| Date |
|
Name |
Title |
Abstract |
File |
| 4/10 |
|
Asai |
Solar Seminar 2023 |
|
pdf
22.7 MB |
| 4/17 |
|
Ueno |
Consideration of the importance of measuring 3D velocity field of
erupting filaments for the space weather prediction |
Until now, our observatory has focused on the measurement of three-
dimensional velocity field of erupting filaments from the viewpoint of
space weather research by using SMART/T1, CHAIN-project.
On the other hand, recently, especially arrival time of the CME to the
geo-magnetosphere has been able to be predicted in higher accuracy than
before by computer simulations without information of filament's 3D
velocity field.
I would like to consider and discuss the present importance of
measuring 3D velocity field of erupting filaments for the space weather
prediction with everyone.
Moreover, I will introduce the result of improvement of the
spectroheliograph at Ica University, Peru that we did in last March in
order to raise the capture rate of filament eruptions.
|
pdf
6.0 MB |
| 4/24 |
|
Nagata |
Next Generation Ground based Solar Telescope of Kyoto University |
|
pptx
44.1 MB |
| 5/1 |
|
Ishii |
Event Report of SMART
(Solar Magnetic Activity Research Telescope)
/ SDDI (Solar Dynamics Doppler Imager)
from 2022 to 2023 |
Today, I would like to talk about
'Event Report of SMART
(Solar Magnetic Activity Research Telescope)
/ SDDI (Solar Dynamics Doppler Imager)
from 2022 to 2023'.
Movies
https://www.kwasan.kyoto-u.ac.jp/topics/kako.html
https://www.hida.kyoto-u.ac.jp/SMART/SDDI/event_report/
|
pptx
14.7 MB |
| 5/8 |
|
Kou |
ASO-S Data is partially opened |
On Monday I would like to give a talk on the status of ASO-S after launch how the released data looks like
as a continuation of the introduction to the instrument of ASO-S I presented on 2022/10/31.
Most of the information comes from the "ASO-S Data Analysis Guidance" held on 2023/04/11.
|
pdf
2.2 MB |
| 5/15 |
|
Mishra |
Instabilities in Different Magnetized Structures of the Solar Atmosphere |
In this talk I will briefly review some observational results of Rayleigh-Taylor instability, Kelvin-Helmholtz instability, and hybrid KH-RT instability in the solar atmosphere. After that, I will discuss my some new results regarding the evolution and impact of these instability in the solar atmosphere. I will also discuss the limitations of my results and future perspectives that could be explored to enhance our understanding about the evolution, growth, and impact of these instabilities in different magnetized structures. |
pptx
31.8 MB |
| 5/22 |
|
(No seminar because of JpGU) |
|
|
|
| 5/29 |
Practice for M2 interm report |
Natsume |
太陽フレアに伴う諸現象の、 4つの彩層ラインでのSun-as-a-star解析 |
太陽フレアも恒星フレアも、表面での突発的な増光現象であるが、太陽フレアでは
これを空間分解して観測することが可能である一方、恒星フレアでは空間積分したものに
相当するスペクトルや光度が観測でき、空間情報は失われてしまう。そこで、恒星の現象を
太陽物理学の知見で理解するために、Sun-as-a-star解析と呼ばれる、太陽のデータを
空間積分し恒星の観測データを模したデータを得る解析が近年行われている。
Namekata et al 2022aはその解析の活用例であり、太陽型星スーパーフレア
（最大級太陽フレアの 10 倍以上の規模のフレア）に伴う Hα 線の吸収成分と、
フレアに伴う太陽プラズマ 噴出現象の Sun-as-a-star 解析の比較から、
このスーパーフレアもプ ラズマ噴出を伴っていたことを明らかにした。
Namekataらは Hα 線のみを用いたが、他の彩層ラインも含む同時観測により、
各ラインの形成高度や温度、密度等への感度の違いから、より多くの物理情報を得られる可能性がある。
複数の彩層ラインの太陽撮像分光データを用いたSun-as-a-star解析を行い、
どのような相違点があるのかを調べることを目的として、
京都大学飛騨天文台DSTで観測した太陽フレアに伴う吸収と増光について、
Hα 線とCa II K線、Ca II 8542Å、He I 10830Åの4つの彩層ラインのスペクトルの
Sun-as-a-star解析を行った。解析を行った現象は、、2022年8月19日活動領域NOAA 13078の
(1)04:30-05:30(UT)のツーリボンフレア、(2)05:15-60:00のフレアの増光とフィラメントの
ドップラーシフト、(3)08:00-09:00のフレアの増光とフィラメントのドップラーシフトの３つである。
今回の発表では、(2)を発表する。
解析の結果、フィラメントのドップラーシフトについては、
