, and most bursts are associated with small-scale, canceling
opposite-polarity fields in the photosphere that occur in emerging flux
regions, moving magnetic features in sunspot moats, and sunspot light
bridges. We also compare UV bursts with similar transition-region
phenomena found previously in solar ultraviolet spectrometry and
with similar phenomena at optical wavelengths, in particular Ellerman
bombs. Akin to the latter, UV bursts are probably small-scale magnetic
reconnection events occurring in the low atmosphere, at photospheric
and/or chromospheric heights. Their intense emission in lines with
optically thin formation gives unique diagnostic opportunities
for studying the physics of magnetic reconnection in the low solar
atmosphere. This paper is a review report from an International Space
Science Institute team that met in 2016-2017.
Title: Sunspot drawings by Japanese official astronomers in 1749-1750
Authors: Hayakawa, Hisashi; Iwahashi, Kiyomi; Fujiyama, Masashi;
Kawai, Toshiki; Toriumi, Shin; Hotta, Hideyuki; Iijima, Haruhisa;
Imada, Shinsuke; Tamazawa, Harufumi; Shibata, Kazunari
Bibcode: 2018PASJ...70...63H
Altcode: 2018arXiv180408614H; 2018PASJ..tmp...87H
Sunspot observations with telescopes in the 18th century
were carried out in Japan as well as elsewhere. One of these sunspot
observations is recorded in an account called Sansaizusetsu narabini
Kansei irai Jissoku Zusetsu (Charts of Three Worlds and Diagrams of
Actual Observations since Kansei Era). We have analyzed manuscripts
of this account to show a total of 15 sunspot drawings during
1749-1750. These observations are considered to be carried out by
contemporary official astronomers in Japan, with telescopes covered
by zongurasus (< zonglas in Dutch, corresponding to "sunglass"
in English). We counted their group number of sunspots to locate
them in long-term solar activity and show that their observations
were situated near the solar maximum in 1750. We also computed their
locations and areas, while we have to admit differences of the variant
manuscripts with one another. These observational records show the
spread of sunspot observations not only in Europe, but also in Japan,
and hence may contribute to crosscheck, or possibly to improve the
known sunspot indices.
Title: The Great Space Weather Event during 1872 February Recorded
in East Asia
Authors: Hayakawa, Hisashi; Ebihara, Yusuke; Willis, David M.; Hattori,
Kentaro; Giunta, Alessandra S.; Wild, Matthew N.; Hayakawa, Satoshi;
Toriumi, Shin; Mitsuma, Yasuyuki; Macdonald, Lee T.; Shibata, Kazunari;
Silverman, Sam M.
Bibcode: 2018ApJ...862...15H
Altcode: 2018arXiv180705186H
The study of historical great geomagnetic storms is crucial for
assessing the possible risks to the technological infrastructure of
a modern society, caused by extreme space-weather events. The normal
benchmark has been the great geomagnetic storm of 1859 September, the
so-called “Carrington Event.” However, there are numerous records
of another great geomagnetic storm in 1872 February. This storm,
which occurred about 12 years after the Carrington Event, resulted in
comparable magnetic disturbances and auroral displays over large areas
of the Earth. We have revisited this great geomagnetic storm in terms
of the auroral and sunspot records in historical documents from East
Asia. In particular, we have surveyed the auroral records from East Asia
and estimated the equatorward boundary of the auroral oval to be near
24.°2 invariant latitude, on the basis that the aurora was seen near
the zenith at Shanghai (20° magnetic latitude, MLAT). These results
confirm that this geomagnetic storm of 1872 February was as extreme as
the Carrington Event, at least in terms of the equatorward motion of
the auroral oval. Indeed, our results support the interpretation of the
simultaneous auroral observations made at Bombay (10° MLAT). The East
Asian auroral records have indicated extreme brightness, suggesting
unusual precipitation of high-intensity, low-energy electrons during
this geomagnetic storm. We have compared the duration of the East
Asian auroral displays with magnetic observations in Bombay and found
that the auroral displays occurred in the initial phase, main phase,
and early recovery phase of the magnetic storm.
Title: Flare-productive Active Regions: Observations, Modeling,
and their Applications
Authors: Toriumi, Shin
Bibcode: 2018cosp...42E3413T
Altcode:
Strong solar flares and coronal mass ejections are known to occur in
complex active regions (ARs). Then, what kind of AR structures are
important for producing these events, and how can we model them? This
review talk aims at answering to these questions. First, we introduce
the statistical analysis on various flare-productive ARs, in which we
investigated all >M5.0-class events within 45 deg from disk center
for six years from May 2010. We classified the total of 51 events
into four categories based on their formation processes, namely, (1)
Spot-Spot, a complex AR with AR-sized polarity inversion lines (PILs),
(2) Spot-Satellite, in which a newly-emerging flux appears adjacent
to the pre-existing spot, (3) Quadrupole, where two emerging fields
collide against each other, and (4) Inter-AR, the flares occurring
between two apparently separated ARs. As a result, we found that the
characteristics of the flare eruptions strongly depend on the groups;
for example, the flare duration of the majority group (1) is four times
longer than that of another majority group (2). Second, we show the
numerical attempt to model various flaring ARs, where we reproduced
these four types (1-4) by conducting a series of flux-emergence
simulations. We found that the sheared PILs in these ARs are created
through the stretching and advection of horizontal magnetic fields
due to the large-scale flux emergence. As ARs develop, free magnetic
energy becomes stored in the corona, which could be released through
the flare eruptions. Finally, we explore the possibility to apply these
works to some particular ARs by introducing our newest work on NOAA AR
12673, which appeared in September 2017 and produced numerous strong
flares including the X9.3-class event. We show the numerical modeling
of AR 12673 and comparison with observations, discussing the possible
magnetic structures in the subsurface layers that eventually led to
the series of strong flares in this AR.
