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Date	Time	Section	Speaker	File
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Date	Section	Speaker	File
4/8		Asai	upload or download

For Speakers

Presentation time for speaker is: 60 minutes as a guide, and 30 minuites discussion.
(A speaker can use the full time of one seminar.)
Contents of talk are: :about your study
:review of recent interesting paper and share information of recent study of the Sun.
Language of slide and talks: Master cource students : Language of slide and talk could be Japanese
Doctor cource students and over : Slide must be English, and talking language could be Japanese
(If those who could not understand Japanese attend the seminar, it is preferable that you talk in English)
Title and Abstract: Please send the title and abstract of your presentation by the day before.
Presentation files: Please upload your presentation files by the start of the seminar.
If the presentation file has very large volume, please zip the file before uploading.
If you do not want to make public your unpublished results, please delete the relevant part before submission.

For Audiences

Honoring speakers: Plase clap your hands as a closure of a presentation to express your respection to a speaker.

For everyone

Publication sharing: Please send a copy of the submitted version of any paper on which they are working to the zasshikai mailing list just after submission

Useful webpage list for solar observers.

Date		Name	Title	Abstract	File
4/8		Asai	Solar Seminar 2024
4/15		Nagata	Near Infrared Tunable Filter for DIKIST		pptx 67.3 MB
4/22		Ishii	Filament eruptions and two ribbon flares at quiet regions	Today, I would like to introduce the following paper and SMART/SDDI observations of filament eruptions and two ribbon flares at quiet regions. A STUDY OF FAST FLARELESS CORONAL MASS EJECTIONS, H. Q. Song et al, 2013, ApJ, 773, 129.	pptx 10.5 MB
5/13		Mishra	Successive Emerging Flux Triggers Persistent Reconnection Jets in the Solar Atmosphere and Associated Heating	The dynamics of the solar atmosphere, including mass and energy circulation, coronal heating, and the initiation of eruptions both small and large, are governed by magnetic fields. High-resolution observational techniques and computational models are essential for unraveling these intricate phenomena. In my presentation, I will discuss how the successive emergence of magnetic flux influences various phases of jet activity in the solar atmosphere, contributing to the heating of the solar corona. Utilizing AIA multiwavelength imaging and SMART/SDDI spectroscopic observations, we categorized the observation period into three phases: initial, developing, and eruptive. The initial phase featured small-scale jets with velocities between 175-255 km/s. The developing phase was characterized by bidirectional plasma flows within the fan plane, while the eruptive phase saw three homologous jets within the fan-spine magnetic topology. We examined the topological alterations caused by magnetic reconnection and its persistent role in coronal heating. Differential Emission Measure (DEM) analysis indicated the existence of super-hot plasma, around 8-10 MK, which led to the ejection of hot and multithermal plasma into the overlying solar corona.	pptx 94.2 MB
5/20	@ Room 328	Dai	Simultaneous Horizontal and Vertical Oscillation of a Quiescent Filament Observed by CHASE and SDO	In this study, we present the imaging and spectroscopic observations of the simultaneous horizontal and vertical large-amplitude oscillation of a quiescent filament triggered by an extreme-ultraviolet (EUV) wave on 2022 October 2. Particularly, the filament oscillation involved winking phenomenon in H-alpha images and horizontal motions in EUV images. Here we focus on the EUV (Moreton) wave and the filament oscillation.	pdf 3.4 MB
6/3		Shirato	Overview of the IHOP 0473 observation using EIS/Hinode, IRIS and DST/Hida	Today I would like to talk about my rescent observation, through IHOPs (IRIS/Hinode Operations Plans) observation. This is a joint observation using IRIS, Hinode and other instruments. I conducted IHOP observation twice using Domeless Solar Telescope (DST) at Hida Observatory, on November 2023, and on April and May 2024. In today’s talk, I will provide an overview of these observations and the progress made so far, and the future plan.	pdf 18.1 MB
6/10		Otsu	Comparison of Sun-as-a-star and Spatially-resolved Velocity of Prominence Eruptions	Solar and stellar flares are explosive phenomena in atmospheres of the sun and cool stars. As known from imaging observations, solar flares are sometimes associated with filament/prominence eruptions which can lead to coronal mass ejections (CMEs). Such plasma eruptions and CMEs are thought to also accompany some stellar flares and affect exoplanet environments (e.g., Airapetian+ 2020). In stellar cases, Doppler shifted components observed in chromospheric lines such as H-alpha are often interpreted as plasma eruptions. Although most studies reported shifted components with velocities lower than the escape velocities of stars, some studies showed greatly high velocity components which can escape from stars and lead to CMEs (e.g., Inoue+ 2023). Also, some studies made direct