HeとHαのwingでのプロファイルが似ており、フィラメントに関しては似た吸収感度を持つこと、
Hα中心の増光の部分でも、He中心付近では吸収が見えている場合があることが分かった。
フレアの増光はCa II KにＨαに比べて吸収成分の影響が小さく、増光のスペクトルを検出しやすいことが分かった。 |
|
|
Practice for M2 interm report |
Yoshihisa |
衝撃波と乱流的効果によるコロナ加熱を考慮したプロミネンス形成についての1.5次元MHDシミュレーション |
プロミネンスに代表される太陽プラズマの凝縮現象は、長年にわたって観測されているが、
その形成メカニズムや物理的性質は十分に解明されていない。
最も有力なメカニズムの一つである「彩層蒸発-凝縮モデル」では、プロミネンスは熱非平衡と
暴走的な冷却によって形成されると考えられている。プロミネンス形成の熱的進化を理解するためには、
冷却と加熱の両方の物理変数や時間に対する依存性を考慮する必要がある。しかし、多くの先行研究では、
加熱項は簡略化のためにad hocな形でのみ考慮されている。
また、実際の太陽大気が凝結現象に与える影響を考えるには、コロナだけでなく、光球の対流運動や、
温度や密度構造が大きく変化する彩層の影響も考慮する必要がある。
そこで、本研究では、光球からコロナに至る領域でのAlfven波加熱を考慮した1.5次元MHDシミュレーションにより、
形成過程を検討することにした。プロミネンスを再現するために、窪んだ磁力線と足元に集中した局所加熱項を導入した。
その結果、(1)境界摂動に由来する衝撃波の通過と衝突が凝縮を誘発すること、(2)プロミネンスが足元に近づいた際に、
コロナでの加熱が上昇するため圧力が上昇してプロミネンスを押し返していることを確認した。
前者の結果は、表面での対流運動が凝縮を誘発していることを示し、プロミネンスの普遍性を裏付けている。 |
|
| 6/5 |
|
Shirato |
Observational study of the relationship between wave propagation and magnetic fields
in the lower solar atmosphere over the entire solar surface using SMART/SDDI |
One of the most promising mechanisms in the chromospheric and coronal heating problem is
the wave heating theory. Among acoustic waves excited by the turbulence motion
at the photosphere, those with a frequency lower than ‘cutoff frequency’ cannot propagate
into the upper layers. However, in regions where the magnetic field lines are inclined,
it is thought that the cutoff frequency becomes lower than surrounding regions.
To verify this observationally, it is important to focus on the relationship
between the wave propagation and the magnetic field distribution at lower chromosphere.
However, there are a number of studies working on this topic, but the best of my knowledge,
all of them analyzed the relationship in a localized region, espicially disc center.
In order to fill the blank, this study conducted spectroscopic imaging observations
of the entire solar surface for more than 12 hours on May 4, 2022, using the SMART/SDDI
at the Hida Observatory of Kyoto University. We extracted parameters such as intensity
and velocity using Hα lines, calculated power spectra and phase differences,
and investigated the relationship between the magnetic field structure
and wave propagation not only in the quiet region but also in the plage region,
active region, and enhanced network at various scales.
As a result, it was found that there are characteristic distributions of oscillation power,
especially in the 3-minute and 5-minute periods, in the propagation of waves
in the quiet region network, active region, enhanced network, and dark filament.
In addition, many observational studies have shown that the power of
the 5-minute Doppler velocity of absorption lines in the chromosphere is stronger
in the network region where the magnetic field lines are inclined. In this talk,
I will present some of the results obtained and discuss their physical interpretations. |
pptx
29.0 MB |
| 6/12 |
|
Otsu |
Multiwavelength Sun-as-a-star Analysis of an M8.7 Flare on 2022 Oct. 2 Using Hα and EUV with SMART/SDDI and SDO/EVE |
Solar flares are known as explosive phenomena that occur in the solar atmosphere. Thanks to imaging
observations of the Sun, the detailed process of solar flares have been revealed. On the other hand,
sudden brightening called stellar flares have been also observed in other stars. Stellar flares that
emit 10 times more energy than the largest solar flares are called superflares. Recent stellar
observations suggest that stellar flares are aslo followed by various processes like solar flares.
