Author name code: isobe
ADS astronomy entries on 2022-09-14
author:"Isobe, Hiroaki"
------------------------------------------------------------------------
Title: Small-scale Turbulent Motion of the Plasma in a Solar Filament
as the Precursor of Eruption
Authors: Seki, Daikichi; Otsuji, Kenichi; Isobe, Hiroaki; Del Zanna,
Giulio; Ishii, Takako T.; Sakaue, Takahito; Ichimoto, Kiyoshi;
Shibata, Kazunari
Bibcode: 2021ApJ...918...38S
Altcode: 2021arXiv210611875S
A filament, a dense cool plasma supported by the magnetic fields in
the solar corona, often becomes unstable and erupts. It is empirically
known that the filament often demonstrates some activations such
as a turbulent motion prior to eruption. In our previous study, we
analyzed the Doppler velocity of an Hα filament and found that the
standard deviation of the line-of-sight velocity distribution in a
filament, which indicates the increasing amplitude of the small-scale
motions, increased prior to the onset of the eruption. Here, we
present a further analysis on this filament eruption, which initiated
approximately at 03:40 UT on 2016 November 5 in the vicinity of NOAA
Active Region 12605. It includes a coronal line observation and the
extrapolation of the surrounding magnetic fields. We found that both
the spatially averaged microturbulence inside the filament and the
nearby coronal line emission increased 6 and 10 hr prior to eruption,
respectively. In this event, we did not find any significant changes
in the global potential field configuration preceding the eruption for
the past 2 days, which indicates that there is a case in which it is
difficult to predict the eruption only by tracking the extrapolated
global magnetic fields. In terms of space weather prediction, our
result on the turbulent motions in a filament could be used as the
useful precursor of a filament eruption.
Title: On the Ratios of Si IV Lines (λ1394/λ1403) in an Emerging
Flux Region
Authors: Tripathi, Durgesh; Nived, V. N.; Isobe, Hiroaki; Doyle,
G. Gerard
Bibcode: 2020ApJ...894..128T
Altcode: 2020arXiv200404530T
The resonance lines of Si IV formed at λ1394 and 1403 Å are the
most critical for the diagnostics of the solar transition region
in the observations of the Interface Region Imaging Spectrograph
(IRIS). Studying the intensity ratios of these lines (1394 Å/1403 Å),
which under optically thin conditions is predicted to be two, helps us
to diagnose the optical thickness of the plasma being observed. Here
we study the evolution of the distribution of intensity ratios in 31
IRIS rasters recorded for four days during the emergence of an active
region. We found that during the early phase of the development, the
majority of the pixels show intensity ratios smaller than two. However,
as the active region evolves, more and more pixels show the ratios
closer to two. Besides, there are a substantial number of pixels with
ratio values larger than 2. At the evolved stage of the active region,
the pixels with ratios smaller than two were located on the periphery,
whereas those with values larger than 2 were in the core. However,
for quiet Sun regions, the obtained intensity ratios were close to
two irrespective of the location on the disk. Our findings suggest
that the Si IV lines observed in active regions are affected by the
opacity during the early phase of the flux emergence. The results
obtained here could have important implications for the modeling of
the solar atmosphere, including the initial stage of the emergence of
an active region as well as the quiet Sun.
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: Intense Geomagnetic Storm during Maunder Minimum Possibly by
a Quiescent Filament Eruption
Authors: Isobe, Hiroaki; Ebihara, Yusuke; Kawamura, Akito D.; Tamazawa,
Harufumi; Hayakawa, Hisashi
Bibcode: 2019ApJ...887....7I
Altcode: 2019arXiv190308466I
The Sun occasionally undergoes the so-called grand minima, in which its
magnetic activity, measured by the number of sunspots, is suppressed
for decades. The most prominent grand minima, since the beginning of
telescopic observations of sunspots, is called the Maunder minimum
(1645-1715), which occurred when the sunspots became rather scarce. The
mechanism underlying the grand minima remains poorly understood as there
is little observational information of the solar magnetic field at that
time. In this study, we examine the records of one candidate aurora
display in China and Japan during the Maunder minimum. The presence
of auroras in such mid-magnetic latitudes indicates the occurrence
of great geomagnetic storms that are usually produced by strong solar
flares. However, the records of contemporary sunspot observations from
Europe suggest that, at least for the likely aurora event, there was
no large sunspot that could produce a strong flare. Through simple
theoretical arguments, we show that this geomagnetic storm could have
been generated by an eruption giant quiescent filament or a series of
such events.
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: Oxidation behavior of micrometeorites in upper atmosphere
based on melting experiments in controlled oxygen fugacity
Authors: Isobe, H.
Bibcode: 2019AGUFM.P21F3438I
Altcode:
Micrometeorites have the most abundant flux in current accumulation
of planetary materials to the Earth. Micrometeorites are heated and
reacted with upper atmosphere at atmospheric entry. Oxidation behavior
of micrometeorites depends on oxygen concentration, or oxygen fugacity,
in the upper atmosphere. Ancient oxygen concentration of the terrestrial
atmosphere is discussed based on micrometeorites from Archaean sediments
(Tomkins et al., 2016). We reported artificial micrometeorites produced
in high temperature melting and quench experiments under controlled
oxygen fugacity. In this study, analogy of oxidation behavior of
oxidation sensitive elements including iron will be discussed based
on texture and chemistry of artificial micrometeorites produced by
experiments with controlled atmosphere by H2-CO2 gas mixture. In
the melting experiments, oxygen fugacity was controlled from -0.5
to +2.4 log unit relative to FMQ buffer curve. Maximum temperature
of the experimental particles was approximately 1600 °C and higher
than 1400 °C for approximately 0.5 seconds and quenched. Run products
particles were completely melted and show rounded shape with smooth
surface like micrometeorites. Natural micrometeorites react with
oxygen atoms in upper atmosphere in the heating pass at atmospheric
entry. It extends several tens of kilometers. Amount of oxygen atoms
encountered with micrometeorites depends on oxygen concentration of thin
upper atmosphere. In the melting experiments, experimental particles
encounter with H2, CO, CO2 and H2O molecules produced under equilibrium
of these gas species at the temperature. Fraction of oxygen is also
controlled by the equilibrium of these species but fraction of oxygen
is limited from 10 to the third to eighth power. Oxidation behavior of
the artificial micrometeorites may be controlled by transient reaction
of particles with H2, CO, CO2 and H2O molecules rather than oxygen. By the melting experiments producing artificial micrometeorites
with various initial gas mixture, run products show various textures
and composition in iron oxides. Oxidation behavior of micrometeorites
in the upper atmosphere with various oxygen concentrations can be
reproduced by experimental reactions involving H2, CO, CO2 and H2O
molecules in atmospheric pressure.
Title: Effect of Ionization and Recombination on the Evolution of
the Harris-type Current Sheet in Partially Ionized Plasmas
Authors: Singh, K. A. P.; Sakaue, Takahito; Nakamura, Naoki; Kawamura,
Akito D.; Isobe, Hiroaki; Shibata, Kazunari
Bibcode: 2019ApJ...884..161S
Altcode:
Two-dimensional magnetohydrodynamics (MHD) simulations, treating
plasma and neutral populations (hereafter, neutrals) as two
separate components of the magneto-fluid, are performed in order
to investigate the effect of ionization and recombination (or I/R)
on the time evolution of the Harris-type current sheet in partially
ionized plasmas. Our MHD simulations, including the effect of ambipolar
diffusion (arising due to ion-neutral interactions) along with the I/R,
show that the current sheet thinning occurs due to the diffusion of
neutral particles from the current sheet. In addition to ambipolar
diffusion, frictional heating also appears and affects the evolution
of the current sheet. In a current sheet that is formed in a partially
ionized plasma, the neutral population tries to spread outward and the
plasma population tries to converge toward the center of the current
sheet, and the overall process is influenced by the I/R. One of the
important feature that is captured in our 2D simulations is that the
escape of neutrals from the current sheet is sometimes suppressed due
to the increase in ionization rate at the center of the current sheet,
for the case of collisional I/R. As long as the ionization degree
is kept low inside the current sheet, the current sheet thinning and
elongation takes place and the current sheet becomes unstable due to
the tearing-mode and plasmoid formation. The ion-neutral interactions
coupled with I/R and the dynamics of the magnetic reconnection play
an important role in plasmoid-mediated reconnection, therefore, the
present study on the current sheet thinning and plasmoid formation
could serve as a key for understanding bursty and intermittent plasma
ejections observed in the solar chromosphere.
Title: Small-scale motions in solar filaments as the precursors
of eruptions
Authors: Seki, Daikichi; Otsuji, Kenichi; Isobe, Hiroaki; Ishii,
Takako T.; Ichimoto, Kiyoshi; Shibata, Kazunari
Bibcode: 2019PASJ...71...56S
Altcode: 2019arXiv190208718S; 2019PASJ..tmp...48S
Filaments, the dense cooler plasma floating in the solar corona
supported by magnetic fields, generally exhibit certain activations
before they erupt. In our previous study (Seki et al. 2017, ApJ, 843,
L24), we observed that the standard deviation of the line-of-sight (LOS)
velocities of the small-scale motions in a filament increased prior
to its eruption. However, because that study only analyzed one event,
it is unclear whether such an increase in the standard deviation of
LOS velocities is common in filament eruptions. In this study, 12
filaments that vanished in Hα line center images were analyzed in
a manner similar to the one in our previous work; these included two
quiescent filaments, four active region filaments, and six intermediate
filaments. We verified that in all the 12 events, the standard deviation
of the LOS velocities increased before the filaments vanished. Moreover,
we observed that the quiescent filaments had approximately 10 times
longer duration of an increase in the standard deviation than the
other types of filaments. We concluded that the standard deviation
of the LOS velocities of the small-scale motions in a filament can
potentially be used as a precursor of a filament eruption.
Title: Space Weather Prediction from the Ground: Case of CHAIN
Authors: Seki, Daikichi; Ueno, Satoru; Isobe, Hiroaki; Otsuji, Kenichi;
Cabezas, Denis P.; Ichimoto, Kiyoshi; Shibata, Kazunari; Chain Team
Bibcode: 2018SunGe..13..157S
Altcode:
In this article, we insist on the importance and the challenges of the
prediction of solar eruptive phenomena including flares, coronal mass
ejections (CME), and filament eruptions fully based on the ground-based
telescopes. It is true that satellites' data are indispensable for the
space weather prediction, but they are vulnerable to the space weather
effects. Therefore, the ground-based telescopes can be complementary
to them from the viewpoint of space weather prediction. From this
view point, one possible new flare prediction method that makes use of
H-alpha, red wings, and blue wings images obtained by the SDDI/SMART,
the ground-based telescope at Hida Observatory, is presented. And
in order to show the possibility for the actual operation based on
that method, the recent progress of CHAIN project, the international
observation network, is mentioned in terms of their outcomes and
capacity buildings.
Title: Oxidation and evaporation of iron sulfide fine particles by
heating experiments with various oxygen fugacity conditions
Authors: Isobe, H.; Murozono, K.
Bibcode: 2018AGUFM.P53E3004I
Altcode:
Micrometeorites have the most abundant flux in current accumulation of
planetary materials to the Earth. Micrometeorites are heated and reacted
with upper atmosphere at atmospheric entry. Evaporation of meteoritic
materials, especially sulfur species, may have environmental effect
at upper atmosphere (e.g. Court and Sephton, 2011; Tomkins et al.,
2016). Troilite is typical FeS phase in chondritic meteorites. In this
study, quick heating and cooling experiments of FeS reagent particles
were carried out with the fine particles free falling apparatus with
controlled gas flow (Isobe and Gondo, 2013) under various oxygen
fugacity conditions around FMQ buffer curve. Starting material reagent
is inhomogeneous mixture of troilite, iron oxide and iron metal. Oxygen
fugacity was controlled to FMQ buffer and FMQ ±1.5 log unit. Maximum
temperature of the particles was approximately 1600°C and higher than
1400°C for approximately 0.5 seconds. Run products particles were
completely melted and show rounded shape with smooth surface. Chemical
compositions of particles were analyzed on cross sections including
oxygen. Generally, spherical products were well homogenized from
inhomogeneous starting materials by complete melting. Molar ratios of
Fe in melted spherules are close to 0.5, while compositions of S and O
are various. Distribution of compositions in Fe-S-O system is plotted
in liquidus compositions of FeO and FeS saturated melt (Ueda et al.,
2008). Varieties of S and O compositions show progress of oxidation
with increasing of oxygen fugacity. Evaporation of sulfur depends on
temperature rather than oxygen fugacity conditions. Troilite in
micrometeorite is melted and oxidized by atmospheric entry. Compositions
of iron sulfide melt in fine spherules are initially close to FeS and
are losing S and oxidizing following Fe-S-O phase relations depending on
oxygen fugacity even in a few seconds. Varieties of S and O compositions
show various degree of oxidation and evaporation of sulfur. Evaporation
of sulfur from meteoritic materials in atmospheric entry heating may
depend on oxygen content of the upper atmosphere. Sulfur supply from
meteoritic materials to atmosphere may be limited on planets with
oxygen-free atmosphere.
Title: A great space weather event in February 1730
Authors: Hayakawa, Hisashi; Ebihara, Yusuke; Vaquero, José M.;
Hattori, Kentaro; Carrasco, Víctor M. S.; de la Cruz Gallego, María;
Hayakawa, Satoshi; Watanabe, Yoshikazu; Iwahashi, Kiyomi; Tamazawa,
Harufumi; Kawamura, Akito D.; Isobe, Hiroaki
Bibcode: 2018A&A...616A.177H
Altcode: 2018arXiv180706496H
Aims: Historical records provide evidence of extreme magnetic
storms with equatorward auroral extensions before the epoch of
systematic magnetic observations. One significant magnetic storm
occurred on February 15, 1730. We scale this magnetic storm with
auroral extension and contextualise it based on contemporary solar
activity.
Methods: We examined historical records in East Asia
and computed the magnetic latitude (MLAT) of observational sites to
scale magnetic storms. We also compared them with auroral records
in Southern Europe. We examined contemporary sunspot observations
to reconstruct detailed solar activity between 1729 and 1731.
Results: We show 29 auroral records in East Asian historical documents
and 37 sunspot observations.
Conclusions: These records show
that the auroral displays were visible at least down to 25.8° MLAT
throughout East Asia. In comparison with contemporary European records,
we show that the boundary of the auroral display closest to the equator
surpassed 45.1° MLAT and possibly came down to 31.5° MLAT in its
maximum phase, with considerable brightness. Contemporary sunspot
records show an active phase in the first half of 1730 during the
declining phase of the solar cycle. This magnetic storm was at least
as intense as the magnetic storm in 1989, but less intense than the
Carrington event.
Title: Space Weather Prediction from the Ground: Case of CHAIN
Authors: Seki, Daikichi; Ueno, Satoru; Isobe, Hiroaki; Otsuji, Kenichi;
Cabezas, Denis P.; Ichimoto, Kiyoshi; Shibata, Kazunari; CHAIN team
Bibcode: 2018arXiv180806295S
Altcode:
In this article, we insist on the importance and the challenges of the
prediction of solar eruptive phenomena including flares, coronal mass
ejections (CME), and filament eruptions fully based on the ground-based
telescopes. It is true that satellites' data are indispensable for the
space weather prediction, but they are vulnerable to the space weather
effects. Therefore, the ground-based telescopes can be complementary
to them from the viewpoint of space weather prediction. From this
view point, one possible new flare prediction method that makes use of
H-alpha, red wings, and blue wings images obtained by the SDDI/SMART,
the ground-based telescope at Hida Observatory, is presented. And
in order to show the possibility for the actual operation based on
that method, the recent progress of CHAIN project, the international
observation network, is mentioned in terms of their outcomes and
capacity buildings.
Title: Reproduction of Type I Chondrules and the Implications
Authors: Imae, N.; Horie, K.; Isobe, H.
Bibcode: 2018LPICo2067.6101I
Altcode:
Type I chondrules were recently synthesized using a newly constructed
H2 gas mixing furnace controlled under medium vacuum. New analytical
preliminary data on isotopes would be included.
Title: Physics of Partial Ionization in the Solar Chromosphere
Revealed by the Solar Optical Telescope Onboard Hinode
Authors: Isobe, Hiroaki
Bibcode: 2018ASSL..449..211I
Altcode:
No abstract at ADS
Title: Long-lasting Extreme Magnetic Storm Activities in 1770 Found
in Historical Documents
Authors: Hayakawa, Hisashi; Iwahashi, Kiyomi; Ebihara, Yusuke;
Tamazawa, Harufumi; Shibata, Kazunari; Knipp, Delores J.; Kawamura,
Akito D.; Hattori, Kentaro; Mase, Kumiko; Nakanishi, Ichiro; Isobe,
Hiroaki
Bibcode: 2017ApJ...850L..31H
Altcode: 2017arXiv171100690H
Dim red aurora at low magnetic latitudes is a visual and recognized
manifestation of magnetic storms. The great low-latitude auroral
displays seen throughout East Asia on 1770 September 16-18 are
considered to manifest one of the greatest storms. Recently found,
111 historical documents in East Asia attest that these low-latitude
auroral displays appeared in succession for almost nine nights during
1770 September 10-19 in low magnetic latitude areas (<30°). This
suggests that the duration of the great magnetic storm is much longer
than usual. Sunspot drawings from 1770 reveal that the sunspot areas
were twice as large as those observed in another great storm of 1859,
which substantiates these unusual storm activities in 1770. These spots
likely ejected several huge, sequential magnetic structures in short
duration into interplanetary space, resulting in spectacular worldwide
aurorae in mid-September of 1770. These findings provide new insight
into the history, duration, and effects of extreme magnetic storms that
may be valuable for those who need to mitigate against extreme events.
Title: Records of auroral candidates and sunspots in Rikkokushi,
chronicles of ancient Japan from early 7th century to 887
Authors: Hayakawa, Hisashi; Iwahashi, Kiyomi; Tamazawa, Harufumi;
Ebihara, Yusuke; Kawamura, Akito Davis; Isobe, Hiroaki; Namiki,
Katsuko; Shibata, Kazunari
Bibcode: 2017PASJ...69...86H
Altcode: 2017arXiv170801045H
We present the results of the surveys on sunspots and auroral candidates
in Rikkokushi, Japanese official histories from the early 7th century
to 887, to review the solar and auroral activities. In total, we found
one sunspot record and 13 auroral candidates in Rikkokushi. We then
examine the records of the sunspots and auroral candidates, compare the
auroral candidates with the lunar phase to estimate their reliability,
and compare the records of the sunspots and auroral candidates with the
contemporary total solar irradiance reconstructed from radioisotope
data. We also identify the locations of the observational sites to
review possible equatorward expansion of the auroral oval. These
discussions suggest a major gap in auroral candidates from the late
7th to early 9th centuries, which includes the candidate of the grand
minimum reconstructed from the radioisotope data, a similar tendency
as the distributions of sunspot records in contemporary China, and a
relatively high magnetic latitude of observational sites with a higher
potential for observing aurorae more frequently than at present.