comparison of stellar shifted components and solar H-alpha data of filament/prominence eruptions using Sun-as-a-star analyses, and confirmed their qualitative similarities (Namekata+ 2022, 2024, Leitzinger+ 2024). Thus, the existence of stellar plasma eruptions is becoming more certain. To clarify the quantitative relations between stellar activities and exoplanet environments, it’s required to investigate detailed dynamics of stellar plasma eruptions such as kinematic and thermal evolutions. In this study, I focused on kinematic evolution of plamsa eruptions in spatially integrated data. In order to clarify the relation between velocity distribution in resolved data and Sun-as-a-star velocity of plasma (prominence) eruptions, I conducted cloud model fitting for spatially resolved H-alpha data of SMART/SDDI and compare the fitting results with velocities obtained from Sun-as-a-star H-alpha spectra. I’d like to introduce some preliminary results and future plans.	pptx 9.9 MB
6/17		Shimada	Mean-Field Study of Stellar Activity-Rotation Relationship	This study explores the relationship between stellar surface magnetic fields and rotation rates. Previous observations (e.g., Wright+ 2011, 2018) have established a connection between stellar activity and rotation rates, with recent observations by Reiners (2022) indicating a parallel trend in surface magnetic fields. Observations suggest an anti-correlation between the magnetic field and Ro within the moderate Ro range (0.1 $<$ Ro $<$ 1), reaching saturation at extremely low Ro. Here, the Rossby number (Ro) is a crucial measure in assessing the impact of rotation on dynamics defined as the rotation period over convective turnover time. While global magnetohydrodynamic (MHD) simulations, such as those by Brun+ (2022), successfully replicate the anticorrelation in moderate Ro, the saturation phenomenon at extremely low Ro remains beyond the reach of current global simulations, and its driving mechanism remains unclear. To elucidate the saturation of the stellar magnetic field at extremely low Ro, We perform non-kinematic mean-field dynamo simulations by extending the solar case by Rempel (2006). Our findings reveal that the magnetic field strength is influenced by both stellar rotation rates and the assumed turbulent angular momentum (AM) transport process. Through detailed analysis, we demonstrate that the dependence of the magnetic field on Ro is intricately determined by the balance between AM transport by turbulence and the magnetic field. Notably, our results, in conjunction with recent insights into turbulence properties at low Ro (e.g. Kapyla 2024), align closely with observed magnetic field saturation patterns reported by Reiners (2022). We are also going to discuss the methods to justify the assumed turbulent effects.	pptx 9.9 MB
6/24		Yoshihisa	Non-thermal velocities in Corona and Coronal Rain	The coronal heating problem of why the corona reaches a million K relative to 6000 K at the photosphere is one of the key open questions in the stellar physics. From an observational perspective, non-thermal line broadening are observed and considered to be the indicator of heating properties. However, previous numerical simulations have not explained this observation. This work attempt to reproduce observed non-thermal vel. by taking into account turbulent heating. We also investigate the non-thermal vel. in the coronal rain.	pptx 12.9 MB
7/1		Kida	Canceled
7/8		Natsume	Comparison of multiple chromospheric lines for post-flare loop		pdf 3.3 MB
7/8	Guest Seminar 15:30-17:00	Prof. Petr Heinzel (Astronomical Institute, Czech Academy of Sciences and University of Wroclaw, Center of Excellence 'Solar and Stellar Activity')	Radiative transfer in solar prominences: A historical overview and current trends	Similarly as in other branches of solar atmospheric spectroscopy, development of the non-LTE (i.e. departures from Local Thermodynamic Equilibrium) physics and related numerical tools in 60-ties and 70-ties of the last century largely influenced also the prominence research. First 1D prominence models have been constructed showing the critical importance of an external illumination in the relevant spectral lines and continua. Later on the effects of 2D geometry and partial redistribution have been investigated and the modeling turned to problems of heterogeneous media, multithread structures and finally studies of the energy balance. In parallel, new multi-wavelength spectral data became available at higher spatial and temporal resolution. We will review the progress from 70-ties till now and finally summarise the current modern trends in numerical non-LTE radiative-transfer modeling, focusing on both quiescent as well as eruptive prominences. Namely the coupling of up-to-date MHD simulations with optically-thick radiative transfer will be highlighted.
7/22		Suzuki	Observation of M dwarf's magnetic fields	Understanding details of the stellar winds of M-type stars is important for study of exoplanetary atmospheres. In order to simulate stellar winds, knowledge of magnetic fields of M dwarfs is required as a numerical setup. Here, I will summarize observational studies of magnetic fields of M dwarfs. They clarified magnetic field strength and geometries.	pdf 1.0 MB

