A5081066564- Solar and Space Plasma Dynamics
- Ionosphere and magnetosphere dynamics
- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Astrophysics and Star Formation Studies
- Geomagnetism and Paleomagnetism Studies
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Astrophysics and Cosmic Phenomena
- Astronomy and Astrophysical Research
- Pulsars and Gravitational Waves Research
- Geophysics and Gravity Measurements
- Magnetic confinement fusion research
- Astronomical Observations and Instrumentation
- Solar Radiation and Photovoltaics
- Earthquake Detection and Analysis
- High-pressure geophysics and materials
- Cosmology and Gravitation Theories
- Galaxies: Formation, Evolution, Phenomena
- Fluid Dynamics and Turbulent Flows
- Atmospheric Ozone and Climate
- Scientific Research and Discoveries
- History and Developments in Astronomy
- Superconducting Materials and Applications
- Quantum, superfluid, helium dynamics
Kyoto University
2015-2024
Doshisha University
2021-2024
National Astronomical Observatory of Japan
1996-2019
Astronomical Observatory
1996-2019
Japan Society for the Promotion of Science
2017
Centre National de la Recherche Scientifique
2011
European Incoherent Scatter Scientific Association
2011
Laboratoire d’études spatiales et d’instrumentation en astrophysique
2011
Observatoire de Paris
2011
European Space Research and Technology Centre
2008
This paper outlines the current understanding of solar flares, mainly focused on magnetohydrodynamic (MHD) processes responsible for producing a flare. Observations show that flares are one most explosive phenomena in atmosphere Sun, releasing huge amount energy up to about 1032 erg timescale hours. Flares involve heating plasma, mass ejection, and particle acceleration generates high-energy particles. The key physical flare are: emergence magnetic field from interior (flux emergence), local...
Observations indicate that reconnection-favored emerging flux has a strong correlation with coronal mass ejectons (CMEs). Motivated by this observed and based on the rope model, an trigger mechanism is proposed for onset of CMEs, using two-dimensional magnetohydrodynamic (MHD) numerical simulations: when such emerges within filament channel, it cancels magnetic field below rope, leading to rise (owing loss equilibrium) formation current sheet it. Similar global restructuring resulting motion...
The heating of the solar chromosphere and corona is a long-standing puzzle in physics. Hinode observations show ubiquitous presence chromospheric anemone jets outside sunspots active regions. They are typically 3 to 7 arc seconds = 2000 5000 kilometers long 0.2 0.4 second 150 300 wide, their velocity 10 20 per second. These small have an inverted Y-shape, similar shape x-ray corona. features imply that magnetic reconnection occurring at much smaller spatial scale throughout suggest may be...
Solar prominences are cool 10(4) kelvin plasma clouds supported in the surrounding 10(6) coronal by as-yet-undetermined mechanisms. Observations from Hinode show fine-scale threadlike structures oscillating plane of sky with periods several minutes. We suggest that these represent Alfvén waves propagating on magnetic field lines and may play a role heating corona.
Recent observations of solar type stars with the Kepler satellite by Maehara et al. have revealed existence superflares (with energy 10^33 - 10^35 erg) on Sun-like stars, which are similar to our Sun in their surface temperature (5600 K 6000 K) and slow rotation (rotational period > 10 days). From statistical analysis these superflares, it was found that 10^34 erg occur once 800 years 5000 stars. In this paper, we examine whether could present through use simple order-of-magnitude estimates...
By extending our previous study by Maehara et al., we searched for superflares on G-type dwarfs (solar-type stars) using Kepler data a longer period (500 days) than that (120 in study. As result, found 1547 279 dwarfs, which is much more the 365 148 stars. Using these new data, studied statistical properties of occurrence rate superflares, and confirmed results, i.e., (dN/dE) versus flare energy (E) shows power-law distribution with dN/dE∝E−α, where α ∼ 2. It interesting this roughly similar...
We searched for superflares on solar-type stars using Kepler data with 1 min sampling in order to detect short duration. found 187 23 whose bolometric energy ranges from the of $10^{32}$ erg $10^{36}$ erg. Some show multiple peaks peak separation $100$-$1000$ seconds which is comparable periods quasi-periodic pulsations solar and stellar flares. Using these new combined results 30 sampling, we occurrence frequency ($dN/dE$) as a function flare ($E$) shows power-law distribution ($dN/dE...
Abstract We report the latest view of Kepler solar-type (G-type main-sequence) superflare stars, including recent updates with Apache Point Observatory (APO) 3.5 m telescope spectroscopic observations and Gaia -DR2 data. First, we newly conducted APO 18 stars found from 1-minute time-cadence More than half (43 stars) are confirmed to be “single” among 64 in total that have been spectroscopically investigated so far this our previous Subaru/HDS observations. The measurements v sin i...
Abstract We trace the evolution of research on extreme solar and solar-terrestrial events from 1859 Carrington event to rapid development last twenty years. Our focus is largest observed/inferred/theoretical cases sunspot groups, flares Sun Sun-like stars, coronal mass ejections, proton events, geomagnetic storms. The reviewed studies are based modern observations, historical or long-term data including auroral cosmogenic radionuclide record, Kepler observations stars. compile a table 100-...
