explanation blue bibcodes open ADS page with paths to full text
Author name code: kurokawa
ADS astronomy entries on 2022-09-14
author:"Kurokawa, Hiroki"
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Title: Approach to the Mapping of Water Environment on Present Mars
- Validation of Possible Water Vapor Emission from Recurring Slope
Lineae Using a GCM
Authors: Kuroda, T.; Kurokawa, H.; Aoki, S.; Nakagawa, H.; Kobayashi,
M.
2022mamo.conf.3515K Altcode:
No abstract at ADS
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Title: The Origin of Earth's Mantle Nitrogen: Primordial or Early
Biogeochemical Cycling?
Authors: Kurokawa, H.; Laneuville, M.; Li, Y.; Zhang, N.; Fujii, Y.;
Sakuraba, H.; Houser, C.; Cleaves, H. J.
2022GGG....2310295K Altcode: 2022arXiv220414002K
Earth's mantle nitrogen (N) content is comparable to that found in
its N-rich atmosphere. Mantle N has been proposed to be primordial
or sourced by later subduction, yet its origin has not been
elucidated. Here we model N partitioning during the magma ocean
stage following planet formation and the subsequent cycling between
the surface and mantle over Earth history using argon (Ar) and N
isotopes as tracers. The partitioning model, constrained by Ar,
shows that only about 10% of the total N content can be trapped
in the solidified mantle due to N's low solubility in magma and low
partitioning coefficients in minerals in oxidized conditions supported
from geophysical and geochemical studies. A possible solution for the
primordial origin is that Earth had about 10 times more N at the time
of magma ocean solidification. We show that the excess N could be
removed by impact erosion during late accretion. The cycling model,
constrained by N isotopes, shows that mantle N can originate from
efficient N subduction, if the sedimentary N burial rate on early
Earth is comparable to that of modern Earth. Such a high N burial rate
requires biotic processing. Finally, our model provides a methodology
to distinguish the two possible origins with future analysis of the
surface and mantle N isotope record.
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Title: Mars Atmospheric Neon Probes Mantle Volatile Content and
Early Surface Environment
Authors: Kurokawa, H.; Sugita, S.; Yoshida, T.; Miura, Y. N.; Cho,
Y.; Kumagai, H.; Leblanc, F.; Terada, N.; Nakagawa, H.; Kasahara,
S.; Yoshioka, K.; Iwata, N.; Saito, Y.
2022LPICo2678.1722K Altcode:
Mars' atmospheric Ne abundance suggests volatile-rich
interior. Determination of its isotopic ratio is crucial to elucidate
Mars' accretion and early evolution.
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Title: Speciation of Sulfur in Carbonates in a 4.1-Billion-Year-Old
Martian Meteorite
Authors: Kajitani, I.; Nakada, R.; Koike, M.; Tanabe, G.; Usui, T.;
Matsu'ura, F.; Fukushi, K.; Kurokawa, H.; Yokoyama, T.
2022LPICo2678.1863K Altcode:
XANES analysis of carbonates in ALH 84001 showed peaks corresponding
to S(Ⅵ) at all analytical points and the S(Ⅵ) exists as carbonate
associated sulfate (CAS).
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Title: Distant Formation and Water-Rock Differentiation of Large
C-Complex Asteroids
Authors: Kurokawa, H.; Shibuya, T.; Sekine, Y.; Ehlmann, B. L.; Usui,
F.; Kikuchi, S.; Yoda, M.
2022LPICo2678.1676K Altcode:
Spectral identification of ammoniated minerals and water-rock reaction
modeling suggest distant formation and differentiation of large
C-complex asteroids.
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Title: Distant Formation and Differentiation of Outer Main Belt
Asteroids and Carbonaceous Chondrite Parent Bodies
Authors: Kurokawa, H.; Shibuya, T.; Sekine, Y.; Ehlmann, B. L.; Usui,
F.; Kikuchi, S.; Yoda, M.
2022AGUA....300568K Altcode: 2021arXiv211210284K
Volatile compositions of asteroids provide information on the Solar
System history and the origins of Earth's volatiles. Visible to
near-infrared observations at wavelengths of <2.5 µm have suggested
a genetic link between outer main belt asteroids located at 2.5-4 au and
carbonaceous chondrite meteorites (CCs) that show isotopic similarities
to volatile elements on Earth. However, recent longer wavelength data
for large outer main belt asteroids show 3.1 μm absorption features
of ammoniated phyllosilicates that are absent in CCs and cannot
easily form from materials stable at those present distances. Here, by
combining data collected by the AKARI space telescope and hydrological,
geochemical, and spectral models of water-rock reactions, we show
that the surface materials of asteroids having 3.1 μm absorption
features and CCs can originate from different regions of a single,
water-rock-differentiated parent body. Ammoniated phyllosilicates form
within the water-rich mantles of the differentiated bodies containing
NH<SUB>3</SUB> and CO<SUB>2</SUB> under high water-rock ratios
(>4) and low temperatures (<70°C). CCs can originate from the
rock-dominated cores, that are likely to be preferentially sampled as
meteorites by disruption and transport processes. Our results suggest
that multiple large main belt asteroids formed beyond the NH<SUB>3</SUB>
and CO<SUB>2</SUB> snow lines (currently >10 au) and could be
transported to their current locations. Earth's high hydrogen to carbon
ratio may be explained by accretion of these water-rich progenitors.
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Title: Partitioning and atmospheric loss of major volatile elements on
accreting Venus: Implications for the early runaway greenhouse state
Authors: Sakuraba, H.; Kurokawa, H.
2020AGUFMP018...07S Altcode:
Due to limited information, the climate of early Venus has been
poorly understood. Venus might have been in the runaway greenhouse
state since its formation, in which water forms a steam atmosphere
(e.g., Goldblatt et al., 2013, Hamano et al., 2013). On the other
hand, a habitable climate with liquid oceans has been also suggested
as another possibility (e.g., Way and Del Genio, 2020). <P />Here we
show that the distinct ratios of the major volatile elements, carbon
and nitrogen, on Venus and Earth suggest the early runaway greenhouse
scenario. Present-day Venusian volatile budget shows a deficient in
water by orders of magnitude and low C/N ratio by a factor of ~4
compared to the bulk silicate Earth (e.g., Catling & Kasting,
2017, Bergin et al., 2015). Hydrodynamic escape from the primordial
atmosphere is thought to have contributed to the water loss, but
another mechanism is needed to explain the C/N fractionation. <P />In
this study, we adapted a numerical model of element partitioning
between the atmosphere, crust, mantle (magma ocean), and core as
well as impact-induced atmospheric escape (Sakuraba et al., 2019;
Sakuraba et al., submitted) to accreting Venus. We estimated the
final volatile inventories for both cases of the runaway greenhouse
state and of Earth-like habitable condition. In the former case, all
volatile species on the surface were assumed to be partitioned into
the atmosphere. In the latter case, water and carbon were assumed
to be partitioned into liquid oceans and sedimentary carbonates,
respectively, after the magma ocean solidification. <P />Finally,
Venusian low C/N ratio was reproduced in the runaway greenhouse
case, while Earth-like high C/N ratio was obtained in the habitable
case. In the former case, both C and N were mainly partitioned to the
atmosphere through the accretion due to their low solubilities into
the magma ocean and lack of surface reservoirs after the magma ocean
solidification. Therefore, the impact-induced atmospheric erosion
removed them equally. In contrast, preferential loss of atmospheric N
as a result of C capture in carbonates elevated the C/N ratio in the
latter case. As a conclusion, we propose that the combination of the
runaway greenhouse state and the impact-induced atmospheric escape on
early Venus are required to explain the present-day volatile abundances.
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Title: A Probabilistic Approach to Determination of Ceres' Average
Surface Composition From Dawn Visible-Infrared Mapping Spectrometer
and Gamma Ray and Neutron Detector Data
Authors: Kurokawa, H.; Ehlmann, B. L.; De Sanctis, M. C.; Lapôtre,
M. G. A.; Usui, T.; Stein, N. T.; Prettyman, T. H.; Raponi, A.;
Ciarniello, M.
2020JGRE..12506606K Altcode:
The Visible-Infrared Mapping Spectrometer (VIR) on
board the Dawn spacecraft revealed that aqueous secondary
minerals—Mg-phyllosilicates, NH<SUB>4</SUB>-bearing phases, and Mg/Ca
carbonates—are ubiquitous on Ceres. Ceres' low reflectance requires
dark phases, which were assumed to be amorphous carbon and/or magnetite
(∼80 wt.%). In contrast, the Gamma Ray and Neutron Detector (GRaND)
constrained the abundances of C (8-14 wt.%) and Fe (15-17 wt.%). Here,
we reconcile the VIR-derived mineral composition with the GRaND-derived
elemental composition. First, we model mineral abundances from VIR data,
including either meteorite-derived insoluble organic matter (IOM),
amorphous carbon, magnetite, or combination as the darkening agent and
provide statistically rigorous error bars from a Bayesian algorithm
combined with a radiative-transfer model. Elemental abundances of C
and Fe are much higher than is suggested by the GRaND observations for
all models satisfying VIR data. We then show that radiative transfer
modeling predicts higher reflectance from a carbonaceous chondrite
of known composition than its measured reflectance. Consequently, our
second models use multiple carbonaceous chondrite endmembers, allowing
for the possibility that their specific textures or minerals other than
carbon or magnetite act as darkening agents, including sulfides and
tochilinite. Unmixing models with carbonaceous chondrites eliminate
the discrepancy in elemental abundances of C and Fe. Ceres' average
reflectance spectrum and elemental abundances are best reproduced by
carbonaceous-chondrite-like materials (40-70 wt.%), IOM or amorphous
carbon (10 wt.%), magnetite (3-8 wt.%), serpentine (10-25 wt.%),
carbonates (4-12 wt.%), and NH<SUB>4</SUB>-bearing phyllosilicates
(1-11 wt.%).
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Title: A probabilistic approach to determination of Ceres' average
surface composition from Dawn VIR and GRaND data
Authors: Kurokawa, H.; Ehlmann, B. L.; De Sanctis, M. C.; Lapôtre,
M. G. A.; Usui, T.; Stein, N. T.; Prettyman, T. H.; Raponi, A.;
Ciarniello, M.
2020arXiv201100157K Altcode:
The Visible-Infrared Mapping Spectrometer (VIR) on board the
Dawn spacecraft revealed that aqueous secondary minerals --
Mg-phyllosilicates, NH4-bearing phases, and Mg/Ca carbonates --
are ubiquitous on Ceres. Ceres' low reflectance requires dark
phases, which were assumed to be amorphous carbon and/or magnetite
(~80 wt.%). In contrast, the Gamma Ray and Neutron Detector (GRaND)
constrained the abundances of C (8-14 wt.%) and Fe (15-17 wt.%). Here,
we reconcile the VIR-derived mineral composition with the GRaND-derived
elemental composition. First, we model mineral abundances from VIR data,
including either meteorite-derived insoluble organic matter, amorphous
carbon, magnetite, or combination as the darkening agent and provide
statistically rigorous error bars from a Bayesian algorithm combined
with a radiative-transfer model. Elemental abundances of C and Fe are
much higher than is suggested by the GRaND observations for all models
satisfying VIR data. We then show that radiative transfer modeling
predicts higher reflectance from a carbonaceous chondrite of known
composition than its measured reflectance. Consequently, our second
models use multiple carbonaceous chondrite endmembers, allowing for
the possibility that their specific textures or minerals other than
carbon or magnetite act as darkening agents, including sulfides and
tochilinite. Unmixing models with carbonaceous chondrites eliminate
the discrepancy in elemental abundances of C and Fe. Ceres' average
reflectance spectrum and elemental abundances are best reproduced by
carbonaceous-chondrite-like materials (40-70 wt.%), IOM or amorphous
carbon (10 wt.%), magnetite (3-8 wt.%), serpentine (10-25 wt.%),
carbonates (4-12 wt.%), and NH4-bearing phyllosilicates (1-11 wt.%).
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Title: Proto-atmosphere Accretion on Eccentric Planets and its Impact
on Planet Formation
Authors: Mai, C.; Desch, S.; Kuiper, R.; Kurokawa, H.; Kuwahara, A.;
Marleau, G.
2020AAS...23522405M Altcode:
Protoplanets are believed to form before gas dissipates in the
protoplanetary disk and are likely to capture proto-atmospheres from
the nebula gas. Such hydrogen-rich atmospheres have been detected and
characterized in exoplanetary systems (e.g. low-density super-Earths
and mini-Neptunes). The accretion process and the structure of
the proto-atmosphere is subject to the disk environment such as the
evaporation of nebula gas, the eccentricity of the planet's orbit and
the planet mass, etc. A gaseous envelope could also greatly change
the behaviors of solids in the proximity of a protoplanet and affect
the planet formation processes. We used the hydrodynamics code PLUTO
and the radiation transport module MAKEMAKE to model the accretion
event of H<SUB>2</SUB>-dominated atmospheres. We established a 2-D
radiative accretion model with sophisticated opacity treatment to
simulate protoplanets capturing atmospheres on eccentric orbits. The
solutions reveal recycling behaviors of gas flow in a planetary
bow shock structure. We found that a supersonic environment turns
out to be favorable for planets to keep an early stable atmosphere,
rather than harmful. The orbital evolution of the planet can also
insert a forced oscillation on the atmosphere properties. Based on
the hydrodynamics solutions, we have been computing the dynamics
of incoming pebbles subject to the planet's gravity and aerodynamic
drag forces. We have been looking into how the accretion efficiency
of different sized pebbles on terrestrial planets is affected by
the proto-atmospheres. When planets are on eccentric orbits, the
trajectories of incoming solids are deflected in the bow shock, but
the recycling gas could also bring back solids for accretion behind
the planet. Updated results will be presented in the meeting. Our
study explores and provides important insights into the impacts of
migration and scattering on the formation planetary proto-atmospheres
and subsequent solid accretion onto planetary embryos.
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Title: Thermodynamic Analysis of Water-Rock Reactions in the Parent
Body of Ryugu
Authors: Shibuya, T.; Sekine, Y.; Kikuchi, S.; Kurokawa, H.; Fukushi,
K.; Nakamura, T.; Watanabe, S.
2019LPICo2189.2095S Altcode:
Thermodynamic modeling of water-chondrite reactions under various
conditions suggests that a large redox gradient in the parent body could
generate various secondary mineral assemblages and organic contents.
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Title: Modeling of Infrared Reflectance Spectra of Volatile-Rich
Asteroids
Authors: Kurokawa, H.; Shibuya, T.; Sekine, Y.; Ehlmann, B. L.
2019LPICo2189.2083K Altcode:
We computed the model infrared reflectance spectra of asteroids
using the results of chemical equilibrium calculations for water-rock
reactions. We constrained the aqueous environments experienced by Ryugu,
Bennu, Ceres, and the main-belt asteroids.
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Title: Laboratory Study on Morphological Features of Repeated Brine
Flows on Mars: Implications for Detection of Hydrated Salts on
Recurring Slope Lineae
Authors: Imamura, S.; Sekine, Y.; Kurokawa, H.; Maekawa, Y.; Sasaki, T.
2019LPICo2089.6408I Altcode:
Under martian small gravity, brine flow could form elongated streaks
on Mars due to precipitated salts. Even if the precipitated salts
exist on RSL, They are unlikely to be detected with CRISM because of
the insufficient spatial resolution of CRISM.
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Title: A Forward Modeling of Infrared Reflectance Spectra of
Asteroids: The Implications for Ryugu's Parent Body
Authors: Kurokawa, H.; Shibuya, T.; Sekine, Y.; Ehlmann, B. L.
2019LPI....50.1815K Altcode:
We show the model reflectance spectra of mineral assemblages obtained
by chemical equilibrium calculations. We discuss the implications for
Ryugu's parent body.
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Title: A Bayesian Approach to Deriving Ceres Surface Composition
from Dawn VIR Data: Initial Quantification of Bright Spot and Typical
Dark Material Phases with this Method
Authors: Kurokawa, H.; Ehlmann, B. L.; Ammannito, E.; De Sanctis,
M. C.; Lapotre, M.; Usui, T.; Stein, N. T.; Prettyman, T.; Raponi,
A.; Ciarniello, M.
2018LPI....49.1908K Altcode:
We determined Ceres surface composition and statistically rigorous
error bars from Dawn VIR data using a Bayesian approach.
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Title: Hydrogen Isotopic Constraints on the Evolution of Surface
and Subsurface Water on Mars
Authors: Usui, T.; Kurokawa, H.; Wang, J.; Alexander, C. M. O'D.;
Simon, J. I.; Jones, J. H.
2017LPI....48.1278U Altcode:
We constrain the atmospheric loss and possible exchange of surface
and subsurface water since 4 Ga based on our new D/H data of Noachian
carbonates.
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Title: Tracing the Origin and Evolution of Volatiles on Mars:
Constraints from Elemental and Isotopic Compositions of Nitrogen
and Noble Gases
Authors: Kurokawa, H.; Kurosawa, K.; Usui, T.
2017LPI....48.1204K Altcode:
Using a model of the loss and supply of volatiles, we simulated the
evolution of the atmospheric composition to constrain the origin of
the volatiles on Mars.
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Title: The Evolution of Water in Martian Atmosphere, Hydrosphere,
and Cryosphere: Insights from Hydrogen Isotopes
Authors: Usui, T.; Kurokawa, H.; Alexander, C.; Simon, J. I.; Wang,
J.; Jones, J. H.