Date

Name

Title

Abstract

File

4/8

Asai

Solar Seminar 2024

4/15

Nagata

Near Infrared Tunable Filter for DIKIST

pptx
67.3 MB

4/22

Ishii

Filament eruptions and two ribbon flares at quiet regions

Today, I would like to introduce the following paper and SMART/SDDI observations of filament eruptions and two ribbon flares at quiet regions.
A STUDY OF FAST FLARELESS CORONAL MASS EJECTIONS, H. Q. Song et al, 2013, ApJ, 773, 129.

pptx
10.5 MB

5/13

Mishra

Successive Emerging Flux Triggers Persistent Reconnection Jets in the Solar Atmosphere and Associated Heating

The dynamics of the solar atmosphere, including mass and energy circulation, coronal heating, and the initiation of eruptions both small and large, are governed by magnetic fields. High-resolution observational techniques and computational models are essential for unraveling these intricate phenomena. In my presentation, I will discuss how the successive emergence of magnetic flux influences various phases of jet activity in the solar atmosphere, contributing to the heating of the solar corona. Utilizing AIA multiwavelength imaging and SMART/SDDI spectroscopic observations, we categorized the observation period into three phases: initial, developing, and eruptive. The initial phase featured small-scale jets with velocities between 175-255 km/s. The developing phase was characterized by bidirectional plasma flows within the fan plane, while the eruptive phase saw three homologous jets within the fan-spine magnetic topology. We examined the topological alterations caused by magnetic reconnection and its persistent role in coronal heating. Differential Emission Measure (DEM) analysis indicated the existence of super-hot plasma, around 8-10 MK, which led to the ejection of hot and multithermal plasma into the overlying solar corona.

pptx
94.2 MB

5/20

@ Room 328

Dai

Simultaneous Horizontal and Vertical Oscillation of a Quiescent Filament Observed by CHASE and SDO

In this study, we present the imaging and spectroscopic observations of the simultaneous horizontal and vertical large-amplitude oscillation of a quiescent filament triggered by an extreme-ultraviolet (EUV) wave on 2022 October 2. Particularly, the filament oscillation involved winking phenomenon in H-alpha images and horizontal motions in EUV images. Here we focus on the EUV (Moreton) wave and the filament oscillation.

pdf
3.4 MB

6/3

Shirato

Overview of the IHOP 0473 observation using EIS/Hinode, IRIS and DST/Hida

Today I would like to talk about my rescent observation, through IHOPs (IRIS/Hinode Operations Plans) observation. This is a joint observation using IRIS, Hinode and other instruments. I conducted IHOP observation twice using Domeless Solar Telescope (DST) at Hida Observatory, on November 2023, and on April and May 2024. In today’s talk, I will provide an overview of these observations and the progress made so far, and the future plan.

pdf
18.1 MB

6/10

Otsu

Comparison of Sun-as-a-star and Spatially-resolved Velocity of Prominence Eruptions

Solar and stellar flares are explosive phenomena in atmospheres of the sun and cool stars. As known from imaging observations, solar flares are sometimes associated with filament/prominence eruptions which can lead to coronal mass ejections (CMEs). Such plasma eruptions and CMEs are thought to also accompany some stellar flares and affect exoplanet environments (e.g., Airapetian+ 2020). In stellar cases, Doppler shifted components observed in chromospheric lines such as H-alpha are often interpreted as plasma eruptions. Although most studies reported shifted components with velocities lower than the escape velocities of stars, some studies showed greatly high velocity components which can escape from stars and lead to CMEs (e.g., Inoue+ 2023). Also, some studies made direct comparison of stellar shifted components and solar H-alpha data of filament/prominence eruptions using Sun-as-a-star analyses, and confirmed their qualitative similarities (Namekata+ 2022, 2024, Leitzinger+ 2024). Thus, the existence of stellar plasma eruptions is becoming more certain. To clarify the quantitative relations between stellar activities and exoplanet environments, it’s required to investigate detailed dynamics of stellar plasma eruptions such as kinematic and thermal evolutions. In this study, I focused on kinematic evolution of plamsa eruptions in spatially integrated data. In order to clarify the relation between velocity distribution in resolved data and Sun-as-a-star velocity of plasma (prominence) eruptions, I conducted cloud model fitting for spatially resolved H-alpha data of SMART/SDDI and compare the fitting results with velocities obtained from Sun-as-a-star H-alpha spectra. I’d like to introduce some preliminary results and future plans.