Title: Oxidation and evaporation of sulfur species at atmospheric
entry of iron sulfide fine particles
Authors: Isobe, H.; Murozono, K.
Bibcode: 2017AGUFM.P23B2722I
Altcode:
Micrometeorites have the most abundant flux in current accumulation of
planetary materials to the Earth. Micrometeorites are heated and reacted
with upper atmosphere at atmospheric entry. Evaporation of meteoritic
materials, especially sulfur species, may have environmental effect
at upper atmosphere (e.g. Court and Sephton, 2011; Tomkins et al.,
2016). Troilite is typical FeS phase in chondritic meteorites. In this
study, quick heating and cooling experiments of FeS reagent particles
were carried out with a fine particles free falling apparatus with
controlled gas flow (Isobe and Gondo, 2013). Starting material reagent
is inhomogeneous mixture of troilite, iron oxide and iron metal. Oxygen
fugacity was controlled to FMQ +1.5 log unit. Maximum temperature of
the particles was higher than 1400°C for approximately 0.5 seconds. Run
products with rounded shape and smooth surface show the particles were
completely melted. Chemical compositions of particles analyzed on cross
sections are generally well homogenized from inhomogeneous starting
materials by complete melting. Molar ratios of Fe in melted regions are
close to 0.5, while compositions of S and O are various. Varieties of
S and O compositions show various degree of oxidation and evaporation
of sulfur. Distribution of compositions of melted regions in Fe-S-O
system is plotted in liquidus compositions of FeO and FeS saturated
melt. Troilite in micrometeorite is melted and oxidized by atmospheric
entry. Compositions of FeS melt in fine spherules are following Fe-S-O
phase relations even in a few seconds. Molar ratios of Fe in melt are
close to 0.5, while compositions of S and O are various. Varieties of
S and O compositions show various degree of oxidation and evaporation
of sulfur. Evaporation of sulfur from meteoritic materials in
atmospheric entry heating may depend on oxygen fugacity of the upper
atmosphere. Sulfur supply from meteoritic materials to atmosphere may
be limited on planets with oxygen-free atmosphere.
Title: Records of sunspots and aurora candidates in the Chinese
official histories of the Yuán and Míng dynasties during 1261-1644
Authors: Hayakawa, Hisashi; Tamazawa, Harufumi; Ebihara, Yusuke;
Miyahara, Hiroko; Kawamura, Akito Davis; Aoyama, Tadanobu; Isobe,
Hiroaki
Bibcode: 2017PASJ...69...65H
Altcode: 2017arXiv170502238H
Records of observations of sunspots and auroras in pre-telescopic
historical documents provide useful information about past solar
activity both in long-term trends and short-term space weather
events. In this study, we present the results of a comprehensive survey
of the records of sunspots and aurora candidates in the Yuánshĭ and
Míngshĭ, Chinese Official Histories spanning 1261-1368 and 1368-1644,
based on continuous observations with well-formatted reportds conducted
by contemporary professional astronomers. We then provide a brief
comparison of these data with Total Solar Irradiance (TSI) as an
indicator of the solar activity during the corresponding periods to
show significant active phases between the 1350s-80s and 1610s-30s. We
then compared the former with contemporary Russian reports concerning
naked-eye sunspots and the latter with contemporary sunspot drawings
based on Western telescopic observations. Especially some of the latter
are consistent with nitrate signals preserved in ice cores. These
results show us some insights on and beyond minima and maxima of solar
activity during the 13th-17th centuries.
Title: Increase in the Amplitude of Line-of-sight Velocities of the
Small-scale Motions in a Solar Filament before Eruption
Authors: Seki, Daikichi; Otsuji, Kenichi; Isobe, Hiroaki; Ishii,
Takako T.; Sakaue, Takahito; Hirose, Kumi
Bibcode: 2017ApJ...843L..24S
Altcode: 2017arXiv170509041S
We present a study on the evolution of the small-scale velocity field
in a solar filament as it approaches the eruption. The observation
was carried out by the Solar Dynamics Doppler Imager (SDDI) that was
newly installed on the Solar Magnetic Activity Research Telescope at
Hida Observatory. The SDDI obtains a narrowband full-disk image of
the Sun at 73 channels from Hα - 9.0 Å to Hα + 9.0 Å, allowing us
to study the line-of-sight (LOS) velocity of the filament before and
during the eruption. The observed filament is a quiescent filament
that erupted on 2016 November 5. We derived the LOS velocity at each
pixel in the filament using the Becker’s cloud model, and made the
histograms of the LOS velocity at each time. The standard deviation
of the LOS velocity distribution can be regarded as a measure for the
amplitude of the small-scale motion in the filament. We found that
the standard deviation on the previous day of the eruption was mostly
constant around 2-3 km s-1, and it slightly increased to
3-4 km s-1 on the day of the eruption. It shows a further
increase, with a rate of 1.1 m s-2, about three hours before
eruption, and another increase, with a rate of 2.8 m s-2,
about an hour before eruption. From this result we suggest that the
increase in the amplitude of the small-scale motions in a filament
can be regarded as a precursor of the eruption.
Title: Records of sunspot and aurora activity during 581-959 CE in
Chinese official histories concerning the periods of Suí, Táng,
and the Five Dynasties and Ten Kingdoms
Authors: Tamazawa, Harufumi; Kawamura, Akito Davis; Hayakawa, Hisashi;
Tsukamoto, Asuka; Isobe, Hiroaki; Ebihara, Yusuke
Bibcode: 2017PASJ...69...22T
Altcode: 2016arXiv161203283T; 2017PASJ..tmp..135T
Recent studies concerning radioisotopes in tree rings or ice cores
suggest that extreme space weather events occurred during the
pre-telescope age. Observational records of naked-eye sunspots and
low-latitude auroras in historical documents during this age can
provide useful information about past solar activity. In this paper,
we present the results of a comprehensive survey of records of sunspots
and auroras in Chinese official histories from the 6th century to the
10th century, in the period of Suí, Táng, the Five Dynasties and
Ten Kingdoms. These official histories contain records of continuous
observations with well-formatted reports conducted under the policy of
the governments. A brief comparison of the frequency of observations
of sunspots and auroras based on observations of radioisotopes as
an indicator of solar activity during the corresponding periods is
provided. Using our data, we surveyed and compiled the records of
sunspots and auroras in historical documents from various locations
and in several languages, and ultimately provide these as open data
to the scientific community.
Title: The earliest drawings of datable auroras and a two-tail comet
from the Syriac Chronicle of Zūqnīn
Authors: Hayakawa, Hisashi; Mitsuma, Yasuyuki; Fujiwara, Yasunori;
Kawamura, Akito Davis; Kataoka, Ryuho; Ebihara, Yusuke; Kosaka,
Shunsuke; Iwahashi, Kiyomi; Tamazawa, Harufumi; Isobe, Hiroaki
Bibcode: 2017PASJ...69...17H
Altcode: 2017PASJ..tmp..120H; 2016arXiv161008690H
People have probably been watching the sky since the beginning of
human history. Observers in pre-telescopic ages recorded anomalous
events, which now provide uniquely valuable information for modern
scientists. Records that include drawings are particularly useful, since
the verbal expressions recorded by pre-telescopic observers, who did not
know the physical nature of the phenomena, are often ambiguous. However,
drawings concerning specific datable events in the historical documents
are far fewer than the verbal records. Therefore, in this paper we
show the possible earliest drawings of datable auroras and a two-tail
comet included in a manuscript of the Chronicle of Zūqnīn, a Syriac
chronicle up to 775/776 CE, to interpret their nature. Careful perusing
the original Syriac autograph manuscript, MS Vat.Sir.162, provide not
only historical facts in the realm around Amida, but also information
concerning low-latitude aurora observations due to extreme space
weather events and the existence of sun-grazing comets.
Title: Historical Auroras in the 990s: Evidence of Great Magnetic
Storms
Authors: Hayakawa, Hisashi; Tamazawa, Harufumi; Uchiyama, Yurina;
Ebihara, Yusuke; Miyahara, Hiroko; Kosaka, Shunsuke; Iwahashi, Kiyomi;
Isobe, Hiroaki
Bibcode: 2017SoPh..292...12H
Altcode: 2016arXiv161201106H
A significant carbon-14 enhancement has recently been found in tree
rings for the year 994, suggesting an extremely strong and brief cosmic
ray flux event. The origin of this particular cosmic ray event has
not been confirmed, but one possibility is that it might be of solar
origin. Contemporary historical records of low-latitude auroras can
be used as supporting evidence of intense solar activity around that
time. We investigate previously reported as well as new records that
have been found in contemporary observations from the 990s to determine
potential auroras. Records of potential red auroras in late 992 and
early 993 were found around the world, i.e. in the Korean Peninsula,
Saxonian cities in modern Germany, and the Island of Ireland, suggesting
the occurrence of an intense geomagnetic storm driven by solar activity.
Title: Solar Flare Activities before Carrington event based on
Low-Latitude-Aurora Survey with Historical Documents from Eastern Asia
Authors: Kawamura, A. D.; Hayakawa, H.; Iwahashi, K.; Tamazawa, H.;
Miyahara, H.; Mitsuma, Y.; Takei, M.; Fujiwara, Y.; Kataoka, R.;
Isobe, H.
Bibcode: 2016AGUFMSH31B2546K
Altcode:
For discussions of solar activities in terms of long time period or
rare occurrence, our scientific observations of about 400-year history
for sunspots and about 150-year history for flares are sometimes not
sufficient simply because of the shortness on temporal scale. To
complement our scientific records, historical records of aurora
observations in traditional manner could be helpful. Especially,
the records of low-latitude auroras as results of huge Coronal
Mass Ejections (CMEs) hitting the Earth magnetosphere could be a
good indicator of extreme solar activities beyond our scientific
observation history. In this reason, we focus on Eastern Asia where
magnetic latitude is relatively low and there exits a rich tradition
of text-based records for thousands of years. In this presentation,
we discuss the solar activities of 17th to 19th centuries when sunspot
observations are available but no solar flare observation had been
done yet. Our discussion is mainly based on the official history of
Qīng dynasty on China, and some historical documents from Japan with
sunspot numbers and western aurora observations as references. We also
briefly introduce our project of aurora survey based on historical
documents beyond Qīng dynasty.
Title: East Asian observations of low-latitude aurora during the
Carrington magnetic storm
Authors: Hayakawa, Hisashi; Iwahashi, Kiyomi; Tamazawa, Harufumi;
Isobe, Hiroaki; Kataoka, Ryuho; Ebihara, Yusuke; Miyahara, Hiroko;
Kawamura, Akito Davis; Shibata, Kazunari
Bibcode: 2016PASJ...68...99H
Altcode: 2016arXiv160807702H; 2016PASJ..tmp..100H
A magnetic storm around 1859 September 2, caused by a so-called
Carrington flare, was the most intense in the history of modern
scientific observations, and hence is considered to be a benchmark
event concerning space weather. The magnetic storm caused worldwide
observations of auroras, even at very low latitudes, such as Hawaii,
Panama, or Santiago. Available magnetic-field measurements at Bombay,
India, showed two peaks: the main was the Carrington event, which
occurred in day time in East Asia; a second storm after the Carrington
event occurred at night in East Asia. In this paper, we present
results from surveys of aurora records in East Asia, which provide new
information concerning the aurora activity of this important event. We
found some new East Asian records of low-latitude aurora observations
caused by a storm which occurred after the Carrington event. The size
of the aurora belt of the second peak of the Carrington magnetic storm
was even wider than that of usual low-latitude aurora events.
Title: Earliest datable records of aurora-like phenomena in the
astronomical diaries from Babylonia
Authors: Hayakawa, Hisashi; Mitsuma, Yasuyuki; Ebihara, Yusuke;
Kawamura, Akito Davis; Miyahara, Hiroko; Tamazawa, Harufumi; Isobe,
Hiroaki
Bibcode: 2016EP&S...68..195H
Altcode: 2016arXiv161105197H
The astronomical diaries from Babylonia (ADB) are excellent sources
of information of natural phenomena, including astronomical ones,
in pre-Christ era because it contains the record of highly continuous
and systematic observations. In this article, we present results of a
survey of aurora-like phenomena in ADB, spanning from BCE 652 to BCE
61. We have found nine records of aurora-like phenomena. Philological
and scientific examinations suggest that five of them can be considered
as likely candidate for aurora observations. They provide unique
information about the solar and aurora activities in the first
millennium BCE. [Figure not available: see fulltext.]
Title: Aurora candidates from the chronicle of Qíng dynasty in
several degrees of relevance
Authors: Kawamura, Akito D.; Hayakawa, Hisashi; Tamazawa, Harufumi;
Miyahara, Hiroko; Isobe, Hiroaki
Bibcode: 2016PASJ...68...79K
Altcode: 2016PASJ..tmp...83K; 2016arXiv160802739K
We present the result of a survey of sunspots and auroras in
Qíngshǐgǎo (清史稿), a draft chronicle of Qíng dynasty, for
the period of 1559-1912 CE. This is a sequel to a series of works
surveying historical sunspot and aurora records, and providing online
data to the scientific community regarding the attained results. In
total of this Qíngshǐgǎo survey, we found 111 records of night-sky
luminous events with such keywords as vapor (氣, qì), cloud (雲,
yún), and light (光, guāng), which may indicate auroras as well
as some other phenomena. Similarly, a keyword survey for sunspots
was conducted, but no sunspot record was found. In comparison with
the aurora records in the western world, we found that 14 of the 111
records have a corresponding record of simultaneous observation in
the western world, and hence are very likely to be aurora. In order to
investigate the likeliness of the remainder of the record being aurora,
we calculated the lunar age and the phase of a solar cycle for each
record. After these calculations, a notable fraction of these records
clustered near the full moon were to be found statistically doubtful
in considerations with atmospheric optics; meanwhile, a few records
of observations near the new moon could be more likely interpreted as
being auroras, including three records during the Maunder minimum.
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: Unusual rainbow and white rainbow: A new auroral candidate
in oriental historical sources
Authors: Hayakawa, Hisashi; Isobe, Hiroaki; Davis Kawamura, Akito;
Tamazawa, Harufumi; Miyahara, Hiroko; Kataoka, Ryuho
Bibcode: 2016PASJ...68...33H
Altcode: 2016PASJ..tmp...36H; 2016arXiv160302374H
Solar activity has been recorded as auroras or sunspots in various
historical sources. These records are of great importance for
investigating both long-term solar activities and extremely intense
solar flares. According to previous studies, they were recorded as
"vapor," "cloud," or "light," especially in oriental historical sources;
however, this terminology has not been discussed adequately, and remains
still quite vague. In this paper, we suggest the possibility of using
"unusual rainbow" and "white rainbow" as candidates of historical
auroras in oriental historical sources, and examine if this is
probable. This discovery will help us to make more comprehensive
historical auroral catalogues, and require us to add these terms to
auroral candidates in oriental historical sources.
Title: On the Bright Loop Top Emission in Post-eruption Arcades
Authors: Sharma, Rohit; Tripathi, Durgesh; Isobe, Hiroaki; Ghosh,
Avyarthana
Bibcode: 2016ApJ...823...47S
Altcode: 2016arXiv160304959S
Observations of post-eruption arcades (PEAs) in X-rays and EUV reveal
strong localized brightenings at the loop top regions. The origins
of these brightenings and their dynamics are not well understood
to date. Here, we study the dynamics of PEAs using one-dimensional
hydrodynamic modeling, focusing on understanding the formation of
localized brightening. Our findings suggest that these brightenings are
the result of collisions between the counter-streaming chromospheric
evaporation from both the footpoints. We perform forward modeling
of the emission observed in simulated results in various spectral
lines observed by the Extreme-Ultraviolet Imaging Telescope on board
Hinode. The forward-modeled intensities in various spectral lines are
in close agreement with a flare observed on 2006 December 17 by EIS.
Title: UFCORIN: A fully automated predictor of solar flares in GOES
X-ray flux
Authors: Muranushi, Takayuki; Shibayama, Takuya; Muranushi, Yuko Hada;
Isobe, Hiroaki; Nemoto, Shigeru; Komazaki, Kenji; Shibata, Kazunari
Bibcode: 2015SpWea..13..778M
Altcode: 2015arXiv150708011M
We have developed UFCORIN, a platform for studying and automating
space weather prediction. Using our system we have tested 6160
different combinations of Solar Dynamic Observatory/Helioseismic and
Magnetic Imager data as input data, and simulated the prediction of
GOES X-ray flux for 2 years (2011-2012) with 1 h cadence. We have
found that direct comparison of the true skill statistic (TSS) from
small cross-validation sets is ill posed and used the standard scores
(z) of the TSS to compare the performance of the various prediction
strategies. The z of a strategy is a stochastic variable of the
stochastically chosen cross-validation data set, and the z for the
three strategies best at predicting X-, ≥M-, and ≥C-class flares
are better than the average z of the 6160 strategies by 2.3σ, 2.1σ,
and 3.8σ confidence levels, respectively. The best three TSS values
were 0.75 ± 0.07, 0.48 ± 0.02, and 0.56 ± 0.04, respectively.
Title: Nonlinear instability and intermittent nature of magnetic
reconnection in solar chromosphere
Authors: Singh, K. A. P.; Hillier, Andrew; Isobe, Hiroaki; Shibata,
Kazunari
Bibcode: 2015PASJ...67...96S
Altcode: 2016arXiv160201999S; 2015PASJ..tmp..234S
The recent observations of Singh et al. (2012, ApJ, 759, 33) have shown
multiple plasma ejections and the intermittent nature of magnetic
reconnection in the solar chromosphere, highlighting the need for
fast reconnection to occur in highly collisional plasma. However,
the physical process through which fast magnetic reconnection occurs
in partially ionized plasma, like the solar chromosphere, is still
poorly understood. It has been shown that for sufficiently high
magnetic Reynolds numbers, Sweet-Parker current sheets can become
unstable leading to tearing mode instability and plasmoid formation,
but when dealing with a partially ionized plasma the strength of
coupling between the ions and neutrals plays a fundamental role
in determining the dynamics of the system. We propose that as the
reconnecting current sheet thins and the tearing instability develops,
plasmoid formation passes through strongly, intermediately, and weakly
coupled (or decoupled) regimes, with the time scale for the tearing
mode instability depending on the frictional coupling between ions
and neutrals. We present calculations for the relevant time scales for
fractal tearing in all three regimes. We show that as a result of the
tearing mode instability and the subsequent non-linear instability due
to the plasmoid-dominated reconnection, the Sweet-Parker current sheet
tends to have a fractal-like structure, and when the chromospheric
magnetic field is sufficiently strong the tearing instability can
reach down to kinetic scales, which are hypothesized to be necessary
for fast reconnection.