2016AGUFM.P52A..04U Altcode:
Mars exploration missions provide compelling evidence for the presence
of liquid water during the earliest geologic era (Noachian: >
3.9 Ga) of Mars. The amount and stability of liquid water on the
surface is strongly influenced by the composition and pressure of
the atmosphere. However, the evolution of Noachian atmosphere has
been poorly constrained due to uncertainties of atmospheric loss
regimes and internal/external factors such as impact flux and volcanic
degassing. We can trace the evolution of the early Martian atmosphere
and its interaction with the hydrosphere and cryosphere with hydrogen
isotope ratios (D/H) because they fractionate during atmospheric
escape and during hydrological cycling between the atmosphere,
surface waters, and the polar ice caps. This study reports D/H ratios
of primordial and 4 Ga-old atmosphere by ion microprobe analyses of
Martian meteorites. Analyses of olivine-hosted glass inclusions in the
most primitive shergottite (Yamato 980459) provide a near-chondritic
D/H ratio (1.3×SMOW) for the 4.5 Ga primordial water preserved in the
mantle. On the other hand, carbonates in Allan Hills 84001 provide
a D/H range (1.5-2.0×SMOW) for the Noachian surface water that
was isotopically equilibrated with the 4 Ga atmosphere. The latter
observation requires that even after the Noachian period the hydrogen
isotopes were fractionated significantly to reach the present-day value
of 6×SMOW. Using the one-reservoir model of Kurokawa et al. (2014)
we can provide minimum estimates on the amounts of hydrogen loss
before and after 4 Ga based on the D/H data from the meteorites
(1.3×SMOW at 4.5 Ga and 1.5-2.0×SMOW at 4 Ga) assuming the volume of
polar surface-ice (20-30 m global equivalent layers, GEL). The model
indicates that the hydrogen loss during the first 0.5 billion years
(16-54 m GEL) was comparable to those (42-93 mGEL) in the remaining
Martian history. These values are distinctly lower than the geological
estimates on the volumes of paleo-oceans (e.g., 550 mGEL, Di Achille
& Hynek, 2010). This difference implies that a buried cryosphere
must accounted for a large part of the water budget (Usui et al. 2015).
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Title: A Lower Limit of Atmospheric Pressure on Early Mars Inferred
from Nitrogen and Argon Isotopes
Authors: Kurokawa, H.; Kurosawa, K.; Usui, T.
2016LPI....47.1220K Altcode:
Comparing model calculations of the atmospheric evolution with isotope
data of trapped gas in ALH 84001 gave a lower limit of the atmospheric
pressure at 4.1 Ga.
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Title: Escape of Early Martian Atmosphere and Hydrosphere: Constraints
from Isotopic Compositions
Authors: Kurokawa, H.; Kurosawa, K.; Usui, T.
2015LPI....46.1643K Altcode: 2015LPICo1832.1643K
This study of the evolution of the martian isotopic compositions
suggests the presence of thick early atmosphere lost during the heavy
bombardment period.
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Title: The Effect of Compositional Inhomogeneity on Radii of Hot
Jupiters
Authors: Kurokawa, H.; Inutsuka, S.
2015LPI....46.1710K Altcode: 2015LPICo1832.1710K
We evaluate the effect of compositional inhomogeneity on radii of hot
Jupiters by a structure calculation with self-consistent treatment of
convection regimes.
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Title: Hydrogen Isotopes Record the History of the Martian Hydrosphere
and Atmosphere
Authors: Usui, T.; Simon, J. I.; Jones, J. H.; Kurokawa, H.; Sato,
M.; Alexander, C. M. O'D.; Wang, J.
2015LPI....46.1593U Altcode: 2015LPICo1832.1593U
This study presents insights from hydrogen isotopes for the origin
and evolution of martian water reservoirs.
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Title: Evolution of water reservoirs on Mars: Constraints from
hydrogen isotopes in martian meteorites
Authors: Kurokawa, H.; Sato, M.; Ushioda, M.; Matsuyama, T.; Moriwaki,
R.; Dohm, J. M.; Usui, T.
2014E&PSL.394..179K Altcode: 2014arXiv1403.4211K
Martian surface morphology implies that Mars was once warm enough to
maintain persistent liquid water on its surface. While the high D/H
ratios (∼6 times the Earth's ocean water) of the current martian
atmosphere suggest that significant water has been lost from the surface
during martian history, the timing, processes, and the amount of the
water loss have been poorly constrained. Recent technical developments
of ion-microprobe analysis of martian meteorites have provided accurate
estimation of hydrogen isotope compositions (D/H) of martian water
reservoirs at the time when the meteorites formed. Based on the D/H
data from the meteorites, this study demonstrates that the water loss
during the pre-Noachian (>41-99 m global equivalent layers, GEL)
was more significant than in the rest of martian history (>10-53
m GEL). Combining our results with geological and geomorphological
evidence for ancient oceans, we propose that undetected subsurface
water/ice (≃100-1000 m GEL) should exist, and it exceeds the
observable present water inventory (≃20-30 m GEL) on Mars.
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Title: Mass-loss Evolution of Close-in Exoplanets: Evaporation of
Hot Jupiters and the Effect on Population
Authors: Kurokawa, H.; Nakamoto, T.
2014ApJ...783...54K Altcode: 2014arXiv1401.2511K
During their evolution, short-period exoplanets may lose envelope
mass through atmospheric escape owing to intense X-ray and extreme
ultraviolet (XUV) radiation from their host stars. Roche-lobe
overflow induced by orbital evolution or intense atmospheric escape
can also contribute to mass loss. To study the effects of mass loss on
inner planet populations, we calculate the evolution of hot Jupiters
considering mass loss of their envelopes and thermal contraction. Mass
loss is assumed to occur through XUV-driven atmospheric escape and
the following Roche-lobe overflow. The runaway effect of mass loss
results in a dichotomy of populations: hot Jupiters that retain
their envelopes and super Earths whose envelopes are completely
lost. Evolution primarily depends on the core masses of planets
and only slightly on migration history. In hot Jupiters with small
cores (sime 10 Earth masses), runaway atmospheric escape followed by
Roche-lobe overflow may create sub-Jupiter deserts, as observed in both
mass and radius distributions of planetary populations. Comparing our
results with formation scenarios and observed exoplanets populations,
we propose that populations of closely orbiting exoplanets are formed
by capturing planets at/inside the inner edges of protoplanetary disks
and subsequent evaporation of sub-Jupiters.
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Title: Mass-Loss Evolution of Super-Earths: Effects of Stellar Types
Authors: Kurokawa, H.; Kaltenegger, L.; Nakamoto, T.
2014LPI....45.1355K Altcode:
We show evolution of super-Earths with H/He envelopes, considering
XUV-driven escape and Roche-lobe overflow. Their compositions are
shaped by mass loss.
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Title: Thickness of Martian Ground Ice: Implication from
Multi-Water-Reservoir Model
Authors: Kurokawa, H.; Usui, T.; Demura, H.; Sato, M.
2014LPI....45.1815K Altcode:
Recent observations propose the existence of ground ice on Mars. Our
model suggests that the thickness is at least a few hundred meters
based on D/H data.
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Title: Atmospheric mass-loss and evolution of short-period exoplanets:
the examples of CoRoT-7b and Kepler-10b
Authors: Kurokawa, H.; Kaltenegger, L.
2013MNRAS.433.3239K Altcode: 2013arXiv1306.0973K; 2013MNRAS.tmp.1613K
Short-period exoplanets potentially lose envelope masses during their
evolution because of atmospheric escape caused by the intense X-ray and
extreme UV (XUV) radiation from their host stars. We develop a combined
model of atmospheric mass-loss calculation and thermal evolution
calculation of a planet to simulate its evolution and explore the
dependences on the formation history of the planet. Thermal atmospheric
escape as well as the Roche lobe overflow contributes to mass-loss. The
maximum initial planetary model mass depends primarily on the assumed
evolution model of the stellar XUV luminosity. We adapt the model to
CoRoT-7b and Kepler-10b to explore the evolution of both planets and
the maximum initial mass of these planets. We take the recent X-ray
observation of CoRoT-7 into account and explore the effect of different
XUV evolution models on the planetary initial mass. Our calculations
indicate that both hot super-Earths could be remnants of Jupiter-mass
gas planets.
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Title: Significant Water Loss During Noachian Era: Constraints from
Hydrogen Isotopes in Martian Meteorites
Authors: Kurokawa, H.; Sato, M.; Ushioda, M.; Matsuyama, T.; Moriwaki,
R.; Usui, T.
2013LPI....44.1853K Altcode: 2013LPICo1719.1853K
Based on the D/H data from the meteorites, we determine the amount of
water loss during Noachian and post-Noachian periods.
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Title: A Study on Red Asymmetry of Hα Flare Ribbons Using a
Narrowband Filtergram in the 2001 April 10 Solar Flare
Authors: Asai, Ayumi; Ichimoto, Kiyoshi; Kita, Reizaburo; Kurokawa,
Hiroki; Shibata, Kazunari
2012PASJ...64...20A Altcode: 2011arXiv1112.5912A
We report on a detailed examination of the “red asymmetry” of the
Hα emission line seen during the 2001 April 10 solar flare by using
a narrowband filtergram. We investigated the temporal evolution and
the spatial distribution of the red asymmetry by using Hα data taken
with the 60-cm Domeless Solar Telescope at Hida Observatory, Kyoto
University. We confirmed that the red asymmetry clearly appeared all
over the flare ribbons, and the strong red asymmetry is located on the
outer narrow edges of the flare ribbons, with a width of about 1.5"-3.0"
(1000-2000 km), where strong energy releases occur. Moreover, we found
that the red asymmetry, which also gives a measure of the Doppler
shift of the Hα emission line, concentrates on a certain value,
not depending on the intensity of the Hα kernels. This implies not
only that the temporal evolutions of the red asymmetry and those of
the intensity are not synchronous in each flare kernel, but also that
the peak asymmetry (or velocity of the chromospheric condensation)
of individual kernel is not a strong function of their peak intensity.
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Title: Radiation Limits of Ocean Planets: Effects of the Atmospheric
Absorption of the Incoming Radiation with One-Dimensional
Radiative-Convective Equilibrium Model
Authors: Kurokawa, H.; Nakamoto, T.
2011LPI....42.1328K Altcode:
We investigate the effects of the absorption of the incoming radiation
on the radiation limit of the troposphere of ocean planets. To clarify
the effects, we use a simple parameterization of the absorption. We
have found two important cases.
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Title: Energetic Relations between the Disappearing Solar Filaments
and the Associated Flare Arcades
Authors: Morimoto, Taro; Kurokawa, Hiroki; Shibata, Kazunari; Ishii,
Takako T.
2010PASJ...62..939M Altcode:
We present the temporal and statistical relations between the mechanical
energies of disappearing solar filaments and the thermal energies
of the associated flare arcades in soft X-rays. Measuring the 3-D
velocity fields of 10 eruptive filaments, we calculated their mechanical
energy gain rate, ɛ<SUB>mc</SUB>, per unit volume and compared it to
the thermal energy release rate per unit volume, ɛ<SUB>th</SUB>,
derived with Yohkoh/SXT data. For the statistical relation, we
found a relation that can be approximated as ɛ<SUB>th</SUB> ∝
ɛ<SUP>1.9</SUP><SUB>mc</SUB>. This relation can be explained by
interpreting the energy input to an arcade via the Poynting flux in
the magnetic reconnection process and the acceleration of a filament
by the Lorentz force. This explanation is also supported by the strong
dependence of the observed increase rates of both the thermal and
mechanical energy densities on the mean magnetic field strength of
the source region. We also investigated their temporal variations,
and found that the start time of increase in the mechanical energy of
a filament preceded that of the thermal energy of the coronal arcade
in some cases. These relations imply that the basic mechanisms that
accelerate a filament and create a hot plasma are different, and
both energy increase rates are determined primary by the magnetic
field strengths.
---------------------------------------------------------
Title: New Observation of Failed Filament Eruptions: The Influence
of Asymmetric Coronal Background Fields on Solar Eruptions
Authors: Liu, Y.; Su, J.; Xu, Z.; Lin, H.; Shibata, K.; Kurokawa, H.
2009ApJ...696L..70L Altcode:
Failed filament eruptions not associated with a coronal mass ejection
(CME) have been observed and reported as evidence for solar coronal
field confinement on erupting flux ropes. In those events, each
filament eventually returns to its origin on the solar surface. In
this Letter, a new observation of two failed filament eruptions is
reported which indicates that the mass of a confined filament can be
ejected to places far from the original filament channel. The jetlike
mass motions in the two failed filament eruptions are thought to be
due to the asymmetry of the background coronal magnetic fields with
respect to the locations of the filament channels. The asymmetry of the
coronal fields is confirmed by an extrapolation based on a potential
field model. The obvious imbalance between the positive and negative
magnetic flux (with a ratio of 1:3) in the bipolar active region is
thought to be the direct cause of the formation of the asymmetric
coronal fields. We think that the asymmetry of the background fields
can not only influence the trajectories of ejecta, but also provide
a relatively stronger confinement for flux rope eruptions than the
symmetric background fields do.
---------------------------------------------------------
Title: The Power-Law Distribution of Flare Kernels and Fractal
Current Sheets in a Solar Flare
Authors: Nishizuka, N.; Asai, A.; Takasaki, H.; Kurokawa, H.;
Shibata, K.
2009ApJ...694L..74N Altcode: 2013arXiv1301.6244N
We report a detailed examination of the fine structure inside flare
ribbons and the temporal evolution of this fine structure during
the X2.5 solar flare that occurred on 2004 November 10. We examine
elementary bursts of the C IV (~1550 Å) emission lines seen as local
transient brightenings inside the flare ribbons in the ultraviolet
(1600 Å) images taken with Transition Region and Coronal Explorer,
and we call them C IV kernels. This flare was also observed in Hα
with the Sartorius 18 cm Refractor telescope at Kwasan observatory,
Kyoto University, and in hard X-rays (HXR) with Reuven Ramaty High
Energy Solar Spectroscopic Imager. Many C IV kernels, whose sizes were
comparable to or less than 2”, were found to brighten successively
during the evolution of the flare ribbon. The majority of them were
well correlated with the Hα kernels in both space and time, while
some of them were associated with the HXR emission. These kernels were
thought to be caused by the precipitation of nonthermal particles at the
footpoints of the reconnecting flare loops. The time profiles of the C
IV kernels showed intermittent bursts, whose peak intensity, duration,
and time interval were well described by power-law distribution
functions. This result is interpreted as evidence for "self-organized
criticality" in avalanching behavior in a single flare event, or for
fractal current sheets in the impulsive reconnection region.
---------------------------------------------------------
Title: Multi-scale reconnections in a complex CME
Authors: van Driel-Gesztelyi, L.; Goff, C. P.; Démoulin, P.; Culhane,
J. L.; Matthews, S. A.; Harra, L. K.; Mandrini, C. H.; Klein, K. -L.;
Kurokawa, H.
2008AdSpR..42..858V Altcode:
A series of three flares of GOES class M, M and C, and a CME were
observed on 20 January 2004 occurring in close succession in NOAA
10540. Types II, III, and N radio bursts were associated. We use
the combined observations from TRACE, EIT, Hα images from Kwasan
Observatory, MDI magnetograms, GOES, and radio observations from
Culgoora and Wind/ WAVES to understand the complex development of this
event. We reach three main conclusions. First, we link the first two
impulsive flares to tether-cutting reconnections and the launch of
the CME. This complex observation shows that impulsive quadrupolar
flares can be eruptive. Second, we relate the last of the flares, an
LDE, to the relaxation phase following forced reconnections between
the erupting flux rope and neighbouring magnetic field lines, when
reconnection reverses and restores some of the pre-eruption magnetic
connectivities. Finally, we show that reconnection with the magnetic
structure of a previous CME launched about 8 h earlier injects electrons
into open field lines having a local dip and apex (located at about six
solar radii height). This is observed as an N-burst at decametre radio
wavelengths. The dipped shape of these field lines is due to large-scale
magnetic reconnection between expanding magnetic loops and open field
lines of a neighbouring streamer. This particular situation explains
why this is the first N-burst ever observed at long radio wavelengths.
---------------------------------------------------------
Title: Three Successive and Interacting Shock Waves Generated by a
Solar Flare
Authors: Narukage, Noriyuki; Ishii, Takako T.; Nagata, Shin'ichi;
UeNo, Satoru; Kitai, Reizaburo; Kurokawa, Hiroki; Akioka, Maki;
Shibata, Kazunari
2008ApJ...684L..45N Altcode:
We discovered three successive Moreton waves generated by a single solar
flare on 2005 August 3. Although this flare was not special in magnitude
or configuration, Moreton waves (shock waves) successively occurred
three times. Multiple shock waves generated during a single flare have
not been reported before. Furthermore, the faster second-generated
Moreton wave caught up and merged with the slower first-generated
one. This is the first report of shock-shock interaction associated with
a solar flare. The shock-plasma interaction was also detected. When
the third-generated Moreton wave passed through an erupting filament,
the filament was accelerated by the Moreton wave. In this event,
filaments also erupted three times. On the basis of this observation,
we consider that filament eruption is indispensable to the generation
of Moreton waves.
---------------------------------------------------------
Title: Observation of Magnetic Field Reconnection at the Base of
EFR Surges
Authors: Kurokawa, H.; Liu, Y.; Sano, S.; Ishii, T. T.
2007ASPC..369..347K Altcode:
We show that surges are the first manifestation of the birth of emerging
flux region (EFR) or active regions by demonstarating the evolutions of
the earliest stage of EFRs. We call such surges as EFR-surges. We show
that almost all surges are associated with the increase or new emergence
of the satellite polarity flux at their bases, by presenting the results
of quantitative analyses of the magnetic field variations in the surge
bases. Our finding is that the eleven of fourteen events showed the
increase of the magnetic flux of isolated or satellite polarity at
the bases of the surges. Examining these results, we conclude that
the emergence of new magnetic flux plays an essential role for the
production of Hα surges and that the magnetic fileld reconnection
between the EFR and the pre-existing and surounding magnetic field
produces surges. We also discuss the future observational target to
confirm the validity of the magnetic reconnection model of surges in
more details by using the SOT of Solar-B.
---------------------------------------------------------
Title: The Relationship between EUV Brightenings and Dark Mottles
in the Quiet Sun
Authors: Kamio, S.; Kurokawa, H.; Brooks, D. H.
2007ASPC..369..257K Altcode:
The relationship between EUV brightenings in the transition region and
dark mottles in the chromosphere is studied using data obtained in an
observational campaign between the Coronal Diagnostic Spectrometer (CDS)
on SOHO and the Domeless Solar Telescope (DST) at Hida Observatory. We
found several examples of EUV brightenings accompanied by upflowing
dark mottles in the chromosphere. This suggests that EUV blinkers are
formed by the heating of dark mottles or spicules.
