Author name code: asai
ADS astronomy entries on 2022-09-14
author:"Asai, Ayumi"
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Title: Solar Energetic Particle Events with Delayed Onsets
Authors: Kihara, Kosuke; Asai, Ayumi; Nitta, Nariaki; Yashiro, Seiji
Bibcode: 2022cosp...44.1169K
Altcode:
Solar energetic particles (SEPs) give rise to critical radiation
hazards for astronauts and airline passengers and cause damages to
satellites. They have a significant impact on the social infrastructure
and are an important subject in space weather. One of the major
origins of SEPs is considered to be coronal mass ejections (CMEs),
and the shocks at the fronts accelerate the charged particles to be
SEPs. In order to understand how SEPs are accelerated by CMEs and
reach the Earth, we conducted a statistical study of the relation
between CMEs and SEP events. We measured the onset time (TO), defined
as the time from the CME launch to the proton arrival in Earth orbit,
and studied the relation between CME or SEP parameters. Our study
showed that TO tends to be shorter if the source CMEs erupt near the
nominal footpoints of parker spiral magnetic fields connecting to the
instrument. The relation between the speed of CMEs and TO is negative in
that longitude. On the other hand, even if the source and speed of CMEs
are similar, the distribution of TO is slightly dispersed. Therefore,
we now focus on the SEP events that occurred on July 14, 2017, which has
a relatively long TO among those events, and are conducting a detailed
analysis. We extracted a total of 4 events that have long and short
TO originating from similar CMEs, including this event. This analysis
has shown that the characteristics of the accompanying flares were
significantly different between long and short TO events. Furthermore,
we compared the time of type II radio burst, which is considered to
be an indicator of particle acceleration in coronal shock waves, with
that of particle release measured by velocity dispersion analysis and
found that the interval between them is longer in the long TO event
on July 14, 2017.
Title: Universal Correlation between the Ejected Mass and Total
Flare Energy for Solar and Stellar Cold Plasma Ejection
Authors: Kotani, Yuji; Otsuji, Kenichi; Shibata, Kazunari; Asai,
Ayumi; Ichimoto, Kiyoshi; Ishii, Takako; Yamasaki, Daiki
Bibcode: 2022cosp...44.2450K
Altcode:
We often find spectral signatures of chromospheric plasma ejections
accompanied by flares in various spatial scales in the solar and stellar
atmospheres. Similar spectral signatures are found regardless of their
wide range of scale. However, no physical quantities such as mass and
energy have been estimated for flare energies covering over 10 orders
of magnitude until now. In this study, we analyzed the spectra of
cold plasma ejections associated with flares by performing H$\alpha$
imaging spectroscopy of the solar full-disk with SMART/SDDI. We
determined the ejected mass by cloud model fitting to the H$\alpha$
spectrum. We estimated flare energy by DEM analysis using SDO/AIA
for small-scale flares and by estimating the bolometric energy for
large-scale flares. In addition, we constructed a scaling law for
the total flare energy and the ejected mass and compared it with our
observation. The results are in good agreement with the scaling law for
small mass ejections with small flares in the quiet region for a coronal
field strength of 5 G and filament eruptions with flares for that of 5 -
50 G. We also compared it with the observations interpreted as stellar
filament eruptions, and found that they were roughly consistent with
the scaling law. These results suggest that cold plasma ejections with
flares taking place on the sun and stars in a wide range of the energy
scale are caused by a common mechanism.
Title: Sun-as-a-star analysis of H-alpha spectra for various active
events on the Sun
Authors: Otsu, Takato; Asai, Ayumi; Ichimoto, Kiyoshi; Namekata,
Kosuke; Ishii, Takako
Bibcode: 2022cosp...44.1380O
Altcode:
The surface of the Sun can be observed with high spatial resolution. On
the other hand, the surfaces of distant stars cannot be spatially
resolved. From this background, detailed data of the Sun have been
utilized for analysis of stellar data in recent years (e.g., Toriumi
et al. 2020, Namekata et al. 2021). For comparison with stellar data,
solar data are spatially integrated and such an analysis is called
Sun-as-a-star analysis. Namekata et al. (2021) carried out Sun-as-a-star
analysis of the H$\alpha$ spectra for solar flares accompanied by
filament eruptions in order to interpret the H$\alpha$ spectra for a
stellar flare. From a resemblance between them, the authors concluded
that a stellar filament eruption associated the detected stellar
flare. On the basis of Namekata et al. (2021), Sun-as-a-star analysis
of H$\alpha$ spectra is useful to investigate the motion of plasma on
a stellar surface. Therefore, it is important to study Sun-as-a-star
analysis of H$\alpha$ spectra for, in addition to flares, other various
active events on the Sun. Here we report a result of Sun-as-a-star
analysis of H$\alpha$ spectra for various solar active events,
namely, flares, filament eruptions, and prominence eruptions. We used
full-disk solar H$\alpha$ spectral data observed by SMART/SDDI at Hida
observatory, Kyoto University. SMART/SDDI can takes full-disk solar
images in the wavelengths from H$\alpha$ $-9.0$~{\AA} to H$\alpha$
$+9.0$~{\AA} with the spectral resolution of 0.25~{\AA} and the time
cadence of 12-16 sec (Ichimoto et al. 2017). All analyzed events show
brightening relative to pre-event and their changes in H$\alpha$
equivalent width are the same orders of $10^{-4}$~{\AA}. However,
there are different features in H$\alpha$ spectra depending on
causes of brightening: brightening near H$\alpha$ center with red
asymmetry and line broadening due to flares, brightening near H$\alpha$
center accompanied by shifted absorptions due to filament eruptions,
and shifted brightening due to prominence eruptions. These spectral
features can be used to diagnose the causes of brightening even though
the changes in the H$\alpha$ equivalent width are similar. Our result
can be helpful in studying various active events on stars.
Title: Investigation on the Evolution of the Nonpotential Magnetic
Field and the Onset Mechanism of the Successive M-class Solar Flares
in the Active Region NOAA 12673 Based on a Nonlinear Force-Free
Modeling
Authors: Yamasaki, Daiki; Inoue, Satoshi; Kusano, Kanya; Ishii,
Takako; Asai, Ayumi; Nagata, Shin'ichi; Ichimoto, Kiyoshi
Bibcode: 2021AGUFMSH23B..03Y
Altcode:
In September 2017, Active region (AR) NOAA 12673 has produced many
M-class and several X-class flares, one of which being an X9.3 flare,
which is recorded as the largest solar flare in solar cycle 24. Although
many M- and C-class flares have been observed before the occurrence
of the X-flares, the magnetic field structure before the flares and
the flare triggering mechanism have been not studied well. Therefore,
in this study, we reveal the magnetic field structure prior to the
flares and flare triggering mechanism, in particular, of M5.5 flare,
which is the largest M-class flare observed in AR 12673. In our study,
we analyzed the evolution of the three-dimensional magnetic field in AR
12673, using a time series of nonlinear force-free field extrapolations
of every 12 hours from 2017 September 4 00:00 UT to 6 00:00 UT. We
found that three magnetic flux ropes (MFRs) formed by September 4,
one of which produced the X9.3 flare on September 6. One MFR has
positive magnetic twist, which is a different sign from the other two
MFRs. Since the several M-class flares were observed when the time
profile of the magnetic flux of the MFR accumulating the positive
twist had a peak, we suggest that the formation of the MFR having the
positive twist is closely related to the occurrence of the M-class
flares, including an M5.5 flare. We further found a magnetic null in
the magnetic field surrounding the MFRs, which, in particular, locates
above the MFR having positive twist. By comparing with Atmospheric
Imaging Assembly 1600 angstrom images, we found that the footpoints
of the overlying field lines are anchored to the area where initial
brightening associated with the M5.5 flare was observed. Therefore,
we suggest that reconnection at the magnetic null possibly drove the
M5.5 flare. In addition, M4.2 flares was observed about 4.5 hours after
the onset of the M5.5 flare, and the initial brightenings and the flare
ribbons were observed in spatially similar location in AIA 1600 angstrom
in both flares. Interestingly, CME was only observed shortly after the
peak time of the M5.5 flare. In our presentation, we further discuss
the onset mechanism of the successive M-class flares and the cause of
the difference on the CME association in these two M-class flares.
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: Relationship between three-dimensional velocity of filament
eruptions and CME association
Authors: Seki, Daikichi; Otsuji, Kenichi; Ishii, Takako T.; Asai,
Ayumi; Ichimoto, Kiyoshi
Bibcode: 2021EP&S...73...58S
Altcode: 2021arXiv210204578S
It is widely recognised that filament disappearances or eruptions are
frequently associated with Coronal Mass Ejections (CMEs). Since CMEs
are a major source of disturbances of the space environment surrounding
the Earth, it is important to investigate these associations in detail
for the better prediction of CME occurrence. However, the proportion
of filament disappearances associated with CMEs is under debate. The
estimates range from ∼ 10 to ∼ 90% and could be affected by the
manners to select the events. In this study, we aim to reveal what
parameters control the association between filament eruptions and
CMEs. We analysed the relationships between CME associations and the
physical parameters of filaments including their length, maximum
ascending velocity, and direction of eruptions using 28 events of
filament eruptions observed in Hα . We found that the product of the
maximum radial velocity and the filament length is well correlated with
the CME occurrence. If the product is larger than 8.0 ×106
km2s-1, the filament will become a CME with a
probability of 93%, and if the product is smaller than this value,
it will not become a CME with a probability of 100%. We suggest a
kinetic-energy threshold above which filament eruptions are associated
with CMEs. Our findings also suggest the importance of measuring the
velocity vector of filament eruption in three-dimensional space for
the better prediction of CME occurrence.
Title: 20 Years of Gender Equality Activities in Astronomical Society
of Japan
Authors: Bamba, Aya; Asai, Ayumi; Ishikawa, Ryohko; Sato, Kosuke;
Nobukawa, Masayoshi; Nomura, Hideko; Furusawa, Hisanori; Machida, Mami
Bibcode: 2021AstHe.114..688B
Altcode:
The female ratio in science field, including astronomy and astrophysics,
is still low in Japan. We, the Astronomical Society of Japan, keep
making efforts for the better gender balance. In this article, we
summarize our survey results, how members' thinking changed within
these 20 years from our questionnaire, the history and accomplishments
of day-care system during annual meeting, other activities, and so on.
Title: A three-dimensional velocity of an erupting prominence prior
to a coronal mass ejection
Authors: Gutierrez, Maria V.; Otsuji, Kenichi; Asai, Ayumi; Terrazas,
Raul; Ishitsuka, Mutsumi; Ishitsuka, Jose; Nakamura, Naoki; Yoshinaga,
Yusuke; Morita, Satoshi; Ishii, Takako T.; Ueno, Satoru; Kitai,
Reizaburo; Shibata, Kazunari
Bibcode: 2021PASJ...73..394G
Altcode: 2021arXiv210108575G; 2021PASJ..tmp...23G
We present a detailed three-dimensional (3D) view of a prominence
eruption, coronal loop expansion, and coronal mass ejections (CMEs)
associated with an M4.4 flare that occurred on 2011 March 8 in the
active region NOAA 11165. Full-disk Hα images of the flare and filament
ejection were successfully obtained by the Flare Monitoring Telescope
(FMT) following its relocation to Ica University, Peru. Multiwavelength
observation around the Hα line enabled us to derive the 3D velocity
field of the Hα prominence eruption. Features in extreme ultraviolet
were also obtained by the Atmospheric Imager Assembly onboard the Solar
Dynamic Observatory and the Extreme Ultraviolet Imager on board the
Solar Terrestrial Relations Observatory - Ahead satellite. We found
that, following collision of the erupted filament with the coronal
magnetic field, some coronal loops began to expand, leading to the
growth of a clear CME. We also discuss the succeeding activities of
CME driven by multiple interactions between the expanding loops and
the surrounding coronal magnetic field.
Title: Statistical Analysis of the Relation between Coronal Mass
Ejections and Solar Energetic Particles
Authors: Kihara, K.; Nitta, N.; Yashiro, S.; Asai, A.; Ichimoto, K.
Bibcode: 2020AGUFMSH012..02K
Altcode:
To improve the forecasting capability of impactful solar energetic
particle (SEP) events, the relation between coronal mass ejections
(CMEs) and SEP events needs to be better understood. Here we present
a statistical study of SEP occurrences and timescales with respect
to the CME source locations and speeds, considering all 257 fast
(vCME ≥ 900 km/s) and wide (angular width ≥ 60°) CMEs
that occurred between December 2006 and October 2017. We associate
them with SEP events at energies above 10 MeV. Examination of the
source region of each CME reveals that CMEs more often accompany a
SEP event if they originate from the longitude of E20-W100 relative
to the observer. However, a SEP event could still be absent if the
CME is < 2000 km/s. For the associated CME-SEP pairs, we compute
three timescales for each of the SEP events, following Kahler (2005,
2013); namely the timescale of the onset (TO), the rise time (TR),
and the duration (TD). They are correlated with the longitude of
the CME source region relative to the footpoint of the Parker spiral
(ΔΦ) and vCME. The TO tends to be short for |ΔΦ| <
60° . This trend is weaker for TR and TD. The SEP timescales are only
weakly correlated with vCME. Positive correlations of both
TR and TD with vCME are seen in poorly connected (large
|ΔΦ|) events. Additionally, TO appears to be negatively correlated
with vCME for events with small |ΔΦ|.
Title: Statistical Analysis of the Relation between Coronal Mass
Ejections and Solar Energetic Particles
Authors: Kihara, Kosuke; Huang, Yuwei; Nishimura, Nobuhiko; Nitta,
Nariaki V.; Yashiro, Seiji; Ichimoto, Kiyoshi; Asai, Ayumi
Bibcode: 2020ApJ...900...75K
Altcode: 2020arXiv200708062K
To improve the forecasting capability of impactful solar energetic
particle (SEP) events, the relation between coronal mass ejections
(CMEs) and SEP events needs to be better understood. Here we present
a statistical study of SEP occurrences and timescales with respect
to the CME source locations and speeds, considering all 257 fast
(vCME ≥ 900 km s-1) and wide (angular width
≥60°) CMEs that occurred between 2006 December and 2017 October. We
associate them with SEP events at energies above 10 MeV. Examination of
the source region of each CME reveals that CMEs more often accompany a
SEP event if they originate from the longitude of E20-W100 relative to
the observer. However, an SEP event could still be absent if the CME is
<2000 km s-1. For the associated CME-SEP pairs, we compute
three timescales for each of the SEP events, namely the timescale of
the onset (TO), the rise time (TR), and the duration (TD). They are
correlated with the longitude of the CME source region relative to
the footpoint of the Parker spiral (ΔΦ) and vCME. The
TO tends to be short for $| {\rm{\Delta }}{\rm{\Phi }}| \ \lt $
60°. This trend is weaker for TR and TD. The SEP timescales are only
weakly correlated with vCME. Positive correlations of both
TR and TD with vCME are seen in poorly connected (large $|
{\rm{\Delta }}{\rm{\Phi }}| $ ) events. Additionally, TO appears to
be negatively correlated with vCME for events with small $|
{\rm{\Delta }}{\rm{\Phi }}| $ .
Title: SMART/SDDI Filament Disappearance Catalogue
Authors: Seki, Daikichi; Otsuji, Kenichi; Ishii, Takako T.; Hirose,
Kumi; Iju, Tomoya; UeNo, Satoru; Cabezas, Denis P.; Asai, Ayumi;
Isobe, Hiroaki; Ichimoto, Kiyoshi; Shibata, Kazunari
Bibcode: 2020arXiv200303454S
Altcode:
This paper describes a new SMART/SDDI Filament Disappearance Catalogue,
in which we listed almost all the filament disappearance events
that the Solar Dynamics Doppler Imager (SDDI) has observed since
its installation on the Solar Magnetic Activity Research Telescope
(SMART) in May 2016. Our aim is to build a database that can help
predict the occurrence and severity of coronal mass ejections
(CMEs). The catalogue contains miscellaneous information associated
with filament disappearance such as flare, CME, active region,
three-dimensional trajectory of erupting filaments, detection in
Interplanetary Scintillation (IPS), occurrence of interplanetary CME
(ICME) and Dst index. We also provide statistical information on the
catalogue data. The catalogue is available from the following website:
https://www.kwasan.kyoto-u.ac.jp/observation/event/sddi-catalogue/.
Title: SMART/SDDI Filament Disappearance Catalogue
Authors: Seki, D.; Otsuji, K.; Ishii, T.; Hirose, K.; Iju, T.; UeNo,
S.; Cabezas, D.; Asai, A.; Isobe, H.; Ichimoto, K.; Shibata, K.
Bibcode: 2019SunGe..14...95S
Altcode:
This paper describes a new "SMART/SDDI Filament Disappearance
Catalogue," in which we listed almost all the filament disappearance
events that the Solar Dynamics Doppler Imager (SDDI) has observed since
its installation on the Solar Magnetic Activity Research Telescope
(SMART) in May 2016. Our aim is to build a database that can help
predict the occurrence and severity of coronal mass ejections
(CMEs). The catalogue contains miscellaneous information associated
with filament disappearance such as flare, CME, active region,
three-dimensional trajectory of erupting filaments, detection in
Interplanetary Scintillation (IPS), occurrence of interplanetary CME
(ICME) and Dst index. We also provide statistical information on the
catalogue data. The catalogue is available from the following website:
https://www.kwasan.kyoto-u.ac.jp/observation/event/sddi-catalogue/.
Title: Lunar Occultation Observations of Double Stars - Report #7
Authors: Loader, Brian; Asada, Y.; Asai, A.; Bardecker, J.; Bourgeois,
J.; Bradshaw, J.; Chad, C.; Ellington, C.; Gault, D.; Giacchini, B.;
Haymes, T.; Herald, D.; Ishida, M.; Iverson, E.; Kerr, S.; Manek, J.;
McKay, G.; Messner, S.; Pratt, A.; Sandy, R.; Watanabe, H.; Yamamura,
H.; Yoshida, H.
Bibcode: 2019JDSO...15..503L
Altcode:
Reports are presented of lunar occultations of close double
stars observed using video techniques. Included are cases where a
determination of the position angle and separation of the pair can
be made as well as instances where no duplicity has been observed of
known or reported double stars. Twenty-six double stars discovered as
a result of a lunar occultation are also included together with the
light curves for the discovery event.
Title: Dynamic Processes of the Moreton Wave on 2014 March 29
Authors: Cabezas, Denis P.; Asai, Ayumi; Ichimoto, Kiyoshi; Sakaue,
Takahito; UeNo, Satoru; Ishitsuka, José K.; Shibata, Kazunari
Bibcode: 2019ApJ...883...32C
Altcode: 2019arXiv190803534C
On 2014 March 29, an intense solar flare classified as X1.0 occurred
in active region 12017. Several associated phenomena accompanied this
event, among them a fast-filament eruption, large-scale propagating
disturbances in the corona and the chromosphere including a Moreton
wave, and a coronal mass ejection. This flare was successfully detected
in multiwavelength imaging in the Hα line by the Flare Monitoring
Telescope (FMT) at Ica University, Peru. We present a detailed study
of the Moreton wave associated with the flare in question. Special
attention is paid to the Doppler characteristics inferred from the
FMT wing (Hα ± 0.8 Å) observations, which are used to examine
the downward/upward motion of the plasma in the chromosphere. Our
findings reveal that the downward motion of the chromospheric material
at the front of the Moreton wave attains a maximum velocity of 4 km
s-1, whereas the propagation speed ranges between 640 and
859 km s-1. Furthermore, using the weak-shock approximation
in conjunction with the velocity amplitude of the chromospheric motion
induced by the Moreton wave, we derive the Mach number of the incident
shock in the corona. We also performed the temperature-emission measure
analysis of the coronal wave based on the Atmospheric Imaging Assembly
observations, which allowed us to derive the compression ratio, and to
estimate Alfvén and fast-mode Mach numbers on the order of 1.06-1.28
and 1.05-1.27. Considering these results and the magnetohydrodynamics
linear theory, we discuss the characteristics of the shock front and
the interaction with the chromospheric plasma.