Title: Three-dimensional MHD Magnetic Reconnection Simulations with
a Finite Guide Field: Proposal of the Shock-evoking Positive-feedback
Model
Authors: Wang, Shuoyang; Yokoyama, Takaaki; Isobe, Hiroaki
Bibcode: 2015ApJ...811...31W
Altcode: 2015arXiv150803140W
Using a three-dimensional (3D) magnetohydrodynamic model, we simulate
the magnetic reconnection in a single current sheet. We assume a
finite guide field, a random perturbation on the velocity field, and
uniform resistivity. Our model enhances the reconnection rate relative
to the classical Sweet-Parker model in the same configuration. The
efficiency of magnetic energy conversion is increased by interactions
between the multiple tearing layers coexisting in the global current
sheet. This interaction, which forms a positive-feedback system,
arises from coupling of the inflow and outflow regions in different
layers across the current sheet. The coupling accelerates the elementary
reconnection events, thereby enhancing the global reconnection rate. The
reconnection establishes flux tubes along each tearing layer. Slow-mode
shocks gradually form along the outer boundaries of these tubes, further
accelerating the magnetic energy conversion. Such a positive-feedback
system is absent in two-dimensional simulations, 3D reconnection without
a guide field, and reconnection under a single perturbation mode. We
refer to our model as the “shock-evoking positive-feedback” model.
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: Records of sunspot and aurora during CE 960-1279 in the
Chinese chronicle of the Sòng dynasty
Authors: Hayakawa, Hisashi; Tamazawa, Harufumi; Kawamura, Akito Davis;
Isobe, Hiroaki
Bibcode: 2015EP&S...67...82H
Altcode: 2015arXiv150603715H
Records of sunspot and aurora observations in pre-telescopic historical
documents can provide useful information about solar activity in the
past. This is also true for extreme space weather events, as they
may have been recorded as large sunspots observed by the naked eye
or as low-latitude auroras. In this paper, we present the results
of a comprehensive survey of records of sunspots and auroras in
the Sòngshǐ, a Chinese formal chronicle spanning the tenth to the
thirteenth century. This chronicle contains a record of continuous
observations with well-formatted reports conducted as a policy of
the government. A brief comparison of the frequency of observations
of sunspots and auroras and the observations of radioisotopes as
an indicator of the solar activity during corresponding periods is
provided. This paper is the first step of our project in which we
survey and compile the records of sunspots and auroras in historical
documents from various locations and languages, ultimately providing
it to the science community as online data.
Title: Crystallographic Textures of Olivine in Artificial Cosmic
Spherules Produced by Quick Quench Experiments
Authors: Isobe, H.; Gondo, T.
Bibcode: 2015LPI....46.1697I
Altcode: 2015LPICo1832.1697I
Crystallization of olivine controls external and internal structures
of cosmic spherules in rapid growth processes of quench crystals from
chondritic materials.
Title: Aqueous Alteration Experiments with Hydrothermal Fluid Based
on the Solar Abundance in the Early Solar System
Authors: Tokunaga, M.; Isobe, H.
Bibcode: 2015LPI....46.1704T
Altcode: 2015LPICo1832.1704T
Oxidative fluid based on the solar abundance may constrain carbonate
formation temperature in aqueous alteration processes on carbonaceous
chondrites.
Title: Hydrothermal Alteration Experiments with Aqueous Fluid on
the Early Ceres
Authors: Horiguchi, K.; Isobe, H.
Bibcode: 2015LPI....46.1703H
Altcode: 2015LPICo1832.1703H
Hydrothermal experiments with fluid simulated the early Ceres revealed
that mineral species and compositions of carbonate and phyllosilicates
are essential.
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: Initiation of Coronal Mass Ejection Event Observed on 2010
November 3: Multi-wavelength Perspective
Authors: Mulay, Sargam; Subramanian, Srividya; Tripathi, Durgesh;
Isobe, Hiroaki; Glesener, Lindsay
Bibcode: 2014ApJ...794...78M
Altcode: 2014arXiv1407.5837M
One of the major unsolved problems in solar physics is that of coronal
mass ejection (CME) initiation. In this paper, we have studied the
initiation of a flare-associated CME that occurred on 2010 November 3
using multi-wavelength observations recorded by the Atmospheric Imaging
Assembly on board the Solar Dynamics Observatory and the Reuven Ramaty
High Energy Solar Spectroscopic Imager. We report an observation of
an inflow structure initially in the 304 Å and the 1600 Å images
a few seconds later. This inflow structure was detected as one of
the legs of the CME. We also observed a non-thermal compact source
concurrent and near co-spatial with the brightening and movement of the
inflow structure. The appearance of this compact non-thermal source,
brightening, and movement of the inflow structure and the subsequent
outward movement of the CME structure in the corona led us to conclude
that the CME initiation was caused by magnetic reconnection.
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: Flux Emergence (Theory)
Authors: Cheung, Mark C. M.; Isobe, Hiroaki
Bibcode: 2014LRSP...11....3C
Altcode:
Magnetic flux emergence from the solar convection zone into the
overlying atmosphere is the driver of a diverse range of phenomena
associated with solar activity. In this article, we introduce
theoretical concepts central to the study of flux emergence and
discuss how the inclusion of different physical effects (e.g.,
magnetic buoyancy, magnetoconvection, reconnection, magnetic twist,
interaction with ambient field) in models impact the evolution of the
emerging field and plasma.
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: Atmospheric response to flux emergence
Authors: Isobe, Hiroaki
Bibcode: 2014cosp...40E1294I
Altcode:
Atmospheric response to flux emergence
Title: Reconnection in partially ionized plasmas - fluid theory
and application
Authors: Isobe, Hiroaki
Bibcode: 2014cosp...40E1293I
Altcode:
The lower atmosphere of the Sun, namely the photosphere and the
chromosphere, is fully collisional and partially ionized. Recent
observations, in particular those from the Solar Optical Telescope on
board Hinode spacecraft, have revealed that the solar chromosphere is
full of dynamic activities, such as plasma jets and Ellerman bombs
(transient heating of low-chromosphere). These dynamic phenomena
are believed to be associated with magnetic reconnection in the
chromosphere, but the nature of magnetic reconnection in such plasma
environment has been much less studied compared with reconnection
in fully ionized, collisionless plasmas. The solar lower atmosphere
is therefore an unique laboratory for the physics of reconnection
in partially ionized plasmas. In this paler we first present the
observations of chromospheric reconnection events that show the ejection
of multiple plasma blobs and bursty nature of reconnection. Then we
present the result of 1-fluid MHD simulation with Cowling resistivity
(also called Pederson resistivity or ambipolar resistivity) to
investigate the effect of partial ionization on reconnection. We found
that the nonuniformity of Cowling resistivity is an essential factor
that determines the structure of reconnection region and hence the
reconnection rate.
Title: Superflares on Solar type Stars and Their Impacts on
Habitability of Exoplanets
Authors: Shibata, Kazunari; Maehara, Hiroyuki; Shibayama, Takuya;
Notsu, Yuta; Notsu, Shota; Honda, Satoshi; Nogami, Daisaku; Isobe,
Hiroaki
Bibcode: 2014cosp...40E3035S
Altcode:
Using Kepler data, Maehara et al. (2012) have discovered 365 superflares
(10(34) -10(36) erg) on 148 solar type stars (G type dwarfs). They
revealed that the occurrence frequency of superflares of 10(34) erg is
once in 800 years, and that of 10(35) erg is once in 5000 years. It was
also found that these superflare stars show quasi-periodic brightness
variation, which can be interpreted as a result of rotation of stars
with large star spots (Notsu Y. et al. 2013). This interpretation
is consistent with theory of solar flares and dynamo (Shibata et
al. 2013). Furthermore, there were no evidence of hot Jupiters around
these superflare stars, suggesting the possibility that superflares may
occur on our Sun without hot Jupiters. Superflares tend to occur more in
cooler stars (K and M type dwarfs) than G type dwarfs. More recently,
Shibayama et al. (2013) extended Maehara et al.'s work to find 1547
superflares on 279 solar type stars from 500 days Kepler data. They
basically confirmed the results of Maehara et al., but found that in
some G-type dwarfs the occurrence rate of superflares was extremely
high, 57 superflares in 500 days (i.e., once in 10 days). Such an
extreme superflare activity would give a strong influence on the
environmental condition of exoplanets around these stars. We shall
discuss implication of these observations for habitability of exoplanets
around solar type stars. References Maehara et al. (2012) Nature 485,
478; Shibata et al. (2013) PASJ 65, 49; Shibayama et al. (2013) ApJS
209, 5; Notsu, Y. et al. (2013) ApJ 771,127; Notsu, S. et al. (2013)
PASJ 65, 112
Title: Can Superflares Occur on Our Sun?
Authors: Shibata, Kazunari; Isobe, Hiroaki; Hillier, Andrew; Choudhuri,
Arnab Rai; Maehara, Hiroyuki; Ishii, Takako T.; Shibayama, Takuya;
Notsu, Shota; Notsu, Yuta; Nagao, Takashi; Honda, Satoshi; Nogami,
Daisaku
Bibcode: 2013PASJ...65...49S
Altcode: 2012arXiv1212.1361S
Recent observations of Sun-like stars, similar to our Sun in their
surface temperature (5600-6000 K) and slow rotation (rotational period
> 10 d), using the Kepler satellite by Maehara et al. (2012, Nature,
485, 478) have revealed the existence of superflares (with energy
of 1033-1035 erg). From statistical analyses
of these superflares, it was found that superflares with energy
of 1034 erg occur once in 800 yr, and superflares with
1035 erg occur once in 5000 yr. In this paper, we examine
whether superflares with energy of 1033-1035
erg could occur on the present Sun through the use of simple
order-of-magnitude estimates based on current ideas related to
the mechanisms of the solar dynamo. If magnetic flux is generated
by differential rotation at the base of the convection zone, as
assumed in typical dynamo models, it is possible that the present Sun
would generate a large sunspot with a total magnetic flux of ∼2 ×
1023 Mx (= G cm2) within one solar cycle period,
and lead to superflares with an energy of 1034 erg. To
store a total magnetic flux of ∼1024 Mx, necessary for
generating 1035 erg superflares, it would take ∼40 yr. Hot
Jupiters have often been argued to be a necessary ingredient for the
generation of superflares, but we found that they do not play any
essential role in the generation of magnetic flux in the star itself,
if we consider only the magnetic interaction between the star and the
hot Jupiter. This seems to be consistent with Maehara et al.'s finding
of 148 superflare-generating solar-type stars that do not have a hot
Jupiter-like companion. Altogether, our simple calculations, combined
with Maehara et al.'s analysis of superflares on Sun-like stars,
show that there is a possibility that superflares of 1034
erg would occur once in 800 yr on our present Sun.
Title: Numerical Simulations of Solar Chromospheric Jets Associated
with Emerging Flux
Authors: Takasao, Shinsuke; Isobe, Hiroaki; Shibata, Kazunari
Bibcode: 2013PASJ...65...62T
Altcode: 2013arXiv1301.7325T
We studied the acceleration mechanisms of chromospheric jets associated
with emerging flux using a two-dimensional magnetohydrodynamic (MHD)
simulation. We found that slow-mode shock waves generated by magnetic
reconnection in the chromosphere and the photosphere play key roles
in the acceleration mechanisms of chromospheric jets. An important
parameter is the height of magnetic reconnection. When magnetic
reconnection takes place near the photosphere, the reconnection outflow
collides with the region where the plasma beta is much larger than
unity. Then, the plasma moves along a magnetic field. This motion
generates a slow-mode wave. The slow-mode wave develops to a strong
slow shock as it propagates upward. When the slow shock crosses the
transition region, this region is lifted up. As a result, we obtain
a chromospheric jet as the lifted transition region. When magnetic
reconnection takes place in the upper chromosphere, the chromospheric
plasma is accelerated due to the combination of the Lorentz force
and the whip-like motion of the magnetic field. We found that the
chromospheric plasma is further accelerated through the interaction
between the transition region (steep density gradient) and a slow shock
emanating from the reconnection point. In the process, the magnetic
energy released by magnetic reconnection is efficiently converted into
the kinetic energy of jets. This is an MHD effect that has not been
discussed before.
Title: Simulations of the Dynamics of the Magnetic Rayleigh-Taylor
Instability in Solar Prominences
Authors: Hillier, A.; Berger, T.; Shibata, K.; Isobe, H.
Bibcode: 2013ASPC..474..147H
Altcode:
The magnetic Rayleigh-Taylor instability plays an important role in the
mass and magnetic flux transport in many astrophysical bodies. Solar
prominences also display this instability and recent observations using
the Solar Optical Telescope onboard the Hinode satellite have revealed
these dynamics in amazing detail. The observations show rising plumes,
approximately 1 Mm in width, that propagate through the dense prominence
material from low-density bubbles, i.e. the situation expected when the
magnetic Rayleigh-Taylor instability occurs. To study this phenomenon,
we performed 3D simulations of the magnetic Rayleigh-Taylor instability
in the Kippenhahn-Schlüter prominence model. The plumes formed in
these simulations are filamentary structures that are aligned with
the magnetic field created as 3D modes of the magnetic Rayleigh-Taylor
instability. The plumes rise, developing large structures from smaller
structures through an inverse cascade process driven by nonlinear
interaction. The results suggest that the plumes observed in the
prominence may be used to study the conditions inside the prominence.
Title: Aqueous Alteration Experiments of Chondrule Analogue and Iron
Sulfide Mixture with H_2O-CO_2 Fluid
Authors: Watanabe1, K.; Isobe, H.
Bibcode: 2013LPI....44.1878W
Altcode: 2013LPICo1719.1878W
We carried out aqueous alteration experiments of mixture of olivine,
mesostasis glass, and pyrrhotite with H_2O-CO_2 fluid.
Title: Artificial Cosmic Spherules Produced by Melting Experiments
of the Powdered Allende Meteorite
Authors: Gondo, T.; Isobe, H.
Bibcode: 2013LPI....44.1882G
Altcode: 2013LPICo1719.1882G
We successfully reproduced artificial cosmic spherules with remarkably
analogous textures to natural ones by rapid heating and cooling
experiments.
Title: Numerical Simulation of Three-dimensional Asymmetric
Reconnection and Application to a Physical Mechanism of Penumbral
Microjets
Authors: Nakamura, Naoki; Shibata, Kazunari; Isobe, Hiroaki
Bibcode: 2012ApJ...761...87N
Altcode:
Three-dimensional (3D) component reconnection, where reconnecting
field lines are not perfectly anti-parallel, is studied with a
3D magnetohydrodynamic simulation. In particular, we consider the
asymmetry of the field strength of the reconnecting field lines. As
the asymmetry increases, the generated reconnection jet tends to be
parallel to stronger field lines. This is because weaker field lines
have higher gas pressure in the initial equilibrium, and hence the
gas pressure gradient along the reconnected field lines is generated,
which accelerates the field-aligned plasma flow. This mechanism may
explain penumbral microjets and other types of jets that are parallel
to magnetic field lines.
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: Multiple Plasma Ejections and Intermittent Nature of Magnetic
Reconnection in Solar Chromospheric Anemone Jets
Authors: Singh, K. A. P.; Isobe, H.; Nishizuka, N.; Nishida, K.;
Shibata, K.
Bibcode: 2012ApJ...759...33S
Altcode:
The recent discovery of chromospheric anemone jets with the Solar
Optical Telescope (SOT) on board Hinode has shown an indirect evidence
of magnetic reconnection in the solar chromosphere. However, the basic
nature of magnetic reconnection in chromosphere is still unclear. We
studied nine chromospheric anemone jets from SOT/Hinode using Ca II H
filtergrams, and we found multiple bright, plasma ejections along the
jets. In most cases, the major intensity enhancements (larger than
30% relative to the background intensity) of the loop correspond to
the timing of the plasma ejections. The typical lifetime and size of
the plasma ejecta are about 20-60 s and 0.3-1.5 Mm, respectively. The
height-time plot of jet shows many sub-structures (or individual jets)
and the typical lifetime of the individual jet is about one to five
minutes. Before the onset of the jet activity, a loop appears in Ca II
H and gradually increases in size, and after few minutes several jets
are launched from the loop. Once the jet activity starts and several
individual jets are launched, the loop starts shrinking with a speed
of ~4 km s-1. In some events, a downward moving blob with a
speed of ~35 km s-1 was observed, associated with the upward
moving plasma along one of the legs of the loop hosting the jets. The
upward moving plasma gradually developed into jets. Multiple plasma
ejections in chromospheric anemone jet show the strongly time-dependent
as well as intermittent nature of magnetic reconnection in the solar
chromosphere.
Title: Systematic Motion of Fine-scale Jets and Successive
Reconnection in Solar Chromospheric Anemone Jet Observed with the
Solar Optical Telescope/Hinode
Authors: Singh, K. A. P.; Isobe, H.; Nishida, K.; Shibata, K.
Bibcode: 2012ApJ...760...28S
Altcode:
The Solar Optical Telescope (SOT) on board Hinode allows observations
with high spatiotemporal resolution and stable image quality. A
λ-shaped chromospheric anemone jet was observed in high resolution with
SOT/Hinode. We found that several fine-scale jets were launched from one
end of the footpoint to the other. These fine-scale jets (~1.5-2.5 Mm)
gradually move from one end of the footpoint to the other and finally
merge into a single jet. This process occurs recurrently, and as time
progresses the jet activity becomes more and more violent. The time
evolution of the region below the jet in Ca II H filtergram images
taken with SOT shows that various parts (or knots) appear at different
positions. These bright knots gradually merge into each other during
the maximum phase. The systematic motion of the fine-scale jets is
observed when different knots merge into each other. Such morphology
would arise due to the emergence of a three-dimensional twisted flux
rope in which the axial component (or the guide field) appears in the
later stages of the flux rope emergence. The partial appearance of
the knots could be due to the azimuthal magnetic field that appears
during the early stage of the flux rope emergence. If the guide field
is strong and reconnection occurs between the emerging flux rope and
an ambient magnetic field, this could explain the typical feature of
systematic motion in chromospheric anemone jets.
Title: Numerical Simulations of the Magnetic Rayleigh-Taylor
Instability in the Kippenhahn-Schlüter Prominence
Model. II. Reconnection-triggered Downflows
Authors: Hillier, Andrew; Isobe, Hiroaki; Shibata, Kazunari; Berger,
Thomas
Bibcode: 2012ApJ...756..110H
Altcode: 2011arXiv1106.2613H
The launch of the Hinode satellite has allowed high-resolution
observations of supersonic bright downflows in quiescent prominences,
known as prominence knots. We present observations in the Ca
II H spectral line using the Solar Optical Telescope on board
the Hinode satellite of a descending plasma knot of size ~900
km. The knot initially undergoes ballistic motion before undergoing
impulsive accelerations at the same time as experiencing increases
in intensity. We also present a subset of our three-dimensional
magnetohydrodynamic simulations, performed to investigate the
nonlinear stability of the Kippenhahn-Shlüter prominence model
to the magnetic Rayleigh-Taylor instability in which interchange
reconnection occurs. The interchange reconnection in the model
breaks the force balance along the field lines which initiates the
downflows. The downflows propagate with a downward fluid velocity
of ~15 km s-1 and a characteristic size of ~700 km. We
conclude that the observed plasma blob and the simulated downflow are
driven by the breaking of the force balance along the magnetic field
as a result of a change in magnetic topology caused by reconnection
of the magnetic field.