pptx
9.9 MB

6/17

Shimada

Mean-Field Study of Stellar Activity-Rotation Relationship

This study explores the relationship between stellar surface magnetic fields and rotation rates. Previous observations (e.g., Wright+ 2011, 2018) have established a connection between stellar activity and rotation rates, with recent observations by Reiners (2022) indicating a parallel trend in surface magnetic fields. Observations suggest an anti-correlation between the magnetic field and Ro within the moderate Ro range (0.1 $<$ Ro $<$ 1), reaching saturation at extremely low Ro. Here, the Rossby number (Ro) is a crucial measure in assessing the impact of rotation on dynamics defined as the rotation period over convective turnover time. While global magnetohydrodynamic (MHD) simulations, such as those by Brun+ (2022), successfully replicate the anticorrelation in moderate Ro, the saturation phenomenon at extremely low Ro remains beyond the reach of current global simulations, and its driving mechanism remains unclear. To elucidate the saturation of the stellar magnetic field at extremely low Ro, We perform non-kinematic mean-field dynamo simulations by extending the solar case by Rempel (2006). Our findings reveal that the magnetic field strength is influenced by both stellar rotation rates and the assumed turbulent angular momentum (AM) transport process. Through detailed analysis, we demonstrate that the dependence of the magnetic field on Ro is intricately determined by the balance between AM transport by turbulence and the magnetic field. Notably, our results, in conjunction with recent insights into turbulence properties at low Ro (e.g. Kapyla 2024), align closely with observed magnetic field saturation patterns reported by Reiners (2022). We are also going to discuss the methods to justify the assumed turbulent effects.

pptx
9.9 MB

6/24

Yoshihisa

Non-thermal velocities in Corona and Coronal Rain

The coronal heating problem of why the corona reaches a million K relative to 6000 K at the photosphere is one of the key open questions in the stellar physics. From an observational perspective, non-thermal line broadening are observed and considered to be the indicator of heating properties. However, previous numerical simulations have not explained this observation. This work attempt to reproduce observed non-thermal vel. by taking into account turbulent heating. We also investigate the non-thermal vel. in the coronal rain.

pptx
12.9 MB

7/1

Kida

Canceled

7/8

Natsume

Comparison of multiple chromospheric lines for post-flare loop

pdf
3.3 MB

7/8

Guest
Seminar
15:30-17:00

Prof. Petr Heinzel
(Astronomical Institute, Czech Academy of Sciences and University of Wroclaw, Center of Excellence 'Solar and Stellar Activity')

Radiative transfer in solar prominences: A historical overview and current trends

Similarly as in other branches of solar atmospheric spectroscopy, development of the non-LTE (i.e. departures from Local Thermodynamic Equilibrium) physics and related numerical tools in 60-ties and 70-ties of the last century largely influenced also the prominence research. First 1D prominence models have been constructed showing the critical importance of an external illumination in the relevant spectral lines and continua. Later on the effects of 2D geometry and partial redistribution have been investigated and the modeling turned to problems of heterogeneous media, multithread structures and finally studies of the energy balance. In parallel, new multi-wavelength spectral data became available at higher spatial and temporal resolution. We will review the progress from 70-ties till now and finally summarise the current modern trends in numerical non-LTE radiative-transfer modeling, focusing on both quiescent as well as eruptive prominences. Namely the coupling of up-to-date MHD simulations with optically-thick radiative transfer will be highlighted.

7/22

Suzuki

Observation of M dwarf's magnetic fields

Understanding details of the stellar winds of M-type stars is important for study of exoplanetary atmospheres. In order to simulate stellar winds, knowledge of magnetic fields of M dwarfs is required as a numerical setup. Here, I will summarize observational studies of magnetic fields of M dwarfs. They clarified magnetic field strength and geometries.