---------------------------------------------------------
Title: Observation of Interactions and Eruptions of Two Filaments
Authors: Su, Jiangtao; Liu, Yu; Kurokawa, Hiroki; Mao, Xinjie; Yang,
Shangbin; Zhang, Hongqi; Wang, Haimin
2007SoPh..242...53S Altcode:
We present new observations of the interactions of two close, but
distinct, Hα filaments and their successive eruptions on 5 November
1998. The magnetic fields of the filaments are both of the sinistral
type. The interactions between the two filaments were initiated mainly
by an active filament of one of them. Before the filament eruptions, two
dark plasma ejections and chromospheric brightenings were observed. They
indicate that possible magnetic reconnection had occurred between the
two filaments. During the first filament eruption, salient dark mass
motions transferring from the left erupting filament into the right
one were observed. The right filament erupted 40 minutes later. This
second filament eruption may have been the result of a loss of stability
owing to the sudden mass injection from the left filament. Based on
the Hα observations, we have created a sketch for understanding the
interactions between two filaments and accompanying activities. The
traditional theory of filament merger requires that the filaments
share the same filament channel and that the reconnection occurs
between the two heads, as simulated by DeVore, Antiochos, and Aulanier
(Astrophys. J.629, 1122, 2005; 646, 1349, 2006). Our interpretation
is that the external bodily magnetic reconnection between flux ropes
of the same chirality is another possible way for two filament bodies
to coalesce.
---------------------------------------------------------
Title: Evolution of Magnetic Nonpotentiality in NOAA AR 10486
Authors: Dun, J.; Kurokawa, H.; Ishii, T. T.; Liu, Y.; Zhang, H.
2007ApJ...657..577D Altcode:
The active region NOAA 10486 was one of the most flare-productive
regions during solar cycle 23. In this paper, we focus our analysis
on the daily evolution of magnetic nonpotentiality for this region
from 2003 October 26 to October 30. Daily averaged values of three
nonpotential parameters: magnetic shear angle, line-of-sight current,
and current helicity of the selected regions along the main neutral
lines are calculated using the vector magnetograms obtained at
Huairou Solar Observing Station. The magnetic flux evolution and
proper motion of magnetic features are also studied in detail for
the initial brightening regions of the two large X-class flares
(X17 on October 28 and X10 on October 29). The main results are as
follows. (1) Three parameters of the magnetic nonpotentiality in
the photosphere obviously increased at the impulsively brightening
flare sites from at least 1 day before the two large X-class flares,
and most of the three parameters decreased after the flares around
the main flare regions. (2) The increase of magnetic flux and complex
proper motions of the magnetic knots were found to be simultaneously
occurring at the non-potentiality developing sites along the main
neutral lines. Such increases and motions of the magnetic flux can be
explained by the model of emerging twisted flux ropes, and we conclude
that the emergence of twisted magnetic flux ropes are a main reason
for the development of nonpotentiality along the neutral line and for
the production of strong X-class flares.
---------------------------------------------------------
Title: A Multiple Flare Scenario where the Classic Long-Duration
Flare Was Not the Source of a CME
Authors: Goff, C. P.; van Driel-Gesztelyi, L.; Démoulin, P.; Culhane,
J. L.; Matthews, S. A.; Harra, L. K.; Mandrini, C. H.; Klein, K. L.;
Kurokawa, H.
2007SoPh..240..283G Altcode:
A series of flares (GOES class M, M and C) and a CME were observed in
close succession on 20 January 2004 in NOAA 10540. Radio observations,
which took the form of types II, III and N bursts, were associated with
these events. We use the combined observations from TRACE, EIT, Hα
images from Kwasan, MDI magnetograms and GOES to understand the complex
development of this event. Contrary to a standard interpretation,
we conclude that the first two impulsive flares are part of the CME
launch process while the following long-duration event flare represents
simply the recovery phase. Observations show that the flare ribbons
not only separate but also shift along the magnetic inversion line
so that magnetic reconnection progresses stepwise to neighboring flux
tubes. We conclude that "tether cutting" reconnection in the sheared
arcade progressively transforms it to a twisted flux tube, which
becomes unstable, leading to a CME. We interpret the third flare,
a long-duration event, as a combination of the classical two-ribbon
flare with the relaxation process following forced reconnection between
the expanding CME structure and neighboring magnetic fields.
---------------------------------------------------------
Title: The X10 Flare on 29 October 2003: Was It Triggered by Magnetic
Reconnection between Counter-Helical Fluxes?
Authors: Liu, Yu; Kurokawa, Hiroki; Liu, Chang; Brooks, David H.;
Dun, Jingping; Ishii, Takako T.; Zhang, Hongqi
2007SoPh..240..253L Altcode: 2007astro.ph..1794L
Vector magnetograms taken at Huairou Solar Observing Station (HSOS)
and Mees Solar Observatory (MSO) reveal that the super active region
(AR) NOAA 10486 was a complex region containing current helicity flux of
opposite signs. The main positive sunspots were dominated by negative
helicity fields, while positive helicity patches persisted both inside
and around the main positive sunspots. Based on a comparison of two days
of deduced current helicity density, pronounced changes associated with
the occurrence of an X10 flare that peaked at 20:49 UT on 29 October
2003 were noticed. The average current helicity density (negative) of
the main sunspots decreased significantly by about 50%. Accordingly,
the helicity densities of counter-helical patches (positive) were also
found to decay by the same proportion or more. In addition, two hard
X-ray (HXR) "footpoints" were observed by the Reuven Ramaty High Energy
Solar Spectroscopic Imager (RHESSI) during the flare in the 50 - 100
keV energy range. The cores of these two HXR footpoints were adjacent
to the positions of two patches with positive current helicity that
disappeared after the flare. This strongly suggested that the X10
flare on 29 October 2003 resulted from reconnection between magnetic
flux tubes having opposite current helicity. Finally, the global
decrease of current helicity in AR 10486 by ∼50% can be understood
as the helicity launched away by the halo coronal mass ejection (CME)
associated with the X10 flare.
---------------------------------------------------------
Title: An Hα Surge Provoked by Moving Magnetic Features near an
Emerging Flux Region
Authors: Brooks, D. H.; Kurokawa, H.; Berger, T. E.
2007ApJ...656.1197B Altcode:
We present a detailed study of Hα surges from cotemporal
high-resolution multiwavelength images of NOAA AR 8227 obtained by
the 50 cm Swedish Vacuum Solar Telescope (formerly situated on La
Palma, Spain) and TRACE. We find that two kinds of collisions between
opposite polarity magnetic flux produce the surges. First, one edge of
an emerging flux region (EFR) collides with the preexisting magnetic
field and causes continual surge activities, which have already been
named EFR surges by previous authors. Secondly, moving magnetic features
(MMFs), which emerge near the sunspot penumbra, pass through the ambient
plasma and eventually collide with the opposite polarity magnetic
field of the EFR. During their passage from the sunspot penumbra to
the EFR, the MMFs constantly interacted with other magnetic elements
and had a close relationship and showed similar flow patterns to Ca
II K bright points. These brightenings were located at the leading
edges of the MMFs. Cancellation of opposite polarity magnetic flux
at the surge footpoint is observed, accompanied by chromospheric and
coronal brightenings. We explain the evolutionary and morphological
characteristics of the multiwavelength features associated with the Hα
surges in both cases by the extension of previous 2D schematic models of
reconnection in surges. Furthermore, by measuring the expansion velocity
and photospheric magnetic field around the surge footpoint, we estimate
a dimensionless reconnection rate of 0.04 (ratio of inflow velocity to
Alfvén velocity). This is sufficient to produce a significant surge
that heats the chromospheric plasma to coronal temperatures.
---------------------------------------------------------
Title: Build-up of a CME and its Interaction with Large-Scale
Magnetic Structures
Authors: van Driel-Gesztelyi, L.; Goff, C. P.; Demoulin, P.; Culhane,
J. L.; Klein, K. L.; Mandrini, C. H.; Matthews, S. A.; Harra, K. L.;
Kurokawa, H.
2006IAUJD...3E..86V Altcode:
Introduction: A series of flares (GOES class M, M and C) and a
CME were observed on 20-JAN-2004 occurring in close succession in
NOAA 10540. Types II, III and a N radio bursts were associated. We
investigate the link between the flares (two impulsive flares followed
by an LDE) and the CME as well as the origin of the rare decametric
N-burst. Methods: We use the combined observations from TRACE, SOHO/EIT,
H-alpha images from Kwasan Observatory, SOHO/MDI magnetograms, GOES
and radio observations from Culgoora and Wind/WAVES as well as magnetic
modelling to understand the complex development of this event. Results:
We link the first two impulsive flares to tether-cutting reconnections
and the launch of the CME, while the last of the flares, an LDE,
to the relaxation phase following forced reconnections between the
erupting flux rope and neighbouring magnetic field lines. We show
that reconnection with the magnetic structure of a previous CME,
launched about 8 hours earlier, injects electrons into open field
lines having a local dip and apex of about 6 solar radii height. The
dipped shape of these field lines was due to large-scale magnetic
reconnection between expanding magnetic loops and open field lines of a
neighbouring streamer. This particular situation explains the observed
decametric N burst. Discussion: This complex observation shows that
impulsive quadrupolar flares can be eruptive, while an LDE may remain
a confined event. We find that reconnection forced by the expanding CME
structure is followed by a relaxation phase, when reconnection reverses
and restores some of the pre-eruption magnetic connectivities. The
observed decametric N-burst was caused by the interaction of two CMEs
and reconnection of their expanding magnetic field with neighbouring
streamer field lines - a very particular interplay, which explains
why N-bursts are so rare.
---------------------------------------------------------
Title: Magnetic Field Configuration and Evolution of a Highly
Flare-producitve Region NOAA 10808 (2005-Sep)
Authors: Ishii, T. T.; Nagashima, K.; Kurokawa, H.; Kitai, R.; Ueno,
S.; Nagata, S.; Shibata, K.
2006IAUJD...3E..59I Altcode:
Active regions on the Sun have different flare productivities with each
other. Some regions produce many large flares, while others produce no
flares. The key factor of a high flare productivity is the complexity
of magnetic field configuration of the region. In our previous studies,
we found that the twisted structure of emerging magnetic flux bundles
is the essential feature of flare-productive active regions. Vector
magnetic field data sets are necessary to examine the twisted
magnetic field structures (e.g., shear and helicity). Recently we
have constructed our new telescope, Solar Magnetic Activity Research
Telescope (SMART) at Hida Observatory, Kyoto University. We can obtain
high resolution full disk H-alpha images (with Lyot filter; H-alpha
center, blue and reg wing) and full disk vector magnetograms with
SMART. The active region NOAA 10808 showed the highest flare activity
during the current solar cycle (cycle 23) in September 2005. We
studied the formation process of delta-type magnetic configuration
using SOHO/MDI magnetograms and flares using TRACE data. We also
studied the evolution of magnetic shear and H-alpha filaments using
H-alpha full disk images and full disk vector magnetograms obtained
with SMART. In this paper, we summarize the characteristics of magnetic
field configuration of this region and discuss the relation between
the configuration and the high flare activity.
---------------------------------------------------------
Title: The relation between Ca bright grains and oscillations in
the photosphere
Authors: Kamio, S.; Kurokawa, H.
2006A&A...450..351K Altcode:
Context: .Ca bright grains are small and repetitive brightenings
ubiquitously found in the quiet Sun.<BR /> Aims: .The relationship
between the formation of Ca bright grains and the dynamics in the
chromosphere and the photosphere is studied.<BR /> Methods: .We
simultaneously observed the time series of spectra in Ca II H, Hα, and
Fe I with the horizontal spectrograph of the Domeless Solar Telescope
(DST) at Hida Observatory.<BR /> Results: .Our wavelet analysis revealed
that the occurrence of Ca II H 2V brightenings are correlated with
enhanced 5 mHz velocity oscillations in the chromosphere and the
photosphere.<BR /> Conclusions: .Ca bright grains can be explained
by acoustic shocks in the chromosphere that are associated with 5 mHz
oscillations in the photosphere below.
---------------------------------------------------------
Title: Horizontal and Vertical Flow Structure in Emerging Flux Regions
Authors: Kozu, Hiromichi; Kitai, Reizaburo; Brooks, David H.; Kurokawa,
Hiroki; Yoshimura, Keiji; Berger, Thomas E.
2006PASJ...58..407K Altcode:
In order to obtain an overall view of the flow structure of convective
gas in emerging flux regions (EFRs), we studied three EFRs in two
solar active regions, NOAA 8218 and NOAA 10774. Using the Local
Correlation Tracking method, we found several horizontally divergent
flow structures, which were stable over a period of 1 hour, in 2
EFRs in NOAA 8218. The horizontal flow velocities and the sizes
of the structures were around 500m s<SUP>-1</SUP> and about 4Mm
in radius, respectively. We analyzed another dataset of NOAA 10774
using spectroscopic methods and found temporarily stable up-ward gas
flows in the central part of the EFR. The line-of-sight velocities
were around 150m s<SUP>-1</SUP> and the size of the flow patch was
2 to 5Mm in radius. These results support our previous findings that
convective-cell-like flow appears in the central part of an EFR. We
estimated from these results that the depth of the flow cell in EFRs
is about 600km, and the turn-over time of the cell is about 2 hours.
---------------------------------------------------------
Title: Multi-scale reconnections in a complex CME
Authors: van Driel-Gesztelyi, L.; Goff, C.; Demoulin, P.; Culhane,
J. L.; Matthews, S. A.; Harra, L. K.; Mandrini, C. H.; Klein, K. L.;
Kurokawa, H.
2006cosp...36.2371V Altcode: 2006cosp.meet.2371V
A series of flares GOES class M M and C and a CME were observed on
20-JAN-2004 occurring in close succession in NOAA 10540 Types II III
and an N radio bursts were associated We use the combined observations
from TRACE EIT H-alpha images from Kwasan Observatory MDI magnetograms
GOES and radio observations from Culgoora and Wind WAVES to understand
the complex development of this event We link the first two impulsive
flares to tether-cutting reconnections and the launch of the CME while
the last of the flares an LDE to the relaxation phase following forced
reconnections between the erupting flux rope and neighbouring magnetic
field lines We show that reconnection with the magnetic structure of
a previous CME launched about 8 hours earlier injects electrons into
open field lines having a local dip and apex of about 6 solar radii
height The dipped shape of these field lines was due to large-scale
magnetic reconnection between expanding magnetic loops and open field
lines of a neighbouring streamer This particular situation explains
the observed decametric N burst and why N-bursts are so rare
---------------------------------------------------------
Title: Close causal relation between emergence of twisted flux rope
and strong flares
Authors: Kurokawa, H.; Ishii, T.; Ueno, S.; Nagata, S.; Kitai, R. .;
Shibata, K.
2006cosp...36.2230K Altcode: 2006cosp.meet.2230K
Solar flares are considered to occur in the solar corona by magnetic
field reconnection Shibata 1995 The flare energy which is stored in the
twisted magnetic field is supplied to the corona through the photosphere
from the convection zone For this reason observations of evolutional
changes in the magnetic field configuration of flare-productive regions
are fundamentally important for the flare energy build-up study and
the forecast of strong flares Hagyard 1984 showed that flares occurred
along the neutral line of strong magnetic shear The magnetic shear is
however not a sufficient condition for strong flare occurrence and it
is important to study the active region evolutions and examine which
type of magnetic shear development produces strong flares Until now
several works made detailed studies of magnetic shear developments in
flare-productive sunspot regions and suggested that the emergence of a
twisted magnetic flux rope which is originally formed in the convection
zone must be the source of the strong magnetic shear development in a
sunspot region to produce a strong flare activity Kurokawa 1987 Tanaka
1991 Ishii et al 1998 Kurokawa 2002 In this paper we present our recent
studies of energy build-up processes of flare-productive active regions
We studied the evolutional changes of 11 super active regions which
produced more than three X-class flares observed from 1998 through 2005
during the 23 solar sunspot cycle in details We found all these regions
show some common magnetic evolutional features in the course of the
---------------------------------------------------------
Title: CAWSES Related Projects in Japan : Grant-in-Aid for Creative
Scientific Research ügBasic Study of Space Weather Predictionüh
and CHAIN (Continuous H Alpha Imaging Network)
Authors: Shibata, K.; Kurokawa, H.
2006cosp...36.3288S Altcode: 2006cosp.meet.3288S
The Grant-in-Aid for Creative Scientific Research of the Ministry of
Education Science Sports Technology and Culture of Japan The Basic
Study of Space Weather Prediction PI K Shibata Kyoto Univ has started
in 2005 as 5 years projects with total budget 446Myen The purpose
of this project is to develop a physical model of solar-terrestrial
phenomena and space storms as a basis of space weather prediction by
resolving fundamental physics of key phenomena from solar flares and
coronal mass ejections to magnetospheric storms under international
cooperation program CAWSES Climate and Weather of the Sun-Earth System
Continuous H Alpha Imaging Network CHAIN Project led by H Kurokawa
is a key project in this space weather study enabling continuous H
alpha full Sun observations by connecting many solar telescopes in
many countries through internet which provides the basis of the study
of space weather prediction
---------------------------------------------------------
Title: a Series of Compact Flares with AN Associated CME
Authors: Goff, C. P.; van Driel-Geszrelyi, L.; Culhane, J. L.;
Matthews, S. A.; Harra, L. K.; Démoulin, P.; Mandrini, C. H.;
Kurokawa, H.
2005ESASP.600E.157G Altcode: 2005ESPM...11..157G; 2005dysu.confE.157G
No abstract at ADS
---------------------------------------------------------
Title: Multi-Line Spectroscopy of Grains
Authors: Kamio, S.; Kurokawa, H.
2005ESASP.600E..18K Altcode: 2005ESPM...11...18K; 2005dysu.confE..18K
No abstract at ADS
---------------------------------------------------------
Title: Evolution of Barb Angle and Filament Eruption
Authors: Su, J. T.; Liu, Y.; Zhang, H. Q.; Kurokawa, H.; Yurchyshyn,
V.; Shibata, K.; Bao, X. M.; Wang, G. P.; Li, C.
2005ApJ...630L.101S Altcode:
Hα observations of a quiescent U-shaped filament were obtained at Big
Bear Solar Observatory and at Hida Observatory with the Flare Monitoring
Telescope. The filament was located in the southern hemisphere on
1998 November 4. We study the evolution of the angle of a barb with
respect to the axis of the filament and find the evolution can be
divided into two phases: a rise from the acute phase to the obtuse
phase and a fall. Thus, this indicates that the chirality of this barb
changes with time. Moreover, in the process of evolution, we find that
interconnection of the part of the filament bearing the barb with the
whole filament became either weakened or strengthened. We impute the
final eruption of the filament to the chirality evolution of the barb.