Title: Observation of Reconnection Features in the Chromosphere
through a Chromospheric Jet Observed by SOT/Hinode
Authors: Singh, K. A. P.; Isobe, H.; Shibata, K.
Bibcode: 2012ASPC..454...99S
Altcode:
High-resolution observations from Solar Optical Telescope (SOT)
onboard Hinode has shown number of jet-like structures in the solar
chromosphere. One of the key features in the observations is the clear
presence of tiny, inverted Y-shaped jets called Chromospheric Anemone
Jets. These jets are supposed to be formed as a result of the magnetic
reconnection, however, whether and how fast magnetic reconnection
is realized in partially ionized, fully collisional chromosphere is
poorly understood. In this paper, we report the observation of a well
resolved jet phenomenon observed from SOT. The jets were found to recur
at the same location. We observed multiple blobs ejected along the
jet. The jets occur after the ejection of blobs. It is noticed that
the brightness enhancements at the footpoint of the jet are related
with the height of the jet. These features indicate an important role
of plasmoid dynamics and intermittent nature of the chromospheric
reconnection. The lifetime of the plasmoid is 30 s - 50 s. We noticed
the undulations in chromospheric anemone jets. The evolution of a
single jet is consistent with the Sweeping-Magnetic-Twist mechanism
proposed by Shibata and Uchida (1986).
Title: Simulations of the Magnetic Rayleigh-Taylor Instability in
the Kippenhahn-Schlüter Prominence Model
Authors: Hillier, A.; Berger, T.; Shibata, K.; Isobe, H.
Bibcode: 2012ASPC..456..157H
Altcode:
The launch of the Hinode satellite, with the Solar Optical Telescope,
allowed for high resolution, high time cadence observations of
prominences to be performed in the seeing free environment of
space. The most striking discovery from these observations is of
plumes, approximately 1 Mm in width, that propagate through the
prominence material. The plumes initiate from underdense bubbles that
form beneath prominences, rise at constant speeds of approximately 20
km s-1 and are formed in the conditions required for the
magnetic Rayleigh-Taylor instability to occur. To study this phenomenon,
we performed 3D simulations of the magnetic Rayleigh-Taylor instability
in the Kippenhahn-Schlüter prominence model. The plumes formed in
these simulations are filamentary structures that are aligned with
the magnetic field created as 3D modes of the magnetic Rayleigh-Taylor
instability. The plumes rise, developing large structures from smaller
structures through an inverse cascade process driven by nonlinear
interaction. The results suggest that the plumes observed in the
prominence may be used to study the conditions inside the prominence.
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: Observations and modeling of magnetic reconnection in the
coupled solar atmosphere
Authors: Isobe, Hiroaki
Bibcode: 2012decs.confE.101I
Altcode:
The plasma parameters in the solar atmosphere varies drastically
with height. The corona is fully ionized and almost collisionless,
the photosphere and chromosphere is partially ionized and fully
collisional, and the transition region is a marginal region in terms
of collisionality and ionization. These very different regions
are dynamically coupled by magnetic fields and waves. It is also
interesting that, similarly to terrestrial ionosphere, the ratio of
ion-cyclotron frequency and ion-neutral collisional frequency varies
with height, giving rise to differnt effects by neutrals such as
ambipolar diffusion and Hall effect. Recent observations have shown
that magnetic reconnection occurs throughout the solar atmosphere,
not only in the fully ionized and collisionless corona but also in the
partially ionized and fully collisinal lower atmosphere, in similar
mophologies but different scales. Therefore the solar atmosphere can be
considered as an unique laboratory for magnetic reconnection in various
plasma parameters. In this talk I will review the recent observations
and the advances in theoretical modelings of magnetic reconnection in
different part of the solar atmosphere.
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: Numerical Simulations of the Magnetic Rayleigh-Taylor
Instability in the Kippenhahn-Schlüter Prominence Model. I. Formation
of Upflows
Authors: Hillier, Andrew; Berger, Thomas; Isobe, Hiroaki; Shibata,
Kazunari
Bibcode: 2012ApJ...746..120H
Altcode:
The launch of the Hinode satellite led to the discovery of rising
plumes, dark in chromospheric lines, that propagate from large
(~10 Mm) bubbles that form at the base of quiescent prominences. The
plumes move through a height of approximately 10 Mm while developing
highly turbulent profiles. The magnetic Rayleigh-Taylor instability
was hypothesized to be the mechanism that drives these flows. In this
study, using three-dimensional (3D) MHD simulations, we investigate the
nonlinear stability of the Kippenhahn-Schlüter prominence model for the
interchange mode of the magnetic Rayleigh-Taylor instability. The model
simulates the rise of a buoyant tube inside the quiescent prominence
model, where the interchange of magnetic field lines becomes possible
at the boundary between the buoyant tube and the prominence. Hillier
et al. presented the initial results of this study, where upflows of
constant velocity (maximum found 6 km s-1) and a maximum
plume width ≈1.5 Mm which propagate through a height of approximately
6 Mm were found. Nonlinear interaction between plumes was found to be
important for determining the plume dynamics. In this paper, using
the results of ideal MHD simulations, we determine how the initial
parameters for the model and buoyant tube affect the evolution of
instability. We find that the 3D mode of the magnetic Rayleigh-Taylor
instability grows, creating upflows aligned with the magnetic field
of constant velocity (maximum found 7.3 km s-1). The width
of the upflows is dependent on the initial conditions, with a range
of 0.5-4 Mm which propagate through heights of 3-6 Mm. These results
are in general agreement with the observations of the rising plumes.
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: Simulations of the magnetic Rayleigh-Taylor instability in
a quiescent prominence model to study the dark upflows observed
in prominences
Authors: Hillier, A. S.; Berger, T. E.; Shibata, K.; Isobe, H.
Bibcode: 2011AGUFMSH33A2033H
Altcode:
Observations of quiescent prominences by the Solar Optical Telescope
(SOT) on board the Hinode satellite show plumes of hot, underdense
material rising through the prominence. These plumes form at the
boundary between the prominence and low density bubbles, approximately
10 Mm in size, that appear beneath the prominence, and then rise
through the prominence material at speeds of approximately 20 km/s and
widths of approximately 1.5 Mm. The plume profile ranges from highly
turbulent to smooth, suggesting that the prominence conditions, as well
as those of the bubble, are important in determining the dynamics. To
investigate this phenomenon, we perform simulations of the magnetic
Rayleigh-Taylor instability in a local prominence model. The instability
creates rising plumes of hot, underdense material that propagate through
the prominence material at a velocity of approximately 6-7 km/s and
widths of approximately 1.5 Mm, in rough agreement with the Hinode
observations. Nonlinear effects, in which the interaction between
plumes drives an inverse cascade process creating large plumes from
smaller plumes, are found to be important. Increasing the magnetic
field strength creates smoother plume structures. The addition of a
strong guide field, which is suggested in some prominence models, does
not hinder plume formation but does change the dynamic scaling. The
Rayleigh-Taylor instability drives an upward flow of magnetic energy
and a downward flow of mass. The results from the simulations well
match the characteristics of the observed plumes, suggesting that
the magnetic Rayleigh-Taylor instability could be important in
determining prominence structure as well as changing the magnetic
energy distribution in overlying coronal cavities which ultimately
erupt as coronal mass ejections.
Title: Formation of Hematite fine crystals by hydrothermal alteration
of synthetic Martian basalt, static and fluid flow experiments
Authors: Kobayashi, K.; Isobe, H.
Bibcode: 2011AGUFM.P33B1766K
Altcode:
Exploration made by Martian rovers and probes provided enormous
information on the composition of the Martian surface materials. Origin
and formation processes of the Martian surface materials should
be various depending on topography and history of the Martian
crust. Especially, iron minerals in the Martian soil should have
essential role to characterize surface environment of the "red
planet". In the present study, experimental reproduction of the Martian
soil was carried out by hydrothermal alteration of the synthetic
iron-rich basaltic rock. Experimental conditions for temperature
and fluid composition followed Isobe and Yoshizawa (2010). Static
alteration experiments are carried out at 100 °C and 150 °C, and mass
ratio of the starting material to the pH1.0 sulfuric acid solution
is 1:50. Run durations are 1, 2, 4 or 8 weeks. Appropriate mass of
dry ice was sealed in the experimental vessels to expel atmospheric
oxygen with CO2. For the static experiments, powdered
starting materials were charged in PFA vial to keep textures of the
run products. For the fluid flow experiments, we constructed closed
loop with Teflon tube inclined approximately 45°. One of the vertical
tube is charged with crushed synthetic basalt and heated approximately
150°C by aluminum block with ribbon heater. Surlfuric acid solution
flows through the tube from bottom to top and cooled at the end of the
aluminum block. Cooled solution returns to the bottom of the heated
tube through another vertical tube without heating block. In the static
condition run products, characteristic iron mineral particles are formed
for 100°C and 150°C concordant with Isobe and Yoshizawa (2010). These
iron minerals distributed not only inside the starting material powder
but also on the surface of the reaction vessel and the PFA vial in the
reactive solution. The surface of the reaction vessel shows orange and
reddish color on 100°C and 150°C run products, respectively. By SEM
observation, dissolution of melt and olivine grains were observed,
and iron mineral particles substituted olivine partly. Diameters of
the iron mineral particles are submicron to several micron meters at
100°C, and slowly increase with run durations and temperatures. In
the fluid flow experiment, deposition of the characteristic iron
minerals occur inside the heated tube. Distribution of iron minerals
corresponds to temperature gradient and fluid flow direction. Iron
minerals are partially covered by silica phase with submicron meters
in thickness. The occurrence of the iron minerals in the run products
of this study suggests that characteristic iron mineral fine particles
including hematite and goethite were formed by acidic hydrothermal
alteration of iron-rich basaltic rock even at remote region from the
source materials.
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: Chromospheric anemone jets and magnetic reconnection in
partially ionized solar atmosphere
Authors: Singh, K. A. P.; Shibata, K.; Nishizuka, N.; Isobe, H.
Bibcode: 2011PhPl...18k1210S
Altcode:
The solar optical telescope onboard Hinode with temporal resolution
of less than 5 s and spatial resolution of 150 km has observed the
lower solar atmosphere with an unprecedented detail. This has led to
many important findings, one of them is the discovery of chromospheric
anemone jets in the solar chromosphere. The chromospheric anemone jets
are ubiquitous in solar chromosphere and statistical studies show
that the typical length, life time and energy of the chromospheric
anemone jets are much smaller than the coronal events (e.g.,
jets/flares/CMEs). Among various observational parameters, the apparent
length and maximum velocity shows good correlation. The velocity of
chromospheric anemone jets is comparable to the local Alfvén speed
in the lower solar chromosphere. Since the discovery of chromospheric
anemone jets by Hinode, several evidences of magnetic reconnection
in chromospheric anemone jets have been found and these observations
are summarized in this paper. These observations clearly suggest that
reconnection occurs quite rapidly as well as intermittently in the solar
chromosphere. In the solar corona (λi > δSP), anomalous resistivity
arises due to various collisionless processes. Previous MHD simulations
show that reconnection becomes fast as well as strongly time-dependent
due to anomalous resistivity. Such processes would not arise in the
solar chromosphere which is fully collisional and partially-ionized. So,
it is unclear how the rapid and strongly time-dependent reconnection
would occur in the solar chromosphere. It is quite likely that the
Hall and ambipolar diffusion are present in the solar chromosphere
and they could play an important role in driving such rapid, strongly
time-dependent reconnection in the solar chromosphere.
Title: Numerical Simulations of the Magnetic Rayleigh-Taylor
Instability in the Kippenhahn-Schlüter Prominence Model
Authors: Hillier, Andrew; Isobe, Hiroaki; Shibata, Kazunari; Berger,
Thomas
Bibcode: 2011ApJ...736L...1H
Altcode: 2011arXiv1107.4882A
The launch of the Hinode satellite has allowed unprecedented
high-resolution, stable images of solar quiescent prominences to
be taken over extended periods of time. These new images led to the
discovery of dark upflows that propagated from the base of prominences,
developing highly turbulent profiles. As yet, how these flows are driven
is not fully understood. To study the physics behind these phenomena,
we use three-dimensional magnetohydrodynamic simulations to investigate
the nonlinear stability of the Kippenhahn-Shlüter prominence model
to the magnetic Rayleigh-Taylor instability. The model simulates the
rise of a buoyant tube inside a quiescent prominence, where the upper
boundary between the tube and prominence model is perturbed to excite
the interchange of magnetic field lines. We found upflows of constant
velocity (maximum found 6 km s-1) and a maximum plume
width ≈1500 km which propagate through a height of approximately 6
Mm in the no guide field case. The case with the strong guide field
(initially By = 2Bx ) results in a large plume
that rises through the prominence model at ~5 km s-1 with
width ~900 km (resulting in width of 2400 km when viewed along the
axis of the prominence), reaching a height of ~3.1 Mm. In both cases,
nonlinear processes were important for determining plume dynamics.
Title: Observations of Plasma Blob Ejection from a Quiescent
Prominence by Hinode Solar Optical Telescope
Authors: Hillier, Andrew; Isobe, Hiroaki; Watanabe, Hiroko
Bibcode: 2011PASJ...63L..19H
Altcode: 2011arXiv1103.3750H
We report findings from 0''.2 resolution observations of the
2007 October 03 quiescent prominence observed with the Solar
Optical Telescope on the Hinode satellite. The observations show
clear ejections from the top of the quiescent prominence of plasma
blobs. The ejections, originating from the top of prominence threads,
are impulsively accelerated to approximately Alfvén velocities and
then undergo ballistic motion. The ejections have a characteristic
size between ∼ 1000-2000 km. These characteristics are similar
to downwardly propagating knots (typical size ∼ 700 km) that have
been observed in prominence threads, we suggest that the plasma blob
ejections could be the upward moving counterpart to the downwardly
propagating knots. We discuss the tearing instability as a possible
mechanism to explain the ejections.
Title: Detailed analysis of fan-shaped jets in three dimensional
numerical simulation
Authors: Jiang, Rong-Lin; Shibata, K.; Isobe, H.; Fang, Cheng
Bibcode: 2011RAA....11..701J
Altcode: 2011arXiv1101.4598J
We performed three dimensional resistive magnetohydrodynamic simulations
to study the magnetic reconnection using an initially shearing magnetic
field configuration (force free field with a current sheet in the middle
of the computational box). It is shown that there are two types of
reconnection jets: the ordinary reconnection jets and fan-shaped jets,
which are formed along the guide magnetic field. The fan-shaped jets
are significantly different from the ordinary reconnection jets which
are ejected by magnetic tension force. There are two driving forces
for accelerating the fan-shaped jets. One is the Lorentz force which
initially dominates the motion of fluid elements, and then the gas
pressure gradient force accelerates the fluid elements in the later
stage. The dependence on magnetic reconnection angle and resistivity
value has also been studied. The formation and evolution of these jets
provide a new understanding of dynamic magnetohydrodynamic jets.
Title: Dependence of the Magnetic Energy of Solar Active Regions on
the Twist Intensity of the Initial Flux Tubes
Authors: Toriumi, Shin; Miyagoshi, Takehiro; Yokoyama, Takaaki; Isobe,
Hiroaki; Shibata, Kazunari
Bibcode: 2011PASJ...63..407T
Altcode: 2011arXiv1101.0978T
We present a series of numerical experiments that model the evolution
of magnetic flux tubes with a different amount of initial twist. As a
result of calculations, tightly twisted tubes reveal a rapid two-step
emergence to the atmosphere with a slight slowdown at the surface,
while weakly twisted tubes show a slow two-step emergence waiting
longer the secondary instability to be triggered. This picture of the
two-step emergence is highly consistent with recent observations. These
tubes show multiple magnetic domes above the surface, indicating that
the secondary emergence is caused by an interchange mode of magnetic
buoyancy instability. In the case of the weakest twist, the tube
exhibits an elongated photospheric structure, and never rises into
the corona. The formation of the photospheric structure is due to an
inward magnetic tension force of the azimuthal field component of
the rising flux tube (i.e., tube's twist). When the twist is weak,
the azimuthal field cannot hold the tube's coherency, and the tube
extends laterally at the subadiabatic surface. In addition, we newly
found that the total magnetic energy measured above the surface depends
on the initial twist. Strong twist tubes follow the initial relation
between the twist and the magnetic energy, while weak twist tubes
deviate from this relation, because these tubes store their magnetic
energy in the photospheric structure.
Title: MHD simulations of quiescent prominence upflows in the
Kippenhahn-Schlüter prominence model
Authors: Hillier, A. S.; Isobe, H.; Shibata, K.; Berger, T. E.
Bibcode: 2011ASInC...2..331H
Altcode:
Images from the Hinode satellite have led to the discovery of dark
upflows that propagate from the base of prominences, developing highly
turbulent profiles. The magnetic Rayleigh-Taylor instability has been
hypothesized as the mechanism to create these plumes. To study the
physics behind this phenomenon we use 3D magnetohydrodynamic simulations
to investigate the nonlinear stability of the Kippenhahn-Shlüter
prominence model to the magnetic Rayleigh-Taylor instability. The model
simulates the rise of a buoyant tube inside a quiescent prominence,
where the upper boundary between the tube and prominence model is
perturbed to excite the interchange of magnetic field lines. We
find upflows of constant velocity (maximum found 6 km s^{-1}) and a
maximum plume width ≈ 1500 km which propagate through a height of
approximately 6 Mm, in general agreement with the Hinode observations.
Title: Magnetic Reconnection in the Solar Atmopshere Observed
by Hinode
Authors: Imada, Shinsuke; Isobe, Hiroaki; Shimizu, Toshifumi
Bibcode: 2011sswh.book...63I
Altcode:
No abstract at ADS
Title: Fan-shaped Jets in Three-dimensional Reconnection Simulation
as a Model of Ubiquitous Solar Jets
Authors: Jiang, Rong Lin; Shibata, Kazunari; Isobe, Hiroaki; Fang,
Cheng
Bibcode: 2011ApJ...726L..16J
Altcode: 2010arXiv1012.2551J
Magnetic reconnection is a fundamental process in space and
astrophysical plasmas in which the oppositely directed magnetic
field changes its connectivity and eventually converts its energy
into kinetic and thermal energy of the plasma. Recently, ubiquitous
jets (for example, chromospheric anemone jets, penumbral microjets,
umbral light bridge jets) have been observed by the Solar Optical
Telescope on board the satellite Hinode. These tiny and frequently
occurring jets are considered to be a possible evidence of small-scale
ubiquitous reconnection in the solar atmosphere. However, the details
of three-dimensional (3D) magnetic configuration are still not very
clear. Here, we propose a new model based on 3D simulations of magnetic
reconnection using a typical current sheet magnetic configuration with
a strong guide field. The most interesting feature is that the jets
produced by the reconnection eventually move along the guide field
lines. This model provides a fresh understanding of newly discovered
ubiquitous jets and moreover a new observational basis for the theory
of astrophysical magnetic reconnection.