Title: Blue-wing enhancement of the chromospheric Mg II h and k
lines in a solar flare
Authors: Tei, Akiko; Sakaue, Takahito; Okamoto, Takenori J.; Kawate,
Tomoko; Heinzel, Petr; UeNo, Satoru; Asai, Ayumi; Ichimoto, Kiyoshi;
Shibata, Kazunari
Bibcode: 2018PASJ...70..100T
Altcode: 2018PASJ..tmp...61T; 2018arXiv180305237T
We performed coordinated observations of AR 12205, which showed a
C-class flare on 2014 November 11, with the Interface Region Imaging
Spectrograph (IRIS) and the Domeless Solar Telescope (DST) at Hida
Observatory. Using spectral data in the Si IV 1403 Å, C II 1335 Å,
and Mg II h and k lines from IRIS and the Ca II K, Ca II 8542 Å, and
Hα lines from DST, we investigated a moving flare kernel during the
flare. In the Mg II h line, the leading edge of the flare kernel showed
an intensity enhancement in the blue wing and a smaller intensity of the
blue-side peak (h2v) than that of the red-side one (h2r). The blueshift
lasted for 9-48 s with a typical speed of 10.1 ± 2.6 km s-1,
which was followed by a high intensity and a large redshift with a speed
of up to 51 km s-1 detected in the Mg II h line. The large
redshift was a common property for all six lines, but the blueshift
prior to it was found only in the Mg II lines. Cloud modeling of the
Mg II h line suggests that the blue-wing enhancement with such a peak
difference could have been caused by a chromospheric-temperature (cool)
upflow. We discuss a scenario in which an upflow of cool plasma is
lifted up by expanding hot plasma owing to the deep penetration of
non-thermal electrons into the chromosphere. Furthermore, we found
that the blueshift persisted without any subsequent redshift in the
leading edge of the flare kernel during its decaying phase. The cause
of such a long-lasting blueshift is also discussed.
Title: Observational study on the fine structure and dynamics of a
solar jet. II. Energy release process revealed by spectral analysis
Authors: Sakaue, Takahito; Tei, Akiko; Asai, Ayumi; Ueno, Satoru;
Ichimoto, Kiyoshi; Shibata, Kazunari
Bibcode: 2018PASJ...70...99S
Altcode: 2017arXiv171008441S; 2018PASJ..tmp....6S
We report on a solar jet phenomenon associated with the C5.4 class
flare on 2014 November 11. The data of the jet was provided by the Solar
Dynamics Observatory, the X-Ray Telescope (XRT) aboard Hinode, and the
Interface Region Imaging Spectrograph and Domeless Solar Telescope (DST)
at Hida Observatory, Kyoto University. These plentiful data enabled
us to present this series of papers to discuss all the processes of
the observed phenomena, including energy storage, event trigger,
and energy release. In this paper, we focus on the energy release
process of the observed jet, and mainly describe our spectral analysis
on the Hα data of DST to investigate the internal structure of the
Hα jet and its temporal evolution. This analysis reveals that in the
physical quantity distributions of the Hα jet, such as line-of-sight
velocity and optical thickness, there is a significant gradient in
the direction crossing the jet. We interpret this internal structure
as the consequence of the migration of the energy release site, based
on the idea of ubiquitous reconnection. Moreover, by measuring the
horizontal flow of the fine structures in the jet, we succeeded in
deriving the three-dimensional velocity field and the line-of-sight
acceleration field of the Hα jet. The analysis result indicates that
part of the ejecta in the Hα jet experienced additional acceleration
after it had been ejected from the lower atmosphere. This secondary
acceleration was found to occur in the vicinity of the intersection
between the trajectories of the Hα jet and the X-ray jet observed by
Hinode/XRT. We propose that a fundamental cause of this phenomenon is
magnetic reconnection involving the plasmoid in the observed jet.
Title: VizieR Online Data Catalog: Statistical studies of solar
white-light flares (Namekata+, 2017)
Authors: Namekata, K.; Sakaue, T.; Watanabe, K.; Asai, A.; Maehara,
H.; Notsu, Y.; Notsu, S.; Honda, S.; Ishii, T. T.; Ikuta, K.; Nogami,
D.; Shibata, K.
Bibcode: 2018yCat..18510091N
Altcode:
Our white-light flare (WLF) catalog contains M- and X-class solar
flares that occurred from 2011 to 2015 and were observed by both Solar
Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) and
RHESSI. The 43 flares in our catalog that occurred from 2011 to 2014
were taken from Kuhar+ (2016ApJ...816....6K); we enlarged the sample
by adding 10 flares that occurred in 2015. To present whether the
cadence of SDO/HMI is short enough to resolve the evolution of WLFs,
we compared the obtained light curves with those observed by the Solar
Magnetic Activity Research Telescope (SMART) at Hida Observatory of
Kyoto University for one event and the Hinode/Solar Optical Telescope
(SOT) for four events. (3 data files).
Title: Blue wing enhancement of the chromospheric Mg II h and k
lines in a solar flare
Authors: Tei, Akiko; Shibata, Kazunari; Asai, Ayumi; Ichimoto,
Kiyoshi; Heinzel, Petr; Ueno, Satoru; Okamoto, Joten; Sakaue, Takahito;
Kawate, Tomoko
Bibcode: 2018cosp...42E3350T
Altcode:
We performed coordinated observations of NOAA AR 12205, which produced
a C-class flare on 2014 November 11, with the Interface Region Imaging
Spectrograph (IRIS) and the Domeless Solar Telescope (DST) at Hida
Observatory.Using spectral data in the Si IV 1403 Å, C II 1335 Å,
and Mg II h and k lines from IRIS and the Ca II K, Ca II 8542 Å,
and Hα lines from DST, we investigated the temporal and spatial
evolution around a moving flare kernel.In the Mg II h line, the leading
edge of the kernel showed intensity enhancement in the blue wing and
difference between the blue-side peak and red-side one (I_{h2v} <
I_{h2r}).Then, the drastic change of the intensity in the red wing
occurred.The blueshift lasted for 9-48 s with a speed of 10.1 ± 2.6
km s^{-1} and it was followed by the strong redshift with a speed of
up to 51 km s^{-1} detected in the Mg II h line.The strong redshift
was a common property for all six lines but the blueshift prior to it
was found only in the Mg II lines.A cloud modeling of the Mg II h line
suggests that the blue wing enhancement with such peak difference can
be caused by a chromospheric-temperature (cool) upflow.We discuss a
scenario in which an upflow of cool plasma is lifted up by expanding
(hot) plasma owing to the deep penetration of non-thermal electrons
into the chromosphere.In addition, at the leading edge of the final
flare footpoints, the blueshift persisted in the Mg II h line, which
was not followed by any large redshift and intensity enhancement.Such
long-lasting blueshift can be explained by cool upflow caused by small
energy flux into the lower atmosphere.
Title: Statistical Studies of Solar White-light Flares and Comparisons
with Superflares on Solar-type Stars
Authors: Namekata, Kosuke; Ishii, Takako; Watanabe, Kyoko; Shibata,
Kazunari; Asai, Ayumi; Notsu, Yuta; Honda, Satoshi; Maehara, Hiroyuki;
Notsu, Shota; Nogami, Daisaku; Sakaue, Takahito; Ikuta, Kai
Bibcode: 2018cosp...42E2404N
Altcode:
Recently, many superflares on solar-type stars have been discovered
as white-light flares. Our statistical study found a correlation
between their energies (E) and durations (t): t∝ E^{0.39} (Maehara
et al. 2015, EP&S), similar to those of solar hard/soft X-ray
flares: t∝ E^{0.2-0.33}. This indicates a universal mechanism
of energy release on solar and stellar flares, i.e., magnetic
reconnection. We here carried out a statistical research on 50 solar
white-light flares with SDO/HMI and examined the correlation between
the energies and durations, aiming to universally explain solar and
stellar white-light flares. As a result, the t-E relation on solar
white-light flares (t∝ E^{0.38}) is similar to that on stellar
superflares (t∝ E^{0.39}). However, the durations of stellar
superflares are one order of magnitude shorter than those expected
from solar white-light flares. We proposed that the discrepancy can be
understood by applying a scaling law (t∝ E^{1/3}B^{-5/3}) which is
derived from the magnetic reconnection theory (Namekata et al. 2017,
ApJ, 851, 91). In this case, the observed superflares are expected to
have 2-4 times stronger magnetic field than solar flares. Although
there might be another effect like the cooling time of white-light
flares, the scaling law has a potential to estimate coronal magnetic
field strength of spatially unresolved stellar flares.
Title: Statistical Study of Solar White-light Flares and Comparison
with Superflares on Solar-type Stars
Authors: Namekata, Kosuke; Sakaue, Takahito; Watanabe, Kyoko; Asai,
Ayumi; Maehara, Hiroyuki; Notsu, Yuta; Notsu, Shota; Honda, Satoshi;
Ishii, Takako T.; Ikuta, Kai; Nogami, Daisaku; Shibata, Kazunari
Bibcode: 2018IAUS..340..221N
Altcode: 2018arXiv180407122N
Recently, many superflares on solar-type stars were discovered as
white-light flares (WLFs). A correlation between the energies (E)
and durations (t) of superflares is derived as t~E0.39,
and this can be theoretically explained by magnetic reconnection
(t~E1/3). In this study, we carried out a statistical
research on 50 solar WLFs with SDO/HMI to examine the t-E relation. As
a result, the t-E relation on solar WLFs (t~E0.38) is quite
similar stellar superflares, but the durations of stellar superflares
are much shorter than those extrapolated from solar WLFs. We present
the following two interpretations; (1) in solar flares, the cooling
timescale of WL emission may be longer than the reconnection one,
and the decay time can be determined by the cooling timescale;
(2) the distribution can be understood by applying a scaling law
t~E1/3B-5/3 derived from the magnetic reconnection
theory.
Title: Statistical Studies of Solar White-light Flares and Comparisons
with Superflares on Solar-type Stars
Authors: Namekata, Kosuke; Sakaue, Takahito; Watanabe, Kyoko; Asai,
Ayumi; Maehara, Hiroyuki; Notsu, Yuta; Notsu, Shota; Honda, Satoshi;
Ishii, Takako T.; Ikuta, Kai; Nogami, Daisaku; Shibata, Kazunari
Bibcode: 2017ApJ...851...91N
Altcode: 2017arXiv171011325N
Recently, many superflares on solar-type stars have been discovered
as white-light flares (WLFs). The statistical study found a
correlation between their energies (E) and durations (τ): τ \propto
{E}0.39, similar to those of solar hard/soft X-ray flares,
τ \propto {E}0.2{--0.33}. This indicates a universal
mechanism of energy release on solar and stellar flares, i.e., magnetic
reconnection. We here carried out statistical research on 50 solar
WLFs observed with Solar Dynamics Observatory/HMI and examined the
correlation between the energies and durations. As a result, the E-τ
relation on solar WLFs (τ \propto {E}0.38) is quite similar
to that on stellar superflares (τ \propto {E}0.39). However,
the durations of stellar superflares are one order of magnitude
shorter than those expected from solar WLFs. We present the following
two interpretations for the discrepancy: (1) in solar flares, the
cooling timescale of WLFs may be longer than the reconnection one, and
the decay time of solar WLFs can be elongated by the cooling effect;
(2) the distribution can be understood by applying a scaling law (τ
\propto {E}1/3{B}-5/3) derived from the magnetic
reconnection theory. In the latter case, the observed superflares
are expected to have 2-4 times stronger magnetic field strength than
solar flares.
Title: Observational study on the fine structure and dynamics of a
solar jet. I. Energy build-up process around a satellite spot
Authors: Sakaue, Takahito; Tei, Akiko; Asai, Ayumi; Ueno, Satoru;
Ichimoto, Kiyoshi; Shibata, Kazunari
Bibcode: 2017PASJ...69...80S
Altcode: 2017arXiv170701262S
We report on a solar jet phenomenon associated with successive flares
on 2014 November 10. These explosive events were involved with the
satellite spots' emergence around a δ-type sunspot in the decaying
active region NOAA 12205. The data for this jet were provided by the
Solar Dynamics Observatory, the X-Ray Telescope aboard Hinode, and the
Interface Region Imaging Spectrograph and Domeless Solar Telescope
at Hida Observatory, Kyoto University. These abundant data enabled
us to present this series of papers to discuss the entire process of
the observed phenomena, including the energy storage, event trigger,
and energy release. In this paper, we focus on the energy build-up and
trigger phases, by analyzing the photospheric horizontal flow field
around the active region by an optical flow method. The analysis shows
the following results: (1) The observed explosive phenomena involved
three satellite spots, the magnetic fluxes of which successively
reconnected with their pre-existing ambient fields; (2) All of these
satellite spots emerged in the moat region of a pivotal δ-type
sunspot, especially near its convergent boundary with the neighboring
supergranules or moat regions of adjacent sunspots; (3) Around the
jet ejection site, the positive polarities of the satellite spot and
adjacent emerging flux encountered the global magnetic field with a
negative polarity in the moat region of the pivotal δ-type sunspot,
and thus the polarity inversion line was formed along the convergent
boundary of the photospheric horizontal flow channels.
Title: Variation of the Solar Microwave Spectrum in the Last Half
Century
Authors: Shimojo, Masumi; Iwai, Kazumasa; Asai, Ayumi; Nozawa, Satoshi;
Minamidani, Tetsuhiro; Saito, Masao
Bibcode: 2017ApJ...848...62S
Altcode: 2017arXiv170903695S
The total solar fluxes at 1, 2, 3.75, and 9.4 GHz were observed
continuously from 1957 to 1994 at Toyokawa, Japan, and from 1994 until
now at Nobeyama, Japan, with the current Nobeyama Radio Polarimeters. We
examined the multi-frequency and long-term data sets, and found that not
only the microwave solar flux but also its monthly standard deviation
indicate the long-term variation of solar activity. Furthermore, we
found that the microwave spectra at the solar minima of Cycles 20-24
agree with each other. These results show that the average atmospheric
structure above the upper chromosphere in the quiet-Sun has not varied
for half a century, and suggest that the energy input for atmospheric
heating from the sub-photosphere to the corona have not changed in
the quiet-Sun despite significantly differing strengths of magnetic
activity in the last five solar cycles.
Title: Lunar Occultation Observations of Double Stars â Report #6
Authors: Loader, Brian; Anderson, P.; Asai, A.; Bradshaw, J.; Breit,
D.; Forbes, M.; Gault, D.; George, T.; Haymes, T.; Herald, D.; Ishida,
M.; Kerr, S.; Manek, J.; Martin, G.; McKay, G.; Messner, S.; Miyashita,
K.; Oona, T.; Pennell, A.; Pratt, A.; Sandy, R.; Suzuki, H.; Watanabe,
H.; Yamamura, H.
Bibcode: 2017JDSO...13..585L
Altcode:
Reports are presented of lunar occultations of close double
stars observed using video techniques. Included are cases where a
determination of the position angle and separation of the pair can
be made as well as instances where no duplicity has been observed of
known or reported double stars. A number of double stars discovered as
a result of an occultation are also included together with the light
curves for the discovery event.
Title: Temporal Evolution and Spatial Distribution of White-light
Flare Kernels in a Solar Flare
Authors: Kawate, Tomoko; Ishii, Takako; Nakatani, Yoshikazu; Ichimoto,
Kiyoshi; Asai, Ayumi; Morita, Satoshi; Masuda, Satoshi
Bibcode: 2017SPD....4810002K
Altcode:
On 2011 September 6, we observed an X2.1-class flare in continuum
and Hα with a frame rate of about 30 Hz. After processing images
of the event by using a speckle-masking image reconstruction, we
identified white-light (WL) flare ribbons on opposite sides of the
magnetic neutral line. We derive the light curve decay times of the
WL flare kernels at each resolution element by assuming that the
kernels consist of one or two components that decay exponentially,
starting from the peak time. As a result, 42% of the pixels have two
decay-time components with average decay times of 15.6 and 587 s,
whereas the average decay time is 254 s for WL kernels with only one
decay-time component. The peak intensities of the shorter decay-time
component exhibit good spatial correlation with the WL intensity,
whereas the peak intensities of the long decay-time components tend
to be larger in the early phase of the flare at the inner part of
the flare ribbons, close to the magnetic neutral line. The average
intensity of the longer decay-time components is 1.78 times higher than
that of the shorter decay-time components. If the shorter decay time is
determined by either the chromospheric cooling time or the nonthermal
ionization timescale and the longer decay time is attributed to the
coronal cooling time, this result suggests that WL sources from both
regions appear in 42% of the WL kernels and that WL emission of the
coronal origin is sometimes stronger than that of chromospheric origin.
Title: Study of the Plutino Object (208996) 2003 AZ84
from Stellar Occultations: Size, Shape, and Topographic Features
Authors: Dias-Oliveira, A.; Sicardy, B.; Ortiz, J. L.; Braga-Ribas,
F.; Leiva, R.; Vieira-Martins, R.; Benedetti-Rossi, G.; Camargo,
J. I. B.; Assafin, M.; Gomes-Júnior, A. R.; Baug, T.; Chandrasekhar,
T.; Desmars, J.; Duffard, R.; Santos-Sanz, P.; Ergang, Z.; Ganesh,
S.; Ikari, Y.; Irawati, P.; Jain, J.; Liying, Z.; Richichi, A.;
Shengbang, Q.; Behrend, R.; Benkhaldoun, Z.; Brosch, N.; Daassou,
A.; Frappa, E.; Gal-Yam, A.; Garcia-Lozano, R.; Gillon, M.; Jehin,
E.; Kaspi, S.; Klotz, A.; Lecacheux, J.; Mahasena, P.; Manfroid, J.;
Manulis, I.; Maury, A.; Mohan, V.; Morales, N.; Ofek, E.; Rinner,
C.; Sharma, A.; Sposetti, S.; Tanga, P.; Thirouin, A.; Vachier, F.;
Widemann, T.; Asai, A.; Hayato, Watanabe; Hiroyuki, Watanabe; Owada,
M.; Yamamura, H.; Hayamizu, T.; Bradshaw, J.; Kerr, S.; Tomioka, H.;
Andersson, S.; Dangl, G.; Haymes, T.; Naves, R.; Wortmann, G.
Bibcode: 2017AJ....154...22D
Altcode: 2017arXiv170510895D
We present results derived from four stellar occultations by the
plutino object (208996) 2003 AZ84, detected on 2011 January 8
(single-chord event), 2012 February 3 (multi-chord), 2013 December 2
(single-chord), and 2014 November 15 (multi-chord). Our observations
rule out an oblate spheroid solution for 2003 AZ84's
shape. Instead, assuming hydrostatic equilibrium, we find that a Jacobi
triaxial solution with semiaxes (470+/- 20)× (383+/- 10)× (245+/- 8)
km can better account for all our occultation observations. Combining
these dimensions with the rotation period of the body (6.75 hr) and the
amplitude of its rotation light curve, we derive a density ρ =0.87+/-
0.01 g cm-3, a geometric albedo {p}V=0.097+/-
0.009. A grazing chord observed during the 2014 occultation reveals
a topographic feature along 2003 AZ84's limb, which can
be interpreted as an abrupt chasm of width ∼23 km and depth >
8 km, or a smooth depression of width ∼80 km and depth ∼13 km
(or an intermediate feature between those two extremes).