pdf
1.0 MB

Date		Name	Title	Abstract	File
10/7		Ueno	Compensation of the Instrumental Polarization of the Adaptive Optics (AO) on the Hida/DST and Improvement of the Accuracy of Spectro-polarimetry	In the instruments session of the ASJ 2024 fall meeting, I talked about compensation of the instrumental polarization of the permanently installed AO on the Hida/DST and improvement of the accuracy of spectro-polarimetry by AO. I think that many of members of the Solar Sminar didn't attend the instruments session. Therefore, I would like to explain the contents of that talk in this seminar again with adding some other information, such as instrumental polarization of the telescope itself, and future plans of the spectro-polarimetry with the DST.	pdf 6.6 MB
10/21		Ishii	Flares observed by SMART/SDDI in this year	Today, I would like to talk about flares observed by SMART/SDDI in this year. https://www.kwasan.kyoto-u.ac.jp/topics/kako.html Iju-san will introduce the categories and examples of event report in 'observation log'. ex.) https://www.hida.kyoto-u.ac.jp/SMART/daily/24Oct/log/20241015_smart.log	pptx 4.3 MB
10/28		Special Seminar
11/11		Shirato		Today, I will introduce these papers. ;---------------------------- #1 Chae et al. 2022 Propagating Alfvénic Waves Observed in the Chromosphere around a Small Sunspot_Tales of 3-minute Waves and 10-minute Waves #2 Kwak et al. 2023 Spectroscopic Detection of Alfvénic Waves in the Chromospheric Fibrils of a Solar-quiet Region ;---------------------------	pptx 6.3 MB
11/18		Suzuki	Importance of Alfven wave turbulence in the solar winds and M dwarf's winds.	Understanding details of stellar winds of M dwarfs is important for the study of exoplanet atmosphere. Stellar winds simulations are conducted by applying solar wind models. In the solar wind model, Alfven wave turbulence (AWT) is regarded to play a main role for accelerating solar winds. However, there is no study comparing with AWT case and without AWT case. In this study, we calculated solar winds and compared them, confirming importance of AWT. In addition to that, we simulated M dwarf's winds with AWT model and concluded that current solar wind model may not explain M dwarf's winds.	pdf 1.5 MB
11/25	interim report 14:30-15:30	Otsu	恒星磁気活動の理解に向けた太陽活動現象のSun-as-a-star解析(Sun-as-a-star Analyses of Solar Active Phenomena for Understanding Stellar Magnetic Activity)	Solar and stellar flares are explosive phenomena in atmospheres of the sun and cool stars. Solar flares can be investigated with spatially resolved data, whereas stellar flares cannot be spatially resolved with current instruments. To understand the dynamics of stellar flares, we have made use of solar deteiled data by perforing Sun-as-a-star analyeses in which solar data is spatially integrated to be directoly compared with stellar data. As expected from solar cases, stellar flares are also related to various active phenomena such as flare ribbons, filament/prominence eruptions, and postflare loops. In order to isolate the information of these active phenomena from spatially integrated data, we have characterized their dynamics in spatially integrated solar data. In this talk, I will introduce our recent study focusing on dynamics of postflare loops in spatially integrated data (Otsu+ 24). I will also talk about our ongoing study on the cooling process of postflare loops using multiple flare events.	pdf 3.2 MB
12/2		Mishra	1. Successive flux emergence triggers persistent reconnection jets and associated steady heating. 2. Mass circulations and dynamics inside the solar prominences.	Magnetic reconnection and magnetohydrodynamic (MHD) instabilities are fundamental plasma processes that play a critical role in triggering small-to-large scale eruptions, governing mass and energy circulation, and addressing the long-standing coronal heating problem. Using high-resolution, multiwavelength imaging observations from the Solar Dynamics Observatory (SDO/AIA) and spectroscopic data from SMART/SDDI, I will discuss our findings on how successive emerging magnetic flux triggers persistent reconnection jets in the solar atmosphere and contributes to associated heating. Additionally, I will present ongoing research exploring the role of reconnection-generated turbulence and its impact on mass loading in solar prominences.	pptx 80.5 MB
12/9	Guest Seminar 12:30-14:00	Anan	Measurements of reconnection electric fields	Magnetic reconnection in the solar atmosphere can release stored magnetic energy efficiently into the solar atmosphere and the heliosphere. However, there were no measurements of electric fields that plasma feels when the magnetic field lines reconnect, because it is commonly assumed that electric fields must vanish quickly or only exist at unresolvable spatial scales due to the high electric conductivity. Using the newly commissioned US National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST), we observed NOAA active region 12995 on February 23rd, 2022, in three spectral ranges, i.e., 397 nm, 630 nm, and 854 nm, using the Visible SpectroPolarimeter (ViSP). We successfully obtained Stokes spectra of Ellerman bombs, which are brightenings in the lower chromosphere and are thought to be associated with magnetic reconnection. At the Ellerman bomb, we discovered a broadband circular polarization in a Balmer line of the neutral hydrogen at 397 nm, H epsilon, that can only be explained by the presence of an electric field. In this presentation, we will discuss physics in the magnetic diffusivity, which allows magnetic field lines to reconnect, from what we measured.