Title: Evolution of the Kippenhahn-Schlüter Prominence Model Magnetic
Field under Cowling Resistivity
Authors: Hillier, Andrew; Shibata, Kazunari; Isobe, Hiroaki
Bibcode: 2010PASJ...62.1231H
Altcode: 2010arXiv1007.1909H
We present the results from 1.5D diffusion simulations of the
Kippenhahn-Schlüter prominence model magnetic field evolution under the
influence of the ambipolar terms of Cowling resistivity. We show that
initially the evolution is determined by the ratio of the horizontal
and vertical magnetic fields, which gives current sheet thinning
(thickening) when this ratio is small (large) and a marginal case
where a new characteristic current sheet length scale is formed. After
a timespan greater than the Cowling resistivity time, the current
sheet thickens as a power law of t independent of the ratio of the
field strengths. These results imply that when Cowling resistivity is
included in the model, the tearing instability time scale is reduced
by more than one order of magnitude when the ratio of the horizontal
field to the vertical field is 20% or less. These results imply that,
over the course of its lifetime, the structure of the prominence can
be significantly altered by Cowling resistivity, and in some cases
will allow the tearing instability to occur.
Title: Spicule Dynamics over a Plage Region
Authors: Anan, Tetsu; Kitai, Reizaburo; Kawate, Tomoko; Matsumoto,
Takuma; Ichimoto, Kiyoshi; Shibata, Kazunari; Hillier, Andrew; Otsuji,
Kenichi; Watanabe, Hiroko; Ueno, Satoru; Nagata, Shin'ichi; Ishii,
Takako T.; Komori, Hiroyuki; Nishida, Keisuke; Nakamura, Tahei; Isobe,
Hiroaki; Hagino, Masaoki
Bibcode: 2010PASJ...62..871A
Altcode: 2010arXiv1002.2288A
We studied spicular jets over a plage area and derived their
dynamic characteristics using Hinode Solar Optical Telescope (SOT)
high-resolution images. A target plage region was near to the west limb
of the solar disk. This location permitted us to study the dynamics
of spicular jets without any overlapping effect of spicular structures
along the line of sight. In this work, to increase the ease with which
we could identify spicules on the disk, we applied the image processing
method `MadMax' developed by Koutchmy et al. (1989). It enhances fine,
slender structures (like jets), over a diffuse background. We identified
169 spicules over the target plage. This sample permited us to derive
statistically reliable results regarding spicular dynamics. The
properties of plage spicules can be summarized as follows: (1) In a
plage area, we clearly identified spicular jet features. (2) They were
shorter in length than the quiet region limb spicules, and followed a
ballistic motion under constant deceleration. (3) The majority (80%)
of the plage spicules showed a cycle of rise and retreat, while 10% of
them faded out without a complete retreat phase. (4) The deceleration
of the spicule was proportional to the velocity of ejection (i.e.,
the initial velocity).
Title: CaII K Spectral Study of an Emerging Flux Region using the
Domeless Solar Telescope in Hida Observatory
Authors: Otsuji, Kenichi; Kitai, Reizaburo; Matsumoto, Takuma;
Ichimoto, Kiyoshi; Ueno, Satoru; Nagata, Shin'ichi; Isobe, Hiroaki;
Shibata, Kazunari
Bibcode: 2010PASJ...62..893O
Altcode: 2010arXiv1005.2025O
A cooperative observation with Hida Observatory and the Hinode
satellite was performed on an emerging flux region. Successive CaII
K spectro-heliograms of the emerging flux region were taken by the
Domeless Solar Telescope of Hida Observatory. Hinode observed the
emerging flux region with CaII H and FeI Stokes IQUV filtergrams. In
this study, detailed dynamics and the temporal evolution of the
magnetic flux emergence was studied observationally. The event was first
detected in the photospheric magnetic field signals; 3 minutes later,
a horizontal expansion of the dark area was detected. Then, 7 minutes
later than the horizontal expansion, the emerging loops were detected
with a maximal rise speed of 2.1 km s-1 at chromospheric
heights. The observed dynamics of the emerging magnetic flux from the
photosphere to the upper chromosphere was very consistent with the
results of previous simulation studies. A gradual rising phase of flux
tubes with a weak magnetic strength was confirmed by our observation.
Title: Three-dimensional MHD Simulations Of Magnetic Reconnection
With Finite Fluctuations
Authors: Yokoyama, Takaaki; Isobe, H.
Bibcode: 2010AAS...21640802Y
Altcode: 2010BAAS...41R.815Y
The magnetic reconnection is one of the fundamental processes for
the heating, bulk flow acceleration, and magnetic topology change
in the solar/stellar atmospheres and other astrophysical energetic
phenomena. For the quantitative understanding of these phenomena,
it is crucially important to determine the energy release rate or,
equivalently, the reconnection rate from numerical studies. Owing
to the enormously large magnetic Reynolds number, it is expected
that the MHD turbulence or some stochastic process may play a role
for the magnetic diffusion in the reconnection region. By performing
three-dimensional MHD simulations, we are working on this issue. The
temporal evolution of a simple current sheet with initially imposed
fluctuations in the resistivity is studied. A substantial increase of
energy release ratewas found by adding the guide field, i.e. the field
parallelto the electric current. It is interpreted that this is due
to the mutual interactions of magnetic islands formed in a spatially
separated parallel resonant layers.
Title: Iron Mineral Fine Particles Produced by Acidic Hydrothermal
Alteration Experiments of the Synthetic Martian Basalt
Authors: Isobe, H.; Yoshizawa, M.
Bibcode: 2010LPI....41.1292I
Altcode:
Acidic hydrothermal alteration experiments of synthetic iron-rich
martian basalt revealed that iron mineral fine particles with quite
characteristic morphology can be produced by alteration spots related
to the martian volcanic activities.
Title: Magnetic reconnection with finite fluctuations
Authors: Yokoyama, Takaaki; Isobe, Hiroaki
Bibcode: 2010cosp...38.1935Y
Altcode: 2010cosp.meet.1935Y
The magnetic reconnection is one of the fundamental processes for
the heating, bulk flow acceleration, and magnetic topology change in
the solar atmosphere. For the quantitative understanding of these
phenomena, it is crucially important to determine the reconnection
rate from theoretical/numerical studies. Owing to the enormously large
magnetic Reynolds number, it is expected that the MHD turbulence or
some stochastic process may play a role for the magnetic diffusion
in the reconnection region. In this talk, we would like to review the
studies related on this idea and show our recent works. In our study,
by performing three-dimensional MHD simulations, the temporal evolution
of a simple current sheet with initially imposed fluctuations in the
resistivity is investigated. Although the enhancement is limited only
by a few percent beyond the Sweet-Parker rate in cases with initially
anti-parallel fields, a substantial increase of energy release rate
was found by adding the guide field, i.e. the field parallelto the
electric current. It is interpreted that this is due to the mutual
interactions of magnetic islands formed in a spatially separated
parallel resonant layers.
Title: Comparison of reconnection in magnetosphere and solar corona
Authors: Imada, Shinsuke; Hirai, Mariko; Isobe, Hiroaki; Oka, Mitsuo;
Watanabe, Kyoko; Minoshima, Takashi
Bibcode: 2010cosp...38.1940I
Altcode: 2010cosp.meet.1940I
One of the most famous rapid energy conversion mechanisms in space is a
magnetic reconnec-tion. The general concept of a magnetic reconnection
is that the rapid energy conversion from magnetic field energy to
thermal energy, kinetic energy or non-thermal particle energy. The
understanding of rapid energy conversion rates from magnetic field
energy to other energy is the fundamental and essential problem in
the space physics. One of the important goals for studying magnetic
reconnection is to answer what plasma condition/parameter controls
the energy conversion rates. Earth's magnetotail has been paid
much attention to discuss a mag-netic reconnection, because we can
discuss magnetic reconnection characteristics in detail with direct
in-situ observation. Recently, solar atmosphere has been focused as a
space laboratory for magnetic reconnection because of its variety in
plasma condition. So far considerable effort has been devoted toward
understanding the energy conversion rates of magnetic reconnection,
and various typical features associated with magnetic reconnection have
been observed in the Earth's magnetotail and the solar corona. In this
talk, we first introduce the variety of plasma condition/parameter in
solar corona and Earth's magnetotail. Later, we discuss what plasma
condition/parameter controls the energy conversion from magnetic field
to especially non-thermal particle. To compare non-thermal electron and
ion acceleration in magnetic reconnection, we used Hard X-ray (electron)
/Neu-tron monitor (ion) for solar corona and Geotail in-situ measurement
(electron and ion) for magnetoatil. We found both of electron and ion
accelerations are roughly controlled by re-connection electric field
(reconnection rate). However, some detail points are different in ion
and electron acceleration. Further, we will discuss what is the major
difference between solar corona and Earth's magnetotail for particle
acceleration.
Title: MHD simulations of upflows in the Kippenhahn-Schlueter
prominence model
Authors: Hillier, Andrew; Shibata, Kazunari; Isobe, Hiroaki; Berger,
Thomas
Bibcode: 2010cosp...38.2914H
Altcode: 2010cosp.meet.2914H
The launch of SOT on the Hinode satellite, with it's previously
unprecedented high resolution, high cadence images of solar prominences,
led to the discovery of small scale, highly dynamic flows in quiescent
prominences. Berger et al. (2008) reported dark upflows that propagated
from the base of the prominence through a height of approximately 10
Mm before ballooning into the familiar mushroom shape often associated
with the Rayleigh-Taylor instability. Whether such phenomena can be
driven by instabilities and, if so, how the instability evolve is yet
to be fully investigated. In this study, we use the Kippenhahn-Schlueter
(K-S) prominence model as the base for 3D numerical MHD simulations. The
K-S prominence model is linearly stable for ideal MHD perturbationss,
but can be made unstable through nonlinear perturbations, which we
impose through inserting a low density (high temperature) tube through
the centre of the prominence. Our simulations follow the linear and
nonlinear evolution of upflows propagating from the hot tube through the
K-S prominence model. We excited Rayleigh-Taylor like modes inside the
K-S model with a wave along the contact discontinuity created between
the hot tube and the K-S prominence, and solved the pertur-bations
of this system. For such a complex setting, the linear evolution of
the instability has 0.7 not been studied, and we found the growth
rate to be ∼ ( ρ+ -ρ- - 0.05)k 0.22 . The most ρ+ +ρ- unstable
wavelength was ∼ 100 km which, through the inverse cascade process,
created upflows of ∼ 300 km. The rising plumes obtained a constant
rise velocity in the nonlinear stage due to the creation of adverse
magnetic and gas pressure gradients at the top of the plume.
Title: Large Amplitude Oscillations in Prominences
Authors: Tripathi, D.; Isobe, H.; Jain, R.
Bibcode: 2009SSRv..149..283T
Altcode: 2009arXiv0910.4059T
Since the first reports of oscillations in prominences in the 1930s,
there have been major theoretical and observational developments to
understand the nature of these oscillatory phenomena, leading to the
whole new field of the so-called “prominence seismology”. There
are two types of oscillatory phenomena observed in prominences;
“small-amplitude oscillations” (2-3 km s-1), which
are quite common, and “large-amplitude oscillations” (>20 km
s-1) for which observations are scarce. Large-amplitude
oscillations have been found as “winking filament” in H α as
well as motion in the plane-of-sky in H α, EUV, micro-wave and
He 10830 observations. Historically, it has been suggested that
the large-amplitude oscillations in prominences were triggered by
disturbances such as fast-mode MHD waves (Moreton wave) produced by
remote flares. Recent observations show, in addition, that near-by
flares or jets can also create such large-amplitude oscillations in
prominences. Large-amplitude oscillations, which are observed both in
transverse as well as longitudinal direction, have a range of periods
varying from tens of minutes to a few hours. Using the observed period
of oscillation and simple theoretical models, the obtained magnetic
field in prominences has shown quite a good agreement with directly
measured one and, therefore, justifies prominence seismology as a
powerful diagnostic tool. On rare occasions, when the large-amplitude
oscillations have been observed before or during the eruption, the
oscillations may be applied to diagnose the stability and the eruption
mechanism. Here we review the recent developments and understanding
in the observational properties of large-amplitude oscillations and
their trigger mechanisms and stability in the context of prominence
seismology.
Title: Reconnection in solar flares: Outstanding questions
Authors: Isobe, Hiroaki; Shibata, Kazunari
Bibcode: 2009JApA...30...79I
Altcode:
No abstract at ADS
Title: Multiwavelength Observation of Electron Acceleration in the
2006 December 13 Flare
Authors: Minoshima, T.; Imada, S.; Morimoto, T.; Kawate, T.;
Koshiishi, H.; Kubo, M.; Inoue, S.; Isobe, H.; Masuda, S.; Krucker,
S.; Yokoyama, T.
Bibcode: 2009ApJ...697..843M
Altcode: 2009arXiv0903.1144M
We present a multiwavelength observation of a solar flare occurring on
2006 December 13 with Hinode, RHESSI, and the Nobeyama Radio Observatory
to study the electron acceleration site and mechanism. The Solar Optical
Telescope (SOT) on board Hinode observed elongated flare ribbons, and
RHESSI observed double-footpoint hard X-ray (HXR) sources appearing
in part of the ribbons. A photospheric vector magnetogram obtained
from SOT reveals that the HXR sources are located at the region where
horizontal magnetic fields change direction. The region is interpreted
as the footpoint of magnetic separatrix. Microwave images taken
with the Nobeyama Radioheliograph show a loop structure connecting
the HXR sources. The brighter parts of the microwave intensity are
located between the top and footpoints of the loop. We consider these
observations as evidence of electron acceleration near the magnetic
separatrix and injection parallel to the field line.
Title: Experimental Reproduction of Martian Soil by Alteration of
the Synthetic Martian Basalt Under Hydrothermal Conditions with
Sulfuric acid and CO2
Authors: Yoshizawa, M.; Isobe, H.
Bibcode: 2008AGUFM.P43B1407Y
Altcode:
The formation process of the Martian soil is one of the most essential
problems to understand the surface environment of the Mars. Especially,
iron minerals in the Martian soil should be the key component to
characterize the red planet. The major Martian volcanoes consist of
iron-rich basaltic rocks. Volcanic activities of the Martian volcanoes
should involve fluid rich in sulfuric components and CO2. CO2 may have
more essential role in the alteration processes related to fluids in
Martian volcanic activities than that in the terrestrial volcanoes. In
this study, hydrothermal alteration experiments are conducted to
elucidate the soil formation processes on the Martian surface. We
carried out alteration experiments of the synthetic iron-rich
basaltic material with sulfuric acid and CO2-bearing hydrothermal
fluid. Experimental temperatures are 100 ~ 300°C. Acidities of the
solutions are pH1.0, 3.0 or 7.0. Run durations are 4, 8 or 16 weeks
(100°C) or 3, 6 or 12 weeks (150 ~ 300°C). CO2 are introduced to the
experimental vessels by appropriate mass of dry ice (100 ~ 150°C)
or silver oxalate (200 ~ 300°C) for approximately 1 MPa of CO2. We
reported preliminary results of alteration experiments of mafic minerals
with sulfuric acid-bearing hydrothermal fluid without CO2 (Yoshizawa
and Isobe, 2007). In the run products of the preliminary experiments,
we found characteristic hematite fine particles which may bring
about reddish color of the Martian soil. Morphology of the hematite
produced at 100 ~ 150°C was granular to spheroidal with diameters
of 0.5 to 3 micron meters. Major run products of the experiments
are clay minerals and iron oxide/hydroxide minerals. Run products
of the alteration experiments show characteristic reddish to brown
color depending on the acidity and temperature. Iron mineral species
have distinctive color. SEM/EDS and XRD observations also revealed
representative iron mineral species in the run products. Alteration
products by CO2-bearing hydrothermal fluid are more oxidized than
those by hydrothermal fluid without CO2. CO2 in acidic hydrothermal
fluid may accelerate oxidative alteration of basaltic rocks. Acidic
hydrothermal alteration may have essential role to form the Martian
soil which is rich in iron oxide. Especially, iron mineral species
and morphology strongly depend on temperatures and acidities of the
hydrothermal fluid. Direct observation of the Martian soil may provide
us information on the conditions of hydrothermal alteration related
to the Martian volcanic activities.
Title: Observational Study of Particle Acceleration in the 2006
December 13 Flare
Authors: Minoshima, T.; Morimoto, T.; Kawate, T.; Imada, S.;
Koshiishi, H.; Masuda, S.; Kubo, M.; Inoue, S.; Isobe, H.; Krucker,
S.; Yokoyama, T.
Bibcode: 2008AGUFMSH41B1619M
Altcode:
We study the particle acceleration in a flare on 2006 December 13,
by using the Hinode, RHESSI, Nobeyama Radio Polarimeters (NoRP) and
Nobeyama Radioheliograph (NoRH) observations. For technical reasons,
both RHESSI and NoRH have a problem in imaging in this flare. Since we
have succeeded in solving the problem, it is now possible to discuss
the particle acceleration mechanism from an image analysis. This flare
shows very long-lasting (1 hour) non-thermal emissions, consisting of
many spikes. We focus on the second major spike at 02:29 UT, because
the RHESSI image is available only in this period. The RHESSI 35-100 keV
HXR image shows double sources located at the footpoints of the western
soft X-ray (SXR) loop seen by the Hinode/XRT. The non-linear force-free
(NLFF) modeling based on a magnetogram data by Inoue et al. shows the
NLFF to potential magnetic transition of the loop, which would induce
the electric field and then accelerate particles. Overlaying the HXR
image on the photospheric three-dimensional magnetic field map taken
by the Hinode Spectro-Polarimeter, we find that the HXR sources are
located at the region where the horizontal magnetic fields invert. The
NoRH 34 GHz microwave images show the loop structure connecting the
HXR sources. The microwave peaks do not located at the top of the
loop but between the loop top and the footpoints. The NoRP microwave
spectrum shows the soft-hard-soft pattern in the period, same as the
HXR spectrum (Ning 2008). From these observational results we suggest
that the electrons were accelerated parallel to the magnetic field
line near the magnetic separatrix.
Title: Compositional Variation and Homogenization Kinetics of
Serpentine in Hydrous alteration processes of Carbonaceous chondrite
parent body: An Experimental study under reducing conditions
Authors: Ozaki, H.; Isobe, H.