Title: Validation of a scaling law for the coronal magnetic field
strength and loop length of solar and stellar flares
Authors: Namekata, Kosuke; Sakaue, Takahito; Watanabe, Kyoko; Asai,
Ayumi; Shibata, Kazunari
Bibcode: 2017PASJ...69....7N
Altcode: 2016arXiv161009811N
Shibata and Yokoyama (1999, ApJ, 526, L49; 2002, ApJ, 577, 422)
proposed a method of estimating the coronal magnetic field strength
(B) and magnetic loop length (L) of solar and stellar flares, on the
basis of magnetohydrodynamic simulations of the magnetic reconnection
model. Using the scaling law provided by Shibata and Yokoyama (1999,
ApJ, 526, L49; 2002, ApJ, 577, 422), we obtain B and L as functions of
the emission measure (EM = n2L3) and temperature
(T) at the flare peak. Here, n is the coronal electron density of
the flares. This scaling law enables the estimation of B and L for
unresolved stellar flares from the observable physical quantities EM
and T, which is helpful for studying stellar surface activities. To
apply this scaling law to stellar flares, we discuss its validity for
spatially resolved solar flares. Quantities EM and T are calculated from
GOES (Geostationary Operational Environmental Satellite) soft X-ray flux
data, and B and L are theoretically estimated using the scaling law. For
the same flare events, B and L were also observationally estimated
with images taken by the Solar Dynamics Observatory (SDO)/Helioseismic
and Magnetic Imager (HMI) Magnetogram and Atmospheric Imaging Assembly
(AIA) 94 Å pass band. As expected, a positive correlation was found
between the theoretically and observationally estimated values. We
interpret this result as indirect evidence that flares are caused
by magnetic reconnection. Moreover, this analysis makes us confident
about the validity of applying this scaling law to stellar flares as
well as solar flares.
Title: “Dandelion” Filament Eruption and Coronal Waves Associated
with a Solar Flare on 2011 February 16
Authors: Cabezas, Denis P.; Martínez, Lurdes M.; Buleje, Yovanny J.;
Ishitsuka, Mutsumi; Ishitsuka, José K.; Morita, Satoshi; Asai, Ayumi;
UeNo, Satoru; Ishii, Takako T.; Kitai, Reizaburo; Takasao, Shinsuke;
Yoshinaga, Yusuke; Otsuji, Kenichi; Shibata, Kazunari
Bibcode: 2017ApJ...836...33C
Altcode: 2017arXiv170100308C
Coronal disturbances associated with solar flares, such as Hα Moreton
waves, X-ray waves, and extreme ultraviolet (EUV) coronal waves,
are discussed herein in relation to magnetohydrodynamic fast-mode
waves or shocks in the corona. To understand the mechanism of
coronal disturbances, full-disk solar observations with high spatial
and temporal resolution over multiple wavelengths are of crucial
importance. We observed a filament eruption, whose shape is like a
“dandelion,” associated with the M1.6 flare that occurred on 2011
February 16 in Hα images taken by the Flare Monitoring Telescope at
Ica University, Peru. We derive the three-dimensional velocity field
of the erupting filament. We also identify winking filaments that are
located far from the flare site in the Hα images, whereas no Moreton
wave is observed. By comparing the temporal evolution of the winking
filaments with those of the coronal wave seen in the EUV images data
taken by the Atmospheric Imaging Assembly on board the Solar Dynamics
Observatory and by the Extreme Ultraviolet Imager on board the Solar
Terrestrial Relations Observatory-Ahead, we confirm that the winking
filaments were activated by the EUV coronal wave.
Title: Solar flares in GOES X-ray flux forecast based on SDO/HMI
and SDO/AIA images.
Authors: Hada-Muranushi, Y.; Muranushi, T.; Asai, A.; Nemoto, S.;
Shibata, K.
Bibcode: 2016AGUFMSH11C2239H
Altcode:
We have been studying and operationg methods for automated solar
flare forecasts. The automated forecast of solar flares and other
space-weather related events have two crucial goals. One is to enable
real-time forecast and thus provide truely predictive test for the
space weather theories. The other is to enable numerous variation of
tailor-made space weather forecasts for various space weather users. We
have been building space weather prediction system UFCORIN (Universal
Forecast Constructor by Optimized Regression of INputs), a software
framework that can provide forecast based on generic time-series
data. Recently, we have been updating UFCORIN so that it can handle
image time-series data in addition to scalar-values timeseries,
with the help of convolutional neural network. We have been operating
space weather forecast since August, 2015 that provides 24-hour-ahead
forecast of solar flares, every 12 minutes, based on the time-series
data of GOES X-ray flux and wavelet features of line-of-sight magnetic
field images in SDO/HMI. However, the TSS (True Skill Statistics)
for M and C class flares achieved so far has been approximately 0.3,
much less than those values of 0.7-0.9 reported by simulated forecast
studies. Especially, it is difficult to predict rim flares and those
flares that occur on the East side of the Sun, where active regions
have small, noisy features in the magnetic field images. In order to
better predict rim flares, we are now studying the effect of adding
extreme-ultraviolet images in SDO/AIA to the input set, which includes
solar rim information. In this presentation, we report the methods
and prediction results of the system. In addition, we will report the
results of adding SDO/AIA images to the input data.
Title: Comparative Studies of Prediction Strategies for Solar X-ray
Time Series
Authors: Muranushi, T.; Hattori, T.; Jin, Q.; Hishinuma, T.; Tominaga,
M.; Nakagawa, K.; Fujiwara, Y.; Nakamura, T.; Sakaue, T.; Takahashi,
T.; Seki, D.; Namekata, K.; Tei, A.; Ban, M.; Kawamura, A. D.;
Hada-Muranushi, Y.; Asai, A.; Nemoto, S.; Shibata, K.
Bibcode: 2016AGUFMSH11C2240M
Altcode:
Crucial virtues for operational space weather forecast are
real-timeforecast ability, forecast precision and customizability
to userneeds. The recent development of deep-learning makes it
veryattractive to space weather, because (1) it learns gradually
incomingdata, (2) it exhibits superior accuracy over conventional
algorithmsin many fields, and (3) it makes the customization
of the forecasteasier because it accepts raw images.However, the
best deep-learning applications are only attainable bycareful human
designers that understands both the mechanism of deeplearning and the
application field. Therefore, we need to foster youngresearchers to
enter the field of machine-learning aided forecast. So,we have held
a seminar every Monday with undergraduate and graduatestudents from
May to August 2016.We will review the current status of space weather
science and theautomated real-time space weather forecast engine
UFCORIN. Then, weintroduce the deep-learning space weather forecast
environments wehave set up using Python and Chainer on students' laptop
computers.We have started from simple image classification neural
network, thenimplemented space-weather neural network that predicts
future X-rayflux of the Sun based on the past X-ray lightcurve and
magnetic fieldline-of-sight images.In order to perform each forecast
faster, we have focused on simplelightcurve-to-lightcurve forecast,
and performed comparative surveysby changing following parameters: The size and topology of the neural network Batchsize Neural network
hyperparameters such as learning rates to optimize the preduction
accuracy, and time for prediction.We have found how to design compact,
fast but accurate neural networkto perform forecast. Our forecasters can
perform predictionexperiment for four-year timespan in a few minutes,
and achieveslog-scale errors of the order of 1. Our studies is ongoing,
and inour talk we will review our progress till December.
Title: Temporal Evolution and Spatial Distribution of White-light
Flare Kernels in a Solar Flare
Authors: Kawate, T.; Ishii, T. T.; Nakatani, Y.; Ichimoto, K.; Asai,
A.; Morita, S.; Masuda, S.
Bibcode: 2016ApJ...833...50K
Altcode: 2016arXiv161004328K
On 2011 September 6, we observed an X2.1-class flare in continuum
and Hα with a frame rate of about 30 Hz. After processing images
of the event by using a speckle-masking image reconstruction, we
identified white-light (WL) flare ribbons on opposite sides of the
magnetic neutral line. We derive the light curve decay times of the
WL flare kernels at each resolution element by assuming that the
kernels consist of one or two components that decay exponentially,
starting from the peak time. As a result, 42% of the pixels have two
decay-time components with average decay times of 15.6 and 587 s,
whereas the average decay time is 254 s for WL kernels with only one
decay-time component. The peak intensities of the shorter decay-time
component exhibit good spatial correlation with the WL intensity,
whereas the peak intensities of the long decay-time components tend
to be larger in the early phase of the flare at the inner part of
the flare ribbons, close to the magnetic neutral line. The average
intensity of the longer decay-time components is 1.78 times higher than
that of the shorter decay-time components. If the shorter decay time is
determined by either the chromospheric cooling time or the nonthermal
ionization timescale and the longer decay time is attributed to the
coronal cooling time, this result suggests that WL sources from both
regions appear in 42% of the WL kernels and that WL emission of the
coronal origin is sometimes stronger than that of chromospheric origin.
Title: Observational Evidence of Particle Acceleration Associated
with Plasmoid Motions
Authors: Takasao, Shinsuke; Asai, Ayumi; Isobe, Hiroaki; Shibata,
Kazunari
Bibcode: 2016ApJ...828..103T
Altcode: 2016arXiv161100108T
We report a strong association between the particle acceleration and
plasma motions found in the 2010 August 18 solar flare. The plasma
motions are tracked in the extreme ultraviolet (EUV) images taken by
the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory and the Extreme UltraViolet Imager (EUVI) on the Solar
Terrestrial Relations Observatory spacecraft Ahead, and the signature of
particle acceleration was investigated by using Nobeyama Radioheliograph
data. In our previous paper, we reported that in EUV images many plasma
blobs appeared in the current sheet above the flare arcade. They were
ejected bidirectionally along the current sheet, and the blobs that
were ejected sunward collided with the flare arcade. Some of them
collided or merged with each other before they were ejected from
the current sheet. We discovered impulsive radio bursts associated
with such plasma motions (ejection, coalescence, and collision with
the post flare loops). The radio bursts are considered to be the
gyrosynchrotron radiation by nonthermal high energy electrons. In
addition, the stereoscopic observation by AIA and EUVI suggests
that plasma blobs had a three-dimensionally elongated structure. We
consider that the plasma blobs were three-dimensional plasmoids (I.e.,
flux ropes) moving in a current sheet. We believe that our observation
provides clear evidence of particle acceleration associated with the
plasmoid motions. We discuss possible acceleration mechanisms on the
basis of our results.
Title: A Deep-Learning Approach for Operation of an Automated Realtime
Flare Forecast
Authors: Hada-Muranushi, Yuko; Muranushi, Takayuki; Asai, Ayumi;
Okanohara, Daisuke; Raymond, Rudy; Watanabe, Gentaro; Nemoto, Shigeru;
Shibata, Kazunari
Bibcode: 2016arXiv160601587H
Altcode:
Automated forecasts serve important role in space weather science,
by providing statistical insights to flare-trigger mechanisms, and
by enabling tailor-made forecasts and high-frequency forecasts. Only
by realtime forecast we can experimentally measure the performance of
flare-forecasting methods while confidently avoiding overlearning. We
have been operating unmanned flare forecast service since August,
2015 that provides 24-hour-ahead forecast of solar flares, every 12
minutes. We report the method and prediction results of the system.
Title: Division E Commission 10: Solar Activity
Authors: Schrijver, Carolus J.; Fletcher, Lyndsay; van Driel-Gesztelyi,
Lidia; Asai, Ayumi; Cally, Paul S.; Charbonneau, Paul; Gibson, Sarah
E.; Gomez, Daniel; Hasan, Siraj S.; Veronig, Astrid M.; Yan, Yihua
Bibcode: 2016IAUTA..29..245S
Altcode: 2015arXiv151003348S
After more than half a century of community support related to the
science of ``solar activity'', IAU's Commission 10 was formally
discontinued in 2015, to be succeeded by C.E2 with the same area
of responsibility. On this occasion, we look back at the growth of
the scientific disciplines involved around the world over almost a
full century. Solar activity and fields of research looking into the
related physics of the heliosphere continue to be vibrant and growing,
with currently over 2,000 refereed publications appearing per year from
over 4,000 unique authors, publishing in dozens of distinct journals
and meeting in dozens of workshops and conferences each year. The
size of the rapidly growing community and of the observational and
computational data volumes, along with the multitude of connections
into other branches of astrophysics, pose significant challenges;
aspects of these challenges are beginning to be addressed through,
among others, the development of new systems of literature reviews,
machine-searchable archives for data and publications, and virtual
observatories. As customary in these reports, we highlight some
of the research topics that have seen particular interest over the
most recent triennium, specifically active-region magnetic fields,
coronal thermal structure, coronal seismology, flares and eruptions,
and the variability of solar activity on long time scales. We close
with a collection of developments, discoveries, and surprises that
illustrate the range and dynamics of the discipline.
Title: A Comparative Study of Confined and Eruptive Solar Flares
using Microwave Observations
Authors: Yashiro, S.; Akiyama, S.; Masuda, S.; Shimojo, M.; Asai,
A.; Imada, S.; Gopalswamy, N.
Bibcode: 2015AGUFMSH43B2447Y
Altcode:
It is well known that about 10% X-class solar flares are not associated
with coronal mass ejections (CMEs). These flares are referred to
as confined flares, which are not associated with mass or energetic
particles leaving the Sun. However, electrons are accelerated to MeV
energies as indicated by the presence of microwave emission with a
turnover frequency of ~15 GHz (Gopalswamy et al. 2009, IAU Symposium
257, p. 283). In this paper, we extend the study of confined flares to
lower soft X-ray flare sizes (M and above) that occurred in the time
window of the Nobeyama Radioheliograph (NoRH). We also make use of the
microwave spectral information from the Nobeyama Radio Polarimeters
(NoRP). During 1996 - 2014, NoRH and NoRP observed 663 flares with
size M1.0 or larger. Using the CME observations made by SOHO/LASCO
and STEREO/SECCHI, we found 215 flares with definite CME association
(eruptive flares) and 202 flares that definitely lacked CMEs (confined
flares). The remaining 146 flares whose CME association is unclear are
excluded from the analysis. We examined the peak brightness temperature
and the spatial size obtained by NoRH. Although there is a large
overlap between the two populations in these properties, we found
that microwave sources with the largest spatial extent and highest
brightness temperature are associated with eruptive flares. Spectral
analysis using NoRP data showed a tendency that more confined flares
had higher turnover frequency (≥17 GHz). We also compare the NoRH
images with the photospheric magnetograms to understand the difference
in the magnetic structure of the two types of flare sources.
Title: A Real Source of a Stealth CME - Energetics of a Filament
Eruption and Giant Arcade Formation
Authors: Asai, Ayumi; Ishii, Takako T.; Otsuji, Kenichi; Ichimoto,
Kiyoshi; Shibata, Kazunari
Bibcode: 2015IAUGA..2255125A
Altcode:
Various active phenomena occurring on the solar surface are sources
of disturbances in the solar-terrestrial environment. It is, however,
sometimes said that solar flares, the most energetic explosions in the
active phenome on the sun, are not crucially important for space weather
researches, but coronal mass ejections (CMEs) are more significant. This
is because not all flares are associated with CMEs, and therefore, not
geo-effective, and because geo-effective CMEs sometimes occur without
any notable active phenomena (such as flares) on the sun. The latter
is sometimes called as a “stealth CME” event. However, for even
such cases, we often see filament eruptions in H-alpha observations
and formations of giant arcade in X-ray and/or extreme ultraviolet
(EUV) observations.The geomagnetic storm with the Dst index of -105
nT that occurred on October 8, 2012 was such a stealth event. We,
on the other hand, recognize formation of an X-ray giant arcade and
activation of an H-alpha filament on October 5, 2012. We examined the
velocity field of the filament by using the H-alpha wing data obtained
with SMART telescope at Hida Observatory, Kyoto University. We also
derived the temperature and the volume emission measure by using the
X-ray and EUV data obtained by Hinode/XRT and SDO/AIA. We discuss the
energetics of this event on the solar surface
Title: Internal structure of a coronal mass ejection revealed by
Akatsuki radio occultation observations
Authors: Ando, H.; Shiota, D.; Imamura, T.; Tokumaru, M.; Asai, A.;
Isobe, H.; Päzold, M.; Häusler, B.; Nakamura, M.
Bibcode: 2015JGRA..120.5318A
Altcode:
A coronal mass ejection (CME) was observed at the heliocentric distance
of 12.7 Rυ by radio occultation measurements using the
Akatsuki spacecraft. The temporal developments of the bulk velocity
and the electron column density along the raypath traversing the
CME were obtained, and under the assumption that the irregularities
are transported across the raypath, the internal structure of the
CME covering the region from the core to the tail was retrieved. The
suggested internal structure was compared with Large Angle Spectroscopic
Coronagraph images, a numerical study and previous radio occultation
observations of CMEs to propose a CME model; the bulk velocity and the
electron density have relatively large values in the core, decrease
behind the core, and increase again in the tail region where the fast
plasma flow associated with the magnetic reconnection converges. This
implies that the magnetic reconnection behind the CMEs might continue
up to at least the heliocentric distance of ∼13 Rυ.
Title: Prominence Activation By Coronal Fast Mode Shock
Authors: Takahashi, Takuya; Asai, Ayumi; Shibata, Kazunari
Bibcode: 2015ApJ...801...37T
Altcode: 2015arXiv150101592T
An X5.4 class flare occurred in active region NOAA11429 on 2012 March
7. The flare was associated with a very fast coronal mass ejection
(CME) with a velocity of over 2500 km s-1. In the images
taken with the Solar Terrestrial Relations Observatory-B/COR1, a
dome-like disturbance was seen to detach from an expanding CME bubble
and propagated further. A Type-II radio burst was also observed at the
same time. On the other hand, in extreme ultraviolet images obtained
by the Solar Dynamic Observatory/Atmospheric Imaging Assembly (AIA),
the expanding dome-like structure and its footprint propagating to the
north were observed. The footprint propagated with an average speed
of about 670 km s-1 and hit a prominence located at the
north pole and activated it. During the activation, the prominence was
strongly brightened. On the basis of some observational evidence, we
concluded that the footprint in AIA images and the ones in COR1 images
are the same, that is, the MHD fast mode shock front. With the help
of a linear theory, the fast mode Mach number of the coronal shock is
estimated to be between 1.11 and 1.29 using the initial velocity of the
activated prominence. Also, the plasma compression ratio of the shock
is enhanced to be between 1.18 and 2.11 in the prominence material,
which we consider to be the reason for the strong brightening of the
activated prominence. The applicability of linear theory to the shock
problem is tested with a nonlinear MHD simulation.
Title: Radial Distribution of Compressive Waves in the Solar Corona
Revealed by Akatsuki Radio Occultation Observations
Authors: Miyamoto, Mayu; Imamura, Takeshi; Tokumaru, Munetoshi; Ando,
Hiroki; Isobe, Hiroaki; Asai, Ayumi; Shiota, Daikou; Toda, Tomoaki;
Häusler, Bernd; Pätzold, Martin; Nabatov, Alexander; Nakamura, Masato
Bibcode: 2014ApJ...797...51M
Altcode:
Radial variations of the amplitude and the energy flux of compressive
waves in the solar corona were explored for the first time using a
spacecraft radio occultation technique. By applying wavelet analysis to
the frequency time series taken at heliocentric distances of 1.5-20.5
RS (solar radii), quasi-periodic density disturbances
were detected at almost all distances. The period ranges from 100 to
2000 s. The amplitude of the fractional density fluctuation increases
with distance and reaches ~30% around 5 RS , implying that
nonlinearity of the wave field is potentially important. We further
estimate the wave energy flux on the assumption that the observed
periodical fluctuations are manifestations of acoustic waves. The
energy flux increases with distance below ~6 RS and seems
to saturate above this height, suggesting that the acoustic waves do
not propagate from the low corona but are generated in the extended
corona, probably through nonlinear dissipation of Alfvén waves. The
compressive waves should eventually dissipate through shock generation
to heat the corona.