12/16		Dai	End-view Observations of longitudinal oscillations of a quiescent prominence	I will present a interesting event recorded by SDO/AIA and CHASE/HIS.	pdf 4.3 MB
12/23		Shimada	New picture of field saturation mechanism in the solar convection zone	Strong toroidal magnetic flux tube in the solar convection zone(CZ) are thought to be origin of tilted active regions. Thin flux tube simulations(e.g. Caligari et al, 1995) suggest that 100 kG flux tube at the base of CZ is necessary for them to form tilted active regions. However, global dynamo simulations have failed to account for this field. Moreover, the physics determining field strength in the CZ remains unresolved. Classically, quenching mechanism of α-effect have been proposed within the framework of mean-field dynamo theory. Global dynamo sim. with high magnetic Reynolds numbers (Rm) (Hotta+ 2016) were analyzed by us and concluded that strong α-quenching is effective. However, some negative results that challenge our conclusion were obtained after careful analysis. This motivate us to discard the assumption of α-effect.In this talk, I will present the reanalyzed results. Main findings are as follows: 1. Mean-field approximation should not hold under high Rm 2. Instead of Ω-effect, turbulent stretching plays the dominant role in inducing large-scale magnetic fields. 3. Turbulent stretching is sensitive to large-scale fields, and energy dissipation by turbulence is not These results suggest that saturation mechanism under high Rm is completely different from previous works(e.g. Strugarek+ 2018). Rm dependence of this mechanism is going to be investigated to predict saturation field strength in solar CZ.	pdf 2.1 MB
1/6		Ichihara	Time variation of White-light flare on M-type star EV Lac with Seimei Telescope and TESS	Super flare, which releases the energy greater than 10^{33} erg, occurs frequently on M-dwarfs. Some flares sometimes accompany increment of optical continuum flux, called White-light flare. Although White-light flare is rare event on the sun because of its short duration, it is common event on M-dwarfs. Stellar flares attract attention in terms of Astrobiology. Many researchers have studied about stellar flares for many years, while we have not yet clarified the energy budget of White-light flare and its radiation process. I introduce the White-light flare on EV Lac, which is known as a active flaring M-dwarf. We analyzed the data of EV Lac obtained with spectroscopy of Seimei Telescope and photometry of TESS. The flare emission within optical range is well fitted with ~10000 K Blackbody radiation. I discuss about the time variation of the White-light flare and then talk about our future work.	pdf 2.7 MB
1/20		Natsume	Comparison of multiple chromospheric lines for post-flare loop accompanied by flares	Post-flare loops are the one of the important elements of phenomena accompanied with solar flare. In recent research, the signal considered to come from post-flare loop has been detected. In Sun-as-a-star research, post-flare loop has contribution to the spectrum and equivalent width. To understand stellar observation through the solar physics, qualitative property of solar post-flare loop is needed, especially difference among the chromospheric lines. We observed solar flare with post-flare loop and conducted Sun-as-a-star analysis. In this talk, we are going to present the result of the analysis.	pdf 4.4 MB
1/27		Yoshihisa	On the Occurrence of Thermal Non-Equilibrium in Wave-Heated Coronal Heating	In the solar corona, a phenomenon called "coronal rain" is observed, in which the temperature gradually cools from the coronal temperature to the chromospheric temperature. This cooling is thought to be caused by mechanisms related to thermal non-equilibrium (TNE) and thermal instability(TI). Furthermore, in recent years, 2–16 hour periodic EUV intensity pulsation have been reported in coronal loops. This phenomena are sometimes accompanied by coronal rain and are believed to result from evaporation and cooling (condensation) cycles within the loops. Coronal rain and periodic EUV intensity pulsations are observed less frequently and with longer periods in quiet regions compared to active regions. In this study, the investigation of the aforementioned long-period intensity pulsations was conducted by extending the previously used 1.5-dimensional simulations. Although still in the research phase, discussions are held regarding what determines the periodicity.	pdf 3.2 MB