---------------------------------------------------------
Title: Production of Filaments by Surges
Authors: Liu, Yu; Kurokawa, Hiroki; Shibata, Kazunari
2005ApJ...631L..93L Altcode:
We have recently developed a new method for automatic detection of
solar surges and other dark dynamic features. For the first time we
find that some filaments can be quickly formed by trapping the cold
material supplied by surges originating from the chromosphere. Two clear
examples are presented in this Letter, showing the special process for
new filament formation by surge injection. The data used here were
taken from Hida Observatory and the Global Hα Network operated by
Big Bear Solar Observatory. Both the filaments existed on the solar
surface for not less than 20 hr, with an average length about 200",
and had obvious helical structures and barbs. The surge material
was injected from one terminal along the main axis of the filaments
or the filament channels. We conclude that there are two necessary
conditions for new filament formation by surges at one location:
(1) an “empty” filament channel, or magnetic trap, and (2) enough
mass supplied by surge activity. In most other surge-filament events,
apart from our two examples, the surges are observed moving toward
and acting on a preexisting nearby filament. The close relationship
between surge activity and filament formation and maintenance suggests
that there should be a direct link between the filament axial fields
and the large-scale background fields along which the surge material
can be driven into the filament channel. On the other hand, it also
supports the idea that the frequent injection of flow from below is an
important way to convey mass and energy into the corona through magnetic
reconnections driven by successive emerging flux and converging flow.
---------------------------------------------------------
Title: Observations of an Emerging Flux Region Surge: Implications
for Coronal Mass Ejections Triggered by Emerging Flux
Authors: Liu, Y.; Su, J. T.; Morimoto, T.; Kurokawa, H.; Shibata, K.
2005ApJ...628.1056L Altcode:
It is well known that coronal mass ejections (CMEs) are often associated
with flares and filament eruptions. Previous studies of CMEs, however,
have not established any association between CMEs and surges. In this
paper, we present a detailed analysis of a large emerging flux region
(EFR) surge and a jetlike CME, both observed on 1998 April 16. Our
analysis shows a close temporal and spatial relationship between
the two. Using observations from the Large Angle and Spectrometric
Coronagraph (LASCO) and Hida Flare Monitoring Telescope (Hα, Hα+/-0.8
Å), we found that the CME's onset time and central position angle were
coincident with the surge features. Magnetograms and Hα filtergrams
showed that the surge resulted from the successive emergence of a
bipolar sunspot group, NOAA Active Region 8203, which was the only
active region in the northern hemisphere. The surge was impulsively
accelerated at around the peak time of the GOES SXR flux. The associated
CME appeared in the field of view of LASCO C2 16 minutes after the
surge disappeared. Importantly, observations from the EUV Imaging
Telescope at λ195 Å clearly demonstrate topological changes in the
coronal field due to its interaction with the EFR. An initially closed
EFR-loop system opened up during the surge. There was no filament
involved in this surge-CME event. We propose that the onset of the
CME resulted from the significant restructuring of the large-scale
coronal magnetic field as a result of flux emergence in the active
region. This surge-CME event strongly suggests that emerging flux
may not only trigger a surge but also simultaneously trigger a CME by
means of small-scale reconnection in the lower atmosphere.
---------------------------------------------------------
Title: Transition Region Downflows in the Impulsive Phase of Solar
Flares
Authors: Kamio, S.; Kurokawa, H.; Brooks, D. H.; Kitai, R.; UeNo, S.
2005ApJ...625.1027K Altcode:
We present observations of four flares that occurred during
coordinated observations between the Coronal Diagnostic Spectrometer
(CDS) on board SOHO and the Domeless Solar Telescope (DST) at Hida
Observatory. We studied the evolution of relative Doppler velocities
in the flare kernels by using He I (3.5×10<SUP>4</SUP> K), O V
(2.2×10<SUP>5</SUP> K), and Mg IX (1.0×10<SUP>6</SUP> K) spectra
obtained with high time cadence (42 s) SOHO CDS observations and the
Hα monochromatic images obtained with the DST. We found that the
transition region plasma of O V showed strong downward velocities
up to 87 km s<SUP>-1</SUP> simultaneously with the downflows in the
lower temperature chromospheric emissions in He I and Hα during the
impulsive phase of all four flares. From these results we suggest
that the downflows in the transition region and the chromosphere are a
common feature in the impulsive phase of flares. For the Mg IX line we
did not detect any significant change in velocity, which suggests that
the 10<SUP>6</SUP> K plasma was close to the intermediate temperature
between the upflowing plasma (10<SUP>7</SUP> K) and the downflowing
plasma (10<SUP>4</SUP>-10<SUP>5</SUP> K). These are important for
understanding the dynamics of the solar atmosphere in response to the
sudden energy deposition of a flare.
---------------------------------------------------------
Title: A Study On Surges: I. Automatic Detection Of Dynamic Hα Dark
Features From High-Cadence Full-Disk Observations
Authors: Liu, Y.; Kurokawa, H.; Kitai, R.; Ueno, S.; Su, J. T.
2005SoPh..228..149L Altcode:
We present a new method for the automatic identification and
classification of dynamic Hα dark features found in time series of
full-disk solar images at three Hα wavelengths (center, and ± 0.8
Å). The simultaneous Hα observations are obtained by the multi-channel
Flare Monitoring Telescope (FMT) at Hida Observatory. The program
was developed in order to replace the present visual detection and
classification of the phenomena. Usually, an obvious dark feature
found in the Hα −0.8 Å observations probably corresponds to some
phenomenon such as a surge or chromospheric network enhancement,
or filament activity. Thus, one of our aims in this program
is to distinguish each phenomenon by its own properties and key
parameters. We optimized the threshold values of the key parameters
such as the area and darkness of the transiently darkening features in
Hα −0.8 Å so that the computer can reasonably identify surges and
filament activations. In comparison, for a 7-day observation period,
the number of dark events detected by the program contains 89% of the
events recognized visually. However, 10 times more events are detected
automatically. The missing events are mainly caused by the deletion
of data with poor visibility. It is found that the dark events can be
identified with more precise starting and ending times by a machine
than by a human. Some statistical studies of surges or other activities
can be carried out based on the computer-produced database. With some
modifications the program can be applied to monitor real-time dynamic
features on disk, including flare ribbons.
---------------------------------------------------------
Title: Magnetic Neutral Line Rotations in Flare-Productive Regions
Authors: Ishii, Takako T.; Asai, Ayumi; Kurokawa, Hiroki; Takeuchi,
Tsutomu T.
2005HiA....13..138I Altcode:
We studied what is the common magnetic field configuration among
flare-productive active regions. In our previous studies we have found
that the magnetic neutral line shows a rotational motion in a delta-type
sunspot group NOAA 9026 where three X-class flares successively
occurred. In this paper we show another examples of magnetic neutral
line rotations in flare-productive sunspot groups. During the current
solar maximum (cycle 23) we studied the evolution of all the active
regions that have produced at least one X-class flare and have been
observed by the Solar and Heliospheric Observatory (SOHO) / Michelson
Doppler Imager (MDI). We examined 32 active regions from 1996 through
2002 and found that the rotational sunspot motions are common to these
flare-productive active regions (e.g. vortex-like motions in NOAA 8210
9236; rotation of magnetic neutral line of delta-type sunspots in
NOAA 9026 9393 9415 9591 9661 0039). These motions suggest that the
emergence of twisted magnetic flux bundles are the energy source for
strong flares. We discuss the relation between the magnetic helicity
and such a motion of magnetic neutral line e.g. the hemisphere rule
of helicity sign and the orientation of neutral line rotation.
---------------------------------------------------------
Title: Flare ribbon expansion and energy release rate
Authors: Asai, Ayumi; Shimojo, Masumi; Yokoyama, Takaaki; Masuda,
Satoshi; Kurokawa, Hiroki; Shibata, Kazunari
2005ARAOJ...7....7A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Studies on the Flare Energy Build-Up Process Using SolarB/Solar
Optical Telescope (SOT) and Solar Magnetic Activity Research Telescope
(SMART) at Hida Observatory
Authors: Ishii, T. T.; Nagata, S.; Ueno, S.; Kitai, R.; Kurokawa,
H.; SMART Team
2004ASPC..325..331I Altcode:
Evolution of active regions is one of the key topics for understanding
the energy storage and triggering mechanisms of flares. In our previous
studies, we found that the twisted structure of emerging magnetic
flux bundles is the essential feature of flare-productive active
regions. Vector magnetic field data sets are necessary to examine
the twisted magnetic field structures (e.g. shear and helicity). The
SolarB/Solar Optical Telescope (SOT) enables us to study the detailed
magnetic field configuration with a high spatial resolution. Recently
we have constructed our new telescope, Solar Magnetic Activity Research
Telescope (SMART) at Hida Observatory. Vector magnetic field telescope
of SMART has a much wider field of view (FOV) than that of SOT. In
this paper, we propose an observational plan of the active region
evolution and flare energy build-up process with SOT and SMART.
---------------------------------------------------------
Title: Transition Region Downflows in the Impulsive Phase of Flares
Authors: Kamio, S.; Kurokawa, H.; Brooks, D. H.
2004ESASP.575..479K Altcode: 2004soho...15..479K
No abstract at ADS
---------------------------------------------------------
Title: The Red-Asymmetry Distribution at Hα Flare Kernels Observed
in the 2001 April 10 Solar Flare
Authors: Asai, A.; Ichimoto, K.; Shibata, K.; Kitai, R.; Kurokawa, H.
2004AGUFMSH13A1134A Altcode:
We report a detailed examination about the evolution of the Hα flare
kernels during an X2.3 solar flare which occurred on 2001 April 10. The
Hα red-asymmetry, that is, the red-shifted Hα emission, is observed
at almost all Hα flare kernels, during the impulsive phase of the
flare. At Hα kernels nonthermal particles and/or thermal conduction
precipitate into the chromospheric plasma, and this is thought to lead
the downward compression of the chromospheric plasma, which is observed
as the reddening of Hα emission (e.g. Ichimoto & Kurokawa 1984). We
examined the evolution of the flare kernels inside the flare ribbons
by using the Hα images obtained with the Domeless Solar Telescope
at Hida Observatory, Kyoto University. We also examined the spatial
distribution of the Hα kernels which show the red-asymmetry and their
relationship with the intensity of the Hα kernels. We found that the
stronger the red-asymmetry is, the brighter the Hα kernel is. Then, we
compared the strengthes of the Hα red-asymmetry at hard X-ray emitting
sources with those at the Hα kernels without the hard X-ray emissions.
---------------------------------------------------------
Title: Features of Solar Telescopes at the Hida Observatory and the
Possibilities of Coordinated Observations with SolarB
Authors: Ueno, S.; Nagata, S.; Kitai, R.; Kurokawa, H.
2004ASPC..325..319U Altcode:
At the Hida observatory, two solar telescopes, Domeless Solar Telescope
(DST) and Flare Monitoring Telescope (FMT), have been operated for
studying solar fundamental structures and active phenomena which affect
interplanetary environment. In addition, a new telescope named Solar
Magnetic Activity Research Telescope (SMART) was built from 2002 through
2003 to obtain simultaneously Hα image and the vector magnetogram
of the full solar disk with high spatial and temporal resolution. In
this paper, we give an outline and scientific purposes of these three
telescopes, with emphasis on the SMART, and discuss about possibilities
of coordinated observations with SolarB.
---------------------------------------------------------
Title: Calibration of the instrumental polarization of the Domeless
Solar Telescope at the Hida Observatory
Authors: Kiyohara, Junko; Ueno, Satoru; Kitai, Reizaburo; Kurokawa,
Hiroki; Makita, Mitsugu; Ichimoto, Kiyoshi
2004SPIE.5492.1778K Altcode:
A new spectropolarimeter is developed at the Domeless Solar Telescope
(DST) in Hida Observatory. It consists of a rotating waveplate,
Wollaston prisms, and a high-dispersion spectrograph which is
vertically installed at the focus of the DST. In order to realize
a high-precision measurement, it is inevitable to compensate the
instrumental polarization due to the DST. We observed the quiet
region of the Sun, which is considered to be highly unpolarized,
with and without a sheet linear polarizer or circular polarizer
set at the entrance window of the telescope. The theoretical model
which represents the total instrumental polarization of the DST with
some characteristic parameters was calculated and compared with the
observation. The model that two flat mirrors have different properties
can explain the observation in 0.5% accuracy for the unpolarized light,
and in 7% for the polarized light.
---------------------------------------------------------
Title: The development of filter vector magnetographs for the Solar
Magnetic Activity Research Telescope (SMART)
Authors: UeNo, Satoru; Nagata, Shin-ichi; Kitai, Reizaburo; Kurokawa,
Hiroki; Ichimoto, Kiyoshi
2004SPIE.5492..958U Altcode:
In recent years, it is beginning to be shown observationally and
theoretically that the existence of the magnetic field is indispensable
for active phenomena on the solar surface. In particular, the rotation
or helicity of the magnetic field and their temporal variation are
considered to be important factors which influence solar activity. In
order to confirm this, it is necessary to compute vector components
of the magnetic field with a higher accuracy than before. Therefore,
we developed two kinds of filter-type magnetographs for the Solar
Magnetic Activity Research Telescope (SMART) at Hida observatory, which
allow us to observe the polarization components in sunlight with high
accuracy. We use a Lyot filter in one of two sets of magnetographs. On
the other hand, a tandem-typed Fabry-Perot filter is used in one
more set. For these two instruments, we made the following concrete
advances. 1. The method of coating of the pre-filters. 2. Special
fine-anneal on the main lenses. 3. Highly accurate rotating
wave-plate. 4. Simultaneous observation of two kinds of filtergrams
which have orthogonally polarized light mutually by using Fabry-Perot
channel. 5. Observation in four wavelengths which can suppress various
errors. 6. Low apparent Doppler shift in the FOV due to the oblique
incidence of the rays to the filters. 7. Large format CCD (large-sized
chip, large full-well). 8. High speed data transfer interface between
the CCD and PC. In this paper, we report the details of these points,
the expected effect of them, and the results of initial measurements.
---------------------------------------------------------
Title: On a Surge: Properties of an Emerging Flux Region
Authors: Liu, Yu; Kurokawa, Hiroki
2004ApJ...610.1136L Altcode:
A surge event with multi-instrument and multiwavelength observations
is presented. The event occurred in a surge-productive region on 2001
August 30. TRACE white-light images, Huairou vector magnetograms,
and Hβ filtergrams show that this surge was closely associated with
new bipoles that emerged in 1 hr. Evidence of enhanced magnetic
cancellation is revealed at the footpoints of the surge where a
simultaneous surge flare is shown in the Hβ line. In particular,
the interesting observational results for this surge are that (1)
the surge was associated with pronounced photospheric bright points
near the emerging spots; (2) in vector magnetograms, during the
surge ascending period, reliable transverse fields appeared between
the emerging flux and the ambient fields cancelled at the base of the
surge, and these fresh transverse fields disappeared after 20 minutes;
(3) the preceding spots of the emerged bipoles almost disappeared in
white-light images when the surge activity stopped; and (4) the TRACE
UV (1550 Å) channel showed a bright surge (~10<SUP>5</SUP> K) well
correlated with the dark Hβ surge (~10<SUP>3</SUP>-10<SUP>4</SUP>
K). The UV surge had a bright spike shape and spouted out along the
outer edges of the Hβ surge. Similarly, the bright components in
TRACE EUV (~10<SUP>6</SUP> K) were also located at the edges of the Hβ
surge. Both the SOHO/EIT and Yohkoh/SXT observations demonstrate that
the jet plasma was ejected from one footpoint of a flaring coronal loop
identified during the surge. We estimate the magnetic energy released
from the site of the magnetic cancellation, the kinetic energy of
the surge, and the thermal energy for the loop brightening in SXR,
finding that the magnetic reconnection could supply enough energy for
the surge activities and the coronal loop heating. For this surge,
all the correlated phenomena in multiwavelengths (Hβ, white light,
UV, EUV, and SXR) are in good temporal and spatial relationship. These
facts support a magnetic reconnection model in which surges originate
in the low atmosphere. Moreover, low-altitude magnetic reconnections
can result in the magnetic cancellation observed on the photosphere.
---------------------------------------------------------
Title: Hida Domeless Solar Telescope and SOHO Coronal Diagnostic
Spectrometer Observations of Short-Duration Active Region
Blinkers. II. Extreme-Ultraviolet Properties
Authors: Brooks, D. H.; Kurokawa, H.
2004ApJ...611.1125B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flare Ribbon Expansion and Energy Release Rate
Authors: Asai, Ayumi; Yokoyama, Takaaki; Shimojo, Masumi; Masuda,
Satoshi; Kurokawa, Hiroki; Shibata, Kazunari
2004ApJ...611..557A Altcode:
We have examined the relation between the evolution of the Hα
flare ribbons and the released magnetic energy in a solar flare that
occurred on 2001 April 10. Based on the magnetic reconnection model, the
released energy was quantitatively calculated by using the photospheric
magnetic field strengths and separation speeds of the fronts of the
Hα flare ribbons. We compared the variation of the released energy
with the temporal and spatial fluctuations in the nonthermal radiation
observed in hard X-rays and microwaves. These nonthermal radiation
sources indicate when and where large energy releases occur. We also
estimated the magnetic energy released during the flare. The estimated
energy release rates in the Hα kernels associated with the hard X-ray
sources are locally large enough to explain the difference between the
spatial distributions of the Hα kernels and the hard X-ray sources. We
also reconstructed the peaks in the nonthermal emission by using the
estimated energy release rates.
---------------------------------------------------------
Title: Filament Oscillations and Moreton Waves Associated with
EIT Waves
Authors: Okamoto, Takenori J.; Nakai, Hidekazu; Keiyama, Atsushi;
Narukage, Noriyuki; UeNo, Satoru; Kitai, Reizaburo; Kurokawa, Hiroki;
Shibata, Kazunari
2004ApJ...608.1124O Altcode:
In this paper we compare EUV Imaging Telescope (EIT) waves with
simultaneous phenomena seen in Hα in order to address the question
of what an EIT wave is. We surveyed the events associated with solar
flares larger than GOES M-class in 1999-2002. The Hα data are taken
with the Flare-monitoring Telescope (FMT) at the Hida Observatory
of Kyoto University. Among 14 simultaneous observations of EIT
waves and Hα, 11 were found to have filament eruptions, three were
associated with Moreton waves, and one was found to have only filament
oscillations. This shows that we cannot see clear wave fronts in
Hα even if EIT waves exist, but that it is possible to recognize
invisible waves by means of filament oscillations. The nature of
filament oscillations and Moreton waves associated with EIT waves is
examined in detail, and it is found that the filament oscillations
were caused by EIT waves.