Bibcode: 2008AGUFMMR13B1707O
Altcode:
Carbonaceous chondrites are the most primitive planetary materials
which consist of various disequilibrium assemblages of minerals
derived from various stages of the early solar system. Especially,
hydrous phyllosilicate minerals in CM chondrites are the first
products of aqueous alteration on the meteorite parent body,
and those show huge compositional variation. The main mineral
species of the hydrous phyllosilicate minerals in CM chondrites
are serpentine, saponite and tochilinite. Compositional variation
involving homogenization processes in the phyllosilicate minerals may
have essential information on the timescale of the aqueous alteration
processes on the parent body. In this study, we carried out aqueous
alteration experiments of heterogeneous starting materials with fluid
containing ethanol to keep reducing conditions representative to the
early solar system remaining the solar nebula gas. We have carried
out aqueous alteration experiments of synthetic olivine (Fo55) with
synthetic fayalite or enstatite. Fo55 olivine represents the Mg/
(Mg + Fe) molar ratio of the solar abundance. Fayalite or enstatite
represents Fe-rich or Fe-poor components in the heterogeneous parent
body, respectively. Experimental fluids are ethanol solutions with
0.5, 2.5 or 10.0 vol. %. Decomposition of ethanol supply reducing
agent to the fluid and keep the oxidation condition of the system on
the C-CO buffer. Experimental temperatures are 100, 150, 200, 250
and 300°C with vapor pressure, and 400 and 500°C with 100MPa.Run
durations are 3 to 12 weeks. Run products are analyzed by XRD and SEM /
EDS. Aqueous alteration experiments of Allende meteorites show that
Mg / Fe compositions of serpentine in the run products with higher
temperatures show broader distribution to Mg-rich composition than
that of 200°C experiments. Mg-rich olivine derived form chondrules
contribute to produce serpentine in higher temperature. Mg / Fe
composition range of serpentine is getting narrower with run duration
(Isobe and Ozaki, 2008). Quantitative kinetics of the evolution and
compositional variations of the phyllosilicate produced in the aqueous
alteration from the heterogeneous starting materials will be discussed.
Title: Magnetic flux cancellation associated with a recurring solar
jet observed with Hinode, RHESSI, and STEREO/EUVI
Authors: Chifor, C.; Isobe, H.; Mason, H. E.; Hannah, I. G.; Young,
P. R.; Del Zanna, G.; Krucker, S.; Ichimoto, K.; Katsukawa, Y.;
Yokoyama, T.
Bibcode: 2008A&A...491..279C
Altcode:
Aims: We study the physical properties of a recurring solar active
region jet observed in X-rays and extreme-ultraviolet (EUV).
Methods: Multi-wavelength data from all three instruments on
board Hinode were analysed. X-ray imaging and spectroscopy of the
microflaring emission associated with the jets was performed with the
Reuven Ramaty High Energy Spectroscopic Imager (RHESSI). Associated
EUV jets were observed with the Sun Earth Connection Coronal and
Heliospheric Investigation (SECCHI)/Extreme Ultraviolet Imager
(EUVI) on board STEREO.
Results: We found a correlation between
recurring magnetic flux cancellation close to a pore, the X-ray jet
emission, and associated Ca II H ribbon brightenings. We estimated the
lower limit for the decrease in magnetic energy associated with the
X-ray jet emission at 3 × 1029 erg. The recurring plasma
ejection was observed simultaneously at EUV and X-ray temperatures,
associated with type III radio bursts and microflaring activity at the
jet footpoint.
Conclusions: The recurring jet (EUV and X-ray)
emissions can be attributed to chromospheric evaporation flows due to
recurring coronal magnetic reconnection. In this process, the estimated
minimum loss in the magnetic energy is sufficient to account for the
total energy required to launch the jet. Movie of Fig. 3 is only
available in electronic form via http://www.aanda.org
Title: Active Region Microflares From Hinode and RHESSI
Authors: Chifor, C.; Hannah, I. G.; Mason, H. E.; Isobe, H.; Yokoyama,
T.; Young, P. R.; Tripathi, D.
Bibcode: 2008ASPC..397..164C
Altcode:
We are studying microflares (A, B-C class flares) in active regions
using coordinated observations from Hinode and RHESSI. Hinode/EIS
has unprecedented diagnostic power for small, transient activity
in the solar corona, providing temperature, density, and velocity
information. For this purpose, we designed and ran an EIS observing
sequence to provide high-cadence data at both transition region and
coronal temperatures. A preliminary analysis of these observations is
reported, with one data set given as an example.
Title: Hydrothermal Experiments of Synthetic Amorphous Silicates
with CI Chondritic Composition in the Systems With and Without FeO
Authors: Noguchi, R.; Murata, K.; Tsuchiyama, A.; Isobe, H.; Chihara,
H.; Nakamura, T.; Noguchi, T.
Bibcode: 2008M&PSA..43.5333N
Altcode:
No abstract at ADS
Title: Prominence Seismology: Wavelet Analysis of Filament
Oscillations
Authors: Pintér, Balázs; Jain, Rekha; Tripathi, Durgesh; Isobe,
Hiroaki
Bibcode: 2008ApJ...680.1560P
Altcode:
The temporal and spatial behavior of a large-amplitude
filament oscillation is investigated using wavelet analysis. The
extreme-ultraviolet (EUV) images of the phenomenon, which occurred on
2002 October 15, were taken from the EUV Imaging Telescope on board
the Solar and Heliospheric Observatory (SOHO). The wavelet spectra,
extracted from the intensity data, show that the filament oscillates
as a rigid body, with a period of about 2.5-2.6 hr which is almost
constant along the filament. The period slowly decreases with time
until the filament erupts. No clear sign of the eruption is found in
the wavelet spectrum prior to the eruption, that followed the filament
oscillation. The axial component of the magnetic field is estimated
between 1 and 5 G, which is believed to be reasonable for a polar
crown filament of this kind.
Title: Convection-driven Emergence of Small-Scale Magnetic Fields
and their Role in Coronal Heating and Solar Wind Acceleration
Authors: Isobe, H.; Proctor, M. R. E.; Weiss, N. O.
Bibcode: 2008ApJ...679L..57I
Altcode:
Recent observations by the Solar Optical Telescope (SOT) on board
Hinode have revealed that the surface of the Sun is, on average,
covered with small-scale horizontal magnetic fields. Frequent emergence
of horizontal magnetic flux on a granular scale is found in the quiet
Sun and in plage regions. In this Letter we present the results of
magnetohydrodynamic simulations that cover the upper convection zone
and the corona. It is found that, even when the initial magnetic field
is uniform and vertical, a disordered magnetic field is produced in the
convection zone. The photospheric magnetic field is then characterized
by strong vertical fields concentrated in the intergranular lanes and
relatively weak, horizontal fields both in the granules and in the
intergranular lanes. Occasionally, fragments with large magnetic fluxes
are driven above the photosphere by the upward convective flows. These
characteristics are consistent with the SOT observations. Moreover,
the simulated flux emerging on a granular scale undergoes magnetic
reconnection with the expanding vertical magnetic concentrations in the
chromosphere. These reconnection events heat the local plasma and emit
high-frequency waves that propagate into the corona. Such an interplay
between the small-scale horizontal fields and the vertical flux may
play an important role in coronal heating and wind acceleration in
the Sun and stars.
Title: Transient horizontal magnetic fields in solar plage regions
Authors: Ishikawa, R.; Tsuneta, S.; Ichimoto, K.; Isobe, H.; Katsukawa,
Y.; Lites, B. W.; Nagata, S.; Shimizu, T.; Shine, R. A.; Suematsu,
Y.; Tarbell, T. D.; Title, A. M.
Bibcode: 2008A&A...481L..25I
Altcode: 2008arXiv0802.1769I
Aims:We report the discovery of isolated, small-scale emerging
magnetic fields in a plage region with the Solar Optical Telescope
aboard Hinode.
Methods: Spectro-polarimetric observations were
carried out with a cadence of 34 s for the plage region located near
disc center. The vector magnetic fields are inferred by Milne-Eddington
inversion.
Results: The observations reveal widespread occurrence
of transient, spatially isolated horizontal magnetic fields. The
lateral extent of the horizontal magnetic fields is comparable to
the size of photospheric granules. These horizontal magnetic fields
seem to be tossed about by upflows and downflows of the granular
convection. We also report an event that appears to be driven by the
magnetic buoyancy instability. We refer to buoyancy-driven emergence
as type 1 and convection-driven emergence as type 2. Although both
events have magnetic field strengths of about 600 G, the filling
factor of type 1 is a factor of two larger than that of type 2.
Conclusions: Our finding suggests that the granular convection in
the plage regions is characterized by a high rate of occurrence of
granular-sized transient horizontal fields.
Title: An active region jet observed with Hinode
Authors: Chifor, C.; Young, P. R.; Isobe, H.; Mason, H. E.; Tripathi,
D.; Hara, H.; Yokoyama, T.
Bibcode: 2008A&A...481L..57C
Altcode:
Aims:We study the physical properties of an active region (AR) jet in
order to probe the mechanisms responsible for it.
Methods: We
report 2007 January 15/16 observations of a recurring jet situated on
the west side of NOAA AR 10938. Multi-wavelength data from all three
instruments onboard Hinode were analysed. This paper focuses on one
instance of a jet observed with the Hinode/EUV Imaging Spectrometer
(EIS). Using EIS raster data we measured the temperatures, Doppler
shifts, density, and filling factor.
Results: A strong
blue-shifted component and an indication of a weak red-shifted
component at the base of the jet was observed around Log Te
= 6.2. The up-flow velocities exceeded 150 km s-1. The
jet component was seen over a range of temperatures between 5.4 and
6.4 in Log T_e. Using Fe XII λ186 and λ195 line ratios, we measured
densities above Log Ne = 11 for the high-velocity up-flow
component. We found that the density of the high-velocity up-flow
increases with velocity. We estimate the filling factor in the jet
up-flow to be <0.03. With the Hinode/Solar Optical Telescope (SOT),
we observed recurrent (quasi periodic) magnetic flux cancelations just
before the recurrent jet emission was seen in images taken with the
X-ray Telescope (XRT).
Conclusions: The high-velocity up-flows,
together with the density dependence on velocity, support an evaporation
scenario for the acceleration of this jet. The high density and small
filling factor, coupled with the high Doppler velocities are strongly
suggestive of multiple small-scale magnetic reconnection events being
responsible for the production of both EUV and X-ray jets.
Title: Compositional Variation of Phyllosilicate Minerals in Aqueous
Alteration Experiment of Allende Meteorite Under Reduced Condition
Authors: Isobe, H.; Ozaki, H.
Bibcode: 2008LPI....39.2003I
Altcode:
Hydrothermal alteration experiments of Allende meteorite shows that
heterogeneity of the Mg/Fe composition of phyllosilicate in the run
products depends on run temperatures and durations.
Title: The Martian Soil Formation Experiments by Hydrothermal
Alteration of Basaltic Rock
Authors: Yoshizawa, M.; Isobe, H.
Bibcode: 2007AGUFM.P13D1564Y
Altcode:
Soil formation processes on terrestrial planets have an important
role on evolution of environments of the planets. In this study,
we carried out hydrothermal alteration experiments to elucidate the
soil formation processes on the Martian surface. Major rock of the
Martian crust is iron-rich basaltic rock, and subject to sulfuric
acid-bearing hydrothermal alteration. The experiments are carried out
on the starting material of the simulated Martian basalt with H2SO4
solution in hydrothermal conditions. Experimental temperatures and
pressures are 100 ~ 300°C, water vapor pressure, and 400 ~ 500°C,
100 MPa. Acidity of the solution and fluid-rock ratio are pH1.5 or
3.0, and 50:1 or 10:1 (100 ~ 150°C), 10:1 or 2:1 (200 ~ 500°C). Run
durations are 1 or 4 weeks. Composition of the starting material is
referred to the average Martian surface composition analyzed by Mars
Pathfinder probe. The starting material is prepared from a basaltic
rock, iron rich dunite and peridotite. In the run products, olivine
grains reacted with low pH fluid at low temperature condition including
100 ~ 150°C. Characteristic phases in the run products are hematite
and clay minerals. Hematite occurs in products at 100 ~ 150°C and
400 ~ 500°C. More hematite grains occur in products with pH1.5 and
larger fluid-rock ratio. Morphology of the hematite is granular to
spheroidal with diameters of 0.5 to 3 micron meters in products at 100
and 150°C. Hematite in products at 400 ~ 500° is euhedral crystals
with the diameter of 5 to 20 micron meters. Clay minerals with Fe-rich
rim substituted olivine crystals were formed under low pH and over
300°C. Hydrothermal alteration of mafic minerals including olivine
with sulfuric acid-bearing fluid occurs efficiently at lower pH and
higher fluid-rock ratio. The characteristic products of this alteration
are hematite and clay minerals. Acidic hydrothermal alteration may have
essential role to form the Martian soil rich in iron oxide. Especially,
morphology of hematite is strongly depends on temperatures of the
hydrothermal alteration. Direct observation of the Martian soil may
provide us information on the conditions of hydrothermal alteration
which occurred on the Martian surface.
Title: Intermittent Emission of High-Frequency Waves by Magnetic
Reconnection Between Canopy Field and Small-Scale Horizontal Field
Authors: Isobe, H.
Bibcode: 2007AGUFMSH34A..07I
Altcode:
The energy source of coronal heating and solar wind acceleration
is the interaction of magnetic field and thermal convection in
the photosphere. Magnetoconvection has complicated bifurcation
structure, and the mode, spectra and power of the waves generated
in the photosphere depend on the nature of magnetoconvection
in the photosphere. In order to study the relation between
magnetoconvection and coronal heating/solar wind acceleration,
we performed three-dimensional magnetohydrodynamic simulation of a
domain that includes from upper convection zone to the corona. We
first ran the simulation without magnetic field until convection
developed to quasi-steady state, and then imposed a vertical and
uniform magnetic field. We found that, in addition to the well-known
fact that vertical magnetic field is swept into the downflow region,
small scale horizontal fields as strong as 800G intermittently emerge
in the photosphere. Even though the initial magnetic field is vertical
and uniform, magnetic field in the convection zone become turbulent, and
occasionally a bundle of strong magnetic flux is driven by the upward
convection flow and emerges in the photosphere. Such horizontal fields
undergo magnetic reconnection with pre-existing magnetic field in the
chromosphere (so called "canopy" field), and then emit high-frequency
(>0.05mHz) waves into the corona. We discuss the possible role of
these processes in heating, acceleration and turbulence of the corona
and the solar wind.
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: Flare Ribbons Observed with G-band and FeI 6302Å, Filters
of the Solar Optical Telescope on Board Hinode
Authors: Isobe, Hiroaki; Kubo, Masahito; Minoshima, Takashi; Ichimoto,
Kiyoshi; Katsukawa, Yukio; Tarbell, Theodore D.; Tsuneta, Saku; Berger,
Thomas E.; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi; Shine,
Richard A.; Suematsu, Yoshinori; Title, Alan M.
Bibcode: 2007PASJ...59S.807I
Altcode: 2007arXiv0711.3946I
The Solar Optical Telescope (SOT) on board the Hinode satellite observed
an X3.4 class flare on 2006 December 13. A typical two-ribbon structure
was observed, not only in the chromospheric CaII H line, but also in
the G-band and FeI 6302Å line. The high-resolution, seeing-free images
achieved by SOT revealed, for the first time, sub-arcsec fine structures
of the ``white light'' flare. The G-band flare ribbons on sunspot
umbrae showed a sharp leading edge, followed by a diffuse inside,
as well as a previously known core-halo structure. The underlying
structures, such as umbral dots, penumbral filaments, and granules,
were visible in the flare ribbons. Assuming that the sharp leading
edge was directly heated by a particle beam and the diffuse parts were
heated by radiative back-warming, we estimated the depth of the diffuse
flare emission using an intensity profile of the flare ribbon. We found
that the depth of the diffuse emission was about 100km or less from
the height of the source of radiative back-warming. The flare ribbons
were also visible in the Stokes-V images of FeI 6302Å, as a transient
polarity reversal. This is probably related to a ``magnetic transient''
reported in the literature. The intensity increase in Stokes-I images
indicates that the FeI 6302Å line was significantly deformed by the
flare, which may cause such a magnetic transient.
Title: Magnetohydrodynamic Numerical Simulations of Emerging Flux
Tube for studying Effects of Twist Intensity
Authors: Miyagosh, T.; Isobe, H.; Yokoyama, T.; Shibata, K.
Bibcode: 2007ASPC..369..377M
Altcode:
We present results from numerical MHD simulations of the emergence
of twisted magnetic flux tubes from below the photosphere into the
corona. The aim is to study the influence of the field line twist on the
emergence process. In almost all previous studies of the emergence of
flux tubes, very strong twist (more than one rotation around the buoyant
region of the initial tube) was imposed. Observations of flux emergence,
however, suggest that flux tubes emerging into the solar atmosphere
carry lesser twist. By varying the amount of twist in the initial tube,
we have carried out a parameter study with particular emphasis on the
weakly twisted regime. We found the followings. (1) In weak twist
case, tube fragments once around the photosphere, and emerging motion is
rapidly suppressed. Then the tube expands to horizontal direction. As
time goes on, emergence starts again. (2) In weak twist case, at the
photosphere the magnetic tension force, which keeps tube coherent,
is weak so it expands more largely than strong twist case. So magnetic
fields strength in flux tube is weaker than that of strong twist case
because it expands more largely. As a result of this, buoyancy force
becomes weak and emerging motion is rapidly decelerated. Then expansion
to the horizontal direction drastically occurs.
Title: Three-Dimensional MHD Simulations of Emerging Flux and
Associated Magnetic Reconnection
Authors: Isobe, H.; Miyagoshi, T.; Shibata, K.; Yokoyama, T.
Bibcode: 2007ASPC..369..355I
Altcode:
We present the results of high-resolution three-dimensional MHD
simulations of an emerging flux region. The high-resolution simulations
that have been enabled by the develpment of high-performance computers
have successfully simulated the evolution of fine structure in the
global three-dimension dynamics of the emerging flux and magnetic
reconnection. It has been found that (1) filamentary structure similar
to an arch filament system is spontaneously formed in the emerging
flux due to the magnetic Rayleigh-Taylor instability, (2) filamentary
current sheets are formed in the emerging flux as a result of the
nonlinear development of the magnetic Rayleigh-Taylor instability,
and (3) magnetic reconnection between the emerging flux and the
coronal field occurs in spatially intermittent way, because of the
interchanging of the current sheet due to the magnetic Rayleigh-Taylor
instability. Possible observational signatures expected from Solar-B
are discussed.
Title: XRT and EIS Observations of Reconnection Associated Phenomena
Authors: Shiota, D.; Isobe, H.; Brooks, D. H.; Chen, P. -F.;
Shibata, K.
Bibcode: 2007ASPC..369..439S
Altcode:
Based on the results of numerical simulations, we sythesized EIS and
XRT images of reconnection flows associated with an eruptive flare. The
results suggest that reconnection inflows can be observed as pairs of
blue- and red-shifted components just above the X-ray arcade in the
low temperature lines. It is found that the Doppler velocities are
larger in the lower temperature line spectra. Reconnection outflows
can also be observed as pairs of blue- and red-shifted components with
an asymmetry in the high temperature line spectra.
Title: Three-Dimensional Filament Eruption Driven by an Emerging Flux
Authors: Notoya, S.; Yokoyama, T.; Kusano, K.; Sakurai, T.; Miyagoshi,
T.; Isobe, H.; Yamamoto, T.
Bibcode: 2007ASPC..369..381N
Altcode:
Some important observations have shown that the strong correlation
between emerging flux and eruptions of quiescent filaments
tep{notoya:Feynman, notoya:Wang}. tet{notoya:Chen} performed
two-dimensional simulations including a flux rope in the corona, and
their results suggest that the eruption process is triggered by the
emerging flux through the reconnection. Our purpose in this paper is
to investigate that ``how a filament is produced and how an eruption
process can be initiated by the emerging flux and what effects of
three-dimensionality appear in the process of eruption". For that
purpose, we performed three-dimensional numerical simulations of the
emerging flux model. From our results, a filamentary structure is
produced from the coronal arcade field by the reconnection process,
and when the reconnection process proceeds effectively, the produced
structure is ejected by the magnetic force. These processes can thought
to be a new mechanism of the eruption which is different from, for
example, the one in tet{notoya:Fan}.