Young solar-type stars frequently produce superflares, serving as a unique window into the young Sun-Earth environments. Large solar flares are closely linked to coronal mass ejections (CMEs) associated with filament/prominence eruptions, but its observational evidence for stellar superflares remains scarce. Here, we present 12-day multi-wavelength campaign observation of star EK Draconis (G1.5V, 50-120 Myr age) utilizing TESS, NICER, and Seimei telescope. The has previously exhibited...
Abstract We conducted the time-resolved simultaneous optical spectroscopic and photometric observations of mid-M-dwarf flare stars YZ CMi, EV Lac, AD Leo. Spectroscopic were obtained using Apache Point Observatory 3.5 m Small Moderate Aperture Research Telescope System 1.5 telescopes during 31 nights. Among 41 detected flares, seven flares showed clear blue wing asymmetries in H α line, with various correspondences properties. The duration range from 20 minutes to 2.5 hr, including a showing...
Abstract We have found 100 X-ray jets in the database of full Sun images taken with Soft Telescope (SXT) aboard Yohkoh during period from 1991 November through 1992 April. A statistical study for these results following characteristics: 1) Most are associated small flares (microflaressubflares) at their footpoints. 2) The lengths lie range a few × 104−4 105 km. 3) widths 5 103–105 4) apparent velocities 10–1000 km s−1 an average velocity about 200 . 5) lifetime jet extends to ˜ 10 hours and...
We performed two-dimensional numerical simulations of solar coronal X-ray jets by solving the resistive magnetohydrodynamic (MHD) equations. The were based on magnetic reconnection model, in which plasma an jet is accelerated and heated between emerging flux a pre-existing field. Many observed characteristics could be successfully reproduced. Morphologically, two types jets, two-sided-loop type anemone-jet type, well Here, pair horizontal (or loops), occurs when appears quiet region where...
Solar coronal mass ejections (CMEs) are associated with many dynamical phenomena, among which EIT waves have always been a puzzle. In this Letter MHD processes of CME-induced wave phenomena numerically simulated. It is shown that as the flux rope rises, piston-driven shock formed along envelope expanding CME, sweeps solar surface it propagates. We propose legs produce Moreton waves. Simultaneously, slower moving wavelike structure, an enhanced plasma region ahead, discerned, we corresponds...
view Abstract Citations (274) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS H alpha Surges and X-Ray Jets in AR 7260 Canfield, Richard C. ; Reardon, Kevin P. Leka, K. D. Shibata, Yokoyama, T. Shimojo, M. We discuss nine events, observed simultaneously as jets X-rays surges Hα, which are associated with moving magnetic bipoles. The X-ray share many features those discovered by Yohkoh active regions, emerging flux bright points (see paper...
We propose a model of hard X-ray flares in protostars observed by the ASCA satellite. assumed that dipole magnetic field protostar threads protostellar disk and carried out 2.5 dimensional magnetohydrodynamic (MHD) simulations disk-star interaction. The closed loops connecting central star are twisted rotation disk. As twist accumulates, expand finally approach open configuration. A current sheet is formed inside expanding loops. In presence resistivity, reconnection takes place sheet....
Magnetohydrodynamic simulations are performed for torsional Alfvén waves propagating along an open magnetic flux tube in the solar atmosphere. It is shown that, if root mean square of perturbation greater than ~1 km s-1 photosphere, (1) transition region lifted up to more ~5000 (i.e., spicule produced), (2) energy enough heating quiet corona (~3.0×105 ergs cm−2) transported into corona, and (3) nonthermal broadening emission lines expected be ~20 s-1. We assumed that generated by random...
Two-dimensional magnetohydrodynamic (MHD) simulation of a solar flare including the effect anisotropic heat conduction and chromospheric evaporation based on magnetic reconnection model is performed. In model, coronal energy converted to thermal plasma by reconnection. This transported chromosphere along field lines causes an increase in temperature pressure plasma. The gradient force drives upward motion toward corona, i.e., evaporation. enhances density reconnected loops, such evaporated...
Relativistic jets are observed in both active galactic nuclei (AGNs) and ``microquasars" our Galaxy. It is believed that these relativistic ejected from the vicinity of black holes. To investigate formation mechanism jets, we have developed a new general magnetohydrodynamic (GRMHD) code. We report on basic methods test calculations to check whether code reproduces some analytical solutions, such as standing shock Keplerian disk with steady state infalling corona or hydrostatic equilibrium....
Early observations by the EUV Imaging Telescope (EIT) on Solar and Heliospheric Observatory indicated that propagating diffuse wave fronts, now conventionally referred to as "EIT waves," can often be seen solar disk with a propagation velocity several times smaller than of Hα Moreton waves. They are almost always associated coronal mass ejections. We have previously confirmed existence such phenomenon numerical simulations, which indicate there does exist slower moving "wave" much behind...
Using numerical simulations, we modeled the general relativistic magnetohydrodynamic behavior of a plasma flowing into rapidly rotating black hole in large-scale magnetic field. The results show that torsional Alfvén wave is generated by rotational dragging space near hole. transports energy along field lines outward, causing total to decrease negative values. When this enters horizon, decreases. Through process, spinning extracted magnetically