Title: Analysis of Radiation Damage in On-Orbit Solar Array of Venus
Explorer Akatsuki
Authors: Takahashi, Yu; Toyota, Hirouki; Shimada, Takanobu; Imamura,
Takeshi; Hada, Yuko; Isobe, Hiroaki; Asai, Ayumi; Ishii, Takako T.;
Shiota, Daikou
Bibcode: 2014ESASP.719E..21T
Altcode:
This paper describes an analysis of radiation damage to a solar array of
the Venus explorer Akatsuki, observed on orbit. Three times since its
launch, the output voltage of the solar array has shown sudden drops,
which are most reasonably associated with radiation damage. Analysis of
this radiation damage is difficult because neither the spectra nor the
amount of high-energy particles are directly available. We calculated
the radiation damage by using the relative damage coefficient method
under the assumption of a typical spectral shape of protons.
Title: Outflow Structure of the Quiet Sun Corona Probed by Spacecraft
Radio Scintillations in Strong Scattering
Authors: Imamura, Takeshi; Tokumaru, Munetoshi; Isobe, Hiroaki; Shiota,
Daikou; Ando, Hiroki; Miyamoto, Mayu; Toda, Tomoaki; Häusler, Bernd;
Pätzold, Martin; Nabatov, Alexander; Asai, Ayumi; Yaji, Kentaro;
Yamada, Manabu; Nakamura, Masato
Bibcode: 2014ApJ...788..117I
Altcode:
Radio scintillation observations have been unable to probe flow
speeds in the low corona where the scattering of radio waves is
exceedingly strong. Here we estimate outflow speeds continuously from
the vicinity of the Sun to the outer corona (heliocentric distances
of 1.5-20.5 solar radii) by applying the strong scattering theory to
radio scintillations for the first time, using the Akatsuki spacecraft
as the radio source. Small, nonzero outflow speeds were observed over
a wide latitudinal range in the quiet-Sun low corona, suggesting that
the supply of plasma from closed loops to the solar wind occurs over
an extended area. The existence of power-law density fluctuations
down to the scale of 100 m was suggested, which is indicative of
well-developed turbulence which can play a key role in heating the
corona. At higher altitudes, a rapid acceleration typical of radial
open fields is observed, and the temperatures derived from the speed
profile show a distinct maximum in the outer corona. This study opened
up a possibility of observing detailed flow structures near the Sun
from a vast amount of existing interplanetary scintillation data.
Title: International Collaboration and Academic Exchange of the
CHAIN Project in this Three Years (Period)
Authors: Ueno, Satoru; Shibata, Kazunari; Morita, Satoshi; Kimura,
Goichi; Asai, Ayumi; Kitai, Reizaburo; Ichimoto, Kiyoshi; Nagata,
Shin'ichi; Ishii, Takako; Nakatani, Yoshikazu; Masashi, Yamaguchi;
et al.
Bibcode: 2014SunGe...9...97U
Altcode:
We will introduce contents of international collaboration and
academic exchange of the CHAIN project in recent three years (ISWI
period). After April of 2010, we have not obtained any enough budget
for new instruments. Therefore, we have not been able to install new
Flare Monitoring Telescopes (FMT) in new countries, such as Algeria. On
the other hand, however, we have continued international academic
exchange through scientific and educational collaboration with mainly
Peru, such as data-analysis training, holding scientific workshops
etc. Additionally, in this year, King Saudi University of Saudi Arabia
and CRAAG of Algeria have planned to build a new FMT in their university
by their own budget. Therefore, we have started some collaboration in
the field of technical advices of instruments and scientific themes
etc. Moreover, Pakistan Space and Upper Atmosphere Research Commission
(SUPARCO) also offered us participation in the CHAIN-project. We would
like to continue to consider the possibility of academic collaboration
with such new positive developing nations, too.
Title: Within the International Collaboration CHAIN: a Summary of
Events Observed with Flare Monitoring Telescope (FMT) in Peru
Authors: Ishitsuka, J.; Asai, A.; Morita, S.; Terrazas, R.; Cabezas,
D.; Gutierrez, V.; Martinez, L.; Buleje, Y.; Loayza, R.; Nakamura,
N.; Takasao, S.; Yoshinaga, Y.; Hillier, A.; Otsuji, K.; Shibata, K.;
Ishitsuka, M.; Ueno, S.; Kitai, R.; Ishii, T.; Ichimoto, K.; Nagata,
S.; Narukage, N.
Bibcode: 2014SunGe...9...85I
Altcode:
In 2008 we inaugurated the new Solar Observatory in collaboration with
Faculty of Sciences of San Luis Gonzaga de Ica National University,
300 km south of Lima. In March of 2010 a Flare Monitoring Telescope
of Hida Observatory of Kyoto University arrived to Ica, part of CHAIN
Project (Continuous H-alpha Imaging Network). In October of the same
year we hosted the First FMT Workshop in Ica, then in July of 2011 the
Second FMT Workshop was opened. Since that we are focused on two events
registered by FMT in Peru to publish results. FMT is a good tool to
introduce young people from universities into scientific knowledge;
it is good also for education in Solar Physics and outreach. Details
of this successful collaboration will be explained in this presentation.
Title: Temporal and Spatial Analyses of Spectral Indices of Nonthermal
Emissions Derived from Hard X-Rays and Microwaves
Authors: Asai, Ayumi; Kiyohara, Junko; Takasaki, Hiroyuki; Narukage,
Noriyuki; Yokoyama, Takaaki; Masuda, Satoshi; Shimojo, Masumi;
Nakajima, Hiroshi
Bibcode: 2013ApJ...763...87A
Altcode: 2012arXiv1212.1806A
We studied electron spectral indices of nonthermal emissions seen in
hard X-rays (HXRs) and microwaves. We analyzed 12 flares observed by
the Hard X-Ray Telescope aboard Yohkoh, Nobeyama Radio Polarimeters,
and the Nobeyama Radioheliograph (NoRH), and compared the spectral
indices derived from total fluxes of HXRs and microwaves. Except
for four events, which have very soft HXR spectra suffering from the
thermal component, these flares show a gap Δδ between the electron
spectral indices derived from HXRs δ X and those from
microwaves δμ (Δδ = δ X - δμ)
of about 1.6. Furthermore, from the start to the peak times of the
HXR bursts, the time profiles of the HXR spectral index δ
X evolve synchronously with those of the microwave spectral
index δμ, keeping the constant gap. We also examined the
spatially resolved distribution of the microwave spectral index by
using NoRH data. The microwave spectral index δμ tends
to be larger, which means a softer spectrum, at HXR footpoint sources
with stronger magnetic field than that at the loop tops. These results
suggest that the electron spectra are bent at around several hundreds
of keV, and become harder at the higher energy range that contributes
the microwave gyrosynchrotron emission.
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: Evaluation of solar energetic particles exposure on the Venus
orbiter Akatsuki
Authors: Hada, Y.; Isobe, H.; Asai, A.; Ishii, T. T.; Shiota, D.;
Imamura, T.; Toyota, H.
Bibcode: 2012AGUFMSH21A2170H
Altcode:
Space weather researches have become more and more important, according
to the expansion of the "humanosphere" to the space. On the other hand,
current space weather researches are mainly for circumterrestrial
space, not for the deep space probes that are located far from the
earth. We aim to forecast and evaluate the radiation hazard to such
space probes far from the earth by using the data taken by the Solar
Terrestrial RElations Observatory (STEREO). STEREO provides the images
of the part of the Sun that is invisible from the Earth, but only EUV
images and coronagraph images are available. First, we examine the
possibility of the evaluation of the radiation hazard by using EUV and
coronagraph images. It is known that solar energetic particles (SEPs)
flux is well correlated with the speed of coronal mass ejection (CME)
measured by a coronagraph. We focused on two successive flare/CME events
occurred on June 4th, 2011. It occurred in an active region that located
on the invisible side of the Sun, and near the disk center as seen from
Akatsuki (PLANET-C), the Venus Climate Orbiter that was orbiting the Sun
at around 0.7AU. On June 5th, an abrupt decrease in the electric power
of Akatsuki was observed, which may be attributed to the effect of SEPs
associated with the flare/CME events. We measured the velocity of the
two CMEs using the coronagraphic images from STEREO and found that the
second CME was much faster (about 2200 km s-1) than the first one (about
800 km s-1). Considering the time difference between the two events,
it is likely that the second CME caught up the first one before they
arrived at 0.7AU. The estimated arrival time is consistent with the
timing of the power decrease of Akatsuki. According to a statistical
study of CMEs and SEPs preformed by Gopalswamy et al (2004) SEP flux
tends to become large if a preceding CME have been launched within 24
hours ahead of the onset time of the primary CME. Using the empirical
relationship between the SEP flux and the CME velocity derived by
Gopalswamy et al. (2004), we estimate the SEP flux of 10^2 - 10^4
[cm-2 s-1 sr-1].
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: Flare Onset Observed with Hinode in the 2006 December 13 Flare
Authors: Asai, A.; Hara, H.; Watanabe, T.; Imada, S.
Bibcode: 2012ASPC..454..303A
Altcode:
We present a detailed examination of the preflare phenomena of
the X3.4 flare that occurred on 2006 December 13. This flare was
associated with a faint arc-shaped ejection, which is thought to be
an MHD fast-mode shock wave, seen in the soft X-ray images taken
with the Hinode X-Ray Telescope (XRT), just at the start of the
impulsive phase of the flare. Even before the ejection, we found many
preflare features, such as an S-shaped brightening (sigmoid) with XRT,
chromospheric brightening at the footpoints of the sigmoid loops with
the Solar Optical Telescope (SOT), a faint X-ray eruption with XRT,
and so on. The EUV Imaging Spectrometer (EIS) also observed the flare,
and therefore, enabled us to examine the spectroscopic features. We
discuss these phenomena and the energy release prosses.
Title: Kyoto digital database of 44-year synoptic observation of
solar chromosphere
Authors: Kitai, Reizaburo; Asai, Ayumi; Hayashi, Hiroo; Ueno, Satoru
Bibcode: 2012cosp...39..933K
Altcode: 2012cosp.meet..933K
Solar activity is known to cyclically change in 11 years. However,
the amplitude of the variation is not constant but modulated
in long term span. The long term variation of solar activity is
thought as one of the origin of the global warming or cooling of
the earth. In Kyoto University, a continuous synoptic observation
of solar chromospheres in CaIIK monochromatic light had been done
during the years 1926-1969. CaIIK spectroheliographic images and
white light images had been taken on daily base. All the images
were recorded in photographic plates. In view of the long term span
of the data and the uniqueness of full solar disk images, we think
that the data is scientifically a very valuable one. Since we have
a risk of aging and degradation of these old photographic plates,
we have started a project to digitize all the plates and develop a
digital image database for public use via IUGONET (Inter-university
Upper atmosphere Global Observation NETwork) system. Our plan of the
project consists of six stages. (1) Compilation of meta-database and
its publication. (2) Digitization of all the plates and development
of image database. (3) Visualization of long term solar chromospheric
variation. (4) Measurement of solar plage area and brightness. (5)
Comparative study between variations of sunspot number and plage
activity. (6) Study on the long term character of terrestrial upper
atmosphere heating with the solar plage activity as a proxy of solar
EUV irradiation. In the present paper, we will give the basic plan, the
present status of our project and some preliminary scientific results.
Title: Moreton and EUV waves observed by STEREO, SDO, and ground-based
instruments, and their association to CMEs
Authors: Asai, Ayumi
Bibcode: 2012cosp...39...63A
Altcode: 2012cosp.meet...63A
Solar flares are very spectacular, and are associated with
various phenomena. Coronal shocks or disturbances are one of such
flare-related phenomena. Although Moreton waves and X-ray waves are
well explained with MHD first mode shocks propagating in the corona,
there still remains a big problem on the nature of the waves, since
they are very rare phenomena. On the other hand, EIT waves (or EUV
waves) have been paid attention to as another phenomenon of coronal
disturbances. However, the physical features (velocity, opening angle,
and so on) are much different from those for Moreton waves and X-ray
waves. Thanks to the recent developments on solar observations by
STEREO, SDO, Hinode, and ground-based instruments, we have now detailed
informations on coronal disturbances. We review recent observations
on H-alpha Moreton waves, EUV waves, X-ray waves, especially those
associated with the 2011 August 9 flare, the 2010 Feburary 7 flare,
and the 2010 August 18 flare. Associated with the 2011 August 9 flare,
we observed a Moreton wave in the H-alpha images. In the EUV images,
we found not only the corresponding EUV fast ``bright'' coronal wave,
but also the EUV fast ``faint'' wave that is not associated with the
H-alpha Moreton wave. We also found a slow EUV wave, which corresponds
to a typical EIT wave. Furthermore, we observed the oscillations
of a prominence and a filament. To trigger the oscillations by the
flare-associated coronal disturbance, we expect a coronal wave as fast
as the fast-mode MHD wave, and the velocity is consistent with those
of the observed Moreton wave and the EUV fast coronal wave. We also
report detailed features of the coronal disturbances associated with the
2010 February 7 and the 2010 August 18 flares. For the former flare we
analyzed the H-alpha images, the X-ray images, and the EUV images, and
found the Moreton wave, X-ray wave, and EIT wave, simultaneously. In the
latter flare, on the other hand, we observed a very fast EUV wave. The
propagating speed is comparable to the MHD first mode wave, while there
is no obvious evidence of shocks for this flare. From these results,
we discuss the nature of coronal disturbances.
Title: Hinode Observations and Modeling of Small Flares
Authors: Zanna, G. D.; Mitra-Kraev, U.; Bradshaw, S. J.; Mason, H. E.;
Asai, A.
Bibcode: 2012ASPC..455..295Z
Altcode:
We present Hinode observations of a small B-class flare which occurred
on May 22, 2007, supplemented with X-ray, EUV, and radio data. We
found new signatures of chromospheric evaporation, strong (up to 170 km
s-1) blue-shifted emission in lines formed around 2-3 MK,
in a very narrow layer at the footpoints of a 10 MK flare loop. We
have found good agreement between the observed properties and those
predicted by a HYDRAD non-equilibrium hydrodynamic numerical simulation.
Title: Dynamic Features of Flare Plasma Unveiled with Recent
Observations
Authors: Asai, A.
Bibcode: 2012ASPC..455..281A
Altcode:
Solar flares are very spectacular and exhibit a variety of plasma
motions. As a flare evolves, flare loops show many dynamic features,
such as plasma heating and cooling, chromospheric evaporation,
reconnection inflows and outflows, and so on. In addition, many
ejection phenomena, such as filament/prominence eruptions, have been
observed in chromospheric lines, in the extreme ultraviolet (EUV), and
in X-rays. Flare-associated waves and the related plasma motions have
also been studied. These plasma motions can be observed as phenomena
accompanied by Doppler shifts in spectroscopic observations. Therefore,
spectroscopic observations are crucially important for understanding the
dynamics of flare plasma. Moreover, with multi-wavelength observations,
we synergistically understand the flare physics morphologically,
qualitatively, and quantitatively. We overview recent observations of
solar flares, particularly those obtained by Hinode, STEREO, and SDO,
and show (only a small part of) the dynamic features of flare plasma.
Title: Minor Planet Observations [244 Geocentric Occultation
Observations]
Authors: Herald, D.; Van Den Abbeel, F.; Abramson, H.; Aikawa, R.;
Allen, B.; Asai, A.; Atwood, T.; Barry, T.; Baruffetti, P.; Beard,
T.; Bigi, M.; Blank, T.; Bolzoni, S.; Brooks, J.; Broughton, J.;
Campos, F.; Canales, O.; Caton, D.; Conard, S.; Coughlin, K.; Dangl,
G.; Degenhardt, S.; Doyle, D.; Dunham, D.; Ewald, D.; Fleishman,
R.; Frappa, E.; Garcia, R.; Gault, D.; Gualdoni, C.; Hamanowa, H.;
Hashimoto, A.; Haymes, T.; Herchak, S.; Hoskinson, M.; Hunter, M.;
Ida, M.; Iino, K.; Ishida, M.; Jones, R.; Juan, J.; Karasaki, H.;
Kawawaki, S.; Kitazaki, K.; Klotz, A.; Lavayssiere, M.; Lindner, P.;
Ling, A.; Liu, Y.; Loader, B.; Lopesino, J.; Lyzenga, G.; McKay,
G.; McNamara, W.; Messner, S.; Naves, R.; Noble, M.; Nugent, R.;
Oesper, D.; Olsen, A.; Ossola, A.; Owada, M.; Pallares, H.; Paulson,
M.; Perello, C.; Piechowski, O.; Pratt, A.; Purcell, P.; Rothe, W.;
Rovira, J.; Sato, H.; Satou, M.; Schnabel, C.; Selva, A.; Simonson,
R.; Spain, D.; Sposetti, S.; Sugiyama, Y.; Sumner, R.; Swift, T.;
Takashima, H.; Talbot, J.; Thomas, W.; Tolea, A.; Tomioka, H.;
Tonlorenzi, G.; Tremosa, L.; Uchiyama, S.; Uehara, S.; Urabe, M.;
Veliz, C.; Venable, R.; Walzel, K.; Wasson, R.; Watanabe, H.; Watson,
D.; Williams, M.; Winkel, J.; Wortmann, G.; Yaeza, A.; Young, B.;
Hayamizu, T.; Timerson, B.
Bibcode: 2012MPC..79143...3H
Altcode:
No abstract at ADS
Title: Dynamic Features of Current Sheet Associated with the 2010
August 18 Solar Flare
Authors: Takasao, S.; Asai, A.; Isobe, H.; Shibata, K.
Bibcode: 2012ASPC..456..221T
Altcode:
We report the observation of the magnetic reconnection site in the 2010
August 18 flare. We simultaneously found both reconnection inflow and
outflow. By using these velocities, we estimated the nondimensional
reconnection rate and found that it varied from 0.20 to 0.055. We
also observed dynamic plasma blobs in the sheet structure. The plasma
blobs collided with the hot loops and radio emissions were found at
this site, which may suggest particle acceleration. We hypothesize
that the sheet structure is the current sheet and that these plasma
blobs are plasmoids, which could be important for understanding the
dynamics of the reconnection region.
Title: Observation of Dynamic Features of Current Sheet Associated
with 2010 August 18 Solar Flare
Authors: Takasao, S.; Asai, A.; Isobe, H.; Shibata, K.
Bibcode: 2012decs.confE..93T
Altcode:
We report the simultaneous extreme-ultraviolet observation of magnetic
reconnection inflow and outflow in a flare on 2010 August 18 observed
by SDO/AIA. We found that during the rise phase of the flare, some
plasma blobs appeared in a sheet structure above hot loops. The
plasma blobs were ejected bidirectionally along the sheet structure
(i.e. reconnection outflow). Simultaneously, bright threads visible
in the extreme-ultraviolet images moved toward the sheet structure
(i.e. reconnection inflow). Using the velocities of the inflow and
outflow, we estimated the non-dimensional reconnection rate and found
it varies during this period from 0.20 to 0.055. We also found that
the plasma blobs in the sheet structure collided and possibly merged
with each other before they were ejected from the sheet structure. From
these observational results, we hypothesize that the sheet structure
is the current sheet and that these plasma blobs are plasmoids or
magnetic islands. This observational report could be important for
understanding the dynamics of the reconnection region.