Title: Study of 3D magnetic Structure Corresponding to Extremely
Strong Photospheric Magnetic Fields in Active Region 12673
Authors: Wang, Haimin; Yurchyshyn, Vasyl; Liu, Chang; Chen, Bin;
Jing, Ju; Ahn, Kwangsu; Toriumi, Shin; Cao, Wenda
Bibcode: 2018tess.conf31902W
Altcode:
Solar Active Region (AR) 12673 is the most flare productive AR in the
solar cycle 24. It produced four X-class flares including the X9.3 flare
on 06 September 2017 and the X8.2 limb event on 10 September. Sun and
Norton (2017) reported that this region had an unusual high rate of
flux emergence, while Huang et al. (2018) reported that the X9.3 flare
had extremely strong white-light flare emission. Yang et al. (2017)
described the detailed morphological evolution of this AR. In this work,
we first study the unusual behaviors of the light bridge (LB) dividing
the delta configuration of this AR, namely the strong magnetic fields
(above 5500 G) in the LB and the apparent photospheric twist as seen in
observations with a 0.1 arcsec spatial resolution obtained by the 1.6m
Goode Solar Telescope (GST) at the Big Bear Solar Observatory. Using the
newly commissioned Expanded Owens Valley Solar Array (EOVSA), we carried
out diagnoses of magnetic fields in this AR with microwave imaging
spectroscopy from 2.5 to 18 GHz. Finally, we utilized Non-Linear Force
Free Field (NLFFF) extrapolation to reveal 3-D magnetic structure to
gain a physical understanding of GST and EOVSA observations of this AR.
Title: Strong Transverse Photosphere Magnetic Fields and Twist in
Light Bridge Dividing Delta Sunspot of Active Region 12673
Authors: Wang, Haimin; Yurchyshyn, Vasyl; Liu, Chang; Ahn, Kwangsu;
Toriumi, Shin; Cao, Wenda
Bibcode: 2018RNAAS...2....8W
Altcode: 2018RNAAS...2a...8W; 2018arXiv180102928W
Solar Active Region (AR) 12673 is the most flare productive AR in the
solar cycle 24. It produced four X-class flares including the X9.3 flare
on 06 September 2017 and the X8.2 limb event on 10 September. Sun and
Norton (2017) reported that this region had an unusual high rate of
flux emergence, while Huang et al. (2018) reported that the X9.3 flare
had extremely strong white-light flare emissions. Yang at al. (2017)
described the detailed morphological evolution of this AR. In this
report, we focus on usual behaviors of the light bridge (LB) dividing
the delta configuration of this AR, namely the strong magnetic fields
(above 5500 G) in the LB and apparent photospheric twist as shown in
observations with a 0.1 arcsec spatial resolution obtained by the 1.6m
telescope at Big Bear Solar Observatory.
Title: Iwahashi Zenbei's Sunspot Drawings in 1793 in Japan
Authors: Hayakawa, Hisashi; Iwahashi, Kiyomi; Tamazawa, Harufumi;
Toriumi, Shin; Shibata, Kazunari
Bibcode: 2018SoPh..293....8H
Altcode: 2017arXiv171108143H
Three Japanese sunspot drawings associated with Iwahashi Zenbei (1756
- 1811) are shown here from contemporary manuscripts and woodprint
documents with the relevant texts. We reveal the observational date of
one of the drawings to be 26 August 1793, and the overall observations
lasted for over a year. Moreover, we identify the observational site
for the dated drawing as Fushimi in Japan. We then compare Zenbei's
observations with the group sunspot number and the raw group count
from the Sunspot Index and Long-term Solar Observations (SILSO) to
reveal the context of the data, and we conclude that these drawings
fill gaps in our understanding that are due to the fragmental sunspot
observations around 1793. These drawings are important as a clue to
evaluate astronomical knowledge of contemporary Japan in the late
eighteenth century and are valuable as a non-European observation,
considering that most sunspot observations up to the middle of the
nineteenth century are from Europe.
Title: The Direct Relation between the Duration of Magnetic
Reconnection and the Evolution of GOES Light Curves in Solar Flares
Authors: Reep, Jeffrey W.; Toriumi, Shin
Bibcode: 2017ApJ...851....4R
Altcode: 2017arXiv171100422R
GOES soft X-ray light curves are used to measure the timing and
duration of solar flare emission. The timing and duration of the
magnetic reconnection and subsequent energy release that drive solar
flares are unknown, though the light curves are presumably related. It
is therefore critical to understand the physics that connect the two:
how does the timescale of reconnection produce an observed GOES light
curve? In this work, we model the formation and expansion of an arcade
of loops with a hydrodynamic model, which we then use to synthesize
GOES light curves. We calculate the FWHM and the e-folding decay time
of the light curves and compare them to the separation of the centroids
of the two ribbons that the arcade spans, which is representative of
the size scale of the loops. We reproduce a linear relation between
the two, as found observationally in previous work. We show that this
demonstrates a direct connection between the duration of energy release
and the evolution of these light curves. We also show that the cooling
processes of individual loops comprising the flare arcade directly
affect the measured timescales. From the clear consistency between the
observed and modeled linearity, we conclude that the primary factors
that control the flare timescales are the duration of reconnection
and the loop lengths.
Title: Numerical Modeling of Flare-productive Active Regions of
the Sun
Authors: Toriumi, S.; Takasao, S.