To understand stellar data without spatial resolution, some studies use solar data by performing Sun-as-a-star analyses in which solar data are spatially integrated. Especially, spectroscopic Sun-as-a-star analyses are useful to investigate flare and plasma dynamics. So far, H-alpha and Extreme Ultraviolet (EUV) spectroscopic Sun-as-a-star analyses were performed independently. Simultaneous analyses of these lines with different formation tempertaure would provide further understanding of solar active phenomena in the Sun-as-a-star viewpoint.
In this study, we performed a Sun-as-a-star analysis of an M8.7 flare and the associated eruption
that occurred on 2022 October 2 using SMART/SDDI (H-alpha imaging spectroscopy) at Hida Observatory,
Kyoto University and SDO/EVE (EUV full-disk integrated spectroscopy). As a result, a blueshifted
absorption component of ∼300 km/s appeared in the spatially integrated H-alpha line spectra,
although it was fainter than slower components. In addition, a blueshifted emission was observed
in the EUV spectra such as OV 62.97 nm almost simultaneously with the absorption of
the fast component in the H-alpha line. I will report the details of the time evolution of
these blueshifted components in the H-alpha and EUV with a view to their application to
stellar research. Also, I will discuss other key features such as coronal rains
and CME-related dimmings. |
pdf
3.42 MB |
| 6/19 |
|
Shimada |
From the Small-Scale Dynamo to the Solar Cycle |
Solar magnetic fields comprise an 11 yr activity cycle, represented by the number of
sunspots. The maintenance of such a solar magnetic field can be attributed to fluid
motion in the convection zone (CZ), i.e., a dynamo.
Luck of information on the convection forces us to infer the property of the convection
by numerical simulations. Recent high resolution simulations on CZ suggests that
the small-scale dynamo is crucial to understand the dynamics of CZ. On the other hand,
long-term calculations on the solar cycle with sufficient small-scale dynamo is impractical.
From these backgrounds, we develop an Sub-Grid Scale (SGS) model which enable us
to conduct low resolution simulations with the physical information on the small-scale dynamo.
To validate our SGS models, we reproduce the small-scale dynamo in previous work (Hotta+ 2015)
by own developed code and extract SG diffusivity. Our methods successfully extract
the diffusivity which is consistent with the effect suggested by Bekki+ 2017
about small-scale dynamo. By combining our results with Bekki+ 2017,
our SGS can reproduce the effect of the small-scale dynamo on thermal mixing
in lower resolution calculation. |
pptx
5.8 MB |
| 6/26 |
|
Kida |
Analysis of three-dimensional instability of flux ropes in active region flares |
|
pptx
8.3 MB |
| 7/3 |
|
Natsume |
The Sun-as-a-star analysis of multiple
chromospheric lines for active phenomena accompanied by flares |
In order to interpret the magnetic activity phenomena data of stars
spatially unresolvable through the knowledge of solar physics spatially resolvable,
an analysis called "Sun-as-a-star" has been conducted in recent years
by spatial integration of solar observation data into data mimicking stellar observations.
Namekata et al. (2022a) compared Hα absorption components of a solar-type stellar
superflare and of the Sun-as-a-star data of solar filament ejection associated
with the flare, and found that the superflare was also accompanied by a filament eruption.
The chromospheric line used for Sun-as-a-star analysis of short-term magnetic activity phenomena
like flares is mainly Hα line (e.g., Otsu et al. 2022), but simultaneous observation
including other chromospheric lines have the potential to obtain more physical
information due to differences in sensitivity to physical conditions such as formation height,
temperature, and density of each line. For example, a fast component of
solar filament ejection has been detected in He I 10830 Å (Penn 2000),
and the differences from Hα line are of interest.
We performed a Sun-as-a-star analysis of four chromospheric lines
(Hα, Ca II K, Ca II 8542 Å, and He I 10830 Å) for the brightening and
filament activity associated with the solar flare. As a result,
it was found that the Hα and He I absorption component have similar line widths
and sensitivity in their wings, but even when the Hα absorption component
cannot be detected due to the flare brightening near its line center,
the He I absorption component can be detected due to the week brightening
near its line center. On the other hand, it was considered that the Ca II K line
had less influence from the absorption component of the filament compared to the Hα line,
making the flare brightening component easier to detect. |
pdf
4.2 MB |
| 7/10 |
|
Yoshihisa |
Review on coronal loops in thermal non-equilibrium with coronal rain and long-period intensity pulsation |
TNE are thought to be responsible for various dynamic phenomena in the solar corona such as prominences and coronal rains.