Title: First Simultaneous Observation of an Hα Moreton Wave, EUV
Wave, and Filament/Prominence Oscillations
Authors: Asai, Ayumi; Ishii, Takako T.; Isobe, Hiroaki; Kitai,
Reizaburo; Ichimoto, Kiyoshi; UeNo, Satoru; Nagata, Shin'ichi; Morita,
Satoshi; Nishida, Keisuke; Shiota, Daikou; Oi, Akihito; Akioka, Maki;
Shibata, Kazunari
Bibcode: 2012ApJ...745L..18A
Altcode: 2011arXiv1112.5915A
We report on the first simultaneous observation of an Hα Moreton wave,
the corresponding EUV fast coronal waves, and a slow and bright EUV
wave (typical EIT wave). We observed a Moreton wave, associated with
an X6.9 flare that occurred on 2011 August 9 at the active region
NOAA 11263, in the Hα images taken by the Solar Magnetic Activity
Research Telescope at Hida Observatory of Kyoto University. In the
EUV images obtained by the Atmospheric Imaging Assembly on board the
Solar Dynamic Observatory we found not only the corresponding EUV fast
"bright" coronal wave, but also the EUV fast "faint" wave that is not
associated with the Hα Moreton wave. We also found a slow EUV wave,
which corresponds to a typical EIT wave. Furthermore, we observed,
for the first time, the oscillations of a prominence and a filament,
simultaneously, both in the Hα and EUV images. To trigger the
oscillations by the flare-associated coronal disturbance, we expect
a coronal wave as fast as the fast-mode MHD wave with the velocity of
about 570-800 km s-1. These velocities are consistent with
those of the observed Moreton wave and the EUV fast coronal wave.
Title: A Study on Red Asymmetry of Hα Flare Ribbons Using a
Narrowband Filtergram in the 2001 April 10 Solar Flare
Authors: Asai, Ayumi; Ichimoto, Kiyoshi; Kita, Reizaburo; Kurokawa,
Hiroki; Shibata, Kazunari
Bibcode: 2012PASJ...64...20A
Altcode: 2011arXiv1112.5912A
We report on a detailed examination of the ``red asymmetry'' of the
Hα emission line seen during the 2001 April 10 solar flare by using
a narrowband filtergram. We investigated the temporal evolution and
the spatial distribution of the red asymmetry by using Hα data taken
with the 60-cm Domeless Solar Telescope at Hida Observatory, Kyoto
University. We confirmed that the red asymmetry clearly appeared all
over the flare ribbons, and the strong red asymmetry is located on the
outer narrow edges of the flare ribbons, with a width of about 1.5"-3.0"
(1000-2000 km), where strong energy releases occur. Moreover, we found
that the red asymmetry, which also gives a measure of the Doppler
shift of the Hα emission line, concentrates on a certain value,
not depending on the intensity of the Hα kernels. This implies not
only that the temporal evolutions of the red asymmetry and those of
the intensity are not synchronous in each flare kernel, but also that
the peak asymmetry (or velocity of the chromospheric condensation)
of individual kernel is not a strong function of their peak intensity.
Title: Simultaneous Observation of Reconnection Inflow and Outflow
Associated with the 2010 August 18 Solar Flare
Authors: Takasao, Shinsuke; Asai, Ayumi; Isobe, Hiroaki; Shibata,
Kazunari
Bibcode: 2012ApJ...745L...6T
Altcode: 2011arXiv1112.1398T
We report the simultaneous extreme-ultraviolet observation of
magnetic reconnection inflow and outflow in a flare on 2010 August
18 observed by the Atmospheric Imaging Assembly on board the Solar
Dynamics Observatory. We found that during the rise phase of the
flare, some plasma blobs appeared in the sheet structure above the
hot loops. The plasma blobs were ejected bidirectionally along the
sheet structure (outflow), at the same time as the threads visible
in extreme-ultraviolet images moved toward the sheet structure
(inflow). The upward and downward ejection velocities are 220-460 km
s-1 and 250-280 km s-1, respectively. The inflow
speed changed from 90 km s-1 to 12 km s-1 in 5
minutes. By using these velocities, we estimated the nondimensional
reconnection rate, which we found to vary during this period from 0.20
to 0.055. We also found that the plasma blobs in the sheet structure
collided or merged with each other before they were ejected from
the sheet structure. We hypothesize that the sheet structure is the
current sheet and that these plasma blobs are plasmoids or magnetic
islands, which could be important for understanding the dynamics of
the reconnection region.
Title: High speed imaging system in continuum and H-alpha at the Hida
observatory for the study of high energy particles in solar flares
Authors: Ichimoto, K.; Kawate, T.; Yoshikazu, N.; Ishii, T.; Nagata,
S.; Asai, A.; Masuda, S.; Kusano, K.; Yamamoto, T. T.; Minoshima,
T.; Yokoyama, T.; Watanabe, K.
Bibcode: 2011AGUFMSH41A1914I
Altcode:
Non-thermal particles are the fundamental ingredient of solar flares
that carry the bulk energy released from the coronal magnetic fields
and cause subsequent heating of the solar atmosphere to produce the
radiation of wide range of electro-magnetic waves. The observations of
hard X-ray and radio emissions suggest a rapid change of population of
high energy particles with a time scale of sub-second. Flare kernels
observed in visible lights, ex., H-alpha and continuum, show drastic
evolutions in space and time during the rising phase of solar flares,
and thought to be representing the locations of the precipitation of
high energy particles into the chromosphere. Therefore the observations
of flare kernels with high spatial and temporal resolutions provide
valuable diagnosis of the distribution of high energy particles together
with the information of connectivity of coronal magnetic fields. We
developed a new high speed imaging system on a 25cm diameter telescope
of the Solar Magnetic Activity Research Telescope (SMART) at the Hida
observatory of Kyoto University. Images in H-alpha (width~3A) and
continuum (6547A, width~10A) are recorded simultaneously with two CCD
cameras with a spatial sampling of 0.2 arcsec/pix, field coverage of
344 arcsec x 258 arcsec, and a frame rate of 30fr/sec. Observation is
conducted continuously by focusing a targeted active region every day,
while only data sets that capture flare events are permanently stored
for further analysis. The spatial and temporal evolutions of flare
kernels thus obtained are combined with photospheric vector magnetic
field taken by the SMART, SOT/Hinode and HMI/SDO, radio data by NoRH,
hard X-ray image by RHESSI, and X-ray / UV images by SXT/Hinode
and AIA/SDO to identify the instantaneous locations of high energy
particles injection in the corona. In this paper we will present an
overview of the observing system and its initial results. This work
was carried out by the joint research program of the Solar-Terrestorial
Environment Laboratory, Nagoya University.
Title: Center-to-Limb Variation of Microwave Emissions from
Thermal-Rich and Thermal-Poor Solar Flares
Authors: Kawate, T.; Asai, A.; Ichimoto, K.
Bibcode: 2011AGUFMSH41A1913K
Altcode:
Non-thermal microwave emissions observed in the impulsive phase of
solar flares are produced by the gyrosynchrotron mechanism, which
depends on a number of physical parameters such as electron energy
spectra, their pitch angle distribution, magnetic field strength,
angle between line of sight and the magnetic field (viewing angle),
and the number of electrons. Therefore, it is difficult to determine
those physical parameters uniquely only from the observed quantities
of individual microwave burst. Statistical analysis of microwave
bursts by using a number of flare events provide us a way to find
mutual relationships between different quantities, and thus are useful
to restrict the possible domain of those physical quantities of the
microwave source. The pitch angle distribution of accelerated electrons
is of a crucial importance for the problem of particle acceleration in
solar flares. A clue to know the pitch angle distribution of accelerated
particles could be obtained from the center-to-limb variations of
observed microwave emissions, since relativistic electrons trapped in
flare loops emit the microwaves to the direction of their velocity, and
the viewing angle effect, i.e., center-to-limb variation of the flare
emission, can be related to the pitch angle distribution of accelerated
electrons. A statistical analysis of microwave flare events is performed
by using the event list of Nobeyama Radioheliograph in 1996-2009. We
examine center-to-limb variations of17GHz and 34GHz flux by dividing
the flare events into different groups with respect to the 'thermal
plasma richness' (ratio of the peak flux of soft X-ray to non-thermal
microwave emissions) and the duration of microwave bursts. It is
found that peak flux of 17 and 34GHz tend to be higher toward the
limb for thermal-rich flares with short durations. We propose that
the thermal-rich flares, which are supposed to be associated with an
efficient precipitation of high energy particles into the chromosphere,
have a pitch angle distribution of non-thermal electrons with a higher
population along the flare loop.
Title: Center-to-Limb Variation of Radio Emissions from Thermal-Rich
and Thermal-Poor Solar Flares
Authors: Kawate, Tomoko; Asai, Ayumi; Ichimoto, Kiyoshi
Bibcode: 2011PASJ...63.1251K
Altcode: 2011arXiv1107.1905K
A statistical analysis of radio flare events was conducted by using
the event list of Nobeyama Radioheliograph in the years 1996-2009. We
examined center-to-limb variations of 17 GHz and 34 GHz fluxes by
dividing the flare events into different groups according to the
``thermal plasma richness'' (ratio of the peak flux of soft X-ray to
nonthermal radio emissions) and the duration of radio bursts. It was
found that the peak flux at 17 and 34 GHz tended to be higher toward
the limb for thermal-rich flares with short durations. We propose that
the thermal-rich flares, which are supposed to be associated with an
efficient precipitation of high-energy particles into the chromosphere,
have a pitch-angle distribution of nonthermal electrons with a higher
population along the flare loop.
Title: Radio occultation observation of the solar corona with Venus
explorer Akatsuki
Authors: Imamura, T.; Ando, H.; Mochizuki, N.; Isobe, H.; Asai,
A.; Yaji, K.; Futaana, Y.; Miyamoto, M.; Yamamoto, Z.; Toda, T.;
Nabatov, A.
Bibcode: 2011AGUFMSH43F..07I
Altcode:
Radio occultation observations of the solar corona were conducted
during the solar conjunction of the Japanese Venus explorer AKATSUKI
during June 6-July 8 in 2011. The 17 experiments, each of which has
a duration of 6-7 hours, covered solar offset distances of 1.5-20.7
solar radii. One-way, X-band downlink signal stabilized by an onboard
ultra-stable oscillator was transmitted from the spacecraft and received
by an open-loop recording system at the Usuda Deep Space Center. The
stable signal source and the high-speed sampling at the ground station
allow us to probe fine structures in the solar corona. Analyses of the
intensity fluctuation and the frequency fluctuation of the received
radio waves provide various parameters such as the amplitude of density
fluctuation, the power law of the turbulence, and the velocity of the
solar wind and waves. Simultaneous observations with a space solar
telescope HINODE were also conducted over 4 days around the period of
the minimum solar offset distance.
Title: Numerical Investigation of a Coronal Mass Ejection from an
Anemone Active Region: Reconnection and Deflection of the 2005 August
22 Eruption
Authors: Lugaz, N.; Downs, C.; Shibata, K.; Roussev, I. I.; Asai,
A.; Gombosi, T. I.
Bibcode: 2011ApJ...738..127L
Altcode: 2011arXiv1106.5284L
We present a numerical investigation of the coronal evolution of a
coronal mass ejection (CME) on 2005 August 22 using a three-dimensional
thermodynamic magnetohydrodynamic model, the space weather modeling
framework. The source region of the eruption was anemone active
region (AR) 10798, which emerged inside a coronal hole. We validate
our modeled corona by producing synthetic extreme-ultraviolet (EUV)
images, which we compare to EIT images. We initiate the CME with an
out-of-equilibrium flux rope with an orientation and chirality chosen
in agreement with observations of an Hα filament. During the eruption,
one footpoint of the flux rope reconnects with streamer magnetic field
lines and with open field lines from the adjacent coronal hole. It
yields an eruption which has a mix of closed and open twisted field
lines due to interchange reconnection and only one footpoint line-tied
to the source region. Even with the large-scale reconnection, we find
no evidence of strong rotation of the CME as it propagates. We study
the CME deflection and find that the effect of the Lorentz force is
a deflection of the CME by about 3° R -1 sun
toward the east during the first 30 minutes of the propagation. We
also produce coronagraphic and EUV images of the CME, which we compare
with real images, identifying a dimming region associated with the
reconnection process. We discuss the implication of our results for
the arrival at Earth of CMEs originating from the limb and for models
to explain the presence of open field lines in magnetic clouds.
Title: Minor Planet Observations [244 Geocentric Occultation
Observations]
Authors: Herald, D.; van den Abbeel, F.; Allen, B.; Asai, A.; Asmus,
R.; Bianda, M.; Boettcher, S.; Bourtembourg, R.; Bradshaw, J.;
Bredner, E.; Broughton, J.; Caquel, J.; Casalnuovo, G.; Chinaglia,
B.; Christoph, M.; Conard, S.; Corelli, P.; Coughlin, K.; Dangl,
G.; Dechambre, O.; Dentel, M.; Denzau, H.; Dunham, D.; Enskonatus,
P.; Ewald, D.; Fleishman, R.; Frappa, E.; Gault, D.; Gebhard, S.; de
Groot, H.; Gualdoni, C.; Guhl, K.; Hamid, R.; Hasan, A.; Hashimoto, A.;
Haymes, T.; Hengst, R.; Ida, M.; Ishida, M.; Janik, T.; Kattentidt,
B.; Kenmotsu, K.; Kerr, S.; Kitazaki, K.; Klotz, A.; Lecacheux,
J.; Leiter, F.; Leroy, A.; Lindner, P.; Litwinowicz, K.; Loader,
B.; Lucas, A.; Luethen, H.; Maksym, P.; Maley, P.; Metallinos, V.;
Miyashita, K.; Modic, R.; Noda, T.; Okamoto, S.; Owada, M.; Pavlov,
H.; Pratt, A.; Purcell, P.; Ramelli, R.; Rothe, W.; Rothenberg, E.;
Russell, S.; Rutten, H.; Sandor, O.; Scheck, A.; Simonson, R.; Speil,
J.; Sposetti, S.; Takashima, H.; Talbot, J.; Tigani, !
Bibcode: 2011MPC..75402...9H
Altcode:
No abstract at ADS
Title: MHD Simulation of a CME from an Anemone Active Region and
Comparison with EUV Images
Authors: Lugaz, Noe; Downs, C.; Roussev, I.; Shibata, K.; Asai, A.
Bibcode: 2011shin.confE..41L
Altcode:
We present a numerical investigation of the coronal evolution of
the coro- nal mass ejection (CME) on 2005 August 22 using a 3-D
thermodynamics MHD model, the SWMF. The source region of the eruption
was anemone AR 10798, which emerged inside a coronal hole. We validate
our modeled corona by producing synthetic EUV images, which we compare
to EIT images. The eruption yields a mix of open and closed field lines
due to interchange re- connection. We discuss the CME reconnection
process with the ambient magnetic field of the AR and the surrounding
coronal hole and show how it is related to a long-lasting dimming
region.
Title: Minor Planet Observations [244 Geocentric Occultation
Observations]
Authors: Herald, D.; Aikawa, R.; Akazawa, H.; Angeloni, L.; Asai,
A.; Ashkar, F.; Bachini, M.; Barry, T.; Baruffetti, P.; Basso,
S.; Beard, T.; Bernascolle, P.; Bigi, M.; Blank, T.; Bolzoni, S.;
Bonatti, G.; Bradshaw, J.; Broughton, J.; Campbell, T.; Casas, R.;
Christou, A.; Cibin, L.; Clark, D.; Clevenson, A.; Cocchi, R.; Colas,
F.; Comolli, L.; Conard, S.; Coughlin, K.; Cudnik, B.; Curtis, I.;
Dangl, G.; Dantowitz, R.; Davis, J.; Denk, T.; Denyer, P.; Dicicco,
D.; Drakoulakos, P.; Dunham, D.; Dunham, J.; Ellington, C.; Ellington,
M.; Farago, O.; Fleishman, R.; Frankenberger, R.; Frappa, E.; Frisoni,
C.; Gaehrken, B.; Garlitz, J.; Gault, D.; George, T.; de Groot, H.;
Gualdoni, C.; Hashimoto, A.; Hayamizu, T.; Haymes, T.; Herchak,
S.; Hill, M.; Ida, M.; Ikari, Y.; Ishida, M.; Iten, M.; Ito, T.;
Iverson, E.; Jones, R.; Juan, J.; Kageyama, K.; Kenmotsu, K.; Kerr,
S.; Kitazaki, K.; Kloes, O.; Kozubal, M.; Lavari, A.; Lavayssiere,
M.; Lecacheux, J.; Lin, C.; Lowe, D.; Luca, R.; Lucas, !
Bibcode: 2011MPC..74387...2H
Altcode:
No abstract at ADS
Title: Solar Activity in 1992-2003: Solar Cycle 23 Observed by Flare
Monitoring Telescope
Authors: Shibata, Kazunari; Kitai, Reizaburo; Ueno, Satoru; Nogami,
Daisaku; Ishii, Takako T.; Katoda, Miwako; Nasuji, Yoko; Kamobe, Mai;
Kaneda, Naoki; Komori, Hiroyuki; Yagi, Shozo; Asai, Ayumi
Bibcode: 2011fmt..book.....S
Altcode:
No abstract at ADS
Title: The 22 May 2007 B-class flare: new insights from Hinode
observations
Authors: Del Zanna, G.; Mitra-Kraev, U.; Bradshaw, S. J.; Mason,
H. E.; Asai, A.
Bibcode: 2011A&A...526A...1D
Altcode:
We present multi-wavelength observations of a small B-class flare
which occurred on the Sun on 2007 May 22. The observations include
data from Hinode, GOES, TRACE and the Nobeyama Radioheliograph. We
obtained spatially and spectrally-resolved information from the Hinode
EUV Imaging Spectrometer (EIS) during this event. The temporal and
temperature coverage of the EIS observations provides new insights into
our understanding of chromospheric evaporation and cooling. The flare
showed many “typical” features, such as brightenings in the ribbons,
hot (10 MK) loop emission and subsequent cooling. We also observed
a new feature, strong (up to 170 km s-1) blue-shifted
emission in lines formed around 2-3 MK, located at the footpoints of
the 10 MK coronal emission and within the ribbons. Electron densities
at 2 MK in the kernels are high, of the order of 1011
cm-3, suggesting a very narrow layer where the chromospheric
evaporation occurs. We have run a non-equilibrium hydrodynamic numerical
simulation using the HYDRAD code to study the cooling of the 10 MK
plasma, finding good agreement between the predicted and observed
temperatures, densities and ion populations. Line blending for some
potentially useful diagnostic lines for flares, which are observed
with Hinode/EIS, is also discussed.
Title: Multiple Plasmoid Ejections and Associated Hard X-ray Bursts
in the 2000 November 24 Flare
Authors: Nishizuka, N.; Takasaki, H.; Asai, A.; Shibata, K.
Bibcode: 2010ApJ...711.1062N
Altcode: 2013arXiv1301.6241N
The Soft X-ray Telescope (SXT) on board Yohkoh revealed that the
ejection of X-ray emitting plasmoid is sometimes observed in a solar
flare. It was found that the ejected plasmoid is strongly accelerated
during a peak in the hard X-ray (HXR) emission of the flare. In
this paper, we present an examination of the GOES X 2.3 class flare
that occurred at 14:51 UT on 2000 November 24. In the SXT images,
we found "multiple" plasmoid ejections with velocities in the range
of 250-1500 km s-1, which showed blob-like or loop-like
structures. Furthermore, we also found that each plasmoid ejection
is associated with an impulsive burst of HXR emission. Although some
correlation between plasmoid ejection and HXR emission has been
discussed previously, our observation shows similar behavior for
multiple plasmoid ejection such that each plasmoid ejection occurs
during the strong energy release of the solar flare. As a result
of temperature-emission measure analysis of such plasmoids, it was
revealed that the apparent velocities and kinetic energies of the
plasmoid ejections show a correlation with the peak intensities in
the HXR emissions.