Bibcode: 2017AGUFMSH43C..07T
Altcode:
It is known that strong flare events on the Sun take place in active
regions (ARs), especially in delta sunspots with closely-packed positive
and negative polarities. The delta spots are produced as a result of
complex magnetic flux emergence and have strong-field, highly-sheared
polarity inversion lines (PILs). Here we report on the numerical
simulations of four types of such flare-productive ARs, namely, (1)
Spot-Spot, a complex AR with AR-sized PIL, (2) Spot-Satellite, in which
a newly-emerging bipole appears next to the pre-existing sunspot,
(3) Quadrupole, where two emerging bipoles collide against each
other, and (4) Inter-AR, the flares occurring between two separated
ARs. We reproduced these four cases by conducting a series of 3D MHD
flux emergence simulations and found, for example, that the sheared
PILs in these ARs are created through the stretching and advection
of horizontal magnetic fields due to relative spot motions. As ARs
develop, free magnetic energy becomes stored in the corona, which could
be eventually released through flare eruptions. In the presentation,
we also mention the relationship between the HMI/SHARP parameters
measured in the photosphere and the free energy stored in the corona,
and discuss why these parameters successfully predict the flares.
Title: Numerical Simulations of Flare-productive Active Regions:
δ-sunspots, Sheared Polarity Inversion Lines, Energy Storage,
and Predictions
Authors: Toriumi, Shin; Takasao, Shinsuke
Bibcode: 2017ApJ...850...39T
Altcode: 2017arXiv171008926T
Solar active regions (ARs) that produce strong flares and coronal mass
ejections (CMEs) are known to have a relatively high non-potentiality
and are characterized by δ-sunspots and sheared magnetic structures. In
this study, we conduct a series of flux emergence simulations from the
convection zone to the corona and model four types of active regions
that have been observationally suggested to cause strong flares, namely
the spot-spot, spot-satellite, quadrupole, and inter-AR cases. As
a result, we confirm that δ-spot formation is due to the complex
geometry and interaction of emerging magnetic fields, and we find that
the strong-field, high-gradient, highly sheared polarity inversion line
(PIL) is created by the combined effect of the advection, stretching,
and compression of magnetic fields. We show that free magnetic energy
builds up in the form of a current sheet above the PIL. It is also
revealed that photospheric magnetic parameters that predict flare
eruptions reflect the stored free energy with high accuracy, while
CME-predicting parameters indicate the magnetic relationship between
flaring zones and entire ARs.
Title: MHD simulations of formation and eruption of a magnetic flux
rope in an active region with a delta-sunspot
Authors: Yokoyama, Takaaki; Oi, Yoshiaki; Toriumi, Shin
Bibcode: 2017SPD....4840002Y
Altcode:
Active regions holding a delta-sunspot are known to produce the largest
class of solar flares. How, where, and when such large flares occur
above a delta-sunspot are still under debate. For studying this,
3D MHD simulations of the emergence of a subsurface flux tube at two
locations in a simulation box modeling the convection zone to the corona
were conducted. We found that a flux rope is formed as a consequence
of magnetic reconnection of two bipolar loops and sunspot rotation
caused by the twist of the subsurface flux tube. Moreover, the flux
rope stops ascending when the initial background is not magnetized,
whereas it rises up to the upper boundary when a reconnection favorably
oriented pre-existing field is introduced to the initial background.
Title: Magnetic Properties of Solar Active Regions that Govern Large
Solar Flares and Eruptions
Authors: Toriumi, Shin; Schrijver, Carolus J.; Harra, Louise; Hudson,
Hugh S.; Nagashima, Kaori
Bibcode: 2017SPD....4820001T
Altcode:
Strong flares and CMEs are often produced from active regions (ARs). In
order to better understand the magnetic properties and evolutions of
such ARs, we conducted statistical investigations on the SDO/HMI and
AIA data of all flare events with GOES levels >M5.0 within 45 deg
from the disk center for 6 years from May 2010 (from the beginning to
the declining phase of solar cycle 24). Out of the total of 51 flares
from 29 ARs, more than 80% have delta-sunspots and about 15% violate
Hale’s polarity rule. We obtained several key findings including
(1) the flare duration is linearly proportional to the separation
of the flare ribbons (i.e., scale of reconnecting magnetic fields)
and (2) CME-eruptive events have smaller sunspot areas. Depending on
the magnetic properties, flaring ARs can be categorized into several
groups, such as spot-spot, in which a highly-sheared polarity inversion
line is formed between two large sunspots, and spot-satellite, where a
newly-emerging flux next to a mature sunspot triggers a compact flare
event. These results point to the possibility that magnetic structures
of the ARs determine the characteristics of flares and CMEs. In the
presentation, we will also show new results from the systematic flux
emergence simulations of delta-sunspot formation and discuss the
evolution processes of flaring ARs.
Title: Photospheric Velocity Structures during the Emergence of
Small Active Regions on the Sun
Authors: Khlystova, Anna; Toriumi, Shin
Bibcode: 2017ApJ...839...63K
Altcode: 2017arXiv170402482K
We study the plasma flows in the solar photosphere during the
emergence of two small active regions, NOAA 9021 and 10768. Using
Solar and Heliospheric Observatory/Michelson Doppler Imager data,
we find that the strong plasma upflows appear at the initial stage of
active region formation, with maximum upflow velocities of -1650 and
-1320 m s-1. The structures with enhanced upflows have size
∼8 Mm in diameter, and they exist for 1-2 hr. The parameters of the
enhanced upflows are consistent with those of the large active region
NOAA 10488, which may suggest the possibility that the elementary
emerging magnetic loops that appear at the earliest phase of active
region formation have similar properties, irrespective of scales of
active regions. Comparison between the observations and a numerical
simulation of magnetic flux emergence shows a striking consistency. We
find that the driving force of the plasma upflow is at first the gas
pressure gradient and later the magnetic pressure gradient.
Title: Various Local Heating Events in the Earliest Phase of Flux
Emergence
Authors: Toriumi, Shin; Katsukawa, Yukio; Cheung, Mark C. M.