Recently observed periodic time variability of EUV intensity, called long-period intensity pulsation, is considered to be one of them.
The mechanisms underlying these phenomena are not fully understood. The basic idea of TNE is as follows.
Considering a situation in which localized heating is applied steadily to the lower part of the coronal loop,
the chromosphere is first heated, which causes chromospheric evaporation and thereby an increase in coronal density.
This is accompanied by an increase in radiative cooling loss, which leads to the condensation of plasma at chromosphere temperature,
as seen in prominences and coronal rains. Subsequent studies have also shown that a combination of various parameters,
such as the nature of the local heating and the geometry of the loop, is important. In this review, we provide a review of
these parameter surveys. It will also deal with how the TNE studies provide clues to the corona heating problem. |
pptx
20.6 MB |
| 7/17 |
|
(No Seminar because of National Holiday) |
|
|
|
| 7/24 |
Practice for Master thesis defense |
Kida |
(canceled) |
|
|
| Date |
|
Name |
Title |
Abstract |
File |
| 10/2 |
|
Ishii |
A New Magnetic Parameter of Active Regions Distinguishing Large Eruptive and Confined Solar Flares |
Today, I would like to introduce the following paper
https://ui.adsabs.harvard.edu/abs/2022ApJ...926L..14L/abstract
|
pptx
4.9 MB |
| 10/9 |
|
(No Seminar because of National Holiday) |
|
|
|
| 10/16 |
|
(No seminar because of SGRE2023
|
|
|
|
| 10/23 |
|
Mishra |
Quasi-Periodic Pulsation in Small-scale Eruptions in the Solar Atmosphere |
The solar atmosphere possesses marvellous small- to large-scale eruptions that appear on different
spatio-temporal scales. Some of the more violent solar eruptions include solar flares, CMEs, and
prominence/filament eruptions. Smaller eruptions like jets, spicules, and suerges are also visible.
In this talk, I am going to talk about one of my works in which we detect quasi-periodic pulsations (QPPs)
in a coronal blowout jet, which is rare in small-scale eruptions but common in large-scale eruptions
such as solar and stellar flares. In the present work, using imaging and spectroscopic analysis,
we found a QPP signature in the eruptive jet with an average period of ~3 minutes.
Periodic magnetic reconnection is the most acceptable mechanism to trigger these QPPs
in the eruptive phase of the jet. In the later part of my talk, I will also discuss
one of my ongoing works related to the persistent reconnection and triggering of coronal jets
in the solar atmosphere. |
pptx
130 MB |
| 10/30 |
|
Shirato |
Investigation the role of waves in chromospheric and coronal heating in different magnetic field structures |
Today I briefly talk about my new project: Investigation the role of waves
in chromospheric and coronal heating in different magnetic field structures. |
pdf
0.9 MB |
| 11/6 |
|
Otsu |
Sun-as-a-star Analysis of Post-flare Loops |
Post-flare loops are loop-shaped plasma which appears during the decay phases of typical solar flares,
and they are key ingredients of the standard flare model. However, there is no definitive report for detection
of post-flare loops in the case of stellar flares. In this talk, I review the current status of investigation for
stellar post-flare loops and introduce the remarkable points for the detection of them based on
the Sun-as-a-star analysis. Also, I introduce preliminary result of the Sun-as-a-star analysis of the X1.6 flare
on 2023 August 5 which showed clear post-flare loops. |
pdf
2.9 MB |
| 11/13 |
|
Shimada |
Connection between deep and surface small-scale dynamo |
In this talk, I summarize the current understanding of small-scale dynamo(SSD) and
report the progress of my project which was presented in the last solar seminar.
SSD is the dynamo that works at the spatial scales smaller than the forcing in a plasma system. In the solar convection zone(CZ), this scale corresponds to the convection cell size.Independence of the quiet sun internetwork magnetic field on solar cycle suggests the origin of this field is SSD since small-scale dynamo thought not to depend on the cycle. Recent 3D RMHD simulations (Rempel 2014, 2018) reproduce unsigned magnetic flux density on the photosphere by SSD under the condition that simulation allows inflow of the magnetic flux from the deep CZ.
In deep CZ, the importance of the SSD is recognized by the "Convective Conundrum"(Hanasoge+ 2012).