Title: Diagnosis of accelerated electrons in solar flare with radio
observation
Authors: Kawate, Tomoko; Asai, Ayumi; Ichimoto, Kiyoshi
Bibcode: 2010cosp...38.2982K
Altcode: 2010cosp.meet.2982K
Many problems still remain in particle acceleration in solar flare;
energy release site, particle acceleration mechanism, ratio of
nonthermal energy to whole released energy, maximum energy of particles,
energy spectrum of accelerated particles, spatial and temporal scale
of acceleration, difference of accelerated condition between ions
and electrons, etc. In this study, we discuss the characteristics of
accelerated electrons using statistical results of multi-wavelength
observations, mainly radio and hard X-ray data with non-thermal
emission process. The data we analyze are from Nobeyama Radioheliograph
(17GHz intensity and polarization, 34GHz intensity), RHESSI space
telescope (X-ray, gamma-ray), SOHO space telescope (magnetic field
in photosphere, EUV line emission), TRACE space telescope (UV, EUV)
and from optical data of ground-based telescopes. Our aim is to impose
some restrictions on the models of particle acceleration. To achieve
this, we examine pitch angle distribution of accelerated electrons. We
analyze practically in the following way. First, we pick up several
flare events observed with Nobeyama Radioheliograph at different
locations on the sun. Second, we identify the structure of flare
loops from EUV and magnetic field distributions in the photosphere
for each event. Third, we examine the radio flux, its polarization
and the position of the radio source in the flare loops, especially
focusing on their variations with the viewing angle to the magnetic
field by referring to the geometry of the flare loop and the location
of the flare on the sun. Finally, we compare the obtained properties
of the radio sources with the emission mechanisms of gyro-synchrotron
radiation to extract information of the pitch angle anisotropy.
Title: Dynamic features of thermal flare plasma unveiled with recent
observations
Authors: Asai, Ayumi
Bibcode: 2010cosp...38.2957A
Altcode: 2010cosp.meet.2957A
Solar flares are very spectacular, and they are accompanied by a
variety of plasma motions. As a flare evolves, flare loops show many
dynamic features of plasma, such as, flare plasma heating and cooling,
chromospheric evaporation, reconnection inflow and outflow, and so
on. In addition, many ejection phenomena, such as filament/prominence
eruptions have been observed in the chromospheric lines, in the extreme
ultraviolet (EUV), and in X-rays. Flare-associated waves and the related
plasma motions have also been studied. These plasma motions can be
observed as phenomena accompanied by line shifts (Doppler shifts)
in spectroscopic observations. Therefore, spectroscopic observations
are crusially impor-tant for understanding the dynamics of flare
plasma. I overview recent observations of solar flares especially done
by the EUV Imaging Spectrometer (EIS) on board Hinode, and discuss
the thermal aspects.
Title: Imaging Spectroscopy on Preflare Coronal Nonthermal Sources
Associated with the 2002 July 23 Flare
Authors: Asai, Ayumi; Nakajima, Hiroshi; Shimojo, Masumi; Yokoyama,
Takaaki; Masuda, Satoshi; Krucker, Säm
Bibcode: 2009ApJ...695.1623A
Altcode: 2009arXiv0901.3591A
We present a detailed examination on the coronal nonthermal emissions
during the preflare phase of the X4.8 flare that occurred on 2002 July
23. The microwave (17 GHz and 34 GHz) data obtained with Nobeyama
Radioheliograph, at Nobeyama Solar Radio Observatory and the hard
X-ray (HXR) data taken with RHESSI obviously showed nonthermal sources
that are located above the flare loops during the preflare phase. We
performed imaging spectroscopic analyses on the nonthermal emission
sources both in microwaves and in HXRs, and confirmed that electrons
are accelerated from several tens of keV to more than 1 MeV even in this
phase. If we assume the thin-target model for the HXR emission source,
the derived electron spectral indices (~4.7) is the same value as that
from microwaves (~4.7) within the observational uncertainties, which
implies that the distribution of the accelerated electrons follows a
single power law. The number density of the microwave-emitting electrons
is, however, larger than that of the HXR-emitting electrons, unless
we assume low-ambient plasma density of about 1.0 × 109
cm-3 for the HXR-emitting region. If we adopt the
thick-target model for the HXR emission source, on the other hand,
the electron spectral index (~6.7) is much different, while the gap
of the number density of the accelerated electrons is somewhat reduced.
Title: The Power-Law Distribution of Flare Kernels and Fractal
Current Sheets in a Solar Flare
Authors: Nishizuka, N.; Asai, A.; Takasaki, H.; Kurokawa, H.;
Shibata, K.
Bibcode: 2009ApJ...694L..74N
Altcode: 2013arXiv1301.6244N
We report a detailed examination of the fine structure inside flare
ribbons and the temporal evolution of this fine structure during
the X2.5 solar flare that occurred on 2004 November 10. We examine
elementary bursts of the C IV (~1550 Å) emission lines seen as local
transient brightenings inside the flare ribbons in the ultraviolet
(1600 Å) images taken with Transition Region and Coronal Explorer,
and we call them C IV kernels. This flare was also observed in Hα
with the Sartorius 18 cm Refractor telescope at Kwasan observatory,
Kyoto University, and in hard X-rays (HXR) with Reuven Ramaty High
Energy Solar Spectroscopic Imager. Many C IV kernels, whose sizes were
comparable to or less than 2'', were found to brighten successively
during the evolution of the flare ribbon. The majority of them were
well correlated with the Hα kernels in both space and time, while
some of them were associated with the HXR emission. These kernels were
thought to be caused by the precipitation of nonthermal particles at the
footpoints of the reconnecting flare loops. The time profiles of the C
IV kernels showed intermittent bursts, whose peak intensity, duration,
and time interval were well described by power-law distribution
functions. This result is interpreted as evidence for "self-organized
criticality" in avalanching behavior in a single flare event, or for
fractal current sheets in the impulsive reconnection region.
Title: Evolution of the anemone AR NOAA 10798 and the related
geo-effective flares and CMEs
Authors: Asai, Ayumi; Shibata, Kazunari; Ishii, Takako T.; Oka,
Mitsuo; Kataoka, Ryuho; Fujiki, Ken'ichi; Gopalswamy, Nat
Bibcode: 2009JGRA..114.0A21A
Altcode: 2009JGRA..11400A21A; 2008arXiv0812.2063A
We present a detailed examination of the features of the active region
(AR) NOAA 10798. This AR generated coronal mass ejections (CMEs) that
caused a large geomagnetic storm on 24 August 2005 with the minimum Dst
index of -216 nT. We examined the evolution of the AR and the features
on/near the solar surface and in the interplanetary space. The AR
emerged in the middle of a small coronal hole, and formed a sea anemone
like configuration. Hα filaments were formed in the AR, which have
southward axial field. Three M class flares were generated, and the
first two that occurred on 22 August 2005 were followed by Halo-type
CMEs. The speeds of the CMEs were fast, and recorded about 1200 and
2400 km s-1, respectively. The second CME was especially
fast, and caught up and interacted with the first (slower) CME during
their travelings toward Earth. These acted synergically to generate
an interplanetary disturbance with strong southward magnetic field of
about -50 nT, which was followed by the large geomagnetic storm.
Title: Minor Planet Observations [244 Geocentic Occultation
Observations]
Authors: Herald, D.; Abbeel, F.; Adams, J.; Aguirre, S.; Aikawa,
R.; Akazawa, H.; Allen, B.; Anderson, P.; Asai, A.; Audejean, M.;
Barton, J.; Benner, L.; Blanchette, D.; Bourtembourg, R.; Bradshaw,
J.; Breit, D.; Brinkmann, B.; Bulder, H.; Cadmus, R.; Carcich, A.;
Carlisle, R.; Clark, J.; Conard, S.; Coughlin, K.; Criddle, N.;
Dangl, G.; Degenhardt, S.; Ellington, C.; Eriksson, S.; Farris, T.;
Fiel, D.; Fleishman, R.; Frankenberger, R.; Frappa, E.; Garlitz,
J.; Gault, D.; George, T.; Guhl, K.; Hamanowa, H.; Hashimoto, A.;
Herchak, S.; Hicks, M.; Ida, M.; Ishida, M.; Ito, T.; Jennings, M.;
Jones, R.; Kageyama, K.; Karasaki, H.; Kenmotsu, K.; Kerr, S.; Kloes,
O.; Lahuerta, J.; Lambert, R.; Larriba, M.; Lecacheux, J.; Lockhart,
M.; Lowe, D.; Lucas, G.; Lyzenga, G.; Maley, P.; Manek, J.; Melillo,
F.; Messner, S.; Miyashita, K.; Moreno, O.; Morgan, W.; Nakasima,
Y.; Nolthenius, R.; Nugent, R.; Okamoto, S.; Oono, T.; Owada, M.;
Pauwels, T.; Peterson, R.; Poncy, R.; Pool, S.; Preston, S. !
Bibcode: 2009MPC..64752...5H
Altcode:
No abstract at ADS
Title: Strongly Blueshifted Phenomena Observed with Hinode EIS in
the 2006 December 13 Solar Flare
Authors: Asai, Ayumi; Hara, Hirohisa; Watanabe, Tetsuya; Imada,
Shinsuke; Sakao, Taro; Narukage, Noriyuki; Culhane, J. L.; Doschek,
G. A.
Bibcode: 2008ApJ...685..622A
Altcode: 2008arXiv0805.4468A
We present a detailed examination of strongly blueshifted emission
lines observed with the EUV Imaging Spectrometer on board the Hinode
satellite. We found two kinds of blueshifted phenomenon associated
with the X3.4 flare that occurred on 2006 December 13. One was related
to a plasmoid ejection seen in soft X-rays. It was very bright in all
the lines used for the observations. The other was associated with the
faint arc-shaped ejection seen in soft X-rays. The soft X-ray ejection
is thought to be a magnetohydrodynamic (MHD) fast-mode shock wave. This
is therefore the first spectroscopic observation of an MHD fast-mode
shock wave associated with a flare.
Title: Doppler Shifts in the Boundary of the Dimming Region
Authors: Imada, S.; Hara, H.; Watanabe, T.; Asai, A.; Kamio, S.;
Matsuzaki, K.; Harra, L. K.; Mariska, J. T.
Bibcode: 2008ASPC..397..102I
Altcode:
We present Hinode/EIS raster scan observations of the GOES X3.2
flare that occurred on 2006 December 13. There was a small transient
coronal hole which was located 200 arcsec east of the flare arcade. The
transient coronal hole was strongly affected by the X-class flare, and
the strong upflows were observed in Fe XV line 284.2 Å (log{T/{K}}
= 6.3) at the boundary of dimming region. In this paper, we discuss
how to obtain the velocity map by correcting the instrumental effects.
Title: Irreversible fixation of Arsenic during formation of Mg-bearing
minerals at alkaline condition
Authors: Sato, T.; Asai, A.; Morimoto, K.; Anraku, S.; Yoneda, T.
Bibcode: 2008GeCAS..72Q.825S
Altcode:
No abstract at ADS
Title: Non-Gaussian Line Profiles in a Large Solar Flare Observed
on 2006 December 13
Authors: Imada, S.; Hara, H.; Watanabe, T.; Asai, A.; Minoshima, T.;
Harra, L. K.; Mariska, J. T.
Bibcode: 2008ApJ...679L.155I
Altcode:
We have studied the characteristics of the non-Gaussian line profile
of the Fe XIV 274.20 Å line in and around a flare arcade. We found
that broad non-Gaussian line profiles associated with redshifts
are observed in the flare arcade. There were two typical types
of broad line profiles. One was a distorted line profile caused by
multiple flows, and the other was a symmetric line profile without any
additional component. We successfully distinguished those two types
using higher order statistical moments or M—the additional component
contribution—defined in this Letter. The distorted/symmetric broad
line profiles were preferentially observed in new/old flare loops,
respectively.
Title: Minor Planet Observations [244 Geocentic Occultation
Observations]
Authors: Herald, D.; Aguirre, S.; Aikawa, R.; Apitzsch, R.; Armstrong,
P.; Asai, A.; Bernascolle, P.; Bischof, W.; Bolzoni, S.; Bourtembourg,
R.; Brinkmann, B.; Brinsfield, J.; Buchheim, R.; Bulder, H.; Castro,
E.; Chavez, R.; Christophe, B.; Clayson, C.; Corelli, P.; Coughlin,
K.; Dangl, G.; Davila, E.; Degenhardt, S.; Degrelle, P.; Dobosz,
T.; Dunham, D.; Eberle, A.; Edwards, E.; Ellington, C.; Elliott,
A.; Farago, O.; Federspiel, M.; Fleishman, R.; Frappa, E.; Gabel,
A.; Galindez, E.; Garcia, E.; Gault, D.; George, T.; Ginzburg, A.;
Gonzales, P.; Goodman, G.; Gotou, K.; Govaarts, H.; Hamanowa, H.;
Hayamizu, T.; Hills, C.; Holmes, A.; Ida, M.; Ishida, M.; Jacquinot,
H.; James, R.; Jardine, B.; Jones, B.; Kageyama, K.; Karasaki, H.;
Keel, W.; Kenmotsu, K.; Kerr, S.; Kitazaki, K.; Klinglesmith, D.;
Kloes, O.; Kock, M.; Kohl, M.; Kozubal, M.; Lecacheux, J.; Leiter,
F.; Lyzenga, G.; Maley, P.; Matson, R.; McCants, M.; McGaha, J.;
Michels, H.; Mueller, J.; Munoz, E.; Murillo, G.; Nar!
Bibcode: 2008MPC..63124..12H
Altcode:
No abstract at ADS
Title: Characteristics of Anemone Active Regions Appearing in Coronal
Holes Observed with the Yohkoh Soft X-Ray Telescope
Authors: Asai, Ayumi; Shibata, Kazunari; Hara, Hirohisa; Nitta,
Nariaki V.
Bibcode: 2008ApJ...673.1188A
Altcode: 2008arXiv0805.4474A
Coronal structure of active regions appearing in coronal holes is
studied, using data that were obtained with the Soft X-Ray Telescope
(SXT) aboard Yohkoh between 1991 November and 1993 March. The following
characteristics are found. Many of the active regions (ARs) appearing
in coronal holes show a structure that looks like a sea anemone. Such
active regions are called anemone ARs. About one-fourth of all active
regions that were observed with SXT from their births showed the
anemone structure. For almost all the anemone ARs, the order of the
magnetic polarities is consistent with the Hale-Nicholson polarity
law. These anemone ARs also showed, to a greater or lesser extent,
an east-west asymmetry in the X-ray intensity distribution, such that
the following (eastern) part of the AR was brighter than its preceding
(western) part. This, as well as the anemone shape itself, is consistent
with the magnetic polarity distribution around the anemone ARs. These
observations also suggest that an active region appearing in coronal
holes has a simpler (less sheared) and more preceding-spot-dominant
magnetic structure than those appearing in other regions.
Title: Large-Amplitude Oscillation of an Erupting Filament as Seen
in EUV, Hα, and Microwave Observations
Authors: Isobe, H.; Tripathi, D.; Asai, A.; Jain, R.
Bibcode: 2007SoPh..246...89I
Altcode: 2007arXiv0711.3952I
We present multiwavelength observations of a large-amplitude oscillation
of a polar-crown filament on 15 October 2002, which has been reported by
Isobe and Tripathi (Astron. Astrophys.449, L17, 2006). The oscillation
occurred during the slow rise (≈1 km s−1) of the
filament. It completed three cycles before sudden acceleration and
eruption. The oscillation and following eruption were clearly seen in
observations recorded by the Extreme-Ultraviolet Imaging Telescope (EIT)
onboard the Solar and Heliospheric Observatory (SOHO). The oscillation
was seen only in a part of the filament, and it appears to be a standing
oscillation rather than a propagating wave. The amplitudes of velocity
and spatial displacement of the oscillation in the plane of the sky were
about 5 km s−1 and 15 000 km, respectively. The period
of oscillation was about two hours and did not change significantly
during the oscillation. The oscillation was also observed in Hα by
the Flare Monitoring Telescope at the Hida Observatory. We determine
the three-dimensional motion of the oscillation from the Hα wing
images. The maximum line-of-sight velocity was estimated to be a few
tens of kilometers per second, although the uncertainty is large owing
to the lack of line-profile information. Furthermore, we also identified
the spatial displacement of the oscillation in 17-GHz microwave images
from Nobeyama Radio Heliograph (NoRH). The filament oscillation seems
to be triggered by magnetic reconnection between a filament barb and
nearby emerging magnetic flux as was evident from the MDI magnetogram
observations. No flare was observed to be associated with the onset
of the oscillation. We also discuss possible implications of the
oscillation as a diagnostic tool for the eruption mechanisms. We
suggest that in the early phase of eruption a part of the filament
lost its equilibrium first, while the remaining part was still in an
equilibrium and oscillated.
Title: Discovery of a Temperature-Dependent Upflow in the Plage
Region During a Gradual Phase of the X-Class Flare
Authors: Imada, Shinsuke; Hara, Hirohisa; Watanabe, Tetsuya; Kamio,
Suguru; Asai, Ayumi; Matsuzaki, Keiichi; Harra, Louise K.; Mariska,
John T.
Bibcode: 2007PASJ...59S.793I
Altcode:
We present Hinode/EIS raster scan observations of the plage region
taken during the gradual phase of the GOES X3.2 flare that occurred on
2006 December 13. The plage region is located 200" east of the flare
arcade. The plage region has a small transient coronal hole. The
transient coronal hole is strongly affected by an X-class flare,
and upflows are observed at its boundary. Multi-wavelength spectral
observations allow us to determine velocities from the Doppler shifts
at different temperatures. Strong upflows along with stationary plasma
have been observed in the FeXV line 284.2Å (log T / K = 6.3) in the
plage region. The strong upflows reach almost 150kms-1, which
was estimated by a two-component Gaussian fitting. On the other hand,
at a lower corona/transition region temperature (HeII, 256.3Å, log T /
K = 4.9), very weak upflows, almost stationary, have been observed. We
find that these upflow velocities clearly depend on the temperature
with the hottest line, FeXV, showing the fastest upflow velocity and the
second-highest line, FeXIV, showing the second-highest upflow velocity
(130kms-1). All velocities are below the sound speed. The
trend of the upflow dependence on temperature dramatically changes
at 1MK. These results suggest that heating may have an important role
for strong upflow.
Title: Evolution of Hα Kernels and Energy Release in an X-Class Flare
Authors: Asai, A.; Yokoyama, T.; Shimojo, M.; Masuda, S.; Shibata, K.
Bibcode: 2007ASPC..369..461A
Altcode:
The investigation on the evolution of Hα kernels allows us to
derive some key information on the energy release processes and the
particle acceleration mechanisms during a flare. We report a detailed
examination on the relationship between the evolution of the Hα flare
ribbons and the released magnetic energy during an X2.3 solar flare
which occurred on 2001 April 10. In the Hα images, several bright
kernels were observed in the flare ribbons. We identified the conjugated
footpoints, by analyzing the light curve at each Hα kernel, and showed
their connectivities during the flare. Then, based on the magnetic
reconnection model, we calculated quantitatively the released energy
by using the photospheric magnetic field strengths and the separation
speeds of the fronts of the Hα flare ribbons. We confirmed that the
estimated energy release rate corresponds to the nonthermal emission
light curves at the strong emission sources. Finally, we examined the
downward motions at the Hα kernels. The "red-asymmetry" features,
generated by the precipitation of the nonthermal particles and/or
thermal conduction into the chromospheric plasma, were observed for all
the flare ribbons. We also found that the stronger the red-asymmetry
tends to be associated with the brighter Hα kernel.