Bibcode: 2017ApJ...836...63T
Altcode: 2017arXiv170101446T
Emerging flux regions (EFRs) are known to exhibit various sporadic
local heating events in the lower atmosphere. To investigate the
characteristics of these events, especially to link the photospheric
magnetic fields and atmospheric dynamics, we analyze Hinode, Interface
Region Imaging Spectrograph (IRIS), and Solar Dynamics Observatory
data of a new EFR in NOAA AR 12401. Out of 151 bright points (BPs)
identified in Hinode/SOT Ca images, 29 are overlapped by an SOT/SP
scan. Seven BPs in the EFR center possess mixed-polarity magnetic
backgrounds in the photosphere. Their IRIS UV spectra (e.g., Si IV
1402.8 Å) are strongly enhanced and red- or blueshifted, with tails
reaching +/- 150 {km} {{{s}}}-1, which is highly suggestive
of bi-directional jets; each brightening lasts for 10-15 minutes,
leaving flare-like light curves. Most of this group show bald patches,
the U-shaped photospheric magnetic loops. Another 10 BPs are found in
unipolar regions at the EFR edges. They are generally weaker in UV
intensities and exhibit systematic redshifts with Doppler speeds up
to 40 {km} {{{s}}}-1, which could exceed the local sound
speed in the transition region. Both types of BPs show signs of strong
temperature increase in the low chromosphere. These observational
results support the physical picture that heating events in the EFR
center are due to magnetic reconnection within cancelling undular
fields like Ellerman bombs, while the peripheral heating events are
due to shocks or strong compressions caused by fast downflows along
the overlying arch filament system.
Title: Flare-productive active regions: magnetic properties and
evolutions
Authors: Toriumi, Shin
Bibcode: 2017psio.confE..41T
Altcode:
No abstract at ADS
Title: Magnetic Properties of Solar Active Regions That Govern Large
Solar Flares and Eruptions
Authors: Toriumi, Shin; Schrijver, Carolus J.; Harra, Louise K.;
Hudson, Hugh; Nagashima, Kaori
Bibcode: 2017ApJ...834...56T
Altcode: 2016arXiv161105047T
Solar flares and coronal mass ejections (CMEs), especially the larger
ones, emanate from active regions (ARs). With the aim of understanding
the magnetic properties that govern such flares and eruptions, we
systematically survey all flare events with Geostationary Orbiting
Environmental Satellite levels of ≥M5.0 within 45° from disk center
between 2010 May and 2016 April. These criteria lead to a total of 51
flares from 29 ARs, for which we analyze the observational data obtained
by the Solar Dynamics Observatory. More than 80% of the 29 ARs are found
to exhibit δ-sunspots, and at least three ARs violate Hale’s polarity
rule. The flare durations are approximately proportional to the distance
between the two flare ribbons, to the total magnetic flux inside the
ribbons, and to the ribbon area. From our study, one of the parameters
that clearly determine whether a given flare event is CME-eruptive
or not is the ribbon area normalized by the sunspot area, which may
indicate that the structural relationship between the flaring region
and the entire AR controls CME productivity. AR characterization shows
that even X-class events do not require δ-sunspots or strong-field,
high-gradient polarity inversion lines. An investigation of historical
observational data suggests the possibility that the largest solar
ARs, with magnetic flux of 2 × 1023 Mx, might be able to
produce “superflares” with energies of the order of 1034
erg. The proportionality between the flare durations and magnetic
energies is consistent with stellar flare observations, suggesting a
common physical background for solar and stellar flares.
Title: Properties and Developments of Flaring Active Regions
Authors: Toriumi, Shin; Schrijver, Carolus J.; Harra, Louise K.;
Hudson, Hugh; Nagashima, Kaori
Bibcode: 2016usc..confE..15T
Altcode:
Larger flares and CMEs are often produced from active regions (ARs). In
order to better understand the magnetic properties and evolutions
of such ARs, we picked up all flare events with GOES levels >M5.0
with heliocentric angles of <45 deg in the period of May 2010 to
April 2016, which led to a total of 29 ARs with 51 flares. We analyzed
the observational data obtained by SDO and found that more than 80%
of the 29 ARs have delta-sunspots. Most of them can be classified
depending on their magnetic structures into (1) spot-spot, where a long
sheared polarity inversion line (PIL: characterized by flare ribbons)
is formed between two major sunspots, and (2) spot-satellite, where
a newly-emerging minor bipole next to a pre-existing spot creates a
compact PIL. The remaining minor groups are (3) quadrupole, where two
emerging bipoles produce a PIL in between, and (4) inter-AR, which
produces flares not from delta-spots but from between two separated
ARs. From statistical investigations we found for example that the
spot-spot group generally shows long-duration events due to large
coronal structures, while the spot-satellite has impulsive events
because of their compact magnetic nature. We will also present flux
emergence simulations and discuss their formation processes.
Title: The Characteristics of Solar X-Class Flares and CMEs: A
Paradigm for Stellar Superflares and Eruptions?