---------------------------------------------------------
Title: Formation of Opposite-Sign Magnetic Helicity by an Erupting
Filament in a Coronal Mass Ejection
Authors: Liu, Yu; Kurokawa, Hiroki
2004PASJ...56..497L Altcode:
It is unclear whether it is possible for magnetic helical fields of
opposite signs to co-exist in a coronal mass ejection (CME). During
filament eruption with high-cadence observations for the initial stage,
evidence is found for the formation of right-handed helical fields
in a rising dextral filament that is embedded in a CME with helical
fields in a left-handed sense. The data include Mees multi-off-band
Hα observations with 16s cadence and TRACE 1600Å observations of 2s
cadence. The filament material is ejected outward and is associated
with the expanding CME, suggesting that both of the opposite-sign
helical fields are injected into interplanetary space. In this
paper, we consider the key observational features, including the
formation of a coil-like structure (due to barb reconnections) and
the alignment of reconnected field lines with the primary axis of the
filament. It is found that they are consistent with the predicted
changes during filament eruption by the filament model of Martin
and McAllister. However, our results do not reject the filament
model of Rust and Kumar. Moreover, a model that reconciles both of
them seems to be more convenient for understanding the complicated
observations. Therefore, the formation of opposite-sign helicity in
an eruptive flux rope should be common for such types of filament
eruptions.
---------------------------------------------------------
Title: X-Ray Expanding Features Associated with a Moreton Wave
Authors: Noriyuki, Narukage; Morimoto, Taro; Kadota, Miwako; Kitai,
Reizaburo; Kurokawa, Hiroki; Shibata, Kazunari
2004PASJ...56L...5N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Short-Duration Active Region Brightenings Observed in the
Extreme Ultraviolet and Hα by the Solar and Heliospheric Observatory
Coronal Diagnostic Spectrometer and Hida Domeless Solar Telescope
Authors: Brooks, D. H.; Kurokawa, H.; Kamio, S.; Fludra, A.; Ishii,
T. T.; Kitai, R.; Kozu, H.; Ueno, S.; Yoshimura, K.
2004ApJ...602.1051B Altcode:
We present the first detection of an Hα counterpart to the EUV
blinker. The observations come from a coordinated campaign between
the Hida Observatory Domeless Solar Telescope (DST) and the Solar
and Heliospheric Observatory Coronal Diagnostic Spectrometer (CDS)
conducted in 2002 July and August. Utilizing studies designed for
high-cadence observations, many short-duration brightenings (<3
minutes) were identified in the He I λ584.334 and O V λ629.732
spectral lines in CDS data of active region NOAA 10039/10044. These
brightenings show similar characteristics (increases in intensity,
size) to longer duration EUV blinkers previously reported in active
regions and the quiet Sun. Focusing on two events that show pronounced
emission in the upper chromosphere (He I), we have been able to identify
cospatial bright points in the lower chromosphere (Hα center, +/-0.5
Å) that show enhanced emission during the EUV blinker. These bright
features have lifetimes similar to those of their EUV counterparts,
and their peak intensities occur nearly simultaneously with the peak
blinker intensities in the He I and O V lines. In both cases the He
I and O V lines show excess line broadening at the peak of the event
(>15 km s<SUP>-1</SUP>). Our high-cadence observations also enabled
us to examine the dimensions and lifetimes of short-duration active
region blinkers in detail. We find that the instrumental spatial and
temporal resolution can combine to distort their characteristics:
even short-duration blinkers appear to be composed of elementary
brightening events. The optical brightenings also appear to closely
follow the behavior of the elementary brightenings. The spatial and
temporal relationships between the brightenings indicate a causal link
between the EUV and Hα blinkers.
---------------------------------------------------------
Title: Short Duration Active Region Brightenings Observed in the
EUV and Ha by SOHO/CDS and HIDA/DST
Authors: Brooks, D. H.; Kurokawa, H.; Kamio, S.; Fludra, A.; Ishii,
T. T.; Kitai, R.; Kosu, H.; Ueno, S.; Yoshimura, K.
2004ESASP.547..273B Altcode: 2004soho...13..273B
We present the 1st detection of an H counterpart to the EUV blinker,
using observations from a coordinated campaign between the SOHO Coronal
Diagnostic Spectrometer and the Kyoto University Hida Observatory,
Domeless Solar Telescope (DST). The observations were performed during
July and August 2002. By designing the CDS observing sequences for
high cadence and long duration observations, we were able to identify
many short duration (<3 mins.) brightenings simultaneously in the
He I 584.334A and O V 629.732A spectral lines. These brightenings
show similar characteristics (intensity increases, sizes) to longer
duration EUV blinkers previously reported in active regions and the
'quiet' Sun. Focusing on two events which show pronounced emission
in the upper chromosphere (He I), we have been able to identify
cospatial bright points in the lower chromosphere (H line centre,
60.5A) which show enhanced emission during the EUV blinkers. These
bright features have similar lifetimes to their EUV counterparts and
their peak intensities occur close to simultaneously with the peak
blinker intensities in the He I and O V lines. In both cases the He
I and O V lines show excess line broadening at the peak of the event
(>15 km s01) and in one event evidence of downward (red-shifted)
motion is observed. A statistical study is being performed to provide
a complete picture of the line width and velocity characteristics of
these events and to determine whether the H counterparts are common, or
confined to specific blinkers with pronounced He I emission. The high
cadence of our observations also allowed us to examine the eects of
spatial and temporal averaging on the determination of the properties
of blinkers. We find that both short and long duration blinkers are
composed of elementary brightening events and that such events can
be undetectable in observations with low temporal cadence. Finally,
the H brightenings appear to correlate well with the elementary EUV
brightening events.
---------------------------------------------------------
Title: Twisted Magnetic Flux Bundle Models for Solar Flares
Authors: Ishii, T. T.; Kurokawa, H.; Takeuchi, T. T.
2004IAUS..219..693I Altcode: 2003IAUS..219E..79I
We studied what is the key process to trigger the major solar flares
using observational data of the evolutions of active regions. In our
previous studies we have pointed out that the process of magnetic
shear development is important for studying the above topic. We have
constructed schematic models of emerging magnetic flux bundles to
explain observed sunspot proper motions and found that the emergence
of twisted magnetic flux bundles relates to strong flare activities
in several sunspot groups. During the current solar maximum (cycle 23)
we studied the evolution of all the active regions that have produced
at least one X-class flare and have been observed by the Solar and
Heliospheric Observatory (SOHO) / Michelson Doppler Imager (MDI). In
this paper we analyzed 32 active regions from 1996 through 2002 and
studied what is the the common magnetic field configuration among these
active regions. We found that the above-mentioned relation between
sunspot proper motions resulting from the emergence of twisted magnetic
flux tubes and strong flare activities are common among flare-productive
active regions. This result suggests that the emergence of twisted
magnetic flux bundles are the energy source for strong flares.
---------------------------------------------------------
Title: Moreton waves observed at Hida Observatory
Authors: Narukage, Noriyuki; Eto, Shigeru; Kadota, Miwako; Kitai,
Reizaburo; Kurokawa, Hiroki; Shibata, Kazunari
2004IAUS..223..367N Altcode: 2005IAUS..223..367N
Moreton waves are flare-associated waves observed to propagate across
the solar disk in Halpha, especially in the wing of Halpha. The Flare
Monitoring Telescope at Hida Observatory of Kyoto University observed
12 events associated with flare waves (i.e., Moreton waves and/or
filament oscillations) in Halpha from 1997 to 2002. We review our
studies of Moreton waves based on these observations; relation between
EIT wave and Moreton wave (Eto et al. 2002),simultaneous observation
with X-ray wave (Narukage et al. 2002),three dimensional structure of
flare-associated wave (Narukage et al. 2004),relation between Moreton
waves and filament eruptions.
---------------------------------------------------------
Title: Twisted Flux Rope Model for a Flare-productive Sunspot Group
NOAA 10486
Authors: Ishii, T. T.; Kurokawa, H.; Dun, J. P.; Saito, S.; Takeuchi,
T. T.
2004cosp...35.2412I Altcode: 2004cosp.meet.2412I
What is the common magnetic field configuration among flare-productive
active regions? In our previous studies, we have found that the magnetic
neutral line shows a rotational motion in a δ-type active region NOAA
9026, where three X-class flares have occurred successively. During
the current solar maximum (cycle 23), we studied the evolution of all
active regions that have produced at least one X-class flare and have
been observed by SOHO/MDI magnetograms. Active region NOAA 10486 is
the most flare-productive region during this solar cycle, which have
produced seven X-class flares including X28 flare on Nov. 4, 2003. We
studied the formation process of δ-type magnetic configuration using
SOHO/MDI magnetograms. We also studied the evolution of magnetic shear
and Hα filaments using vector magnetograms obtained at Huairou Solar
Observing Station and Hα images obtained with the Sartorius telescope
at Kwasan Observatory, Kyoto University. In this active region, we found
that a development of a strong magnetic shear with a new magnetic flux
emergence along a magnetic neutral line plays an important role as the
trigger of the X-class flare on Oct. 28. Based on these observational
characteristics, we discuss the model of emerging bundles of a magnetic
flux rope and its causal relation to the trigger of strong flares.
---------------------------------------------------------
Title: Evolution of Blue-Shifted Ha Grains Observed in the Cell
Interior
Authors: Kamio, S.; Kurokawa, H.
2004ESASP.547..143K Altcode: 2004soho...13..143K
H grains are small features of strong upward motions in the
chromosphere, which are seen as small dark features in the filter
image centered at H blue wing. They are found ubiquitously in the
interiors of network cells in the quiet region and their typical size
and duration are 1000km and 1 min respectively. We obtained H filter
images and H spectra simultaneously in the quiet region with Domeless
Solar Telescope(DST) at Hida Observatory, Kyoto University. Sequential
data of 80 min in good seeing condition allows us to study the temporal
evolution of H grains in detail. Our analysis of H spectra shows that
the grains appeared repetitively at the same location with interval of
3 min, which means that the generation of grains are closely related
to the chromospheric oscillation. The line broadening preceding
the upward motion of grains suggests that the grains are produced
or triggered by the shock in the chromosphere. Chromospheric grains
have been observed in other lines such as Ca II H and K, and their
characteristics are summarized in the excellent review of [1]. H
and Ca II grains are supposed to be the different aspect of the same
phenomena. The relation between grains of H and other lines should be
studied to determine the origin of chromospheric grains.
---------------------------------------------------------
Title: The Three-Dimensional Velocity Fields Of Solar Disappearing
Filaments And Their Relations To Coronal Activities
Authors: Morimoto, T.; Kurokawa, H.
2003AGUFMSH22B..03M Altcode:
Solar filament disappearance (Disparition Brusque: DB) is often
accompanied by a great magnetic activities such as flares and
transient shock waves on and near the solar surface as well as enormous
disturbances in interplanetary space due to the associated coronal mass
ejection (CMEs). Thus, DBs are of great interest not only to solar
physics research, but also to space science, and solar-terrestrial
study. Since it is impossible to measure the velocity field of DBs
with ordinal observations in the Hα line center alone, most previous
studies have focused on the morphological signatures of DBs. In order
to obtain the physical characteristics of DBs and relate them to other
active phenomena, much effort is put into the calculation of their
three-dimensional (3-D) velocity fields. Using the Hα line center,
blue and red wing (Hα +/- 0.8 Å ) images obtained by the Flare
Monitoring Telescope (FMT) at Hida Observatory, Kyoto University,
and based on the Beckers' cloud model, we developed a new method to
obtain the line-of-sight velocity of disappearing solar filaments. The
line-of-sight velocity is obtained (i) by calculating the Hα line
profile of the filament, and (ii) by measuring the Doppler shift
which best fits the observed temporal variations of contrasts of the
filament. The tangential velocity is obtained by tracing the motions of
internal structures on successive images, and both line-of-sight and
tangential velocities are combined to yield the 3-D velcoty field of
DBs. In this method, corrections for the effective filter bandwidths
of the instrument, stray light and Doppler brightening effect, are
performed. Using the 3-D velocity field of DBs, we also developed a
method to judge whether the DB was ejected into interplanetary space
(eruptive) or remained in the corona (quasi-eruptive). The type of
DBs are compared with the type of the associated coronal activites
such as arcade formations observed in soft X-rays and EUV, CMEs and
we conclude that the calculation of the three dimensional vector
trajectories of disappearing filaments with our method can enhance
the quality of space weather forecast and improve its accuracy.
---------------------------------------------------------
Title: Eruptive and Quasi-Eruptive Disappearing Solar Filaments and
Their Relationship with Coronal Activities
Authors: Morimoto, Taro; Kurokawa, Hiroki
2003PASJ...55.1141M Altcode:
By measuring the 3-D velocity fields of 35 disappearing filaments
(Disparition Brusques: DBs) on the solar disk, we studied the
causal relationship between the motions of Hα DBs and the associated
coronal phenomena. Using the derived 3-D velocity fields of the DBs, we
developed a method to judge whether a DB is ejected into interplanetary
space or whether it remains in the solar atmosphere. We compared the
DB type thus obtained with the presence of coronal mass ejections
(CMEs) and other associated coronal activities. It is inferred that
eruptive filaments are always followed by the formation of arcades,
while most quasi-eruptive events are followed by localized changes
in soft X-rays and the EUV. A close causal relation between eruptive
filaments and CMEs was also found: of 15 DBs for which Solar and
Heliospheric Observatory Large Angle and Spectrometric Coronagraph data
were available, all eight of the eruptive ones were associated with
CMEs, while no CMEs were found following any of the 7 quasi-eruptive
ones. These observational results indicate that the motions of Hα
disappearing filaments are causally related to the associated coronal
activities and also to the appearance of CMEs, and that an accurate
analysis of their 3-D velocities is important not only for a better
understanding of their acceleration and heating mechanisms, but also
for predicting the occurrence of CMEs and geomagnetic storms.
---------------------------------------------------------
Title: A study of the causal relationship between the emergence of
a twisted magnetic flux rope and a small Hα two-ribbon flare
Authors: Brooks, D. H.; Kurokawa, H.; Yoshimura, K.; Kozu, H.; Berger,
T. E.
2003A&A...411..273B Altcode:
We present results from an analysis of a small two-ribbon flare which
occurred above emerging flux in solar active region NOAA 8218 on 1998,
May 13th and which was observed by the Swedish Vacuum Solar Telescope
(SVST) on the island of La Palma, Spain. The relatively simple magnetic
morphology and small size of the flare together with the high quality
of the SVST observations allow us to examine the essential properties
of flares in emerging flux regions in greater detail than before. <P
/>In this paper we compare and contrast the flaring emerging flux region
simultaneously with a non-flaring emerging flux region within the same
field of view. Unusual magnetic footpoint motions are observed in the
flaring region, coincident with the Hα kernels, which result in a
high level of shearing of the magnetic neutral line between opposite
polarities. The Hα images show dark filament structures which form an
inverted S-like shape immediately prior to the flare and then separate
after the energy release disrupts the magnetic field. We interpret
the motions and structures as strong evidence for the emergence of a
twisted magnetic flux rope which developed a sheared configuration with
the overlying magnetic field. In contrast the companion region shows
separating footpoints, with apparent arch-like filament connections in
the Hα images, consistent with the expected appearance of emerging
flux. The observations imply that the attachment of the inverted
S-shaped structure may be an observational consequence of the magnetic
reconnection or untwisting of the field which triggered the flare. We
also find some evidence that the increase in magnetic flux is faster
in the flaring region. <P />Finally, we propose a simple schematic
model of the emergence of a twisted magnetic flux rope and attached
branch which can account for the observed footpoint motions and Hα
structures of the flaring region. Such a model can, in principle,
induce partial magnetic reconnection in the overlying coronal field
and we found some evidence of coronal loop footpoint brightenings
which support our conclusions. Our high resolution study supports the
results of previous authors that even a small twisted structure in an
emerging flux tube can be important for flare production.
---------------------------------------------------------
Title: Evolution of Flare Ribbons and Energy Release
Authors: Asai, A.; Yokoyama, Takaaki; Shimojo, Masumi; Masuda, Satoshi;
Kurokawa, Hiroki; Shibata, Kazunari
2003ICRC....6.3367A Altcode: 2003ICRC...28.3367A
We examined the relation between evolutions of flare ribb ons and
released magnetic energies at a solar flare which occurred on 2001
April 10 in the active region NOAA 9415. We successfully evaluated
the released energy quantitatively, based on the magnetic reconnection
model. We measured the photospheric magnetic field strengths and the
separation speeds of the fronts of the Hα flare ribb on, and estimated
the released magnetic energy at the flare by using those values. Then,
we compared the estimated energy release rates with the nonthermal
behaviors observed in hard X-rays and microwaves. We found that those
at the Hα kernels associated with the HXR sources are locally large
enough to explain the difference between the spatial distribution
the Hα kernels and the hard X-ray sources. Their temporal evolution
of the energy release rates also shows peaks corresponding to hard
X-ray bursts.
---------------------------------------------------------
Title: Precise determination of cooling times of post-flare loops
from the detailed comparison between Hα and soft X-ray images
Authors: Kamio, Suguru; Kurokawa, Hiroki; Ishii, Takako T.
2003SoPh..215..127K Altcode:
A detailed study of the evolution and cooling process of post-flare
loops is presented for a large X9.2 solar flare of 2 November 1992
by using Hα images obtained with Domeless Solar Telescope at Hida
Observatory and soft X-ray images of Yohkoh Soft X-ray Telescope
(SXT). The detailed analysis with a new method allows us to determine
more precise values of the cooling times from 10<SUP>7</SUP> K to
10<SUP>4</SUP> K plasma in the post-flare loops than in previous
works. The subtraction of sequential images shows that soft X-ray
dimming regions are well correlated to the Hα brightening loop
structure. The cooling times between 10<SUP>7</SUP> K and 10<SUP>4</SUP>
K are defined as the time difference between the start of soft X-ray
intensity decrease and the end of Hα intensity increase at a selected
point, where the causal relation between Hα brightening and soft
X-ray dimming loops is confirmed. The obtained cooling times change
with time; about 10 min at the initial stage and about 40 min at the
later stage. The combined conductive and radiative cooling times are
also calculated by using the temperature and density obtained from SXT
data. Calculated cooling times are close to observed cooling times at
the beginning of the flare and longer in the later stage.