Title: Triggering Mechanism for the Filament Eruption on 2005
September 13 in NOAA Active Region 10808
Authors: Nagashima, Kaori; Isobe, Hiroaki; Yokoyama, Takaaki; Ishii,
Takako T.; Okamoto, Takenori J.; Shibata, Kazunari
Bibcode: 2007ApJ...668..533N
Altcode: 2007arXiv0706.3519N
On 2005 September 13 a filament eruption accompanied by a halo coronal
mass ejection (CME) occurred in the most flare-productive active region,
NOAA 10808, in solar cycle 23. Using multiwavelength observations
before the filament eruption on September 13, we investigate the
processes leading to the catastrophic eruption. We find that the
filament slowly ascended at a speed of 0.1 km s-1 over 2
days before the eruption. During slow ascension, many small flares were
observed close to the footpoints of the filament, where new magnetic
elements were emerging. On the basis of the observational facts, we
discuss the triggering mechanism leading to the filament eruption. We
suggest that the process toward the eruption is as follows. First,
a series of small flares played a role in changing the topology of
the loops overlying the filament. Second, the small flares gradually
changed the equilibrium state of the filament and caused the filament
to ascend slowly over 2 days. Finally, a C2.9 flare that occurred when
the filament was close to the critical point for loss of equilibrium
directly led to the catastrophic filament eruption right after it.
Title: Ellerman Bombs and Jets Associated with Resistive Flux
Emergence
Authors: Isobe, H.; Tripathi, D.; Archontis, V.
Bibcode: 2007ApJ...657L..53I
Altcode:
Using two-dimensional (2D) magnetohydrodynamic simulations we study
the effects of resistive processes in the dynamics of magnetic
flux emergence and its relation to Ellerman bombs and other dynamic
phenomena in the Sun. The widely accepted scenario of flux emergence
is the formation and expansion of Ω-shaped loops due to the Parker
instability. Since the Parker instability has the largest growth rate at
finite wavelength λp~10H-20H, where H is the scale height
(~200 km in the solar photosphere), a number of magnetic loops may
rise from the initial flux sheet if it is sufficiently long. This
process is shown in our numerical simulations. The multiple emerging
loops expand in the atmosphere and interact with each other, leading
to magnetic reconnection. At first reconnection occurs in the lower
atmosphere, which allows the sinking part of the flux sheet to emerge
above the photosphere. This reconnection also causes local heating
that may account for Ellerman bombs. In the later stage, reconnection
between the expanding loops occurs at higher levels of the atmosphere
and creates high-temperature reconnection jets, and eventually a large
(>>λp) coronal loop is formed. Cool and dense plasma
structures, which are similar to Hα surges, are also formed. This
is not because of magnetic reconnection but due to the compression of
the plasma in between the expanding loops.
Title: Magnetohydrodynamic Numerical Simulations of Emerging Flux
and Associated Active Phenomena in the Solar Atmosphere
Authors: Miyagoshi, T.; Isobe, H.; Yokoyama, T.; Shibata, K.
Bibcode: 2006ASPC..359..164M
Altcode:
It is suggested that emerging flux build up magnetic energy in the
solar corona that could become the source of flares or jets. Emerging
flux also plays an important role in active region formation and
disappearance. To investigate these phenomena, it is necessary
to study the evolution of an emerging flux from the convection
zone to the corona. The solar atmosphere is highly stratified by
gravity. For example, the density ratio between photosphere and
corona is about ∼ 10^8. However, to study emerging flux process by
numerical simulations, it is needed to treat this process with that
highly stratified calculation domain. In this paper, we introduce
our numerical simulation results for (1) X-ray jets associated with
emerging flux and magnetic reconnection in the solar corona, (2)
twisted magnetic flux tube emergence into the solar corona, and (3)
surge caused by emerging flux tube.
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: 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: On the propagation of brightening after filament/prominence
eruptions, as seen by SoHO-EIT
Authors: Tripathi, D.; Isobe, H.; Mason, H. E.
Bibcode: 2006A&A...453.1111T
Altcode:
Aims.To study the relationship between the propagation of brightening
and erupting filaments/prominences in order to get some insight into
the three-dimensional picture of magnetic reconnection.
Methods:
.Analysis of the observations taken with the EIT (Extreme-ultraviolet
Imaging Telescope) aboard SoHO (Solar and Heliospheric Observatory).
Results: .When the prominences/filaments erupted having one point
fixed - asymmetric eruption - the brightening propagated along the
neutral line together with the expansion/separation from the polarity
inversion line (PIL) as expected from the standard models. However
in case of symmetric eruptions, the brightening propagated towards
both end points starting at the middle. When the prominence/filament
erupted faster then the speed of the propagating brightening was
faster and vice-versa.
Conclusions: .Based on these observations
we conclude that the eruption and magnetic reconnection - propagation
(along the PIL) and separation (away from PIL) of the brightening - are
dynamically coupled phenomena. These observations can be explained by
a simple extension of the 2D models illustrating eruption and magnetic
reconnection to a 3D model.
Title: Large amplitude oscillation of a polar crown filament in the
pre-eruption phase
Authors: Isobe, H.; Tripathi, D.
Bibcode: 2006A&A...449L..17I
Altcode: 2006astro.ph..2432I
Aims.We report observation of a large-amplitude filament oscillation
followed by an eruption. This is used to probe the pre-eruption
condition and the trigger mechanism of solar eruptions.Methods.We used
the EUV images from the Extreme-Ultraviolet Imaging Telescope on board
SOHO satellite and the Hα images from the Flare Monitoring Telescope
at Hida Observatory. The observed event is a polar crown filament
that erupted on 15 Oct. 2002.Results.The filament clearly exhibited
oscillatory motion in the slow-rising, pre-eruption phase. The amplitude
of the oscillation was larger than 20 km s-1, and the motion
was predominantly horizontal. The period was about 2 h and seemed to
increase during the oscillation, indicating weakening of restoring
force.Conclusions.Even in the slow-rise phase before the eruption,
the filament retained equilibrium and behaved as an oscillator, and
the equilibrium is stable to nonlinear perturbation. The transition
from such nonlinear stability to either instabilities or a loss of
equilibrium that leads to the eruption occurred in the Alfvén time
scale (~1 h). This suggests that the onset of the eruption was triggered
by a fast magnetic reconnection that destabilized the pre-eruption
magnetic configuration, rather than by the slow shearing motion at
the photosphere.
Title: Three-Dimensional Simulation of Solar Emerging Flux Using
the Earth Simulator I. Magnetic Rayleigh-Taylor Instability at the
Top of the Emerging Flux as the Origin of Filamentary Structure
Authors: Isobe, Hiroaki; Miyagoshi, Takehiro; Shibata, Kazunari;
Yokoyama, Takaaki
Bibcode: 2006PASJ...58..423I
Altcode:
We present the results of three-dimensional magnetohydrodynamic
simulations of solar emerging flux and its interaction with preexisting
coronal field. In order to resolve the fine structures and the current
sheets, we used high-resolution grids with up to 800×400×620 points;
the calculation was carried out using the Earth Simulator. The model
set up is an extension of a previous two-dimensional simulation by
Yokoyama and Shibata (1995) to include the variation along the third
direction. Based on the same simulation result, we reported in our
previous paper (Isobe et al. 2005): (1) Dense filaments similar to Hα
arch filament system are spontaneously formed in the emerging flux
by the magnetic Rayleigh-Taylor type instability. (2) Filamentary
current sheets are created in the emerging flux due to a nonlinear
development of the magnetic Rayleigh-Taylor instability, which may
cause an intermittent, nonuiform heating of the corona. (3) A magnetic
reconnection between the emerging flux and preexisting coronal field
occurs in a spatially intermittent way. In this paper we describe
the simulation model and discuss the origin and the properties of the
magnetic Rayleigh-Taylor instability in detail. It is shown that the
top-heavy configuration that causes the instability is formed by the
intrinsic dynamics of the emerging flux.
Title: Large-Scale magnetohydrodynamic simulation of solar emerging
flux using the Earth Simulator
Authors: Isobe, Hiroaki
Bibcode: 2006AstHe..99...66I
Altcode:
We present the results of three-dimensional MHD simulation of solar
emerging flux. The simulation was carried out on the Earth Simulator
with high resolution. We found that filamentary structure spontaneously
arose in the emerging flux due to the magnetic Rayleigh-Taylor
instability. Furthermore, filamentary current sheets were formed in the
emerging flux, and magnetic reconnection occurred between the emerging
flux and the pre-existing coronal field in a spatially intermittent
way. These naturally explain the intermittent nature of coronal heating
and the origin of fine structure in flares and jets.
Title: Self-consistent MHD modeling of a coronal mass ejection,
coronal dimming, and a giant cusp-shaped arcade formation
Authors: Shiota, D.; Isobe, H.; Chen, P. F.; Yamamoto, T. T.; Sakajiri,
T.; Shibata, K.
Bibcode: 2006cosp...36.1994S
Altcode: 2006cosp.meet.1994S
Coronal mass ejections CMEs are one of the most spectacular phenomena in
the solar corona Recent observations revealed that CMEs are associated
with either solar flares or giant arcade formations in which magnetic
reconnection is thought to play an essential role Considering these
observations Shibata 1996 1999 suggest that CMEs filament eruptions
flares giant arcades can be understood in a unified view mass ejection
and magnetic energy release via magnetic reconnection We performed
magnetohydrodynamic simulations of CMEs and associated giant arcade
formations The soft X-ray images synthesized from the numerical
results are compared with the soft X-ray images taken with the Soft
X-Ray Telescope aboard Yohkoh The comparison between synthesized and
observed soft X-ray images provides new interpretations of various
features associated with CMEs and giant arcades 1 It is likely that
the Y-shaped ejecting structure observed in the giant arcade on 1992
January 24 corresponds to slow and fast shocks associated with magnetic
reconnection 2 Soft X-ray twin dimming corresponds to the rarefaction
induced by reconnection 3 The inner boundary of the dimming region
corresponds to the slow shocks 4 The three-part structure of a CME
can be explained by our numerical results 5 The numerical results
also suggest that a backbone feature of a flare giant arcade may
correspond to the fast shock formed by the collision of the downward
reconnection outflow
Title: Reproducing Experiment in the Shock-Induced Removal of CO2
From the Atmosphere on the Early Mars
Authors: Ikeda, K.; Isobe, H.
Bibcode: 2005AGUFM.P51A0911I
Altcode:
The evolution of the Mars is one of the most important problems on
the environmental issues of terrestrial planets. The early Martian
atmosphere was formed by degassing and it consisted thick CO2. Most of
the CO2 must have been removed from the early Martian atmosphere in
order to change to the present thin atmosphere. Heavy bombardment of
planetesimals had been one of the important high energy processes on the
primitive Mars. In this study, we experiment to reproduce the reaction
between the early Martian atmosphere and the minerals in the high
temperature condition caused by the shock-induced heating and discuss
its effect of CO2 removal from the atmosphere. Reaction experiments
were carried out with CO2 or CO2- H2O fluid at the pressure of 100MPa
or 50MPa. A range of the temperature is 200-650°C and run duration is
7 days. Starting materials was the mixture of olivine, orthopyroxene,
diopside, and plagioclase represented the main mineral phases of the
early Mars. After the experiment, the reacted CO2 was weighed by CO2
mass remained in the experimental capsule. CO2 reactivity increased with
decreasing temperature. If removed CO2 fixed as carbonate minerals in
the run products, abundance of the carbonate minerals may be as much as
10% of the run products. Presence of H2O has no remarkable effect on
CO2 reactivity. A Martian meteorite, ALH84001 includes approximately
1% of carbonate. Large-scale impact on the Martian surface brought
shock-induced heating up to several hundred degrees C at several
kilometers in depth. Accessory carbonate minerals in Martian rocks may
be formed by reactions of CO2 atmosphere and brecciated rocks under
craters. A layer of 1% carbonate-bearing rocks with 5km in thickness
at Martian surface can settle 0.5MPa of CO2 (1MPa equivalent at the
terrestrial gravity) from the Martian atmosphere. Carbonate formation
by the shock-induced heating may have played a significant role in
the evolution of the primitive Martian atmosphere.
Title: Self-Consistent Magnetohydrodynamic Modeling of a Coronal Mass
Ejection, Coronal Dimming, and a Giant Cusp-shaped Arcade Formation
Authors: Shiota, Daikou; Isobe, Hiroaki; Chen, P. F.; Yamamoto,
Tetsuya T.; Sakajiri, Takuma; Shibata, Kazunari
Bibcode: 2005ApJ...634..663S
Altcode: 2005astro.ph..8478S
We performed magnetohydrodynamic simulations of coronal mass ejections
(CMEs) and associated giant arcade formations, and the results suggest
new interpretations of observations of CMEs. We performed two cases of
the simulation: with and without heat conduction. Comparing between
the results of the two cases, we found that the reconnection rate
in the conductive case is a little higher than that in the adiabatic
case and that the temperature of the loop top is consistent with the
theoretical value predicted by the Yokoyama-Shibata scaling law. The
dynamical properties such as velocity and magnetic field are similar
in the two cases, whereas thermal properties such as temperature and
density are very different. In both cases, slow shocks associated
with magnetic reconnection propagate from the reconnection region
along the magnetic field lines around the flux rope, and the shock
fronts form spiral patterns. Just outside the slow shocks, the plasma
density decreases greatly. The soft X-ray images synthesized from
the numerical results are compared with the soft X-ray images of a
giant arcade observed with the Soft X-Ray Telescope aboard Yohkoh;
it is confirmed that the effect of heat conduction is significant
for the detailed comparison between simulation and observation. The
comparison between synthesized and observed soft X-ray images provides
new interpretations of various features associated with CMEs and
giant arcades. (1) It is likely that the Y-shaped ejecting structure,
observed in the giant arcade on 1992 January 24, corresponds to slow and
fast shocks associated with magnetic reconnection. (2) Soft X-ray twin
dimming corresponds to the rarefaction induced by reconnection. (3)
The inner boundary of the dimming region corresponds to the slow
shocks. (4) The ``three-part structure'' of a CME can be explained by
our numerical results. (5) The numerical results also suggest that a
backbone feature of a flare/giant arcade may correspond to the fast
shock formed by the collision of the downward reconnection outflow.
Title: Formation and Dynamics of Current Sheets
Authors: Isobe, H.
Bibcode: 2005ESASP.596E..24I
Altcode: 2005ccmf.confE..24I
No abstract at ADS
Title: Measurement of the Energy Release Rate and the Reconnection
Rate in Solar Flares
Authors: Isobe, Hiroaki; Takasaki, Hiroyuki; Shibata, Kazunari
Bibcode: 2005ApJ...632.1184I
Altcode: 2005astro.ph..7327I
By using the method presented by Isobe et al., the nondimensional
reconnection rate vin/vA has been determined for
the impulsive phase of three two-ribbon flares, where vin is
the velocity of the reconnection inflow and vA is the Alfvén
velocity. The nondimensional reconnection rate is important to make
a constraint on the theoretical models of magnetic reconnection. In
order to reduce the uncertainty of the reconnection rate, it is
important to determine the energy release rate of the flares from
observational data as accurately as possible. To this end, we have
carried out one-dimensional hydrodynamic simulations of a flare loop
and synthesized the count rate detected by the Soft X-Ray Telescope
(SXT) aboard the Yohkoh satellite. We found that the time derivative
of the thermal energy contents in a flare arcade derived from SXT data
is smaller than the real energy release rate by a factor of 0.3-0.8,
depending on the loop length and the energy release rate. The results
of the simulations are presented in the paper and used to calculate
the reconnection rate. We found that the reconnection rate is 0.047
for the X2.3 flare on 2000 November 24, 0.015 for the M3.7 flare on
2000 July 14, and 0.071 for the C8.9 flare on 2000 November 16. These
values are similar to that derived from the direct observation of the
reconnection inflow by Yokoyama et al. and consistent with the fast
reconnection models such as that of Petschek.
Title: Filamentary structure on the Sun from the magnetic
Rayleigh-Taylor instability
Authors: Isobe, Hiroaki; Miyagoshi, Takehiro; Shibata, Kazunari;
Yokoyama, Takaaki
Bibcode: 2005Natur.434..478I
Altcode:
Magnetic flux emerges from the solar surface as dark filaments
connecting small sunspots with opposite polarities. The regions around
the dark filaments are often bright in X-rays and are associated
with jets. This implies plasma heating and acceleration, which are
important for coronal heating. Previous two-dimensional simulations
of such regions showed that magnetic reconnection between the coronal
magnetic field and the emerging flux produced X-ray jets and flares,
but left unresolved the origin of filamentary structure and the
intermittent nature of the heating. Here we report three-dimensional
simulations of emerging flux showing that the filamentary structure
arises spontaneously from the magnetic Rayleigh-Taylor instability,
contrary to the previous view that the dark filaments are isolated
bundles of magnetic field that rise from the photosphere carrying the
dense gas. As a result of the magnetic Rayleigh-Taylor instability,
thin current sheets are formed in the emerging flux, and magnetic
reconnection occurs between emerging flux and the pre-existing coronal
field in a spatially intermittent way. This explains naturally the
intermittent nature of coronal heating and the patchy brightenings in
solar flares.
Title: Spectroscopic Detection of Magnetic Reconnection Evidence in
the Solar Atmosphere with SolarB/EIS
Authors: Brooks, D. H.; Isobe, H.; Shibata, K.; Chen, P. F.; Lanzafame,
A. C.
Bibcode: 2004ASPC..325..367B
Altcode:
2.5D MHD simulations of CMEs and flares are combined with improved
accuracy density sensitive line emission contribution functions from
the ADAS database to study profiles of spectral lines which will fall
within the wavelength range of the SolarB Extreme ultraviolet Imaging
Spectrometer (EIS). The objective is to study the signatures of magnetic
reconnection associated flow phenomena in the line profiles and provide
a set of recommended lines for EIS observations planning. Here, we
illustrate our methods by considering the profile of the well-known
Ion{Fe{XII}} 195 AA line and its ability to detect reconnection
inflows. We also discuss the effects of altering simulation parameters
such as electron temperature and the inclusion of the effect of heat
conduction. The table of recommended lines following these methods is
being prepared and will be presented in a separate paper.
Title: Simulated XRT and EIS Observations of Magnetic Reconnection
in Coronal Mass Ejection and X-Ray Arcade
Authors: Shiota, D.; Isobe, H.; Brooks, D. H.; Shibata, K.; Chen, P. F.
Bibcode: 2004ASPC..325..373S
Altcode:
We perform a numerical simulation of a coronal mass ejection and an
associated X-ray arcade. Based on the numerical results, we synthesize
theoretical images taken with XRT and EIS aboard SolarB, and discuss
how reconnection inflow and slow shocks would be observed with XRT
and EIS. The mechanism of dimming is also discussed.