Authors: Harra, Louise K.; Schrijver, Carolus J.; Janvier, Miho;
Toriumi, Shin; Hudson, Hugh; Matthews, Sarah; Woods, Magnus M.; Hara,
Hirohisa; Guedel, Manuel; Kowalski, Adam; Osten, Rachel; Kusano,
Kanya; Lueftinger, Theresa
Bibcode: 2016SoPh..291.1761H
Altcode: 2016SoPh..tmp..111H
This paper explores the characteristics of 42 solar X-class flares that
were observed between February 2011 and November 2014, with data from
the Solar Dynamics Observatory (SDO) and other sources. This flare
list includes nine X-class flares that had no associated CMEs. In
particular our aim was to determine whether a clear signature could
be identified to differentiate powerful flares that have coronal
mass ejections (CMEs) from those that do not. Part of the motivation
for this study is the characterization of the solar paradigm for
flare/CME occurrence as a possible guide to the stellar observations;
hence we emphasize spectroscopic signatures. To do this we ask the
following questions: Do all eruptive flares have long durations? Do
CME-related flares stand out in terms of active-region size vs. flare
duration? Do flare magnitudes correlate with sunspot areas, and, if so,
are eruptive events distinguished? Is the occurrence of CMEs related to
the fraction of the active-region area involved? Do X-class flares with
no eruptions have weaker non-thermal signatures? Is the temperature
dependence of evaporation different in eruptive and non-eruptive
flares? Is EUV dimming only seen in eruptive flares? We find only one
feature consistently associated with CME-related flares specifically:
coronal dimming in lines characteristic of the quiet-Sun corona,
i.e. 1 - 2 MK. We do not find a correlation between flare magnitude
and sunspot areas. Although challenging, it will be of importance to
model dimming for stellar cases and make suitable future plans for
observations in the appropriate wavelength range in order to identify
stellar CMEs consistently.
Title: Light Bridge in a Developing Active Region. II. Numerical
Simulation of Flux Emergence and Light Bridge Formation
Authors: Toriumi, Shin; Cheung, Mark C. M.; Katsukawa, Yukio
Bibcode: 2015ApJ...811..138T
Altcode: 2015arXiv150900205T
Light bridges, the bright structure dividing umbrae in sunspot regions,
show various activity events. In Paper I, we reported on an analysis
of multi-wavelength observations of a light bridge in a developing
active region (AR) and concluded that the activity events are caused
by magnetic reconnection driven by magnetconvective evolution. The
aim of this second paper is to investigate the detailed magnetic and
velocity structures and the formation mechanism of light bridges. For
this purpose, we analyze numerical simulation data from a radiative
magnetohydrodynamics model of an emerging AR. We find that a weakly
magnetized plasma upflow in the near-surface layers of the convection
zone is entrained between the emerging magnetic bundles that appear
as pores at the solar surface. This convective upflow continuously
transports horizontal fields to the surface layer and creates a light
bridge structure. Due to the magnetic shear between the horizontal
fields of the bridge and the vertical fields of the ambient pores,
an elongated cusp-shaped current layer is formed above the bridge,
which may be favorable for magnetic reconnection. The striking
correspondence between the observational results of Paper I and the
numerical results of this paper provides a consistent physical picture
of light bridges. The dynamic activity phenomena occur as a natural
result of the bridge formation and its convective nature, which has
much in common with those of umbral dots and penumbral filaments.
Title: Light Bridge in a Developing Active Region. I. Observation
of Light Bridge and its Dynamic Activity Phenomena
Authors: Toriumi, Shin; Katsukawa, Yukio; Cheung, Mark C. M.
Bibcode: 2015ApJ...811..137T
Altcode: 2015arXiv150900183T
Light bridges, the bright structures that divide the umbra of sunspots
and pores into smaller pieces, are known to produce a wide variety
of activity events in solar active regions (ARs). It is also known
that the light bridges appear in the assembling process of nascent
sunspots. The ultimate goal of this series of papers is to reveal
the nature of light bridges in developing ARs and the occurrence of
activity events associated with the light bridge structures from
both observational and numerical approaches. In this first paper,
exploiting the observational data obtained by Hinode, the Interface
Region Imaging Spectrograph, and the Solar Dynamics Observatory, we
investigate the detailed structure of the light bridge in NOAA AR 11974
and its dynamic activity phenomena. As a result, we find that the light
bridge has a weak, horizontal magnetic field, which is transported from
the interior by a large-scale convective upflow and is surrounded by
strong, vertical fields of adjacent pores. In the chromosphere above the
bridge, a transient brightening occurs repeatedly and intermittently,
followed by a recurrent dark surge ejection into higher altitudes. Our
analysis indicates that the brightening is the plasma heating due
to magnetic reconnection at lower altitudes, while the dark surge is
the cool, dense plasma ejected from the reconnection region. From the
observational results, we conclude that the dynamic activity observed
in a light bridge structure such as chromospheric brightenings and dark
surge ejections are driven by magnetoconvective evolution within the
light bridge and its interaction with the surrounding magnetic fields.
Title: Observations and modeling of the solar flux emergence
Authors: Toriumi, Shin
Bibcode: 2014PASJ...66S...6T
Altcode: 2014PASJ..tmp..105T
In a wide variety of magnetic activity phenomena occurring in the Sun,
flux emergence is one of the most prominent events. It is important
to study flux emergence since this is the process that transports
the magnetic flux from the deep interior to the upper atmosphere,
creates active regions, and sometimes causes catastrophic flaring
eruptions. Recent observations have revealed that flux emergence ranges
from the formation of large-scale active regions including sunspots to
small-scale events observable only with advanced instruments, covering
a very broad spectrum of scale involved. In addition, helioseismology
may allow us to investigate the process even before the flux itself
appears at the visible surface of the Sun. At the same time, recent
development in the numerical modeling of flux emergence opens the door
to a further understanding of physical processes, such as resistive and
convective emergence. In this paper, we review the observational and
numerical progress in the field of flux emergence study, while focusing
particularly on three important aspects: emergence in the interior,
the first appearance in the surface layer, and their relation with
flaring activity. Based on these studies, we also discuss what should
be investigated in the future.