Title: Imaging Spectroscopy of a Gradual Hardening Flare on 2000
November 25
Authors: Takasaki, Hiroyuki; Kiyohara, Junko; Asai, Ayumi; Nakajima,
Hiroshi; Yokoyama, Takaaki; Masuda, Satoshi; Sato, Jun; Kosugi, Takeo
Bibcode: 2007ApJ...661.1234T
Altcode:
We present an examination of multiwavelength observations of an M8.2
long-duration flare which occurred on 2000 November 25. During the
flare, we can see a hard X-ray (HXR) source on one Hα flare ribbon in
the HXR images obtained with the Hard X-ray Telescope aboard Yohkoh,
and a compact microwave emission source on the other flare ribbon
in the data taken with the Nobeyama Radioheliograph, while we can
also see an extended microwave emission source that connects both of
these emission sources. The compact microwave and HXR sources clearly
showed gradual hardening tendencies in their spectra. In addition,
we found energy-dependent delays of the peak times in the HXR bursts
and concluded that almost all of the accelerated electrons are trapped
in magnetic loops to generate the extended microwave source and are
dripping into the chromosphere at the compact microwave and the HXR
emission sites. We then performed imaging spectroscopic analyses to
the microwave emission sources. The temporal evolutions of the flux
and the spectral index of the compact microwave footpoint source are
quite similar to those of the HXR source, which is mainly emitted at
the other footpoint, while those at the loop-top extended source do
not show this similarity. Moreover, there is a constant gap between
the electron spectral index derived from the microwave footpoint source
and that from the HXR source. We also discuss the constant gap, based
on the trapped and dripping model.
Title: Loop top nonthermal emission sources associated with an
over-the-limb flare observed with NoRH and RHESSI
Authors: Asai, Ayumi; Nakajima, Hiroshi; Oka, Mitsuo; Nishida, Keisuke;
Tanaka, Yasuyuki T.
Bibcode: 2007AdSpR..39.1398A
Altcode:
We studied the M3.7 class flare which occurred on 2005 July 27, in the
active region NOAA 10792. This flare is an over-the-limb flare, and the
footpoints are entirely occulted by the solar disk. The microwave and
the hard X-ray images obtained with the Nobeyama Radioheliograph and
the RHESSI satellite, respectively, clearly showed emission sources
above the post-flare loop system. We examined the emission sources in
detail spatially, temporally, and spectroscopically. As a result, one
of the hard X-ray emission sources and the microwave emission source
are nonthermal.
Title: Flare Associated Oscillations Observed with NoRH
Authors: Asai, A.
Bibcode: 2006spnr.conf...33A
Altcode:
We present an examination of the multi-wavelength observation of a C7.9
flare which occurred on 1998 November 10. This is an imaging observation
of the quasi-periodic pulsations (QPPs) obtained with Yohkoh/HXT and
Nobeyama Radioheliograph (NoRH). We found that the Alfven transit time
along the flare loop was almost equal to the period of the QPP. We
therefore suggest that variations of macroscopic magnetic structures,
such as oscillations of coronal loops, affect the efficiency of particle
injection/acceleration. We also report other QPP events observed with
NoRH, and review some works on these flare-associated oscillations.
Title: The early phases of a solar prominence eruption and associated
flare: a multi-wavelength analysis
Authors: Chifor, C.; Mason, H. E.; Tripathi, D.; Isobe, H.; Asai, A.
Bibcode: 2006A&A...458..965C
Altcode:
Aims.We aim to examine the precursor phases and early evolution of a
prominence eruption associated with a M4-class flare and a partial
halo coronal mass ejection (CME) observed on 2005 July 27. Our
main goal is to investigate the precursor eruption signatures
observed in EUV, X-ray and microwave emission and their relation
to the prominence destabilisation.
Methods: .We perform a
multi-wavelength study of the prominence morphology and motion using
high-cadence and spatial resolution EUV 171 Å images from the TRACE
satellite. The high-temperature flare radiative emission in soft
and hard X-rays are analysed through imaging and spectral modeling
with RHESSI. Complementary microwave images (17 GHz and 34 GHz)
from NoRH are also investigated.
Results: .The activation
of the filament proceeds from one anchored footpoint. We observe
"pre-eruption" brightenings in X-ray and EUV images, close to the
erupting footpoint of the prominence, being temporally correlated to
the point when the prominence first enters a slow-rise phase, and then
an accelerated fast-rise phase. The brightness temperature (T_b) of the
prominence at 34 GHz is increasing during the eruption. We also find
very good correlation between the prominence height-time profile and
the spatially integrated soft X-ray (SXR) emission.
Conclusions:
.We discuss the observed precursor brightenings with respect to possible
mechanisms that might be responsible for the prominence destabilisation
and acceleration. Our observations suggest that reconnection events
localised beneath the erupting footpoint may eventually destabilise
the entire prominence, causing the eruption.
Title: Flare Ribbon Expansion and Energy Release
Authors: Asai, Ayumi; Yokoyama, Takaaki; Shimojo, Masumi; Masuda,
Satoshi; Shibata, Kazunari
Bibcode: 2006JApA...27..167A
Altcode:
We report a detailed examination about the relationship between the
evolution of the Hα flare ribbons and the released magnetic energy
during the April 10 2001 flare. In the Hα images, several bright
kernels are observed in the flare ribbons.We identified the conjugated
footpoints, by analyzing the lightcurves at each Hα kernels, and showed
their connectivities during the flare. Then, based on the magnetic
reconnection model, we calculated quantitatively the released energy by
using the photospheric magnetic field strengths and separation speeds
of the Hα flare ribbons. Finally, we examined the downward motions
which are observed at the Hα kernels. We found that the stronger the
red-asymmetry tends to be associated with the brighter the Hα kernel.
Title: Anemone structure of Active Region NOAA 10798 and related
geo-effective flares/ CMEs
Authors: Asai, A.; Ishii, T. T.; Shibata, K.; Gopalswamy, N.
Bibcode: 2006IAUJD...3E..72A
Altcode:
Introduction: We report the evolution and the coronal features of an
active region NOAA 10798, and the related magnetic storms. Method:
We examined in detail the photospheric and coronal features of
the active region by using observational data in soft X-rays, in
extreme ultraviolet images, and in magnetogram obtained with GOES,
SOHO satellites. We also examined the interplanetary disturbances from
the ACE data. Results: This active region was located in the middle of
a small coronal hole, and generated 3 M-class flares. The flares are
associated with high speed CMEs up to 2000 km/s. The interplanetary
disturbances also show a structure with southward strong magnetic
field. These produced a magnetic storm on 2005 August 24. Conclusions:
The anemone structure may play a role for producing the high-speed
and geo-effective CMEs even the near limb locations.
Title: Asymmetric Prominence Eruption: A "Domino Effect"?
Authors: Chifor, C.; Mason, H. E.; Tripathi, D.; Isobe, H.; Asai, A.
Bibcode: 2006ESASP.617E.121C
Altcode: 2006soho...17E.121C
No abstract at ADS
Title: Preflare Nonthermal Emission Observed in Microwaves and
Hard X-Rays
Authors: Asai, Ayumi; Nakajima, Hiroshi; Shimojo, Masumi; White,
Stephen M.; Hudson, Hugh S.; Lin, Robert P.
Bibcode: 2006PASJ...58L...1A
Altcode:
We present a detailed examination on nonthermal emissions during
the preflare phase of the X4.8 flare that occurred on 2002 July
23. The microwave (17GHz and 34GHz) data obtained with the Nobeyama
Radioheliograph at Nobeyama Solar Radio Observatory and the hard X-ray
data taken with the Reuven Ramaty High Energy Solar Spectroscopic Imager
obviously showed nonthermal features in the preflare phase. We also
found a faint ejection associated with the flare in the EUV images
taken with the Transition Region and Coronal Explorer. We discuss
the temporal and spatial features of the nonthermal emissions in the
preflare phase, and their relation with the ejection.
Title: One Solar-Cycle Observations of Prominence Activities Using
the Nobeyama Radioheliograph 1992-2004
Authors: Shimojo, Masumi; Yokoyama, Takaaki; Asai, Ayumi; Nakajima,
Hiroshi; Shibasaki, Kiyoto
Bibcode: 2006PASJ...58...85S
Altcode:
We newly developed a method of limb-event detection for the Nobeyama
Radiograph, and show the results over one solar-cycle, 1992 July-2004
December. We detected 785 prominence activities and 31 flares on the
limb by this method. We investigated the relationship between the
distributions of the prominence activities and the solar cycle. As a
result, we found the following facts: 1) The variation in the number of
prominence activities is similar to that of sunspots during one solar
cycle. 2) There are differences between the peak times of prominence
activities and sunspots. 3) The frequency distribution as a function
of the magnitude of the prominence activities (the size of activated
prominences) at each phase shows a power-law distribution. The power-law
index of the distribution does not change, except around the solar
minimum. 4) The number of prominence activities has a dependence on the
latitude. On the other hand, the average magnitude is independent of the
latitude. 5) During the rise phase of the solar cycle, the location of
the high-latitude prominence activities migrates to the pole region. 6)
After a solar polarity reversal, the location of the prominence
activities in the northern hemisphere migrates to the equator. On
the other hand, the prominence activities in the southern hemisphere
occurred in the high-latitude region until the decay phase of Cycle 23.
Title: One solar-cycle observations of prominence activities using
the Nobeyama Radioheliograph 1992--2004
Authors: Shimojo, M.; Yokoyama, T.; Asai, A.; Nakajima, H.;
Shibasaki, K.
Bibcode: 2006cosp...36..417S
Altcode: 2006cosp.meet..417S
We newly developed a method of limb-event detection for the Nobeyama
Radiograph and show the results over one solar-cycle 1992 July --
2004 December We detected 785 prominence activities and 31 flares on
the limb by this method We investigated the relationship between the
distributions of the prominence activities and the solar cycle As a
result we found the following facts 1 The variation in the number of
prominence activities is similar to that of sunspots during one solar
cycle 2 There are differences between the peak times of prominence
activities and sunspots 3 The frequency distribution as a function
of the magnitude of the prominence activities the size of activated
prominences at each phase shows a power-law distribution The power-law
index of the distribution does not change except around the solar
minimum 4 The number of prominence activities has a dependence on the
latitude On the other hand the average magnitude is independent of the
latitude 5 During the rise phase of the solar cycle the location of the
high-latitude prominence activities migrates to the pole region 6 After
a solar polarity reversal the location of the prominence activities
in the northern hemisphere migrates to the equator On the other hand
the prominence activities in the southern hemisphere occurred in the
high-latitude region until the decay phase of Cycle 23
Title: Preflare Features in Microwaves and in Hard X-Rays
Authors: Asai, Ayumi; Nakajima, Hiroshi; Shimojo, Masumi; White,
Stephen M.
Bibcode: 2006aogs....2...33A
Altcode:
We present a detailed examination on the nonthermal emissions during
the pre-flare phase of the X4.8 flare which occurred on July 23,
2002. The microwave (17 and 34 GHz) data obtained with Nobeyama
Radioheliograph (NoRH), at Nobeyama Solar Radio Observatory, National
Astronomical Observatory of Japan, and the hard X-ray (HXR) data taken
with Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
distinctly showed nonthermal features. We examined the temporal,
spatial, and spectroscopic characteristics of the emission sources,
and found loop-top sources during the preflare phase both in HXRs and
in microwaves. Moreover, we found that the electron spectral index
derived from microwave emission closely corresponds to that obtained
from the HXR emission. We also discuss the energy release mechanism
in the preflare phase.
Title: Loop top nonthermal emissin sources associated with an
over-the-limb flare observed with NoRH and RHESSI
Authors: Asai, A.; Nakajima, H.; Oka, M.; Nishida, K.; Tanaka, Y.
Bibcode: 2006cosp...36.2392A
Altcode: 2006cosp.meet.2392A
The finding of loop-top hard X-ray HXR emission sources Masuda et
al 1994 is one of the most important results achieved with Yohkoh
satellite We studied the M3 7 class flare which occurred on 2005 July
27 in the active region NOAA 10786 This flare is an over-the-limb
flare and the footpoints are occulted by the solar disk The microwave
and the HXR images obtained with the Nobeyama Radioheliograph and the
RHESSI satellite respectively clearly showed emission sources above
the post-flare loop system We examined the emission sources in detail
spatially temporally and spectroscopically As a result one of the HXR
emission sources and the microwave emission source are nonthermal
Title: Anemone structure of AR NOAA 10798 and related geo-effective
flares and CMEs
Authors: Asai, A.; Ishii, T. T.; Shibata, K.; Gopalswamy, N.
Bibcode: 2006cosp...36.2406A
Altcode: 2006cosp.meet.2406A
We report coronal features of an active region NOAA 10798 This
active region was located in the middle of a small coronal hole and
generated 3 M-class flares The flares are associated with high speed
CMEs which produced a magnetic storm on 2005 August 24 We examined
the coronal features by using observational data in soft X-rays in
extreme ultraviolets and in microwaves obtained with GOES SOHO TRACE
satellites and Nobeyama Radioheliograph
Title: Coprecipitation of As(III) with synthesized phyllosilicates
and hydrotalcite-like phases
Authors: Pascua, C. S.; Asai, A.; Sato, T.
Bibcode: 2005GeCAS..69R.626P
Altcode:
No abstract at ADS
Title: Downflow motions associated with impulsive nonthermal emissions
Authors: Asai, Ayumi; Shimojo, Masumi; Yokoyama, Takaaki; Shibata,
Kazunari
Bibcode: 2005ARAOJ...7....8A
Altcode:
No abstract at ADS
Title: Magnetic Neutral Line Rotations in Flare-Productive Regions
Authors: Ishii, Takako T.; Asai, Ayumi; Kurokawa, Hiroki; Takeuchi,
Tsutomu T.
Bibcode: 2005HiA....13..138I
Altcode:
We studied what is the common magnetic field configuration among
flare-productive active regions. In our previous studies we have found
that the magnetic neutral line shows a rotational motion in a delta-type
sunspot group NOAA 9026 where three X-class flares successively
occurred. In this paper we show another examples of magnetic neutral
line rotations in flare-productive sunspot groups. During the current
solar maximum (cycle 23) we studied the evolution of all the active
regions that have produced at least one X-class flare and have been
observed by the Solar and Heliospheric Observatory (SOHO) / Michelson
Doppler Imager (MDI). We examined 32 active regions from 1996 through
2002 and found that the rotational sunspot motions are common to these
flare-productive active regions (e.g. vortex-like motions in NOAA 8210
9236; rotation of magnetic neutral line of delta-type sunspots in
NOAA 9026 9393 9415 9591 9661 0039). These motions suggest that the
emergence of twisted magnetic flux bundles are the energy source for
strong flares. We discuss the relation between the magnetic helicity
and such a motion of magnetic neutral line e.g. the hemisphere rule
of helicity sign and the orientation of neutral line rotation.
Title: Flare ribbon expansion and energy release rate
Authors: Asai, Ayumi; Shimojo, Masumi; Yokoyama, Takaaki; Masuda,
Satoshi; Kurokawa, Hiroki; Shibata, Kazunari
Bibcode: 2005ARAOJ...7....7A
Altcode:
No abstract at ADS
Title: Downflow as a Reconnection Outflow
Authors: Asai, A.; Shibata, K.; Yokoyama, T.; Shimojo, M.
Bibcode: 2004ASPC..325..361A
Altcode:
We present a detailed examination about the evolution of TRACE downflow
motions (sunward motions) seen above post-flare loops. We found that
the times when the downflow motions are seen correspond to those of
the bursts of nonthermal emissions in hard X-rays and microwave. These
results mean that the downflows occurred when strong magnetic energy
was released, and that they are, or at least correlated with, the
reconnection outflows. We also propose an observation of downflows as
the reconnection outflows by SolarB.
Title: The Red-Asymmetry Distribution at Hα Flare Kernels Observed
in the 2001 April 10 Solar Flare
Authors: Asai, A.; Ichimoto, K.; Shibata, K.; Kitai, R.; Kurokawa, H.
Bibcode: 2004AGUFMSH13A1134A
Altcode:
We report a detailed examination about the evolution of the Hα flare
kernels during an X2.3 solar flare which occurred on 2001 April 10. The
Hα red-asymmetry, that is, the red-shifted Hα emission, is observed
at almost all Hα flare kernels, during the impulsive phase of the
flare. At Hα kernels nonthermal particles and/or thermal conduction
precipitate into the chromospheric plasma, and this is thought to lead
the downward compression of the chromospheric plasma, which is observed
as the reddening of Hα emission (e.g. Ichimoto & Kurokawa 1984). We
examined the evolution of the flare kernels inside the flare ribbons
by using the Hα images obtained with the Domeless Solar Telescope
at Hida Observatory, Kyoto University. We also examined the spatial
distribution of the Hα kernels which show the red-asymmetry and their
relationship with the intensity of the Hα kernels. We found that the
stronger the red-asymmetry is, the brighter the Hα kernel is. Then, we
compared the strengthes of the Hα red-asymmetry at hard X-ray emitting
sources with those at the Hα kernels without the hard X-ray emissions.
Title: A Quantitative Study of the Homologous Flares on 2000
November 24
Authors: Takasaki, Hiroyuki; Asai, Ayumi; Kiyohara, Junko; Shimojo,
Masumi; Terasawa, Toshio; Takei, Yasuhiro; Shibata, Kazunari
Bibcode: 2004ApJ...613..592T
Altcode:
We present an examination of multiwavelength observations of three
X-class homologous flares that occurred on 2000 November 24. By
investigating the behavior of the two-ribbon flares in Hα and the
ultraviolet (1600 Å), we found that the temporal variation of the
distance between the two ribbons shows a good correlation with the
soft X-ray light curve. From this finding we can derive the relation
dISXR(t)/dt~Vrib(t), where ISXR(t)
is the soft X-ray intensity and Vrib(t) is the separation
velocity of the two ribbons. This relation is similar to the well-known
empirical law, the Neupert effect. We also measured the rise time,
velocity of the plasmoid/filament ejection, and separation velocity of
the two ribbons for each of these homologous flares. Since the magnetic
reconnection model predicts that each of these physical parameters has
a dependence on the coronal magnetic field strength Bc,
we derived the relative Bc between the three flares from
each of the parameters. We compared the relative Bc values,
which are derived from those parameters, and found that they are roughly
equal. Our results successfully support the magnetic reconnection
model. Moreover, the relative hard X-ray maximum intensity in each
flare is consistent with the relative Bc derived above,
if we assume that the hard X-ray intensity is proportional to the
energy release rate as implied by the Neupert effect.
Title: Flare Ribbon Expansion and Energy Release Rate
Authors: Asai, Ayumi; Yokoyama, Takaaki; Shimojo, Masumi; Masuda,
Satoshi; Kurokawa, Hiroki; Shibata, Kazunari
Bibcode: 2004ApJ...611..557A
Altcode:
We have examined the relation between the evolution of the Hα
flare ribbons and the released magnetic energy in a solar flare that
occurred on 2001 April 10. Based on the magnetic reconnection model, the
released energy was quantitatively calculated by using the photospheric
magnetic field strengths and separation speeds of the fronts of the
Hα flare ribbons. We compared the variation of the released energy
with the temporal and spatial fluctuations in the nonthermal radiation
observed in hard X-rays and microwaves. These nonthermal radiation
sources indicate when and where large energy releases occur. We also
estimated the magnetic energy released during the flare. The estimated
energy release rates in the Hα kernels associated with the hard X-ray
sources are locally large enough to explain the difference between the
spatial distributions of the Hα kernels and the hard X-ray sources. We
also reconstructed the peaks in the nonthermal emission by using the
estimated energy release rates.