"Convective Conundrum" is the gap of the large-scale convective velocity in deep CZ between the helioseismology
and numerical simulations. Recent high-resolution simulations(Hotta+2021) show efficient SSD
can compensate for this gap. Although the suppression of the convective velocity by the change of
the stratification through SSD is reported(Bekki+ 2017, Hotta+ 2022), the degree of the suppression is
thought to depend on SSD works in the photosphere which is not included in deep CZ simulations.
Since SSD affects the stratification, differential rotation, and meridional circulation,
it is crucial to consider the effect of SSD on the solar cycle.To understand this effect,
we develop the subgrid-scale(SGS) model which extracts the properties of SSD works in high-reso
simulation. As I presented last solar seminar, we successfully reproduced the SSD effect by
this SGS model under limited spatial resolution and time duration. Recently, we optimized
the parallel computing of my code, and this enables us to compute SSD in deep CZ with sufficient
resolution and time duration. We further discuss the possibility of the modification of our model
which incorporates the surface SSD effect. |
pptx
16.9 MB |
| 11/20 |
|
(No seminar because of Solar Future Plan Symposium) |
|
|
|
| 11/27 |
|
Kida |
Analysis of three-dimensional instability of flux ropes in active
region flares |
It is widely accepted that eruption of magnetic flux rope is
driven by the MHD instability,e.g. torus instability(Kliem and Török
2006). Many previous studies assume the direction of the eruption is
normal to the solar surface, however some of the flares show
non-radially directed CMEs (McCauley+ 2015).
In this study, we carefully analyze the non-radially directed flux rope
eruption observed in NOAA12871 on 21-Sep-2021 associated with M2.8 flare
and CME. A small brightening is observed along the magnetic neutral line
and then the flux rope appears as hot channel in high temperature band
of SDO/AIA images.
The eruption of the flux rope formed along the magnetic neutral line
followed by the slow rise phase is successfully explained using the 1D
numerical solution of the equation of motion for torus instability by
Kliem and Török 2006. We also found that the flux rope is free from
torus stability when the flux rope is formed, and the initial velocity
is required to develop eruption. |
(extension)
MB |
| 12/4 |
|
Yoshihisa |
The prominence formation through a transient impulsive heating |
Solar prominences are relatively dense and cool plasmas in the corona. One of the most plausible
formation mechanisms, the ”Evaporation-Condensation” model suggests that coronal loops are brought
to thermal non-equilibrium state by the (quasi-)steady localized heating at footpoints. And
the condensation occurs locally due to thermal instability (or just runaway cooling). Such a steady heating,
however, unlikely tooccur especially in quiet regions, where the prominence ubiquitously appears.
Recently, an observationstudy reported the condensation caused by a transient impulsive heating event.
Numerical simulationsare necessary to investigate the conditions under which such condensation phenomena occur.
To this end, we conduct 1.5-dimensional magnetohydrodynamics simulations for a dipped magnetic loop
considering energy dissipation by turbulent cascade and shock waves. A single localized heating of
nanoflare-class is additionally introduced. As a result, we found that the amplitude of the localized
heating per unit time necessary for condensation to occur is ∼ 10^3 times larger than in the case of
steady heating. The importance of shock waves originating from photospheric motion for perturbing
the corona is also reconfirmed. Finally new conditions for condensation to occur are derived from our simulations. |
pdf
2.5 MB |
| 12/11 |
|
Natsume |
The Sun-as-a-star analysis of multiple chromospheric lines for active phenomena accompanied by flares |
In order to interpret the magnetic activity phenomena data of stars spatially unresolvable
through the knowledge of solar physics spatially resolvable, an analysis called "Sun-as-a-star"
has been conducted in recent years by spatial integration of solar observation data into
data mimicking stellar observations. Namekata et al. (2022a) compared Hα absorption components of
a solar-type stellar superflare and of the Sun-as-a-star data of solar filament ejection associated with
the flare, and found that the superflare was also accompanied by a filament eruption.
The chromospheric line used for Sun-as-a-star analysis of short-term magnetic activity phenomena like
flares is mainly Hα line (e.g., Otsu et al. 2022), but simultaneous observation including
other chromospheric lines have the potential to obtain more physical information due to differences in
sensitivity to physical conditions such as formation height, temperature, and density of each line.
For example, a fast component of solar filament ejection has been detected in He I 10830 Å (Penn 2000),
and the differences from Hα line are of interest. We performed a Sun-as-a-star analysis of
four chromospheric lines (Hα, Ca II K, Ca II 8542 Å, and He I 10830 Å) for the brightening and
filament activity associated with the solar flare, considering of full-disk and center-to-limb variation.