Title: Statistical Analysis of the Horizontal Divergent Flow in
Emerging Solar Active Regions
Authors: Toriumi, Shin; Hayashi, Keiji; Yokoyama, Takaaki
Bibcode: 2014ApJ...794...19T
Altcode: 2014arXiv1408.2383T
Solar active regions (ARs) are thought to be formed by magnetic fields
from the convection zone. Our flux emergence simulations revealed that
a strong horizontal divergent flow (HDF) of unmagnetized plasma appears
at the photosphere before the flux begins to emerge. In our earlier
study, we analyzed HMI data for a single AR and confirmed presence of
this precursor plasma flow in the actual Sun. In this paper, as an
extension of our earlier study, we conducted a statistical analysis
of the HDFs to further investigate their characteristics and better
determine the properties. From SDO/HMI data, we picked up 23 flux
emergence events over a period of 14 months, the total flux of which
ranges from 1020 to 1022 Mx. Out of 23 selected
events, 6 clear HDFs were detected by the method we developed in our
earlier study, and 7 HDFs detected by visual inspection were added
to this statistic analysis. We found that the duration of the HDF is
on average 61 minutes and the maximum HDF speed is on average 3.1 km
s-1. We also estimated the rising speed of the subsurface
magnetic flux to be 0.6-1.4 km s-1. These values are
highly consistent with our previous one-event analysis as well as our
simulation results. The observation results lead us to the conclusion
that the HDF is a rather common feature in the earliest phase of AR
emergence. Moreover, our HDF analysis has the capability of determining
the subsurface properties of emerging fields that cannot be directly
measured.
Title: Formation of a Flare-Productive Active Region: Observation
and Numerical Simulation of NOAA AR 11158
Authors: Toriumi, S.; Iida, Y.; Kusano, K.; Bamba, Y.; Imada, S.
Bibcode: 2014SoPh..289.3351T
Altcode: 2014SoPh..tmp...40T; 2014arXiv1403.4029T
We present a comparison of the Solar Dynamics Observatory (SDO)
analysis of NOAA Active Region (AR) 11158 and numerical simulations
of flux-tube emergence, aiming to investigate the formation process of
this flare-productive AR. First, we use SDO/Helioseismic and Magnetic
Imager (HMI) magnetograms to investigate the photospheric evolution and
Atmospheric Imaging Assembly (AIA) data to analyze the relevant coronal
structures. Key features of this quadrupolar region are a long sheared
polarity inversion line (PIL) in the central δ-sunspots and a coronal
arcade above the PIL. We find that these features are responsible for
the production of intense flares, including an X2.2-class event. Based
on the observations, we then propose two possible models for the
creation of AR 11158 and conduct flux-emergence simulations of the two
cases to reproduce this AR. Case 1 is the emergence of a single flux
tube, which is split into two in the convection zone and emerges at two
locations, while Case 2 is the emergence of two isolated but neighboring
tubes. We find that, in Case 1, a sheared PIL and a coronal arcade are
created in the middle of the region, which agrees with the AR 11158
observation. However, Case 2 never builds a clear PIL, which deviates
from the observation. Therefore, we conclude that the flare-productive
AR 11158 is, between the two cases, more likely to be created from a
single split emerging flux than from two independent flux bundles.
Title: Flux emergence and formation of a flare-productive active
region
Authors: Toriumi, Shin; Kusano, Kanya; Bamba, Yumi; Imada, Shinsuke;
Iida, Yusuke
Bibcode: 2014cosp...40E3375T
Altcode:
We present a comparison of the SDO observation of NOAA Active Region
(AR) 11158 and numerical simulations, aiming to investigate the flux
emergence and the resultant formation of a flare-productive AR. First,
we use SDO/HMI magnetograms to investigate the emerging flux events
in the photosphere and AIA data to analyze the corresponding coronal
EUV evolutions. Key features of this quadrupolar region are a long
sheared polarity inversion line (PIL) in the central delta-sunspots
and a coronal arcade. We find that these features are responsible
for the production of a series of intense flares including X-
and M-class events. Based on the observations, we then propose two
possible scenarios for the creation of AR 11158 and conduct flux
emergence simulations of the two cases to reproduce this AR. Case
1 is the emergence of a single flux tube, which is split into two
in the convection zone and emerges at two locations, while Case 2
is the emergence of two isolated, but neighboring, flux tubes. We
find that, in Case 1, a sheared PIL and a coronal arcade are created
in the middle of the region, which agrees well with the AR 11158
observation. However, Case 2 never build a clear PIL, which deviates
from the observation. Therefore, we conclude that the flare-productive
AR 11158 is, between the two models, more likely to be created from
a single split emerging flux than two independent flux bundles.
Title: The Magnetic Systems Triggering the M6.6 Class Solar Flare
in NOAA Active Region 11158
Authors: Toriumi, Shin; Iida, Yusuke; Bamba, Yumi; Kusano, Kanya;
Imada, Shinsuke; Inoue, Satoshi
Bibcode: 2013ApJ...773..128T
Altcode: 2013arXiv1306.2451T
We report a detailed event analysis of the M6.6 class flare in the
active region (AR) NOAA 11158 on 2011 February 13. AR 11158, which
consisted of two major emerging bipoles, showed prominent activity
including one X- and several M-class flares. In order to investigate
the magnetic structures related to the M6.6 event, particularly the
formation process of a flare-triggering magnetic region, we analyzed
multiple spacecraft observations and numerical results of a flare
simulation. We observed that, in the center of this quadrupolar AR,
a highly sheared polarity inversion line (PIL) was formed through
proper motions of the major magnetic elements, which built a sheared
coronal arcade lying over the PIL. The observations lend support
to the interpretation that the target flare was triggered by a
localized magnetic region that had an intrusive structure, namely,
a positive polarity penetrating into a negative counterpart. The
geometrical relationship between the sheared coronal arcade and the
triggering region is consistent with the theoretical flare model based
on the previous numerical study. We found that the formation of the
trigger region was due to the continuous accumulation of small-scale
magnetic patches. A few hours before the flare occurred, the series of
emerged/advected patches reconnected with a pre-existing field. Finally,
the abrupt flare eruption of the M6.6 event started around 17:30 UT. Our
analysis suggests that in the process of triggering flare activity,
all magnetic systems on multiple scales are included, not only the
entire AR evolution but also the fine magnetic elements.