Title: Evolution of High Temperature Early Atmosphere Under the
Interaction of H2O-CO2 Super-critical Fluid
With Minerals
Authors: Isobe, H.; Tomita, T.; Ikeda, K.
Bibcode: 2004AGUFM.V43C1439I
Altcode:
The evolution of atmosphere-lithosphere system of the early Earth is
controlled by mutual interaction of high temperature atmosphere with
rocks and minerals. It is assumed that the total pressure of the early
atmosphere and the surface temperature above initial magma ocean are
26MPa (H2O 20MPa, CO2 6MPa) and 130-330° C,
respectively. This composition, temperature and pressure are very close
to an azeotropic critical point of the H2O-CO2
system. Cooling of the hot H2O-CO2 atmosphere
brings the first precipitation of liquid phase at above 300° C. During
the early period, hot rain of the Earth should be a supercritical
acid rain. Cooling rate of the hot atmosphere is regulated by energy
transportation capacity among the surface, atmosphere and radiation
of the early Earth. In this study, we discuss evolution of the
early atmosphere-lithosphere system based on the results of the
alteration experiments of minerals simulated early crust with the
H2O-CO2 fluid and the cooling rate estimation
of the high temperature atmosphere. The H2O-CO2
fluid easily reacts with silicate minerals at around critical point
of the fluid to produce carbonate and hydrous minerals. Consumption of
CO2 increases up to approximately 80% at around 250° C for
olivine starting material. This means that most of Mg and Fe in the
olivine starting material react with CO2. The Formation of
carbonate minerals reduces the CO2 composition of fluid in
the capsule to approximately one fifth. The fixation of CO2
by carbonate formation should be very effective to reduce CO2
pressure from the early atmosphere in cooling through 250° C. The
first sediment of the primitive ocean should contain dolomite and
hydrous silicate. The CO2 and H2O fixed in the
first sediment should take an important role in the evolution of the
early crust. Composition of the early atmosphere, or partial pressures
of CO2 and H2O and temperature gradient of
the atmosphere are essential factors controlling cooling history of
the high temperature early atmosphere. We discuss evolution of the
early atmosphere including effects of precipitation of super-critical
H2O-CO2 fluid and atmosphere-rock interaction.
Title: Three-Dimensional MHD Simulation of Convection and Emerging
Flux
Authors: Isobe, H.; Shibata, K.
Bibcode: 2004ASPC..325...63I
Altcode:
We present results of three dimensional magnetohydrodynamic simulation
of convection and emerging flux. Although simulations of emerging flux
tube have been presented in the literature, effect of convection on the
dynamics of emerging flux has not been studied in detail. We carried out
simulation of emergence of twisted flux tube from vigorously convecting
convection zone. It is found that the flux tube emerges to the upper
atmosphere and forms loop like structures, but finally it is broken
by the convecting flows and loses its coherence in several turnover
time of convection.
Title: Jet Phenomena in the Solar Atmosphere caused by Interaction
between Emerging Flux and Coronal Fields
Authors: Miyagoshi, T.; Yokoyama, T.; Isobe, H.; Shibata, K.
Bibcode: 2004ASPC..325...69M
Altcode:
We have studied jet phenomena in the solar atmosphere with MHD numerical
simulations. Emerging flux could interact coronal magnetic fields
through magnetic reconnection. Then, magnetic energy is released and
magnetic topology drastically changes. Our numerical simulation results
show that coronal jets are produced through this process.
Title: A Study of a Tiny Two-Ribbon Flare Driven by Emerging Flux
Authors: Sakajiri, Takuma; Brooks, David H.; Yamamoto, Tetsuya;
Shiota, Daikou; Isobe, Hiroaki; Akiyama, Sachiko; Ueno, Satoru; Kitai,
Reizaburo; Shibata, Kazunari
Bibcode: 2004ApJ...616..578S
Altcode:
We present observations of the eruption of a miniature filament that
occurred near NOAA Active Region 9537 on 2001 July 14. The eruption was
observed by the Hida Observatory Domeless Solar Telescope, in the Hα
line center and +/-0.4 Å wings, the Solar and Heliospheric Observatory
EUV Imaging Telescope (EIT) and Michelson Doppler Imager, and the Yohkoh
Soft X-Ray Telescope (SXT). The miniature filament began to form and
was clearly visible in Hα images by around 06:50 UT. It erupted about
25 minutes later, accompanied by a small two-ribbon subflare (with
an area of 61 arcsec2). The two ribbons were also found to
approach each other at a speed of 3.33 km s-1. We found that
this event was caused by the emergence of new magnetic flux in a quiet
region. The emerging flux appeared as a bright region in the EIT and
SXT images taken on the previous day. It moved southward into an area
of preexisting opposite-polarity flux, where a cancelling magnetic
flux region was formed. The miniature filament then appeared, and we
suggest that it played some role in inhibiting the release of energy
by delaying reconnection between the emerging and preexisting flux, as
evidenced by the disappearance of the bright region between opposite
polarities in the EUV and soft X-ray images. Consequently, magnetic
energy was stored as a result of the slow converging motion of the two
opposite-polarity flux regions (0.17 km s-1). Reconnection
below the filament provoked the filament eruption, and the two-ribbon
flare occurred. Miniature filaments are thought to be small-scale
analogs of large-scale filaments. Our observations also suggest some
common properties between small-scale and large-scale flares. These
results support the view that a unified magnetic reconnection model
may be able to explain all scales of flares.
Title: A Reexamination of the Evidence for Reconnection Inflow
Authors: Chen, P. F.; Shibata, K.; Brooks, D. H.; Isobe, H.
Bibcode: 2004ApJ...602L..61C
Altcode:
In the flare event of 1999 March 18, a threadlike structure observed
in EUV Imaging Telescope images was found to move inward and collapse
to an X-shaped configuration below the ejecta, strongly suggestive
of the occurrence of magnetic reconnection. On the basis of the
numerical results of a coronal mass ejection (CME) flare model, a
similar threadlike structure in the Fe XII 195 Å image is reproduced
in this Letter. It is found that, as in the observations, the thread
experiences an outward motion in the preflare phase, which is followed
by an inward motion. Our simulation suggests that its formation and
outward motion in the preflare phase result from the CME expansion;
after the onset of the flare, the threadlike structure is always
located on the upstream side of the interface between the reconnection
inflow and outflow. Its apparent inward motion, which is several times
slower than the in situ reconnection inflow, is mainly attributed to
the rising motion of the reconnection X-point.
Title: Hydrodynamic Modeling of a Flare Loop Connecting the Accretion
Disk and Central Core of Young Stellar Objects
Authors: Isobe, Hiroaki; Shibata, Kazunari; Yokoyama, Takaaki;
Imanishi, Kensuke
Bibcode: 2003PASJ...55..967I
Altcode:
Many young stellar objects, such as protostars and T-Tauri stars,
show strong flare activity. In this paper we present a hydrodynamic
simulation of a flare loop that connects the central star and the
accretion disk, and discuss the evaporation of the chromosphere of the
central star and the disk. We assumed a long ( > 10 Rodot)
loop length, and that the flare energy is deposited near the half-way
point between the disk and the stellar surface. We found that in some
cases all of the plasma in the accretion disk is heated to the flare
temperature and spreads over the flare loop. The condition for this
``disk disappearance'' was examined. The X-ray spectrum expected when we
observe the simulation result was synthesized by taking into account the
instrumental response of ASCA/GIS. However, we could not find any clear
observational signature of the existence of the disk, because the bulk
properties of a flare loop are determined by the flare heating flux
and loop length, and not by the involvement of the disk. We found that
the synthesized spectrum is reasonably fitted with a two-temperature
model, and that the temperature of the hotter component is several
factors lower than the maximum temperature of the simulation result.
Title: Diffusion and dissociation behavior of H2O and OH
species in a volcanic glass at super-critical conditions
Authors: Isobe, H.; Nishida, Y.
Bibcode: 2003GeCAS..67R.176I
Altcode:
No abstract at ADS
Title: Erratum: ``Analysis of the Temperature and Emission Measure of
Solar Coronal Arcades and Test of a Scaling Law of Flare/Arcade Loop
Length'' (ApJ, 579, L45 [2002])
Authors: Yamamoto, Tetsuya T.; Shiota, Daikou; Sakajiri, Takuma;
Akiyama, Sachiko; Isobe, Hiroaki; Shibata, Kazunari
Bibcode: 2003ApJ...592L.107Y
Altcode:
Recently, we found an error in our analysis program and have
reanalyzed data. As a result, Table 1 and the right panel of
Figure 3 were altered in the above Letter. The figure shows a
slight change, but our conclusion is not affected. However,
typical values changed to n0=2×108
cm-3, B=5.6 G, narc=4×108
cm-3, EMarc=3.2×1047
cm-3, and β~=0.3, and equation (6)
becameLtheor~=1010(EM3.2×1047
cm-3)3/5(n02×108
cm-3)-2/5(T3.7×106
K)-8/5cm.(6)
Title: Magnetohydrodynamic Numerical Simulations of Coronal Mass
Ejections and Associated Giant Arcades
Authors: Shiota, D.; Shibata, K.; Isobe, H.; Brooks, D. H.; Chen, P. F.
Bibcode: 2003ICRC....6.3379S
Altcode: 2003ICRC...28.3379S
By extending the Chen-Shibata [1] model of coronal mass ejections
(CMEs), we develop physical model of CMEs and associated giant
arcades just below CMEs in two and half dimension, incorporating heat
conduction. On the basis of the simulation results, the theoretical
soft X-ray images are calculated and compared with observations of
CMEs and giant arcades with Yohkoh/SXT (soft X-ray telescope). Detailed
comparison between simulated X-ray images and observations revealed that
(1) the Y-shaped ejection features, often seen at the bottom of some
CMEs, might corresp ond to slow and fast mode MHD shocks associated with
reconnection [3], (2) the dimming, often observed both sides of arcades,
can be produced at least partly by reconnection inflow, (3) the back
bone like bright soft X-ray features seen at the top of some arcades
might corresp ond to fast mode MHD shocks just below reconnection jet.
Title: Slow and Fast MHD Shocks Associated with a Giant Cusp-Shaped
Arcade on 1992 January 24
Authors: Shiota, Daikou; Yamamoto, Tetsuya T.; Sakajiri, Takuma;
Isobe, Hiroaki; Chen, Peng-Fei; Shibata, Kazunari
Bibcode: 2003PASJ...55L..35S
Altcode:
We performed magnetohydrodynamic (MHD) simulations of a giant arcade
formation with a model of magnetic reconnection coupled with heat
conduction, to investigate the dynamical structure of slow and fast MHD
shocks associated with reconnection. Based on the numerical results,
theoretical soft X-ray images were calculated and compared with the
Yohkoh soft X-ray observations of a giant arcade on 1992 January 24. The
Y-shaped structure observed in the event was identified to correspond
to the slow and fast shocks associated with the magnetic reconnection.
Title: ``Dawn-dusk asymmetry'' in solar coronal arcade formations
Authors: Isobe, Hiroaki; Shibata, Kazunari; Machida, Shinobu
Bibcode: 2002GeoRL..29.2014I
Altcode: 2002GeoRL..29u..10I
Solar flares/arcades and magnetospheric substorms are believed
to have a common physical process: energy release via magnetic
reconnection. In substorms, it is known that the reconnection point
tends to occur more in the dusk side of the magnetotail than in the
dawn side. This asymmetry is called the dawn-dusk asymmetry. However,
no one has examined so far the existence of such asymmetry in the
solar corona. We investigated the directions of arcade formation and
-vin × B electric field for 32 events, and found that more
arcades successively formed in the direction of the electric field than
in the opposite direction. This may be a solar analogue of dawn-dusk
asymmetry. We also found that velocity of successive formation of
arcades increases with the aspect ratio of the arcade.
Title: Analysis of the Temperature and Emission Measure of Solar
Coronal Arcades and Test of a Scaling Law of Flare/Arcade Loop Length
Authors: Yamamoto, Tetsuya T.; Shiota, Daikou; Sakajiri, Takuma;
Akiyama, Sachiko; Isobe, Hiroaki; Shibata, Kazunari
Bibcode: 2002ApJ...579L..45Y
Altcode:
We analyze 17 arcades to study the relations between solar flares and
arcades. Soft X-ray images taken with Yohkoh's soft X-ray telescope are
used to derive T0, EM0, and temporal variation
of Tarc and EMarc, where Tarc and
T0 are the temperatures of an arcade and prearcade region
and EMarc and EM0 are the volume emission measures
of an arcade and prearcade region. It is found that T0~2 MK
and Tarc~4 MK. We also estimate prearcade coronal electron
density n0 and arcade electron density narc
to find that narc is comparable to n0
(narc~n0~108 cm-3). Using
these observed EM, T, and n0, we calculate the theoretical
loop length Ltheor based on the scaling law for solar and
stellar flares derived by Shibata & Yokoyama and compare it with
observed flare/arcade loop length Lobs. The result shows a
good correlation between them (Ltheor~Lobs)
and indicates the need of plasma β for the scaling law
(Ltheor~EM3/5T-8/5n-
2/50β-6/5). This supports the theory of
the scaling law and is indirect evidence that flares and arcades are
heated by the same magnetic reconnection mechanism.
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: Reconnection Rate in the Decay Phase of a Long Duration Event
Flare on 1997 May 12
Authors: Isobe, Hiroaki; Yokoyama, Takaaki; Shimojo, Masumi; Morimoto,
Taro; Kozu, Hiromichi; Eto, Shigeru; Narukage, Noriyuki; Shibata,
Kazunari
Bibcode: 2002ApJ...566..528I
Altcode:
Recent analyses of long duration event (LDE) flares indicate successive
occurrences of magnetic reconnection and resultant energy release
in the decay phase. However, quantitative studies of the energy
release rate and the reconnection rate have not yet been made. In
this paper we focus on the decay phase of an LDE flare on 1997 May
12 and derive the energy release rate H and the reconnection rate
MA=vin/vA, where vin is
the inflow velocity and vA is the Alfvén velocity. For this
purpose, we utilize a method to determine vin and the coronal
magnetic field Bcorona indirectly, using the following
relations:H=2B2corona/4πvinAr,Bcoronavin=Bfootvfoot,where
Ar, Bfoot, and vfoot are the area of
the reconnection region, the magnetic field strength at the footpoints,
and the separation velocity of the footpoints, respectively. Since H,
Ar, vfoot, and Bfoot are obtained from
the Yohkoh Soft X-Ray Telescope data and a photospheric magnetogram,
vin and Bcorona can be determined from these
equations. The results are as follows: H is ~1027 ergs
s-1 in the decay phase. This is greater than 1/10th of
the value found in the rise phase. MA is 0.001-0.01,
which is about 1 order of magnitude smaller than found in previous
studies. However, it can be made consistent with the previous
studies under the reasonable assumption of a nonunity filling
factor. Bcorona is found to be in the range of 5-9 G, which
is consistent with both the potential extrapolation and microwave
polarization observed with the Nobeyama Radioheliograph.
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: Statistical Study of the Reconnection Rate in Solar Flares
Authors: Isobe, H.; Morimoto, T.; Eto, S.; Narukage, N.; Shibata, K.
Bibcode: 2002mwoc.conf..171I
Altcode:
The soft X-ray telescope (SXT) aboard Yohkoh has established that the
driving mechanism of solar flares is magnetic reconnection. However,
the physics of reconnection has not been clarified. One of the
current puzzles is: what determines the reconnection rateNULL The
reconnection rate is defined as reconnected magnetic flux per unit time
or equivalently the ratio of inflow speed into reconnection point to
Alfven velocity in non-dimension, and is one of the most important
physical quantities in reconnection physics. However, observations
have not yet succeeded to statistically determine the reconnection rate
because direct observation of reconnection inflow and coronal magnetic
field is difficult. In this poster we present a method to determine
the reconnection rate from observational data, which use the following
relations: H = frac B2 4pi vinL2
vinB = vfootBfoot. Here H, L,
vfoot and Bfoot are respectively the flare
heating rate, size of the flare arcade, separation velocity of the two
ribbon, and magnetic field strength of the foot points. Since these four
quantities can be obtained from observational data, the relations above
give the inflow velocity vin and coronal magnetic field B,
and thus the reconnection rate can be determined. Appling this method
to many flare observations, we will determine the reconnection rate
in solar flares statistically. A preliminary result is presented.
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: Hydrodynamic Modeling of a Protostellar Flare Loop Connecting
a Central Star with its Accretion Disk
Authors: Isobe, H.; Shibata, K.; Yokoyama, T.; Imanishi, K.
Bibcode: 2002aprm.conf..433I
Altcode:
We present a hydrodynamical simulation of a protostellar flare loop
which connects a central star with its accretion disk. To reproduce
the observed X-ray light curves and spectra, the heat conduction and
resultant evaporation of the chromosphere of the central star and the
disk are included. We have found that in some cases all the plasma
in the accretion disk is heated to the flare temperature and spreads
over the flare loop. The condition for this ``disk disappearance''
is examined in this paper. We also synthesized the expected X-ray
spectrum when we observe the simulation result with ASCA/GIS.
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: Numerical Simulation of a Protostar Flare Loop between the
Core and Disk
Authors: Isobe, Hiroaki; Yokoyama, Takaaki; Shibata, Kazunari
Bibcode: 2001JKAS...34..337I
Altcode:
One-dimensional hydrodynamic modeling of a protostellar flare loop is
presented. The model consists of thermally isolated loop connecting the
central core and the accretion disk. We found that the conductive heat
flux of a flare heated the accretion disk up to coronal temperature
and consequently the disk is evaporated and disappeard. This effect
may explain the ovserved feature of the repeated flare from the young
stellar object YLW 15.
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: Formation of pallasite and eucrite-diogenite parent magma by
partial melting.
Authors: Isobe, H.; Tsuchiyama, A.; Kitamura, M.
Bibcode: 1990anme...15...23I
Altcode:
No abstract at ADS
Title: Densities of experimental reproduced diogenitic pyroxenes
and eucritic melts.
Authors: Isobe, H.
Bibcode: 1989anme...14...70I
Altcode:
No abstract at ADS
Title: Fractionation experiments of chondritic material.
Authors: Isobe, H.; Tsuchiyama, A.; Kitamura, M.
Bibcode: 1988anme...13...65I
Altcode:
No abstract at ADS
Title: Relict pyroxene and olivine in chondrules of Y-691 (EH3).
Authors: Kitamura, M.; Watanabe, S.; Isobe, H.
Bibcode: 1987anme...12...30K
Altcode:
No abstract at ADS
Title: Fractional trend of bulk chemistry of chondrules in the
Allende meteorite.
Authors: Isobe, H.; Kitamura, M.; Morimoto, N.
Bibcode: 1985anme...10...80I
Altcode:
No abstract at ADS
Title: Thermal History of 'Relict Pyroxene' in the Allende Meteorite.
Authors: Kitamura, M.; Isobe, H.; Watanabe, S.; Morimoto, N.
Bibcode: 1984anme....9...50K
Altcode:
No abstract at ADS