---------------------------------------------------------
Title: A Method for the Determination of 3-D Velocity Fields of
Disappearing Solar Filaments
Authors: Morimoto, Taro; Kurokawa, Hiroki
2003PASJ...55..503M Altcode: 2003PASJ...55..505M
The 3-D velocity fields of disappearing filaments (Disparition Brusques:
DBs) on the solar disk were extensively studied in order to determine
their 3-D velocity fields. Applying Beckers' cloud model to 5 DB
events observed in the Hα line center and Hα ± 0.8 Å with the Flare
Monitoring Telescope (FMT) at Hida Observatory, we developed a method
to derive the complete 3-D velocity field of DBs. The line-of-sight
velocity is obtained (i) by calculating the Hα line profile of the
filament, and (ii) by measuring the Doppler shift which best fits to
the observed temporal variations of contrasts of the filament. The
tangential velocity is obtained by tracing the motions of the internal
structures on the successive images. In this method, corrections for
the effective filter bandwidths of the instrument, stray lights, and
Doppler brightening effect are performed. We also discuss the velocity
errors which arise from the intrinsic variations of the filament plasma
during its activation, the fluctuations in intensities of the background
chromosphere, and the choice of different forms of the spread function
for estimating the stray light. It is emphasized that the calculation
of three-dimensional vector trajectories of a disappearing filament
with our method can enhance the quality of a space weather forecast
with better certainty.
---------------------------------------------------------
Title: Evolution of Conjugate Footpoints inside Flare Ribbons during
a Great Two-Ribbon Flare on 2001 April 10
Authors: Asai, Ayumi; Ishii, Takako T.; Kurokawa, Hiroki; Yokoyama,
Takaaki; Shimojo, Masumi
2003ApJ...586..624A Altcode:
We report a detailed examination of the fine structure inside flare
ribbons and the temporal evolution of such structure during an
X2.3 solar flare, which occurred on 2001 April 10. We examined fine
structures, such as systems of conjugate footpoints, inside flare
ribbons by using the Hα images obtained with the Sartorius telescope
at Kwasan Observatory, Kyoto University. We identified the conjugate
footpoints of each Hα kernel in both flare ribbons by a new method
that uses cross-correlation functions of the light curves. We also
compared the sites of the Hα kernels with the spatial configurations
of flare loops seen in the extreme-ultraviolet images obtained with
the Transition Region and Coronal Explorer. We found that the highly
correlated pairs of Hα kernels were connected by flare loops seen
in the 171 Å images. Investigating such fine structures inside the
flare ribbons, we can follow the history of energy release and perhaps
acquire key information about particle acceleration.
---------------------------------------------------------
Title: Close Correlation among Hα Surges, Magnetic Flux
Cancellations, and UV Brightenings Found at the Edge of an Emerging
Flux Region
Authors: Yoshimura, Keiji; Kurokawa, Hiroki; Shimojo, Masumi; Shine,
Richard
2003PASJ...55..313Y Altcode:
Surge activities were observed at the edge of an emerging flux
region. We studied the relations between the features around the surges
in various data sets: magnetogram, Hα, G-band, UV, EUV, and soft
X-rays. We showed that the surge activities in Hα and the brightenings
in TRACE 1600Å images correlate well in both time and space with the
cancellation of magnetic fluxes around an emerging flux region. In
particular, at the onset of surge activity, a close correlation among
them was clearly found. These facts are consistent with the magnetic
reconnection model. The released energy through magnetic reconnection,
which is estimated to be 10<SUP>28</SUP> erg, is sufficiently large
to produce surge activities. No prominent brightenings were observed
in soft X-ray and EUV images during the surge activities. This may
suggest that the energy releases occurred at a layer of high densities.
---------------------------------------------------------
Title: Evolution of flare ribbons and energy release
Authors: Asai, A.; Masuda, S.; Yokoyama, T.; Shimojo, M.; Kurokawa,
H.; Ishii, T. T.; Shibatal, K.
2003AdSpR..32.2561A Altcode:
We examined the relation between the evolutions of the H α flare
ribbons and the released magnetic energiesat a solar flare which
occurred on 2001 April 10. This is the first study to evaluate the
released energy quantitatively, based on the magnetic reconnection
model, and by using the data obtained with the multi wavelength
observation. We measured the, photospheric magnetic field strengths
and the separation speeds of the fronts of the H α flare ribbon,
and compared them the nonthermal behaviors observed in HXRs and
microwaves. Those nonthermal radiation sources tell us when and
where large energy releases occur. Then, by using the photospheric
and chromospheric features, we estimated the released magnetic energy
at the flare. The estimated energy release rates at the H α kernels
associated with the HXR sources are locally large enough to explain
the difference between the spatial distribution the H α kernels and
the HXR sources. Their temporal evolution of the energy release rates
also shows peaks corresponding to HXR bursts.
---------------------------------------------------------
Title: Magnetic Neutral Line Rotations in Flare-Productive Regions
Authors: Ishii, Takako T.; Asai, Ayumi; Kurokawa, Hiroki; Takeuchi,
Tsutomu T.
2003IAUJD...3E..15I Altcode:
We studied what is the common magnetic field configuration among
flare-productive active regions. In our previous studies we have found
that the magnetic neutral line shows a rotational motion in a delta-type
sunspot group NOAA 9026 where three X-class flares successively
occurred. In this paper we show another examples of magnetic neutral
line rotations in flare-productive sunspot groups. During the current
solar maximum (cycle 23) we studied the evolution of all the active
regions that have produced at least one X-class flare and have been
observed by the Solar and Heliospheric Observatory (SOHO) / Michelson
Doppler Imager (MDI). We examined 32 active regions from 1996 through
2002 and found that the rotational sunspot motions are common to these
flare-productive active regions (e.g. vortex-like motions in NOAA 8210
9236; rotation of magnetic neutral line of delta-type sunspots in
NOAA 9026 9393 9415 9591 9661 0039). These motions suggest that the
emergence of twisted magnetic flux bundles are the energy source for
strong flares. We discuss the relation between the magnetic helicity
and such a motion of magnetic neutral line e.g. the hemisphere rule
of helicity sign and the orientation of neutral line rotation
---------------------------------------------------------
Title: Difference between Spatial Distributions of the Hα Kernels
and Hard X-Ray Sources in a Solar Flare
Authors: Asai, Ayumi; Masuda, Satoshi; Yokoyama, Takaaki; Shimojo,
Masumi; Isobe, Hiroaki; Kurokawa, Hiroki; Shibata, Kazunari
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: The Large-Scale Coronal Field Structure and Source Region
Features for a Halo Coronal Mass Ejection
Authors: Wang, Tongjiang; Yan, Yihua; Wang, Jialong; Kurokawa, H.;
Shibata, K.
2002ApJ...572..580W Altcode:
On 1998 May 2 a class X1/3B flare occurred at 13:42 UT in NOAA Active
Region 8210 near disk center, which was followed by a halo coronal mass
ejection (CME) at 15:03 UT observed by SOHO/LASCO. Using the boundary
element method (BEM) on a global potential model, we reconstruct
the large-scale coronal field structure from a composite boundary by
SOHO/MDI and Kitt Peak magnetograms. The extrapolated large field lines
well model a transequatorial interconnecting loop (TIL) seen in the
soft X-ray (SXR) between AR 8210 and AR 8214, which disappeared after
the CME. The EUV Imaging Telescope (EIT) observed the widely extending
dimmings, which noticeably deviate from the SXR TIL in position. We find
that the major dimmings are magnetically linked to the flaring active
region but some dimmings are not. The spatial relationships of these
features suggest that the CME may be led by a global restructuring of
multipolar magnetic systems due to flare disturbances. Mass, magnetic
energy, and flux of the ejected material estimated from the dimming
regions are comparable to the output of large CMEs, derived from the
limb events. At the CME source region, Huairou vector magnetograms
show that a strong shear was rapidly developed in a newly emerging
flux region (EFR) near the main spot before the flare. Magnetic field
extrapolations reveal the presence of a “bald patch” (defined as the
locations where the magnetic field is tangent to the photosphere) at the
edge of the EFR. The preflare features such as EUV loop brightenings
and SXR jets appearing at the bald patch suggest a slow reconnection
between the TIL field system and a preexisting overlying field above
the sheared EFR flux system. High-cadence Yohkoh/SXT images reveal a
fast expanding motion of loops above a bright core just several minutes
before the hard X-ray onset. This may be a precursor for the eruption
of the sheared EFR flux to produce the flare. We propose a scenario,
similar to the “breakout” model in principle, that can interpret
many observed features.
---------------------------------------------------------
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
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<SUP>-1</SUP> and 202 km
s<SUP>-1</SUP>, 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: Simultaneous Observation of a Moreton Wave on 1997 November
3 in Hα and Soft X-Rays
Authors: Narukage, N.; Hudson, H. S.; Morimoto, T.; Akiyama, S.;
Kitai, R.; Kurokawa, H.; Shibata, K.
2002ApJ...572L.109N Altcode:
We report the observation of a Moreton wave in Hα (line center and
+/-0.8 Å) with the Flare Monitoring Telescope at the Hida Observatory
of Kyoto University at 4:36-4:41 UT on 1997 November 3. The same
region (NOAA Active Region 8100) was simultaneously observed in soft
X-rays with the soft X-ray telescope on board Yohkoh, and a wavelike
disturbance (“X-ray wave”) was also found. The position of the wave
front as well as the direction of propagation of the X-ray wave roughly
agree with those of the Moreton wave. The propagation speeds of the
Moreton wave and the X-ray wave are about 490+/-40 and 630+/-100 km
s<SUP>-1</SUP>, respectively. Assuming that the X-ray wave is an MHD
fast-mode shock, we can estimate the propagation speed of the shock, on
the basis of MHD shock theory and the observed soft X-ray intensities
ahead of and behind the X-ray wave front. The estimated fast shock
speed is 400-760 km s<SUP>-1</SUP>, which is in rough agreement with
the observed propagation speed of the X-ray wave. The fast-mode Mach
number of the X-ray wave is also estimated to be about 1.15-1.25. These
results suggest that the X-ray wave is a weak MHD fast-mode shock
propagating through the corona and hence is the coronal counterpart
of the Moreton wave.
---------------------------------------------------------
Title: Emergence and Drastic Breakdown of a Twisted Flux Rope to
Trigger Strong Solar Flares in NOAA Active Region 9026
Authors: Kurokawa, Hiroki; Wang, Tongjiang; Ishii, Takako T.
2002ApJ...572..598K Altcode:
An emerging twisted flux rope model to explain the drastic evolution of
a flare-productive NOAA Active Region 9026 is presented. The drastic
changes in the δ-type sunspot configuration were found to start
shortly before the big flares of 2000 June 6: (1) rapid proper motions
of sunspots started at the both sides of the central δ sunspot about 7
hr prior to the strong flare activity, (2) the collapse of the central
δ sunspot with its disintegration and partial disappearance started
about 3 hr before the strong flare activity, (3) a switchback-shaped and
strongly sheared magnetic neutral line was formed with intruding motions
of sunspots into the opposite magnetic polarities, and (4) the direction
of the neutral line rapidly rotated clockwise at the same time when
the switchback neutral line was formed. To explain these outstanding
features of the sunspot evolution, we constructed a schematic model
of an emerging twisted flux rope in which the central writhe helicity
of the flux rope could be formed by continuous transformation of the
twist helicity by means of the kink instability in the course of its
emergence through the convection zone.
---------------------------------------------------------
Title: Dynamical Features and Evolutional Characteristics of
Brightening Coronal Loops
Authors: Shimojo, Masumi; Kurokawa, Hiroki; Yoshimura, Keiji
2002SoPh..206..133S Altcode:
We present a detailed study of coronal loop brightenings observed
in an active region on the solar limb. These brightening loops show
expanding and shrinking motions in EUV coronal line images and also
show downflow along the loops in Lα and Hα images. By means of
time-slice analysis of the images, we found that both the expanding
and shrinking motions of the loops are not real motions of plasma but
apparent motions like post-flare loops, where the loops at the different
height are successively heated and cooled. From a temperature analysis,
the time delay between the brightenings of hot 195 Å and cool Lα
loops is found to be nearly equal to the time-scale of the conduction
cooling. We conclude that these loop brightenings are sources of so
called Hα coronal rains.
---------------------------------------------------------
Title: Multi-wavelength Observations of a Moreton Wave on 2000 March 3
Authors: Narukage, N.; Morimoto, T.; Kitai, R.; Kurokawa, H.;
Shibata, K.
2002aprm.conf..449N Altcode:
Moreton waves are flare-associated waves observed to propagate across
the solar disk in Hα (Moreton, 1960). Such waves have been identified
as the intersections of a coronal fast-mode shock fronts and the
chromosphere (Uchida, 1968). We report the observation of a Moreton
wave in Hα (line center and ± 0.8 Å) with the Flare Monitoring
Telescope (FMT) at the Hida Observatory of Kyoto University on 2000
March 3. The same region (NOAA 8882) was simultaneously observed in
soft X-rays with the soft X-ray Telescope (SXT) on board Yohkoh, and
a coronal wave-like disturbance (“X-ray wave") was also found. The
region (NOAA 8882) is near the solar limb. Hence the chromospheric
Moreton wave propagated on the solar disk at a speed of 1050 km/s,
whereas the coronal X-ray wave propagated towards the outer corona
at 1300 km/s. We identified the X-ray wave as an MHD fast-mode shock,
i.e. a coronal counterpart of the Moreton wave, using MHD shock theory
and the observed soft X-ray intensities (Narukage et al., 2002). On the
basis of this result, the propagation of these two waves indicates the
3-dimensional structure of the flare-associated shock wave. This event
is the first observation of the 3-d structure of the shock. Moreover, a
type II radio burst and a coronal mass ejection (CME) were also observed
simultaneously. The shock speed given by the type II radio burst is 1150
km/s. The CME propagated at a speed of 800 km/s. A basic component of
CME is a density enhancement, and the shock preceding the CME propagates
roughly 1.5 times faster than the CME, in this case at 1200 km/s.
---------------------------------------------------------
Title: Characteristics of flare-productive sunspot groups
Authors: Ishii, Takako T.; Kurokawa, Hiroki; Takeuchi, Tsutomu T.
2002HiA....12..395I Altcode:
No abstract at ADS
---------------------------------------------------------
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.
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: Vortex-like Sunspot Proper Motions in Flare-producing Active
Regions
Authors: Ishii, T. T.; Kurokawa, H.; Takeuchi, T. T.
2002aprm.conf..431I Altcode:
We studied what is the key process to trigger major solar flares
using observational data of active region evolution. In our previous
studies, we have examined the processes of magnetic shear development
in many sunspot groups using high resolution Hα images obtained
with the 60-cm Domeless Solar Telescope (DST) at Hida Observatory,
Kyoto University. We have constructed schematic models of emerging
magnetic flux bundles to explain observed sunspot proper motions,
and found several examples of sunspot groups, where the emergence of
twisted magnetic flux tubes triggered major flares. During the current
solar maximum (cycle 23), we applied our method to the magnetograms
obtained by the Solar and Heliospheric Observatory (SOHO)/Michelson
Doppler Imager (MDI) and white light images by the Transition Region
and Coronal Explorer (TRACE). In this paper, we show several examples
of active regions where we found vortex-like sunspot proper motions
and strong flare activities. These motions suggest that the emergence
of twisted magnetic flux bundles is the energy source for strong flares.
---------------------------------------------------------
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.
2002mwoc.conf..295N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fine Structure inside Flare Ribbons and Temporal Evolution
Authors: Asai, A.; Masuda, S.; Yokoyama, T.; Shimojo, M.; Kurokawa,
H.; Shibata, K.; Ishii, T. T.; Kitai, R.; Isobe, H.; Yaji, K.
2002mwoc.conf..221A Altcode:
Non-thermal particles generated in the impulsive phase of
solar flares are observed mainly in microwave, hard X-rays, and
gamma-rays. Observations in Hα can also give important informations
about non-thermal particles precipitating into the chromosphere with
a higher spatial resolution than in other wavelengths. We observed an
X2.3 flare which occurred in the active region NOAA 9415 on 10 April
2001, in Hα with Sartorius Telescope at Kwasan Observatory, Kyoto
University. Thanks to the short exposure time given for the flare, the
Hα images show fine structures inside the flare ribbons. In addition
to Hα, we analyze microwave, hard X-ray, and EUV data obtained with
Nobeyama Radioheliograph, Yohkoh/HXT, and TRACE, respectively. In Hα,
several bright kernels are observed in the flare ribbons. On the other
hand, the hard X-ray images show only a single pair of bright sources
which correspond to one of several pairs of Hα kernels. Examining
the difference in the magnetic field strength and in the time profiles
of Hα emission for these kernels, we discuss the reason why only one
pair kernels are bright in the hard X-ray among the other bright Hα
kernels. Comparing the Hα images with EUV images, we also examine
the three-dimensional structure of solar flares. While broad and
network-like ribbons are observed in Hα, the width of EUV ribbons is
relatively narrow, and EUV ribbons are located at the outer edges of
the corresponding Hα ribbon.
---------------------------------------------------------
Title: Evolution of flare ribbons and energy release
Authors: Asai, A.; Masuda, S.; Yokoyama, T.; Shimojo, M.; Kurokawa,
H.; Ishii, T.; Shibata, K.
2002cosp...34E1179A Altcode: 2002cosp.meetE1179A
Non-thermal particles generated in the impulsive phase of
solar flares are observed mainly in microwave, hard X-rays, and g
amma-rays. Observations in Halpha can also give important informations
about non-thermal particles precipitating into the chromosphere with a
higher spatial resolution than in other wavelengths. We observed an X2.3
flare which occurred in the active region NOAA 9415 on 10 April 2001,
in Halpha with the Sartorius Telescope at Kwasan Observatory, Kyoto
University. Thanks to the short exposure time given for the flare, the
Halpha images show fine structures inside the flare ribbons. In Halpha,
several bright kernels are observed in the flare ribbons. On the other
hand, the hard X-ray images show only a single pair of bright sources
which correspond to one of several pairs of Halpha kernels. In this
paper, we examined the magnetic field strength at each H kernel and
the separation speed of the H flare ribbons, and estimated the energy
release rate with the method based on the magnetic reconnection model
(Isobe et al. 2002). We found that the energy release rate is well
correlated with the time profiles of hard X-ray and microwave.
---------------------------------------------------------
Title: Simultaneous observations of Moreton waves in Hα and Soft
X-ray
Authors: Narukage, N.; Hudson, H.; Morimoto, T.; Kitai, R.; Kurokawa,
H.; Shibata, K.
