| Date |
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Name |
Title |
Abstract |
File |
| 4/13 |
|
Asai |
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| 4/20 |
|
Denis |
Acceleration process of a solar filament eruption: observation and numerical modeling |
In this talk, I will explore the dynamics and acceleration process of a fast-filament eruption by combining imaging spectroscopy observations and numerical modeling.
By adapting the toroidal current loop equations within the context of the torus instability, we modeled the evolution of the filament eruption and solved the equation of motion for different scenarios involving full and partial toroidal flux rope configurations.
We demonstrate that the eruption process of the filament can be equally described by models based on either the conservation of magnetic flux or conservation of total energy, with the added constraint that the electric current accounting for the free magnetic energy is restricted to the expanding flux rope above the photosphere.
However, neither model independently satisfies the conservation of energy and magnetic flux simultaneously.
We propose a novel composite model that incorporates a non-constant aspect ratio for the toroidal flux rope.
This composite model not only maintains consistency with the conservation laws but also yields a remarkable fit to the observational data, thus offering a more comprehensive representation of the eruption process.
Furthermore, by incorporating the mass-loss effect in our simulations, we successfully reproduced the fast component of the eruption. This confirms that mass loss, manifesting as draining material or downflows, directly modulates the acceleration phase of the filament.
Based on the results of our best-fitting model, we also quantified the energy budget of the high-speed eruption.
Additionally, the role of the driving forces in the evolution of the toroidal flux rope is also investigated.
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pdf
19.2 MB
|
| 4/27 |
|
Ishii |
|
Today, I would like to introduce some websites for space weather.
https://www.kwasan.kyoto-u.ac.jp/~ishii/webpage_list.html
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| 5/11 |
|
Dai |
Pre-eruptive Longitudinal Oscillations of a Kink-unstable Filament Observed by CHASE and SMART |
The current work focuses on the pre-eruptive evolution of a filament, including its longitudinal oscillation, Doppler velocity structures, and the possible connection with increasing twist and flux-rope instability.
Based on the current analysis, we suggest that the filament eruption was likely triggered by kink instability, and that the event eventually developed into a failed eruption.
In addition, the longitudinal oscillation before the eruption shows a strongly damped feature, which may be related to the magnetic-field evolution during the pre-eruptive phase.
Since the analysis is still ongoing, this presentation will mainly summarize the current progress and preliminary interpretation.
I would greatly appreciate your comments and suggestions on the observational evidence, physical scenario, and possible next steps.
|
pdf
3.4 MB
|
| 5/18 |
|
Ueno |
Wide-Field Spectro-Polarimeter and researches on filament magnetic fields |
At Hida Observatory, we are currently developing a wide-field spectro-polarimetric observation system for the Domeless Solar Telescope.
This system consists of two instruments: the Wide-Field Spectro-Polarimeter (WFSP) and the Ground Layer Adaptive Optics (GLAO).
Regarding the WFSP, necessary components were gradually acquired using various funding sources between 2023 and 2025, and the instrument itself is now operational and capable of acquiring observational data.
As for the GLAO, we will continue to conduct fundamental experiments in collaboration with Kitami Institute of Technology in this year also.
In this Solar Seminar, I will first discuss observational researches on filaments and prominences as one of key scientific objectives of this system, and present on WFSP's specific configuration, features and examples of observational data.
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pdf
6.4 MB
|
| 5/25 |
|
Shirato |
Magnetic shadows and power halos |
We want to clarify the contribution of waves to the energy balance in the higher atmosphere.
So we are working on the oscillation analysis using SMART/SDDI and SDO/HMI data.
We have obtained various results so far; some we could interpret, while others remain unexplained.
Among the latter is a phenomenon known in this field as the “magnetic shadows” or “power halos.”
Today, I would like to explain what these phenomena are and what kinds of research have been conducted on them, and finally discuss our findings.
|
pdf
3.1 MB
|
| 6/1 |
|
Natsume |
Comparison of the spectra of a flare with postflare loops in multiple chromospheric lines |
Solar/stellar flares are explosive phenomena where magnetic energy is released by magnetic reconnection.
While solar flares can be observed in a spatially resolved manner, stellar ones can be observed as a single point and we can obtain spectra or light curves.
To understand stellar flares through knowledge of solar physics, an analysis of spatial integration of solar observational data into data mimicking stellar observation (Sun-as-a-star analysis) has been conducted.
Flare ribbons are ribbon-like brightening structures in the chromosphere heated by non-thermal particles and thermal flows.
Postflare loops are ~10^4 K plasmas along reconnected magnetic loops which are cooled from 10^6-7 K plasma evaporated by the heating of chromospheric plasma and are observed in the late phase of the flare. In stellar observation, red-shifted brightening components of H-alpha (Ha) line in a flare on an M-type dwarf have been detected and the component in the late phase can be considered as postflare loops.
In solar research, Sun-as-a-star analysis of postflare loops in Ha line has revealed that the brightening/darkening components from postflare loops can be detected in Sun-as-a-star data.
The chromospheric line used in Sun-as-a-star analysis is mainly H-alpha line like these previous researches.
However, the H-alpha line's brightening and darkening actually cancel each other and lose quantitative information about postflare loops.
By using multiple chromospheric lines with sensitivity to different physical conditions, we can obtain more information about flare than using a single line.
Sun-as-a-star analysis of postflare loops in multiple chromospheric lines has not been conducted and the differences between these lines are not well known.
The aim of our research is to investigate the difference in the signal of postflare loops between multiple chromospheric lines and help to understand stellar flares.
We observed an X1.6 class flare with postflare loops that occurred in NOAA 13386 on 2023 August 5 by using Domeless Solar Telescope (DST) at Hida Observatory of Kyoto University.
Using the horizontal spectrograph on DST, we observed the flare ribbons and the postflare loops in four chromospheric lines simultaneously: Ha, Ca II K (CaK), Ca II 8542 angstroms (CaIR) and He I 10830 angstroms (He).
Flare ribbons were observed and postflare loops appeared almost simultaneously as brightening in line centers of these four lines.
The brightening of the postflare loops in He disappeared 10 minutes after the postflare loop appeared.
Brightening of the postflare loops was detected in the wing images of CaK while darkening of the postflare loops was detected in the wing images of the other lines.
For t < 5, line-center brightening is observed in all lines except He, suggesting that the contribution from the flare ribbons is dominant.
For t ~ 7, an increase in brightness appears at the line center, the emergence of a contribution from the flare loops.
For t > 10, line-center dimming is observed in all lines except He, while wing enhancement is seen in all lines except CaK, suggesting that the flare-loop contribution becomes dominant, particularly in the line wings.
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pdf
3.7 MB
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| 6/8 |
|
Yoshihisa |
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| 6/22 |
Guest Seminar |
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| 6/29 |
|
Ichihara |
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| 7/6 |
|
Fukuchi |
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| 7/13 |
|
Umezawa |
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