Date

Name

Title

Abstract

File

10/7

Ueno

Compensation of the Instrumental Polarization of the Adaptive Optics (AO) on the Hida/DST and Improvement of the Accuracy of Spectro-polarimetry

In the instruments session of the ASJ 2024 fall meeting, I talked about compensation of the instrumental polarization of the permanently installed AO on the Hida/DST and improvement of the accuracy of spectro-polarimetry by AO. I think that many of members of the Solar Sminar didn't attend the instruments session. Therefore, I would like to explain the contents of that talk in this seminar again with adding some other information, such as instrumental polarization of the telescope itself, and future plans of the spectro-polarimetry with the DST.

pdf
6.6 MB

10/21

Ishii

Flares observed by SMART/SDDI in this year

Today, I would like to talk about flares observed by SMART/SDDI in this year. https://www.kwasan.kyoto-u.ac.jp/topics/kako.html
Iju-san will introduce the categories and examples of event report in 'observation log'. ex.) https://www.hida.kyoto-u.ac.jp/SMART/daily/24Oct/log/20241015_smart.log

pptx
4.3 MB

10/28

Special Seminar

11/11

Shirato

Today, I will introduce these papers.
;----------------------------
#1 Chae et al. 2022
Propagating Alfvénic Waves Observed in the Chromosphere around a Small Sunspot_Tales of 3-minute Waves and 10-minute Waves
#2 Kwak et al. 2023
Spectroscopic Detection of Alfvénic Waves in the Chromospheric Fibrils of a Solar-quiet Region
;---------------------------

pptx
6.3 MB

11/18

Suzuki

Importance of Alfven wave turbulence in the solar winds and M dwarf's winds.

Understanding details of stellar winds of M dwarfs is important for the study of exoplanet atmosphere. Stellar winds simulations are conducted by applying solar wind models. In the solar wind model, Alfven wave turbulence (AWT) is regarded to play a main role for accelerating solar winds. However, there is no study comparing with AWT case and without AWT case. In this study, we calculated solar winds and compared them, confirming importance of AWT. In addition to that, we simulated M dwarf's winds with AWT model and concluded that current solar wind model may not explain M dwarf's winds.

pdf
1.5 MB

11/25

interim report
14:30-15:30

Otsu

恒星磁気活動の理解に向けた太陽活動現象のSun-as-a-star解析(Sun-as-a-star Analyses of Solar Active Phenomena for Understanding Stellar Magnetic Activity)

Solar and stellar flares are explosive phenomena in atmospheres of the sun and cool stars. Solar flares can be investigated with spatially resolved data, whereas stellar flares cannot be spatially resolved with current instruments. To understand the dynamics of stellar flares, we have made use of solar deteiled data by perforing Sun-as-a-star analyeses in which solar data is spatially integrated to be directoly compared with stellar data. As expected from solar cases, stellar flares are also related to various active phenomena such as flare ribbons, filament/prominence eruptions, and postflare loops. In order to isolate the information of these active phenomena from spatially integrated data, we have characterized their dynamics in spatially integrated solar data. In this talk, I will introduce our recent study focusing on dynamics of postflare loops in spatially integrated data (Otsu+ 24). I will also talk about our ongoing study on the cooling process of postflare loops using multiple flare events.

pdf
3.2 MB

12/2

Mishra

1. Successive flux emergence triggers persistent reconnection jets and associated steady heating.
2. Mass circulations and dynamics inside the solar prominences.

Magnetic reconnection and magnetohydrodynamic (MHD) instabilities are fundamental plasma processes that play a critical role in triggering small-to-large scale eruptions, governing mass and energy circulation, and addressing the long-standing coronal heating problem. Using high-resolution, multiwavelength imaging observations from the Solar Dynamics Observatory (SDO/AIA) and spectroscopic data from SMART/SDDI, I will discuss our findings on how successive emerging magnetic flux triggers persistent reconnection jets in the solar atmosphere and contributes to associated heating. Additionally, I will present ongoing research exploring the role of reconnection-generated turbulence and its impact on mass loading in solar prominences.

pptx
80.5 MB

12/9

Guest Seminar
12:30-14:00

Anan

Measurements of reconnection electric fields

Magnetic reconnection in the solar atmosphere can release stored magnetic energy efficiently into the solar atmosphere and the heliosphere. However, there were no measurements of electric fields that plasma feels when the magnetic field lines reconnect, because it is commonly assumed that electric fields must vanish quickly or only exist at unresolvable spatial scales due to the high electric conductivity. Using the newly commissioned US National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST), we observed NOAA active region 12995 on February 23rd, 2022, in three spectral ranges, i.e., 397 nm, 630 nm, and 854 nm, using the Visible SpectroPolarimeter (ViSP). We successfully obtained Stokes spectra of Ellerman bombs, which are brightenings in the lower chromosphere and are thought to be associated with magnetic reconnection. At the Ellerman bomb, we discovered a broadband circular polarization in a Balmer line of the neutral hydrogen at 397 nm, H epsilon, that can only be explained by the presence of an electric field. In this presentation, we will discuss physics in the magnetic diffusivity, which allows magnetic field lines to reconnect, from what we measured.