2002cosp...34E1337N Altcode: 2002cosp.meetE1337N
Moreton waves are flare-associated waves observed to propagate
across the solar disk in H (Moreton, 1960). Such waves have been
identified as the intersections of a coronal fast-mode shock fronts
and the chromosphere (Uchida, 1967). We report the two observations of
Moreton waves in H (line center and +/- 0.8 A) with the Flare Monitoring
Telescope (FMT) at the Hida Observatory of Kyoto University. The both
events were simultaneously observed in soft X-rays with the Soft X-ray
Telescope (SXT) on board Yohkoh, and wave-like disturbances ("X-ray
wave") were also found. One event occurred in solar-disk on November 3,
1997, the other near solar limb on March 3, 2000. Assuming that the
X-ray waves are the MHD fast shocks, we can estimate the propagation
speeds of the shocks, based on the MHD shock theory and the observed
soft X-ray intensities ahead and behind the X-ray wave fronts. It is
found that the estimated fast shock speeds are in rough agreement with
the observed propagation speeds of the X-ray waves. The fast mode Mach
numbers of the X-ray waves are also estimated. These results suggest
that the X-ray waves are MHD fast shocks propagating through the corona
and hence are the coronal counterparts of the Moreton waves.
---------------------------------------------------------
Title: On the directions of solar filament eruptions
Authors: Morimoto, T.; Asai, A.; Isobe, H.; Chen, P.; Kurokawa, H.
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.
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: Flight demonstration of a superpressure balloon by
three-dimensional gore design
Authors: Izutsu, N.; Yajima, N.; Ohta, S.; Honda, H.; Kurokawa, H.;
Matsushima, K.
2002AdSpR..30.1221I Altcode:
On May 15, 1999, a balloon with a volume of 3,100 cubic meters
was successfully launched from Sanriku Balloon Center of Japan. It
became a superpressure balloon at 19.2km in altitude with 20% pressure
difference to the ambient atmosphere. This is the first superpressure
balloon capable of suspending a heavy payload. It was designed by the
new 'three-dimensional gore design' method and was based on a pumpkin
shape balloon with bulges of small radii between adjacent load tapes
without the help of film extensibility. The balloon climbed up to
21.6km in altitude by dropping the ballast and held out against a 64%
pressure difference over the ambient atmosphere. This flight test
proved the capability of large stratospheric superpressure balloons
by this new design method.
---------------------------------------------------------
Title: Pre-Flare Heating Around the Temperature Minimum Region Found
Right Prior to an X-Class Flare
Authors: Kurokawa, H.; Ishii, T. T.; Wang, T. J.; Shine, R.
2002mwoc.conf..257K Altcode:
Studies of magnetic shear developments and pre-flare activities in
flare-productive sunspot regions are fundamentally important for the
study of flare energy build-up and energy release mechanism. Several
previous works demonstrated that the emergence of a twisted magnetic
flux rope, which is originally formed in the convection zone, must be
the source of the strong magnetic shear development in a sunspot region
to produce a strong flare activity (Kurokawa 1987, Tanaka 1991, Ishii et
al. 2000). We are still, however, far from sufficiently understanding
how the twisted structures of a magnetic flux rope is formed in the
convection zone, and where and how such a twisted magnetic rope untwists
and releases its energy as flaresNULL A flare productive active region
NOAA 9026, which showed an interesting evolution during a coordinated
observation between the Domeless Solar Telescope of Hida Observatory,
Swedish Telescope of La Palma, and TRACE Satellite from 3 through 12
June of 2000, provided us a rare opportunity to study a new important
aspect of a twisted magnetic flux rope and its rapidly-untwisted motions
to have caused strong flares. From the analyses of the evolution of
this region, we first found a clear evidence of pre-flare heating or
energy release from the upper photosphere through the lower chromosphere
from about two hours before the energy release in the corona as an
X-class flare. We suggest that this pre-flare energy release in the
lower atmosphere is closely related to the emergence of the twisted
magnetic flux rope from below the photosphere.
---------------------------------------------------------
Title: Surges, Magnetic Flux Cancellations, and UV Brightenings
around an Emerging Flux Region
Authors: Yoshimura, K.; Kurokawa, H.; Shimojo, M.; Shine, R.
2002mwoc.conf...99Y Altcode:
Surge activities, which are observed in Hα images, have been
studying for a long time. Many authors noticed that cancellations
of magnetic flux was an important factor for surge activities and
proposed the models based on magnetic reconnection. But there are not
many observations which have enough cadence for comparison changes
of magnetic field with surge activities. So the correlation between
surges and magnetic flux cancellations is not clear yet. (ex. Zhang
et al. 2001) We studied the temporal and spatial relations between
surge activities and other phenomena which may be accompanied by surge
activities. The data we used here are from coordinated observation with
Swedish Vacuum Solar Telescope on La Palma, TRACE and SOHO/MDI. So
high cadence images for the same target are available in various
wavelengths. MDI, for example, took magnetogram data every one minutes
with high resolution mode at that time. The main results from this study
are as follows: (1) We can not find any large time lag between the onset
of the surge and of the magnetic fields cancellation. This is a conflict
result against the one in Zhang et al. (2) There were UV brightenings
which correlated well with rapid cancellation of magnetic fields. (3)
The UV brightenings located just on neutral lines with some displacement
from the region where rapid magnetic cancellation occurred. These
observational fact can be explained by magnetic reconnection model.
---------------------------------------------------------
Title: Plasma Ejections from a Light Bridge in a Sunspot Umbra
Authors: Asai, Ayumi; Ishii, Takako T.; Kurokawa, Hiroki
2001ApJ...555L..65A Altcode: 2001astro.ph.11021A
We present conspicuous activities of plasma ejections along a light
bridge of a stable and mature sunspot in NOAA Active Region 8971 on
2000 May 2. We found the ejections both in the Hα (10<SUP>4</SUP> K)
images obtained with the Domeless Solar Telescope at Hida Observatory
and in the 171 Å (Fe IX/Fe X; ~10<SUP>6</SUP> K) images obtained
with the Transition Region and Coronal Explorer. Main characteristics
of the ejections are as follows: (1) Ejections occur intermittently
and recurrently. (2) The velocities and the timings of the 171 Å
ejections are the same as those of Hα ejections. (3) The appearance of
the ejections are different from one another; i.e., the Hα ejections
have a jetlike appearance, while the 171 Å ejections are like loops.
---------------------------------------------------------
Title: Distribution of the Green- and Red-Line Coronal Emissions
and Their Contribution to the K-Corona
Authors: Takeda, A.; Kurokawa, H.; Kitai, R.; Ishiura, K.
2001AGUSM..SH41B06T Altcode:
We have made a detailed analysis of the high-resolution images of
the corona obtained during the total solar eclipse on 1991, July
11. The purpose of the analysis is to derive the temperature and
density structure of the observed corona as reliable as possible
by using the absolute intensities of the the green (530.3 nm) and
red (637.4 nm) coronal emission lines and then contrasted to the
continuum intensity. First, we focus our attention to the loops
appeared distinctly in emission-line images. With the help of a
structure-enhancement algorithm, we show the following results in a
quantitative way. (1) The green- and red-line loops are quite separately
distributed in space. (2) In the innermost corona, structures in the
red-line tend to contribute more to the total column density than
the green-line structures. Second, we study individual emission-line
loops and find that, (1) The electron densities are almost the same
between the two wavelengths. (2) Density-falls with height are nearly
hydrostatic in most loops, while some red-line loops significantly
deflected from the hydrostatic curve. (3) Column density of the analysed
loops only explains 0.1 to 0.2 of the total column density derived from
the continuum intensity at the same point. Then, we propose a method to
determine the contribution of the non-loop component of these emission
lines to the total column density. It is found that the total column
density in the analyzed region can be reasonably explained by a mixture
of the 530.3 nm component with a line-of-sight length comparable to the
size of the active region, and the 637.4 nm component, which tends to
concentrate in loop structures. We thereby conclude that the observed
corona is well explained by plasma of temperatures ranging from 1 MK
to 2 MK.
---------------------------------------------------------
Title: Active Region Evolution and Flare Activities: From the
Photosphere to the Corona
Authors: Ishii, T. T.; Kurokawa, H.; Takeuchi, T. T.
2001IAUS..203..280I Altcode:
The formation process of magnetic shear is a key to understand the
physical mechanism of solar flare occurrence. In order to examine
such a process, we need observational data of active region evolution
from the photosphere to the corona. In this paper, we study active
region evolutions and its relation with flare activities, using H-alpha
images obtained at Hida and Kwasan Observatories and white light images
with Transition Region And Coronal Explorer (TRACE). We also use the
Solar and Heliospheric Observatory (SOHO) / Michelson Doppler Imager
(MDI) intensitygram and longitudinal magnetogram for investigation of
photospheric structures of active regions. Coronal structures of the
regions are studied by using extreme ultraviolet (EUV) images obtained
with SOHO and TRACE. We investigate the evolution of the several
active regions. We mainly report the evolution of the active region
NOAA 8948 (April 2000) and discuss the relation between evolutionary
characteristics and its flare activities. Many H-alpha sub-flares and
several X-ray (C- and M-class) flares occurred in this active region. We
suggest that the flares are triggered by the magnetic flux emergence
that forms new sunspots in the following part of the active region.
---------------------------------------------------------
Title: Evolution of Hα fine loop structures observed in a
long-duration solar flare
Authors: Ishii, T. T.; Inoue, K.; Kamio, S.; Sakai, K.; Watanabe,
Y.; Kurokawa, H.
2001AdSpR..26.1789I Altcode:
We study the structure and evolution of a large X9 flare, which
was observed at the Western limb on Nov. 2, 1992. We obtained high
resolution Hα images with the 60 cm Domeless Solar Telescope at Hida
Observatory, Kyoto University. Our data sets include the images observed
just at the flare onset, so we could trace the evolution of post-flare
loops from the beginning in detail. In this paper, we present co-aligned
Hα (obtained at Hida Observatory) and soft X-ray (obtained with Yohkoh
Soft X-ray Telescope) images and evolutions of the multiple loops.
---------------------------------------------------------
Title: Soft X-ray flares and magnetic configuration in a solar active
region in February 1992
Authors: Zhang, H. Q.; Sakurai, T.; Shibata, K.; Shimojo, M.;
Kurokawa, H.
2000A&A...357..725Z Altcode:
In this paper, we examine the observational soft X-ray flares and
the relationship with photospheric vector magnetograms in the active
region (NOAA 7070). We analyze the soft X-ray flare on Feb. 24-25,
1992, especially the pre-flare and the relationship with the highly
sheared photospheric vector magnetic field near the photospheric
magnetic neutral line. We find that the initial reconnection of the
magnetic field in the flare on Feb. 24-25, 1992 probably occurs near
the magnetic neutral line in the lower atmosphere of the active region,
where the highly sheared magnetic flux erupts up and triggers the
reconnection of the large-scale magnetic field. The possible process
of the magnetic reconnection of the limb flare on Feb. 20-21, 1992
in this active region is proposed also based on the analogy with the
flare on Feb. 24-25 near the center of the solar disk.
---------------------------------------------------------
Title: Density Structure of the Coronal Loops Derived from the 1991
Total Eclipse Observation
Authors: Takeda, A.; Kurokawa, H.; Kitai, R.; Ishiura, K.
2000ASPC..205..113T Altcode: 2000ltse.conf..113T
High-resolution images of the corona obtained during the total solar
eclipse on 11th July, 1991 were carefully analyzed to derive the
electron densities along the loops of the green(530.3 nm) and red(637.4
nm) emission lines. We found no difference more than a factor of 2
between the averaged densities of the green and the red line loops
at corresponding heights. Most of the analyzed loops were found to be
approximately in hydrostatic equilibrium.
---------------------------------------------------------
Title: Contribution and Properties of the Green- and Red-Line Coronal
Loops in the K-Corona
Authors: Takeda, Aki; Kurokawa, Hiroki; Kitai, Reizaburo; Ishiura,
Kiyomi
2000PASJ...52..375T Altcode:
A set of high-resolution images of corona obtained during the total
solar eclipse on 1991 July 11, was carefully analyzed to investigate
the properties of the loop structures observed in the green (530.3
nm) and red (637.4 nm) emission lines and in the continuum. With the
help of a structure-enhancement algorithm, we have quantitatively
shown that: (1) The green- and red-line loops are quite separately
distributed in space. (2) For most structures seen in the continuum
in the active-region corona, components can be identified in the
green or red line. (3) In the innermost corona, structures in the
red-line tend to contribute more to the total column density than the
green-line structures. We present two schematic models to explain the
spatial relation of the green-line, the red-line, and the continuum
loops. Next, we studied individual loops in the green and red lines,
and derive that their electron densities are almost the same. We
also propose a method to determine the `background contribution' of
the green and red lines to the total column density derived from the
continuum intensity. It is found that the total column density in the
analyzed region can be reasonably explained by a mixture of the 530.3
nm component with a line-of-sight length comparable to the size of the
active region, and the 637.4 nm component, which tends to concentrate
in loop structures. We thereby conclude that the observed corona is
well explained by a plasma of temperatures ranging from 2 MK to 1 MK.
---------------------------------------------------------
Title: Emergence of Twisted Magnetic-Flux Bundles and Flare Activity
in a Large Active Region, NOAA 4201
Authors: Ishii, Takako T.; Kurokawa, Hiroki; Takeuchi, Tsutomu T.
2000PASJ...52..337I Altcode:
To reveal what is the key agent for strong flare activity, we studied
the evolution of a large sunspot group, NOAA 4201, and its flare
activity. We analyzed high-resolution Hα images obtained with
the Domeless Solar Telescope at Hida Observatory, and Kitt Peak
full disk magnetograms. We examined the sunspot proper motions and
evolutionary changes of Hα fine structures and magnetic fields in
this active region, and constructed a schematic model of emerging
twisted magnetic-flux bundles. We also found that the occurrence of
high flare activity was restricted to the rapidly emerging region
of the twisted flux bundle. This fact suggests that the emergence
of a twisted emerging flux bundle should be the key to high flare
productivity of the sunspot group.
---------------------------------------------------------
Title: Characteristics of Flare-productive Sunspot Groups
Authors: Ishii, T. T.; Kurokawa, H.; Takeuchi, T. T.
2000IAUJD...7E..19I Altcode:
The mechanism of flare energy build-up is one of the most fundamental
questions in the solar flare study, but is still to be solved. >From
the review of the previous studies, we notice that the formation process
of the magnetic shear in an active region should be essential for the
flare energy build-up mechanism. Based on this idea, we make detailed
studies of the active region evolutions using high resolution Hα images
obtained with the 60 cm Domeless Solar Telescope at Hida Observatory,
Kyoto University. We study sunspot proper motions and evolutionary
changes of Hα fine structures and magnetic fields in active regions
NOAA 5395 and NOAA 4201. To explain the evolutionary characteristics
found from the analyses of these two active regions, we propose
schematic models of twisted flux bundles emerging from the convection
zone. We also found that the occurrence of high flare activity in each
active region was restricted to the rapidly emerging region of the
twisted flux bundle. In conclusion, we suggest that the emergence of
the twisted flux bundle should be the key to high flare-productivity
of the sunspot group, or the flare energy build-up mechanism.
---------------------------------------------------------
Title: Relationship Between Hα AFS Loops and Soft X-Ray Brightening
Loops in Emerging Flux Regions
Authors: Kurokawa, H.; Yoshimura, K.
2000AdSpR..25.1825K Altcode:
Close correlations were found between Hα dark emerging loops and
soft x-ray loop brightenings from five coordinated observations of
emerging flux regions between the Soft X-ray Telescope (SXT) aboard
Yohkoh satellite and the Domeless Solar Telescope (DST) of Hida
Observatory. The results for the EFR of NOAA 7495 (4-5 May, 1993)
are presented in some detail
---------------------------------------------------------
Title: Hα. Surges in Emerging Flux Regions as an Evidence of Magnetic
Field Reconnection
Authors: Kurokawa, H.; Sano, S.
2000AdSpR..26..441K Altcode:
The morphological and dynamical characteristics of a typical EFR-surge,
which was observed with a high resolution Hα filtergraph are examined
in details. Two kinds of downward-moving features were found in the
Hα surge region: One is along the same magnetic field line as that of
the upward-moving feature. The other streams along a different magnetic
field line where no upward-moving feature was found. It is shown that
these two kinds of downward-moving features along the different magnetic
field lines are well explained by a magnetic field reconnection between
emerging magnetic loops and pre-existing coronal magnetic field
---------------------------------------------------------
Title: Multi-Wavelength Observations of a Large-Scale Jet and an
Eruptive- Prominence on 28 August 1992
Authors: Watanabe, Ta.; Ashizawa, K.; Nakagawa, Y.; Miyazaki, H.;
Irie, M.; Ichimoto, K.; Kurokawa, H.; Hudson, H.; Yatagai, H.
1999spro.proc..171W Altcode:
An eruption of a large (15<SUP>o</SUP>) north-south aligned quiescent
prominence and associated coronal disturbance, which took place above
the eastern solar limb near the equator on 28 August 1992, were observed
at a wide range of wavelengths ranging from soft X-rays (Yohkoh) to
microwaves (Nobeyama). The eruption was preceded by the formation of
a large-scale jet which was apparently ejected near the root of the
southern leg of the prominence. The characteristic outward speed of the
jet was 450 km s<SUP>-1</SUP>. A potential-field presentation of the
coronal magnetic field suggests that the jet was formed along the open
field which was located immediately to the west of the magnetic arcade,
originally surrounding the eruptive prominence. The temperature of the
jet is suggested to be comparable to that of the nearby quiet corona
(2 × 10<SUP>6</SUP> K). In the course of the prominence eruption,
helically twisted loops surrounding the prominence were observed. This
suggests that magnetic reconnection of the sheared arcade took place
underneath the erupting prominence.