Title: Probing the Shallow Convection Zone: Rising Motion of
Subsurface Magnetic Fields in the Solar Active Region
Authors: Toriumi, Shin; Ilonidis, Stathis; Sekii, Takashi; Yokoyama,
Takaaki
Bibcode: 2013ApJ...770L..11T
Altcode: 2013arXiv1305.3023T
In this Letter, we present a seismological detection of a rising motion
of magnetic flux in the shallow convection zone of the Sun, and show
estimates of the emerging speed and its decelerating nature. In order to
evaluate the speed of subsurface flux that creates an active region, we
apply six Fourier filters to the Doppler data of NOAA AR 10488, observed
with the Solar and Heliospheric Observatory/Michelson Doppler Imager,
to detect the reduction of acoustic power at six different depths from
-15 to -2 Mm. All the filtered acoustic powers show reductions, up to 2
hr before the magnetic flux first appears at the visible surface. The
start times of these reductions show a rising trend with a gradual
deceleration. The obtained velocity is first several km s-1
in a depth range of 15-10 Mm, then ~1.5 km s-1 at 10-5 Mm,
and finally ~0.5 km s-1 at 5-2 Mm. If we assume that the
power reduction is actually caused by the magnetic field, the velocity
of the order of 1 km s-1 is well in accordance with previous
observations and numerical studies. Moreover, the gradual deceleration
strongly supports the theoretical model that the emerging flux slows
down in the uppermost convection zone before it expands into the
atmosphere to build an active region.
Title: Three-dimensional magnetohydrodynamic simulation of the
solar magnetic flux emergence. Parametric study on the horizontal
divergent flow
Authors: Toriumi, S.; Yokoyama, T.
Bibcode: 2013A&A...553A..55T
Altcode: 2013arXiv1303.4793T
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.
Title: M6.6 Flare in NOAA AR 11158: Formation of the Flare-triggering
Region
Authors: Toriumi, S.; Iida, Y.; Bamba, Y.; Kusano, K.; Inoue, S.
Bibcode: 2013enss.confE..26T
Altcode:
In this study, we investigate the formation process of the magnetic
field structure in NOAA AR 11158 from its birth to the M6.6 flare,
which occurred at 17:28 UT on 2011 February 13. AR 11158, which
consisted of two major emerging fluxes, showed prominent activities
including one X-class and some M-class flares. Here we report that the
magnetic configuration that triggered the M6.6 flare is consistent
with the Reversed-Shear (RS) type structure, one scenario suggested
by Kusano et al. (2012). We used CaH images and spectropolarization
data obtained by Hinode/SOT, 3D magnetograms by SDO/HMI to study
the formation process of this flare-triggering region. We found that
this region was initially built through the continuous accumulation
of small-scale emerging bipoles. In CaH images, the emerging bipole
collided with the pre-existing field and, through magnetic reconnection,
they created a new loop arching over the both polarities, which had
an RS configuration. The M-flare occurred a few hours later above
this region.
Title: Helioseismic Detection of the Pre-emerging Magnetic Flux in
the Shallow Convection Zone
Authors: Toriumi, S.; Ilonidis, S.; Sekii, T.; Yokoyama, T.
Bibcode: 2013enss.confE..25T
Altcode:
We detect the rising magnetic flux in the shallower convection zone
of the Sun by observing acoustic power reduction, and evaluate its
rising speed. Here we aim to reveal the rising speed of the magnetic
flux in the shallow convection zone, before the active region are
created. We apply six different Fourier filters to the Doppler data of
NOAA AR 10488 taken by SOHO/MDI, to detect the reduction of acoustic
power at six different depths from -15 to -2 Mm. The filtered powers
show reductions before the start of flux appearance at the visible
surface. The start times of these reductions show a rising trend,
first at several km/s in a depth range of 15-10 Mm, then ∼1.5 km/s
at 10-5 Mm, and finally at ∼0.5 km/s at 5-2 Mm. If we assume that
the power reduction is actually caused by the rising magnetic flux,
the rising rate of the order of 1 km/s is well in accordance with
previous observations and numerical simulations. Moreover, the gradual
deceleration supports our simulations and theoretical model that the
rising flux slows down in the uppermost convection zone, just before
its further emergence into the solar atmosphere.
Title: Magnetic Field Structures Triggering Solar Eruptions
Authors: Kusano, K.; Bamba, Y.; Yamamoto, T. T.; Iida, Y.; Toriumi,
S.; Asai, A.
Bibcode: 2012AGUFMSH53B..04K
Altcode:
Although various models have been proposed to determine the onset of
solar eruptions, the types of magnetic structures capable of triggering
the 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 ensemble numerical simulation
based on three-dimensional magnetohydrodynamic model. As a result,
we determined that two different types of small magnetic structures
favor the onset of solar eruptions. These structures include magnetic
fluxes reversed to the potential component or the nonpotential component
of major field on the polarity inversion line. In addition, we analyzed
two large flares, the X-class flare on December 13, 2006 and the M-class
flare on February 13, 2011, 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 time scale of changes in
the small magnetic structures. We also discuss about why two different
magnetic structures are capable of triggering the eruptions from the
perspective of magnetic topology.
Title: Flare Triggering Region of NOAA AR11158
Authors: Toriumi, S.; Iida, Y.; Bamba, Y.; Kusano, K.; Inoue, S.