Title: Downflow Motions Associated with Impulsive Nonthermal Emissions
Observed in the 2002 July 23 Solar Flare
Authors: Asai, Ayumi; Yokoyama, Takaaki; Shimojo, Masumi; Shibata,
Kazunari
Bibcode: 2004ApJ...605L..77A
Altcode:
We present a detailed examination of downflow motions above flare
loops observed in the 2002 July 23 flare. The extreme-ultraviolet
images obtained with the Transition Region and Coronal Explorer show
dark downflow motions (sunward motions) above the postflare loops, not
only in the decay phase but also in the impulsive and main phases. We
also found that the times when the downflow motions start to be
seen correspond to the times when bursts of nonthermal emissions in
hard X-rays and microwaves are emitted. This result implies that the
downflow motions occurred when strong magnetic energy was released
and that they are, or are correlated with, reconnection outflows.
Title: TRACE Downflows and Energy Release
Authors: Asai, A.; Yokoyama, T.; Shimojo, M.; Tandokoro, R.; Fujimoto,
M.; Shibata, K.
Bibcode: 2004ESASP.547..163A
Altcode: 2004soho...13..163A
We have examined in detail the evolution of a big two-ribbon flare which
occurred on 2002 July 23. The extreme ultraviolet images obtained with
TRACE show dark downflow motions (sunward motions) above the post-flare
loop, not only in the decay phase but also in the impulsive and main
phase. We found that the times when the downflow motions are seen
correspond to those of the bursts of nonthermal emissions in hard X-ray
and microwave. This result means that the downflow motions occurred when
strong magnetic energy was released, and that they are, or correlated
with, the reconnection outflows. We also found the ascending motions
of super hot plasma region seen in TRACE and RHESSI associating with
the light curves in hard X-rays and microwaves. This result supports
the Neupert effect.
Title: Flare Ribbon Expansion and Energy Release Rate
Authors: Asai, Ayumi; Yokoyama, Takaaki; Shimojo, Masumi; Masuda,
Satoshi; Shibata, Kazunari
Bibcode: 2004IAUS..223..443A
Altcode: 2005IAUS..223..443A
We report a detailed examination about the relationship between
the evolution of the Halpha flare ribbons and the released magnetic
energy during an X2.3 solar flare which occurred on 2001 April 10. We
successfully evaluated the released energy quantitatively, based on the
magnetic reconnection model. We measured the photospheric magnetic field
strengths and the separation speeds of the fronts of the Halpha flare
ribbon, and estimated the released magnetic energy at the flare by using
those values. Then, we compared the estimated energy release rates with
the nonthermal behaviors observed in hard X-rays and microwaves. We
also estimated the magnetic energy released during the flare. The
estimated energy release rates in the Halpha kernels associated
with the hard X-ray sources are locally large enough to explain the
difference between the spatial distribution of the Halpha kernels and
the hard X-ray sources. Furthermore, we reconstructed the peaks in
the nonthermal emission by using the estimated energy release rates.
Title: Evolution of Flare Ribbons and Energy Release
Authors: Asai, A.; Yokoyama, Takaaki; Shimojo, Masumi; Masuda, Satoshi;
Kurokawa, Hiroki; Shibata, Kazunari
Bibcode: 2003ICRC....6.3367A
Altcode: 2003ICRC...28.3367A
We examined the relation between evolutions of flare ribb ons and
released magnetic energies at a solar flare which occurred on 2001
April 10 in the active region NOAA 9415. We successfully evaluated
the released energy quantitatively, based on the magnetic reconnection
model. We measured the photospheric magnetic field strengths and the
separation speeds of the fronts of the Hα flare ribb on, and estimated
the released magnetic energy at the flare by using those values. Then,
we compared the estimated energy release rates with the nonthermal
behaviors observed in hard X-rays and microwaves. We found that those
at the Hα kernels associated with the HXR sources are locally large
enough to explain the difference between the spatial distribution
the Hα kernels and the hard X-ray sources. Their temporal evolution
of the energy release rates also shows peaks corresponding to hard
X-ray bursts.
Title: Evolution of Conjugate Footpoints inside Flare Ribbons during
a Great Two-Ribbon Flare on 2001 April 10
Authors: Asai, Ayumi; Ishii, Takako T.; Kurokawa, Hiroki; Yokoyama,
Takaaki; Shimojo, Masumi
Bibcode: 2003ApJ...586..624A
Altcode:
We report a detailed examination of the fine structure inside flare
ribbons and the temporal evolution of such structure during an
X2.3 solar flare, which occurred on 2001 April 10. We examined fine
structures, such as systems of conjugate footpoints, inside flare
ribbons by using the Hα images obtained with the Sartorius telescope
at Kwasan Observatory, Kyoto University. We identified the conjugate
footpoints of each Hα kernel in both flare ribbons by a new method
that uses cross-correlation functions of the light curves. We also
compared the sites of the Hα kernels with the spatial configurations
of flare loops seen in the extreme-ultraviolet images obtained with
the Transition Region and Coronal Explorer. We found that the highly
correlated pairs of Hα kernels were connected by flare loops seen
in the 171 Å images. Investigating such fine structures inside the
flare ribbons, we can follow the history of energy release and perhaps
acquire key information about particle acceleration.
Title: Evolution of flare ribbons and energy release
Authors: Asai, A.; Masuda, S.; Yokoyama, T.; Shimojo, M.; Kurokawa,
H.; Ishii, T. T.; Shibatal, K.
Bibcode: 2003AdSpR..32.2561A
Altcode:
We examined the relation between the evolutions of the H α flare
ribbons and the released magnetic energiesat a solar flare which
occurred on 2001 April 10. This is the first study to evaluate the
released energy quantitatively, based on the magnetic reconnection
model, and by using the data obtained with the multi wavelength
observation. We measured the, photospheric magnetic field strengths
and the separation speeds of the fronts of the H α flare ribbon,
and compared them the nonthermal behaviors observed in HXRs and
microwaves. Those nonthermal radiation sources tell us when and
where large energy releases occur. Then, by using the photospheric
and chromospheric features, we estimated the released magnetic energy
at the flare. The estimated energy release rates at the H α kernels
associated with the HXR sources are locally large enough to explain
the difference between the spatial distribution the H α kernels and
the HXR sources. Their temporal evolution of the energy release rates
also shows peaks corresponding to HXR bursts.
Title: Magnetic Neutral Line Rotations in Flare-Productive Regions
Authors: Ishii, Takako T.; Asai, Ayumi; Kurokawa, Hiroki; Takeuchi,
Tsutomu T.
Bibcode: 2003IAUJD...3E..15I
Altcode:
We studied what is the common magnetic field configuration among
flare-productive active regions. In our previous studies we have found
that the magnetic neutral line shows a rotational motion in a delta-type
sunspot group NOAA 9026 where three X-class flares successively
occurred. In this paper we show another examples of magnetic neutral
line rotations in flare-productive sunspot groups. During the current
solar maximum (cycle 23) we studied the evolution of all the active
regions that have produced at least one X-class flare and have been
observed by the Solar and Heliospheric Observatory (SOHO) / Michelson
Doppler Imager (MDI). We examined 32 active regions from 1996 through
2002 and found that the rotational sunspot motions are common to these
flare-productive active regions (e.g. vortex-like motions in NOAA 8210
9236; rotation of magnetic neutral line of delta-type sunspots in
NOAA 9026 9393 9415 9591 9661 0039). These motions suggest that the
emergence of twisted magnetic flux bundles are the energy source for
strong flares. We discuss the relation between the magnetic helicity
and such a motion of magnetic neutral line e.g. the hemisphere rule
of helicity sign and the orientation of neutral line rotation
Title: Difference between Spatial Distributions of the Hα Kernels
and Hard X-Ray Sources in a Solar Flare
Authors: Asai, Ayumi; Masuda, Satoshi; Yokoyama, Takaaki; Shimojo,
Masumi; Isobe, Hiroaki; Kurokawa, Hiroki; Shibata, Kazunari
Bibcode: 2002ApJ...578L..91A
Altcode: 2002astro.ph..9106A
We present the relation of the spatial distribution of Hα kernels
with the distribution of hard X-ray (HXR) sources seen during the 2001
April 10 solar flare. This flare was observed in Hα with the Sartorius
telescope at Kwasan Observatory, Kyoto University, and in HXRs with
the hard X-ray telescope (HXT) on board Yohkoh. We compared the spatial
distribution of the HXR sources with that of the Hα kernels. While many
Hα kernels are found to brighten successively during the evolution
of the flare ribbons, only a few radiation sources are seen in the
HXR images. We measured the photospheric magnetic field strengths
at each radiation source in the Hα images and found that the Hα
kernels accompanied by HXR radiation have magnetic strengths about 3
times larger than those without HXR radiation. We also estimated the
energy release rates based on the magnetic reconnection model. The
release rates at the Hα kernels with accompanying HXR sources are
16-27 times larger than those without HXR sources. These values are
sufficiently larger than the dynamic range of HXT, which is about 10,
so that the difference between the spatial distributions of the Hα
kernels and the HXR sources can be explained.
Title: Relation between a Moreton Wave and an EIT Wave Observed on
1997 November 4
Authors: Eto, Shigeru; Isobe, Hiroaki; Narukage, Noriyuki; Asai, Ayumi;
Morimoto, Taro; Thompson, Barbara; Yashiro, Seiji; Wang, Tongjiang;
Kitai, Reizaburo; Kurokawa, Hiroki; Shibata, Kazunari
Bibcode: 2002PASJ...54..481E
Altcode:
We consider the relationship between two flare-associated waves,
a chromospheric Moreton wave and a coronal EIT wave, based on an
analysis of an X-class flare event in AR 8100 on 1997 November 4. A
Moreton wave was observed in Hα + 0.8 Å, and Hα - 0.8 Å with the
Flare-Monitoring Telescope (FMT) at the Hida Observatory. An EIT wave
was observed in EUV with the Extreme ultraviolet Imaging Telescope
(EIT) on board SOHO. The propagation speeds of the Moreton wave and
the EIT wave were approximately 715 km s-1 and 202 km
s-1, respectively. The times of visibility for the Moreton
wave did not overlap those of the EIT wave, but the continuation of the
former is indicated by a filament oscillation. Data on the speed and
location clearly show that the Moreton wave differed physically from
the EIT wave in this case. The Moreton wave preceded the EIT wave,
which is inconsistent with an identification of the EIT wave with a
fast-mode MHD shock.
Title: Evolution of Flare Ribbons and Energy Release
Authors: Asai, A.; Masuda, S.; Yokoyama, T.; Shimojo, M.; Ishii,
T. T.; Isobe, H.; Shibata, K.; Kurokawa, H.
Bibcode: 2002aprm.conf..415A
Altcode:
We estimated the released magnetic energy via magnetic reconnection
in the corona by using photospheric and chromospheric features. We
observed an X2.3 flare, which occurred in active region NOAA9415 on 2001
April 10, in Hα with the Sartorius Telescope at Kwasan Observatory,
Kyoto University. Comparing the Hα images with the hard X-ray (HXR)
images obtained with Yohkoh/HXT, we see only two HXR sources which
are accompanied by Hα kernels. At these Hα kernels the large energy
release is thought to be larger than at other Hα kernels. We estimated
the energy release rates at each Hα kernel by using the photospheric
magnetic field strength and the separation speed of the Hα flare
ribbons at the same location. The estimated energy release rates at
the Hα kernels associated with the HXR sources are locally large
enough to explain the different appearance. Their temporal evolution
also shows peaks corresponding to HXR bursts.
Title: Multi-Wavelength Observation of A Moreton Wave on November
3, 1997
Authors: Narukage, N.; Shibata, K.; Hudson, H. S.; Eto, S.; Isobe,
H.; Asai, A.; Morimoto, T.; Kozu, H.; Ishii, T. T.; Akiyama, S.;
Kitai, R.; Kurokawa, H.
Bibcode: 2002mwoc.conf..295N
Altcode:
No abstract at ADS
Title: Fine Structure inside Flare Ribbons and Temporal Evolution
Authors: Asai, A.; Masuda, S.; Yokoyama, T.; Shimojo, M.; Kurokawa,
H.; Shibata, K.; Ishii, T. T.; Kitai, R.; Isobe, H.; Yaji, K.
Bibcode: 2002mwoc.conf..221A
Altcode:
Non-thermal particles generated in the impulsive phase of
solar flares are observed mainly in microwave, hard X-rays, and
gamma-rays. Observations in Hα can also give important informations
about non-thermal particles precipitating into the chromosphere with
a higher spatial resolution than in other wavelengths. We observed an
X2.3 flare which occurred in the active region NOAA 9415 on 10 April
2001, in Hα with Sartorius Telescope at Kwasan Observatory, Kyoto
University. Thanks to the short exposure time given for the flare, the
Hα images show fine structures inside the flare ribbons. In addition
to Hα, we analyze microwave, hard X-ray, and EUV data obtained with
Nobeyama Radioheliograph, Yohkoh/HXT, and TRACE, respectively. In Hα,
several bright kernels are observed in the flare ribbons. On the other
hand, the hard X-ray images show only a single pair of bright sources
which correspond to one of several pairs of Hα kernels. Examining
the difference in the magnetic field strength and in the time profiles
of Hα emission for these kernels, we discuss the reason why only one
pair kernels are bright in the hard X-ray among the other bright Hα
kernels. Comparing the Hα images with EUV images, we also examine
the three-dimensional structure of solar flares. While broad and
network-like ribbons are observed in Hα, the width of EUV ribbons is
relatively narrow, and EUV ribbons are located at the outer edges of
the corresponding Hα ribbon.
Title: Evolution of flare ribbons and energy release
Authors: Asai, A.; Masuda, S.; Yokoyama, T.; Shimojo, M.; Kurokawa,
H.; Ishii, T.; Shibata, K.
Bibcode: 2002cosp...34E1179A
Altcode: 2002cosp.meetE1179A
Non-thermal particles generated in the impulsive phase of
solar flares are observed mainly in microwave, hard X-rays, and g
amma-rays. Observations in Halpha can also give important informations
about non-thermal particles precipitating into the chromosphere with a
higher spatial resolution than in other wavelengths. We observed an X2.3
flare which occurred in the active region NOAA 9415 on 10 April 2001,
in Halpha with the Sartorius Telescope at Kwasan Observatory, Kyoto
University. Thanks to the short exposure time given for the flare, the
Halpha images show fine structures inside the flare ribbons. In Halpha,
several bright kernels are observed in the flare ribbons. On the other
hand, the hard X-ray images show only a single pair of bright sources
which correspond to one of several pairs of Halpha kernels. In this
paper, we examined the magnetic field strength at each H kernel and
the separation speed of the H flare ribbons, and estimated the energy
release rate with the method based on the magnetic reconnection model
(Isobe et al. 2002). We found that the energy release rate is well
correlated with the time profiles of hard X-ray and microwave.
Title: On the directions of solar filament eruptions
Authors: Morimoto, T.; Asai, A.; Isobe, H.; Chen, P.; Kurokawa, H.
Bibcode: 2002cosp...34E1178M
Altcode: 2002cosp.meetE1178M
We report on the relation between directions of solar filament
eruptions and the distribution of magnetic field strengths at and
near the source regions. The solar filaments and prominences become
cores of coronal mass ejections (CMEs) when they are ejected into the
interplanetary space. These CMEs appear as halo CMEs when directed
toward the earth, and they often cause geomagnetic storms. It is,
therefore, very important to know the direction of a CME before or
in the initial phase of its onset. Making use of H line center, blue
and red wing images, together with the Doppler method, we measured 3D
velocity field of more than 15 events of solar disappearing filament
(SDF). From the velocity field, we obtained the directions of these
SDFs, and compared it with the distributions of photospheric magnetic
field strengths. We found that both orientation angle (angle by the
solar meridian and a vector of the direction of a filament projected
onto the solar surface) and ejection angle (elevationangle measured
against the solar surface) well match with the vector of local gradient
of photospheric magnetic field strengths. The possibility to predict
the direction of a CME even before its onset is also discussed.
Title: Observations of Moreton Waves and EIT Waves
Authors: Shibata, K.; Eto, S.; Narukage, N.; Isobe, H.; Morimoto,
T.; Kozu, H.; Asai, A.; Ishii, T.; Akiyama, S.; Ueno, S.; Kitai, R.;
Kurokawa, H.; Yashiro, S.; Thompson, B. J.; Wang, T.; Hudson, H. S.
Bibcode: 2002mwoc.conf..279S
Altcode:
The Moreton wave is a flare-associated wave observed in H alpha, and
is now established to be a fast mode MHD shock emitted from the flare,
but the physical mechanism to create the wave is still puzzling. On
the other hand, the EIT wave is a newly discovered flare-associated
wave observed in EUV with the Extreme ultraviolet Imaging Telescope
(EIT) aboard SOHO, and in this case, not only its origin but also
its physical property are both puzzling. We study the relationship
of these two flare-associated waves, Moreton waves and EIT waves, by
analyzing 4 events observed on Nov. 3 and 4, 1997, Aug. 8, 1998, and
Mar. 3, 2000 (Narukage et al. 2001). The Moreton waves were observed
in Ha, Ha+0.8A and Ha-0.8A with the Flare Monitoring Telescope (FMT)
at the Hida Observatory of Kyoto University, while the EIT waves were
observed with SOHO/EIT. In the typical case associated with an X-class
flare in AR 8100 on 4 November 1997 (Eto et al. 2001) the propagation
speeds of the Moreton wave and the EIT wave were approximately 780
km/s and 200 km/s respectively. The data on speed and location show
clearly that the Moreton wave differs physically from the EIT wave in
this case. The detailed analyses of the other events (Nov. 3, 1997,
Aug. 8, 1998, and Mar. 3, 2000) will also be presented, with Yohkoh/SXT
data in the lucky case.
Title: Periodic Acceleration of Electrons in the 1998 November 10
Solar Flare
Authors: Asai, A.; Shimojo, M.; Isobe, H.; Morimoto, T.; Yokoyama,
T.; Shibasaki, K.; Nakajima, H.
Bibcode: 2001ApJ...562L.103A
Altcode: 2001astro.ph.11018A
We present an examination of the multiwavelength observation of
a C7.9 flare that occurred on 1998 November 10. This is the first
imaging observation of the quasi-periodic pulsations (QPPs). Four
bursts were observed with the hard X-ray telescope aboard Yohkoh
and the Nobeyama Radioheliograph during the impulsive phase of the
flare. In the second burst, the hard X-ray and microwave time profiles
clearly showed a QPP. We estimated the Alfvén transit time along
the flare loop using the images of the soft X-ray telescope aboard
Yohkoh and the photospheric magnetograms and found that the transit
time was almost equal to the period of the QPP. We therefore suggest,
based on a shock acceleration model, that variations of macroscopic
magnetic structures, such as oscillations of coronal loops, affect
the efficiency of particle injection/acceleration.
Title: Plasma Ejections from a Light Bridge in a Sunspot Umbra
Authors: Asai, Ayumi; Ishii, Takako T.; Kurokawa, Hiroki
Bibcode: 2001ApJ...555L..65A
Altcode: 2001astro.ph.11021A
We present conspicuous activities of plasma ejections along a light
bridge of a stable and mature sunspot in NOAA Active Region 8971 on
2000 May 2. We found the ejections both in the Hα (104 K)
images obtained with the Domeless Solar Telescope at Hida Observatory
and in the 171 Å (Fe IX/Fe X; ~106 K) images obtained
with the Transition Region and Coronal Explorer. Main characteristics
of the ejections are as follows: (1) Ejections occur intermittently
and recurrently. (2) The velocities and the timings of the 171 Å
ejections are the same as those of Hα ejections. (3) The appearance of
the ejections are different from one another; i.e., the Hα ejections
have a jetlike appearance, while the 171 Å ejections are like loops.