As a result, it was found that the Hα and He I absorption component have similar line widths and sensitivity
in their wings, but even when the Hα absorption component cannot be detected due to the flare brightening near
its line center, the He I absorption component can be detected due to the week brightening near its line center.
We also found that He I equivalent width decreased at flare peek and the dimming of He I is 4 times larger than
that of Hα. We can say that absorption signal of He I can be found in 4 times worse S/N in than that of Hα. |
pdf
3.2 MB |
| 12/18 |
|
Suzuki |
Extension of solar wind model to M dwarf winds |
The M dwarf's magnetic activities have been particularly discussed with the focus on their impact on
the planetary atmosphere. Because of the difficulty of observing the stellar winds, numerical simulation
plays an important role in estimating physical value of the stellar winds. In on-dimensional simulation
of the solar winds, the wind is mainly accelerated by "Nonlinear mode conversion" and
"Alfven wave turbulence(AWT)". However, although the simulations of M dwarf's wind is applied
solar wind model, there is no one-dimensional MHD simulation including AWT.
In order to evaluate more realistic mass-loss rate, we need to calculate stellar
wind simulation including AWT. |
(extension)
MB |
| 12/25 |
D2 interim report |
Shirato |
Investigation of the wave propagation in the solar atmosphere – relation to the magnetic field and the view angle – |
|
pptx
89 MB |
| 1/1 |
|
(No Seminar because of National Holiday) |
|
|
|
| 1/8 |
|
(No Seminar because of National Holiday) |
|
|
|
| 1/15 |
Guest Seminar |
Shin Toriumi (JAXA/ISAS) |
(title) |
|
|
| 1/22 |
|
No seminar |
|
|
|
| 1/29 |
|
No seminar |
|
|
|
| 2/5 |
Practice for Master thesis defense |
Kida |
活動領域フレアにおける、フラックスロープのトーラス不安定性に関する３次元的解 |
(abstract) |
(extension)
MB |
|
Practice for Master thesis defense |
Natsume |
飛騨天文台DSTを用いた太陽磁気活動現象の複数彩層ラインでのスペクトルの比較解析 |
(abstract) |
(extension)
MB |
|
Practice for Master thesis defense |
Yoshihisa |
突発的な加熱による太陽プロミネンス形成に関する１次元磁気流体シミュレーション |
太陽プロミネンスやコロナレインなど、コロナにおける比較的低温高密なプラズマは長年観測されている。これらの形成メカニズムを説明するために様々なモデルが提唱されてきた。その一つと
して挙げられる彩層蒸発-凝縮モデルでは、コロナループ足元に集中した準定常的な加熱が彩層上部を温めて、それによる上昇流がコロナにプラズマを供給して、暴走的な冷却によって凝縮が生じ
ることを想定している。このモデルを用いた数値計算では、数時間に及ぶコロナプラズマの冷却過程が再現されている。しかし、このモデルにおいて加熱分布は鍵であるにも関わらず、想定されて
いる準定常的な足元局所加熱が活動領域を除いた領域においてもみられるかは、観測的にも理論的にも明らかではないという問題点がある。また近年の観測では、突発的な加熱から数十分後に凝縮
が生じるような現象が報告されているが、既存のモデルでは説明できない。これらを踏まえて本研究では、突発的な加熱現象に伴う彩層蒸発-凝縮によるプロミネンス形成についての数値計算を用
いた調査を行う。計算設定としては、窪みを持ったループに沿った輻射冷却、熱伝導、重力、現象論的な加熱を含む 1.5 次元（空間 1 次元、速度場、磁場 3 成分）磁気流体シミュレーションを考
える。足元に加えた速度場により注入されたエネルギーが衝撃波と Alfv´en 波の乱流カスケードによって散逸する（背景加熱）ことで、ループがコロナ温度にまで温められて、そこへ局所加熱を加
えることで凝縮現象を再現する。また、局所加熱を変えるパラメータサーベイを行うことで、凝縮の生じるメカニズムを調べる。結果として、定常的な加熱を加えた場合より約 103 倍大きな加熱率
の突発的な局所加熱を与えることによって凝縮が生じた。十分大きな加熱によって彩層プラズマがコロナに供給された結果、温度が低下して、冷却の時間スケールに対して熱伝導の時間スケールが
長くなることが本質的に重要であることがわかった。ループの長さ L とフィールド長 λF を用いてこれを表すと、λF < L/2 と表される。 |
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