Bibcode: 2012AGUFMSH51A2205T
Altcode:
We investigate the evolution of magnetic structure of NOAA AR 11158
and the corresponding M6.6 flare occurred on February 13, 2011. Solar
flare, a large energy release in the solar outer atmosphere, has a
great influence on the geosphere. Spatially- and temporally-resolved
observational data have been obtained by the recently-launched
satellites Hinode and Solar Dynamics Observatory (SDO). The solar
activity started to rise again in 2011 and a lot of flare data are
now going to be accumulated. NOAA AR 11158 emerged on the solar
surface on February, 2011. It produced a lot of flares including
X-class one. Hinode and SDO observed this region in detail from its
emergence. Spectro-polarimetric data on the photosphere was obtained
by Solar Optical Telescope (SOT) on board Hinode in the vicinity of
M6.6 flare. We analyze the time-evolution of the magnetic structure of
this region, especially the trigger region of M6.6 flare, and compare
the structure with the numerical calculation by Kusano et al.. First
we investigate the magnetic field data obtained by Hinode/SOT and
SDO/HMI. It is found that this region is formed by a collision of the
two emerging fluxes, and that they make a strongly sheared polarity
inversion line (PIL), on which a lot of flares occurred. We also found
a discriminating local magnetic structure on the PIL before the M-class
flare. We investigate Ca images, and find a continuous Ca brightening
just above the discriminating magnetic structure. This is similar to
the character of pre-flare brightening, which is seen in the "reverse
shear type" flare model suggested by Kusano et al. Further we make
comparison of this brightening with current density in the numerical
calculation. The spatial distributions of the Ca brightening in the
observation and the current density in the simulation are coincided
with each other. The relaxed horizontal field continues to be sheared
again by the motion of the whole region. We consider this sheared
field as a pre-flare coronal arcade of the following X-class flare.
Title: Magnetic Field Structures Triggering Solar Flares and Coronal
Mass Ejections
Authors: Kusano, K.; Bamba, Y.; Yamamoto, T. T.; Iida, Y.; Toriumi,
S.; Asai, A.
Bibcode: 2012ApJ...760...31K
Altcode: 2012arXiv1210.0598K
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.
Title: Numerical Experiments on the Two-Step Emergence of Solar
Magnetic Fields from the Convective Layer
Authors: Toriumi, S.; Yokoyama, T.
Bibcode: 2012ASPC..454..259T
Altcode:
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 some discussions in connection with the
results of the thin-flux-tube simulations.
Title: Detection of the Horizontal Divergent Flow Prior to the Solar
Flux Emergence
Authors: Toriumi, S.; Hayashi, K.; Yokoyama, T.
Bibcode: 2012ApJ...751..154T
Altcode: 2012arXiv1204.0726T
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 Hα 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.
Title: Numerical Simulation and SOT Magnetogram Analysis of the
Small-scale Magnetic Elements in a Solar Emerging Flux Region
Authors: Toriumi, S.; Yokoyama, T.
Bibcode: 2012ASPC..456...33T
Altcode:
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 (1990)'s model based on their observation. We also confirmed
that the wavelength 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 ∼3,000km. 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.
Title: Detection of the Horizontal Divergent Flow (HDF) as a Precursor
of Sunspot Emergence
Authors: Toriumi, Shin; Hayashi, K.; Yokoyama, T.
Bibcode: 2012AAS...22052103T
Altcode:
The SDO/HMI data reveals that a horizontal divergent flow (HDF)
appears about 100 min before the sunspot emergence. It is widely
accepted that solar active regions including sunspots are the
consequence of the rising magnetic flux from the convection zone
(flux emergence). In this study we report the detection of the HDF in
the photosphere, prior to the start of flux emergence. The HDF was
previously reported in our numerical study; the plasma on the top
of emerging flux escapes horizontally around the photosphere before
the flux reaches the surface. For the observational study, we use
SDO/HMI Dopplergrams and magnetograms of NOAA AR 11081 on June 11,
2010. We investigate the differences of each (Doppler and magnetic)
profile of this region from that of the quiet Sun, and define the HDF
appearance and the flux emergence as the times when each difference
exceeds one standard deviation level (one-sigma) of the reference
quiet-Sun profile. As a result, it is found that HDF occurs about 100
min before the associated flux emergence. Also, the horizontal speed
of the outflow is measured to be 0.6-1.5 km/s, up to 2.3 km/s. One
importance of observing HDF may be the possibility to predict the
sunspot emergence that occurs in several hours.
Title: Large-scale 3D MHD simulation on the solar flux emergence
and the small-scale dynamic features in an active region
Authors: Toriumi, S.; Yokoyama, T.
Bibcode: 2012A&A...539A..22T
Altcode: 2012arXiv1201.2809T
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.
Title: Numerical Experiments on the Two-step Emergence of Twisted
Magnetic Flux Tubes in the Sun
Authors: Toriumi, S.; Yokoyama, T.
Bibcode: 2011ApJ...735..126T
Altcode: 2011arXiv1105.1904T
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 >~
1.5 × 104 G and the twist >~ 5.0 × 10-4
km-1 at -20,000 km depth.
Title: Dependence of the Magnetic Energy of Solar Active Regions on
the Twist Intensity of the Initial Flux Tubes
Authors: Toriumi, Shin; Miyagoshi, Takehiro; Yokoyama, Takaaki; Isobe,
Hiroaki; Shibata, Kazunari
Bibcode: 2011PASJ...63..407T
Altcode: 2011arXiv1101.0978T
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.
Title: Two-step Emergence of the Magnetic Flux Sheet from the Solar
Convection Zone
Authors: Toriumi, S.; Yokoyama, T.
Bibcode: 2010ApJ...714..505T
Altcode: 2010arXiv1003.4718T
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 1021-1022 Mx with 104
G at z = -20,000 km. We present some discussions in connection with
recent observations and the results of the thin-flux-tube model.