12/16

Dai

End-view Observations of longitudinal oscillations of a quiescent prominence

I will present a interesting event recorded by SDO/AIA and CHASE/HIS.

pdf
4.3 MB

12/23

Shimada

New picture of field saturation mechanism in the solar convection zone

Strong toroidal magnetic flux tube in the solar convection zone(CZ) are thought to be origin of tilted active regions. Thin flux tube simulations(e.g. Caligari et al, 1995) suggest that 100 kG flux tube at the base of CZ is necessary for them to form tilted active regions. However, global dynamo simulations have failed to account for this field. Moreover, the physics determining field strength in the CZ remains unresolved. Classically, quenching mechanism of α-effect have been proposed within the framework of mean-field dynamo theory. Global dynamo sim. with high magnetic Reynolds numbers (Rm) (Hotta+ 2016) were analyzed by us and concluded that strong α-quenching is effective. However, some negative results that challenge our conclusion were obtained after careful analysis. This motivate us to discard the assumption of α-effect.In this talk, I will present the reanalyzed results. Main findings are as follows:
1. Mean-field approximation should not hold under high Rm
2. Instead of Ω-effect, turbulent stretching plays the dominant role in inducing large-scale magnetic fields.
3. Turbulent stretching is sensitive to large-scale fields, and energy dissipation by turbulence is not
These results suggest that saturation mechanism under high Rm is completely different from previous works(e.g. Strugarek+ 2018). Rm dependence of this mechanism is going to be investigated to predict saturation field strength in solar CZ.

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2.1 MB

1/6

Ichihara

Time variation of White-light flare on M-type star EV Lac with Seimei Telescope and TESS

Super flare, which releases the energy greater than 10^{33} erg, occurs frequently on M-dwarfs. Some flares sometimes accompany increment of optical continuum flux, called White-light flare. Although White-light flare is rare event on the sun because of its short duration, it is common event on M-dwarfs. Stellar flares attract attention in terms of Astrobiology. Many researchers have studied about stellar flares for many years, while we have not yet clarified the energy budget of White-light flare and its radiation process. I introduce the White-light flare on EV Lac, which is known as a active flaring M-dwarf. We analyzed the data of EV Lac obtained with spectroscopy of Seimei Telescope and photometry of TESS. The flare emission within optical range is well fitted with ~10000 K Blackbody radiation. I discuss about the time variation of the White-light flare and then talk about our future work.

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2.7 MB

1/20

Natsume

Comparison of multiple chromospheric lines for post-flare loop accompanied by flares

Post-flare loops are the one of the important elements of phenomena accompanied with solar flare. In recent research, the signal considered to come from post-flare loop has been detected. In Sun-as-a-star research, post-flare loop has contribution to the spectrum and equivalent width. To understand stellar observation through the solar physics, qualitative property of solar post-flare loop is needed, especially difference among the chromospheric lines. We observed solar flare with post-flare loop and conducted Sun-as-a-star analysis. In this talk, we are going to present the result of the analysis.

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4.4 MB

1/27

Yoshihisa

On the Occurrence of Thermal Non-Equilibrium in Wave-Heated Coronal Heating

In the solar corona, a phenomenon called "coronal rain" is observed, in which the temperature gradually cools from the coronal temperature to the chromospheric temperature. This cooling is thought to be caused by mechanisms related to thermal non-equilibrium (TNE) and thermal instability(TI). Furthermore, in recent years, 2–16 hour periodic EUV intensity pulsation have been reported in coronal loops. This phenomena are sometimes accompanied by coronal rain and are believed to result from evaporation and cooling (condensation) cycles within the loops. Coronal rain and periodic EUV intensity pulsations are observed less frequently and with longer periods in quiet regions compared to active regions. In this study, the investigation of the aforementioned long-period intensity pulsations was conducted by extending the previously used 1.5-dimensional simulations. Although still in the research phase, discussions are held regarding what determines the periodicity.

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3.2 MB