---------------------------------------------------------
Title: Causal Relations between Hα Loop Emergences and Soft X-Ray
Brightenings
Authors: Yoshimura, Keiji; Kurokawa, Hiroki
1999ApJ...517..964Y Altcode:
We compared high-resolution images of an emerging flux region in Hα
and in soft X-ray, using two types of coalignments. Hα images were
taken at Hida Observatory. Soft X-ray images were taken by the Soft
X-ray telescope onboard Yohkoh. These data were obtained through
coordinated observations by Hida Observatory and Yohkoh. Soft X-ray
brightenings were found above most of the emerging Hα arch filaments,
which are traces of rising magnetic flux tubes. The released energies
in the soft X-ray brightenings were found to be ~10<SUP>27</SUP>
ergs, which is consistent with an estimate of energy release through
magnetic reconnection between coronal fields and rising flux tubes
as an Hα arch filament. These observational results indicate that
an arch filament or rising magnetic flux tube itself is not heated
up to coronal temperature as soon as it has reached coronal heights,
but it can induce a change of magnetic structure through magnetic
reconnection in the overlying corona. We also studied the structure
of an arch filament in detail at its birth stage. Its morphological
feature and evolutionary characteristics can be well explained by the
asymmetric rising of a flux tube.
---------------------------------------------------------
Title: An observational search for giant cells in the sun
Authors: Kitai, R.; Kurokawa, H.; Funakoshi, Y.; Ishiura, K.; Kimura,
G.; Shinkawa, T.
1999AdSpR..24..237K Altcode:
With the supergranular network pattern seen in Hα wing image of the
Sun as tracers, we derived large-scale horizontal flow field over the
solar surface by a local-correlation-tracking method. We have found
some evidences of the existence of large scale flow cells on the Sun.
---------------------------------------------------------
Title: Emergence of a Twisted Magnetic Flux Bundle as a Source of
Strong Flare Activity
Authors: Ishii, Takako T.; Kurokawa, Hiroki; Takeuchi, Tsutomu T.
1998ApJ...499..898I Altcode: 1997astro.ph..8208I
Sunspot proper motions and flares of a super active region NOAA
5395--the largest and most flare-active region in the 22d sunspot
cycle--were analyzed in detail. We measured sunspot proper motions
by using the Hα - 5.0 Å images obtained with the 60 cm Domeless
Solar Telescope (DST) at Hida Observatory, Kyoto University and found
some peculiar vortex-like motions of small satellite spots, which
successively emerged from the leading edge of this sunspot group. To
explain these motions of small sunspots, we proposed a schematic model
of the successive emergence of twisted and winding magnetic flux loops
coiling around a trunk of a magnetic flux tube. The location of the
strongest flare activity was found to coincide with the site of the
vortex-like motions of sunspots. We conclude that the flare-productive
magnetic shear is produced by the emergence of the twisted magnetic
flux bundle. Magnetic energy is stored in the twisted flux bundle,
which is originally formed in the convection zone and released as
flares in the course of the emergence of the twisted flux bundle above
the photosphere.
---------------------------------------------------------
Title: An Interdisciplinary Study of the Eruptive Prominence of 28
August 1992
Authors: Watanabe, Ta.; Yamamoto, M.; Hudson, H.; Irie, M.; Ichimoto,
K.; Kurokawa, H.; Yatagai, H.
1998ASSL..229..101W Altcode: 1998opaf.conf..101W
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Reconnection in the Active Region Inferred by
Homologous Soft X-ray Flares in February 1992
Authors: Zhang, H. Q.; Sakurai, T.; Shibata, K.; Shimojo, M.; Kurokawa,
H.; Morita, S.; Uchida, Y.
1998ASSL..229..391Z Altcode: 1998opaf.conf..391Z
No abstract at ADS
---------------------------------------------------------
Title: Soft X-ray Observations of Eruptive Prominences
Authors: Watanabe, T.; Yamamoto, M.; Hudson, H.; Irie, M.; Ichimoto,
K.; Kurokawa, H.; Yatagai, H.
1998ASPC..150..376W Altcode: 1998IAUCo.167..376W; 1998npsp.conf..376W
No abstract at ADS
---------------------------------------------------------
Title: Coronal and Interplanetary Disturbances Associated with an
Eruptive Prominence of 28 August 1992
Authors: Watanabe, T.; Yamamoto, M.; Hudson, H.; Irie, M.; Ichimoto,
K.; Kurokawa, H.; Yatagai, H.
1998asct.conf..313W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Comparison between arch filaments and coronal loops.
Authors: Yoshimura, K.; Kurokawa, H.; Sano, S.; Hudson, H.
1997IAUJD..19E..60Y Altcode:
Kawai et al. (1992) presented preliminary results from comparison
between arch filament system (AFS) and soft X-ray (SXR) loops. They
found the AFS was covered with the SXR bright features. Coordinated
observations with YOHKOH enable us to make more detail comparison
between arch filament(AFS) and SXR loops. (With small brightening
points both in SXR and H alpha images, we can co-align those images
accurately enough.) We intended to see how each AFS contributes to
SXR brightenings. We will show examples of AFS which no particular
SXR brightening occurred around. And we will present observations of
SXR major brightenings of loops, which was related to H alpha dark
features. The dark features did not seem to be AFS. They may be small
active region filaments which indicates magnetic sheared structure
(evidence for storages of extra magnetic energy).
---------------------------------------------------------
Title: Emergence of Twisted Magnetic Flux Tubes Inferred from Sunspot
Proper Motions
Authors: Ishii, T. T.; Kurokawa, H.
1997IAUJD..19E..25I Altcode:
Solar activities are closely related with magnetic field
characteristics. Especially, some properties of emerging magnetic
fields (e.g. shapes, strength, velocities) concern mechanisms of
solar activities. Twists of magnetic flux tubes are thought to store
energy for flares and surges. A large active region observed in March
1989, NOAA 5395, was an extremely flare-productive sunspot group with
delta-type configuration. We measured proper motions of sunspots in this
region by using H alpha images obtained with the 60-cm Domeless Solar
Telescope (DST) at Hida Observatory, Kyoto University to construct a
schematic model of flux-tube structures in the region. In this study
we demonstrate that twisted magnetic flux tubes successively emerged
at the leading edge of the great sunspot group and that they played an
essential role in the production of strong flare and surge activities
of the region.
---------------------------------------------------------
Title: The H alpha filament disappearance on February 20, 1994
Authors: Shinkawa, T.; Koshiishi, H.; Kurokawa, H.; Hanaoka, Y.;
Enome, S.; Akioka, M.; Liu, Y.
1997IAUJD..19E..46S Altcode:
Solar flares and prominence eruptions are considered as sources of
interplanetary and geomagnetic storms. An H alpha filament disappearance
and a following big flare whose importance was 3B in H alpha and M4
in GOES X-ray class occurred near the solar disc center on February
20, 1994. This event caused a strong geomagnetic storm. The event was
fully observed in H alpha, H alpha+0.8 AA and H alpha-0.8 AA with the
Flare Monitoring Telescope at Hida Observatory, Kyoto University,
and in 17GHz continuum with the Nobeyama Radio Heliograph. The H
alpha, H alpha+0.8 AA and H alpha-0.8 AA images gave us dynamical
features of the disappearing filament at the initial stage of the
eruption. The 17GHz data revealed much faster motions of the erupting
filament across the solar disc and even outside of the solar limb,
since it is insensitive to line-of-sight motion. Combining these data,
we reconstruct a three-dimensional model of the filament eruption.
---------------------------------------------------------
Title: Casual Relation Between Emerging H alpha AFS Loops and Soft
X-ray Transient Brightenings
Authors: Kurokawa, H.; Yoshimura, K.; HIDA Dst Team; YOHKOH SXT Team
1997IAUJD..19E..30K Altcode:
We study the causal relation between H alpha arch filament system
(AFS) loops and corresponding soft X-ray features by using the 60cm
Domeless Telescope (DST) of Hida Observatory and the Soft X-ray
Telescope aboard Yohkoh. The scientific aims are the followings:
(1) Which type of soft X-ray features spatially and temporally
correlate to H alpha dark AFS loops? It is important for the study of
heating of active region corona. (2) Which type of characteristics and
changes in H alpha AFS loops are associated with soft X-ray transient
brightenings. It is important for the mechanism of microflare and a
trigger of a larger flare. We made coordinated observations between the
Hida DST and the Yohkoh SXT four times. Main preliminary results are;
(1) A group of H alpha AFS loops generally correlates in space with
bright X-ray loops. (2) Some examples showing clear causal relation
between a newly emerging H alpha AFS loop and a soft X-ray transient
brightening are found. In many cases it is, however, unclear because of
lack of resolutions. (3) Newly and actively emerging AFS with sheared
structures may cause brighter and frequent X-ray brightenings. We
discuss the importance of more feature coordinated observations with
higher resolution.
---------------------------------------------------------
Title: Global and Fine Scale Distribution of the Innermost Coronal
Temperature
Authors: Takeda, A.; Kurokawa, H.; Kitai, R.; Ishiura, K.
1997IAUJD..19E..50T Altcode:
The observations of the solar corona at the total eclipses continue to
provide us with valuable data, which enables us to study the thermo
dynamic structures. Because of the extremely low scattered lights,
coronal emission intensities measured during the eclipse time are still
higher in accuracy and resolution than the observation from space. It
is rare chance to study temperature and density structure of the very
innermost part of the corona at visible wavelengths. In this paper,
we present the spatial variations of the absolute intensities of the
active region corona from 1.05 to 1.5 R<SUB>odot</SUB> observed at the
total eclipse of 11th July, 1991, in three wavelengths of 2 coronal
emission lines (Fe XIV 530.3 nm and Fe X 637.4 nm) and the continuum
around 610.0nm. Global temperature estimation by taking the intensity
ratio, Fe XIV/Fe X, indicates that average temperature is not always the
highest in the prominent active region corona, since there exists large
amount of the cooler plasma together with the hotter component. Next,
we examine spatial correlation among the fine structures at above
three wavelengths, and show semi-quantitatively that most 1.0 times
10^6K (Fe X) and 2.0 times 10^6K (Fe XIV) plasma are isolated with
each other, and that, if they combined, they explain about 70% of the
continuum structures.
---------------------------------------------------------
Title: A Filament Eruption and Accompanying Coronal Field Changes
on November 5, 1992
Authors: McAllister, A. H.; Kurokawa, H.; Shibata, K.; Nitta, N.
1996SoPh..169..123M Altcode:
An Hα filament eruption on November 5, 1992 was fully observed in Hα
with the Hida Flare Monitoring Telescope, while Yohkoh's Soft X-ray
Telescope observed the pre- and post-eruption evolution of the coronal
magnetic fields. From the Hα data, including the red and blue wings,
we have reconstructed the rise of the filament, including trajectory,
velocity, and acceleration. In combination with the Yohkoh data this
reconstruction suggests that the filament had several interactions
with other coronal magnetic fields during the eruption. The Yohkoh
data also shows pre-eruption changes in the coronal fields and several
post-eruption bright coronal structures. The pre-eruption changes are
interpreted as a partial opening of the corona, indicating that it is
not necessary to have a complete opening of the corona in order for a
filament to erupt and we discuss the several possible contributions
from emerging flux. The post-event bright coronal structures are
compared with theory and with a cleaner filament eruption event on
July 31, 1992. These comparisons suggest that, although there are many
similarities, it is hard to completely reconcile the observations with
the existing theory.
---------------------------------------------------------
Title: The solar origins of two high-latitude interplanetary
disturbances
Authors: Hudson, H. S.; Acton, L. W.; Alexander, D.; Harvey, K. L.;
Kahler, S. W.; Kurokawa, H.; Lemen, J. R.
1996AIPC..382...84H Altcode:
Two extremely similar interplanetary forward/reverse shock events,
with bidirectional electron streaming, were detected by Ulysses in
1994 [Gosling et al., 1994]. Both events resulted in geomagnetic
storms and presumably were associated with coronal mass ejections. In
this paper we use the Yohkoh soft X-ray observations to characterize
the conditions in the lower corona at the times appropriate for the
launching of these two events. We find two strikingly different solar
events to be the likeliest candidates: an LDE flare on 20 Feb. 1994,
and a extremely large-scale arcade event on 14 April 1994.
---------------------------------------------------------
Title: Chromospheric ejections and their signatures in X-ray observed
by YOHKOH
Authors: Schmieder, B.; Mein, N.; Shibata, K.; van Driel-Gesztelyi,
L.; Kurokawa, H.
1996AdSpR..17d.193S Altcode: 1996AdSpR..17..193S
Surges, or condensations of chromospheric material, are commonly
observed in active regions when new emerging magnetic flux (EMF)
occurs. In order to study EMF-related phenomena in the corona, observing
campaigns were organized with the Yohkoh X-ray satellite and ground
based observatories. EMFs could be detected in magnetograms made in
Potsdam and Hawaii, surge and arch filament system (AFS) events (on
Oct 7 1991, May 1 1993, respectively) with the Multichannel Subtractive
Double Pass instruments operating at Meudon and on the Canary Islands
and with the Hida telescope at Kyoto University. Bright X-ray loops
coincident with chromospheric surge activity were detected in the high
resolution Yohkoh SXT images. We also found coincident brightness
variations between an X-ray bright point (XBP) and the underlying
chromospheric plage related to EMF. We interpret the appearance of
AFS as condensation of material among magnetic field lines, the X-ray
bright points as the result of a magnetic reconnection process, and
surges as ejection of cold plasma bubbles squeezed between field lines
as a result of reconnection.
---------------------------------------------------------
Title: X-Ray Bright Point Flares Due to Magnetic Reconnection
Authors: Van Driel-Gesztelyi, L.; Schmieder, B.; Cauzzi, G.; Mein,
N.; Hofmann, A.; Nitta, N.; Kurokawa, H.; Mein, P.; Staiger, J.
1996SoPh..163..145V Altcode:
Ground-based optical observations coordinated with Yohkoh/SXT X-ray
observations of an old, disintegrating bipolar active region AR NOAA
7493 (May 1, 1993) provided a multiwavelength data base to study
a flaring `active region' X-ray bright point (XBP) of about 16 hr
lifetime, and the activity related to it in different layers of the
solar atmosphere. The XBP appeared to be related to a new minor bipole
of about 10<SUP>20</SUP> Mx. Superposed on a global evolution of soft
X-ray brightness, the XBP displayed changes of brightness, lasting for
1-10 min. During the brightenings the XBP apparently had a spatial
structure, which was (tiny) loop-like rather than point-like. The
X-ray brightenings were correlated with chromospheric activity: (i)
brightenings of underlying chromospheric faculae, and (ii) appearance
of strong turbulent velocities in the arch filament system. We propose
that the XBP brightenings were due to reconnection of the magnetic
field lines (sketched in 3D) between the new bipole and a pre-existing
plage field induced by the motion of one of the new pores (v = 0.2
km s<SUP>−1</SUP>) towards the plage, and that the XBP itself was
a reconnected hot loop between them.
---------------------------------------------------------
Title: Causal Relation between H alpha Arch Filament Loops and Soft
X-ray Coronal Loops
Authors: Yoshimura, K.; Kurokawa, H.; Sano, S.; Hudson, H.
1996mpsa.conf..457Y Altcode: 1996IAUCo.153..457Y
No abstract at ADS
---------------------------------------------------------
Title: Energy Build-up Processes of Solar Flares Studied by Optical
Observations
Authors: Kurokawa, H.
1996mpsa.conf..185K Altcode: 1996IAUCo.153..185K
No abstract at ADS
---------------------------------------------------------
Title: Comparison of High Resolution Optical and Soft X-ray Images
of Solar Corona
Authors: Takeda, A.; Kurokawa, H.; Kitai, R.; Ishiura, K.; Golub, L.
1996mpsa.conf..483T Altcode: 1996IAUCo.153..483T
No abstract at ADS
---------------------------------------------------------
Title: Emerging Flux, Reconnection, and XBP
Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Demoulin, P.;
Mandrini, C.; Cauzzi, G.; Hofmann, A.; Nitta, N.; Kurokawa, H.; Mein,
N.; Mein, P.
1996mpsa.conf..459V Altcode: 1996IAUCo.153..459V
No abstract at ADS
---------------------------------------------------------
Title: Emerging flux seen by Yohkoh.
Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Mandrini, C.;
Démoulin, P.; Cauzzi, G.; Hofmann, A.; Nitta, N.; Kurokawa, H.;
Mein, N.; Mein, P.
1996joso.proc..124V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The solar origins of two high-latitude interplanetary
disturbances
Authors: Hudson, H. S.; Acton, L. W.; Alexander, D.; Harvey, K. L.;
Kurokawa, H.; Kahler, S.; Lemen, J. R.
1995sowi.confS..58H Altcode:
Two extremely similar interplanetary forward/reverse shock events,
with bidirectional electron streaming were detected by Ulysses in
1994. Ground-based and Yohkoh/SXT observations show two strikingly
different solar events that could be associated with them: an LDE flare
on 20 Feb. 1994, and a extremely large-scale eruptive event on 14 April
1994. Both events resulted in geomagnetic storms and presumably were
associated with coronal mass ejections. The sharply contrasting nature
of these solar events argues against an energetic causal relationship
between them and the bidirectional streaming events observed by Ulysses
during its S polar passage. We suggest instead that for each pair of
events. a common solar trigger may have caused independent instabilities
leading to the solar and interplanetary phenomena.
---------------------------------------------------------
Title: Evolutional Characteristics of Multiple Spectral Lines during
the Impulsive Phase of Solar Flares
Authors: Shoji, Makiko; Kurokawa, Hiroki
1995PASJ...47..239S Altcode:
A study of the impulsive phase spectra of two chromospheric flares,
for which the Hα , CaII K, HeI D_3, NaI D_{1,2} and other metallic
lines were simultaneously obtained with high temporal and spatial
resolutions, is presented. The main new observational results are:
(1) The red-shifted emission streaks observed in the Hα , K, and D_3\
lines give nearly the same downward velocities, the maximum of which
ranges from 50 to 100 km s(-1) for typical streaks. (2) The broad Hα ,
K, and D_3\ line profiles are well explained by a Doppler broadening
of nearly the same turbulent velocity, the maximum of which ranges
between 120 and 170 km s(-1) . (3) D_{1,2}\ and metallic line emissions
show narrow and slightly red-shifted profiles. Their typical maximum
downward and turbulent velocities are 2--6 km s(-1) \ and 10 km s(-1)
, respectively. (4) K-line emission profiles of the flares consist
of two components, i.e., a red-shifted broad wing and a stationary
narrow core. (5) All of the emission lines show nearly parallel
time-profiles of both the intensity and downward velocity. From these
results we conclude that the emitting region of the chromospheric
flare consists of two layers heated simultaneously: one relatively
thin, fast-downward-moving and very turbulent, and the other almost
stationary and optically thick in metallic-line emissions.
---------------------------------------------------------
Title: Peculiar magnetic field evolution of active region NOAA 7562
in August 1993 - results from campaign observation with Yohkoh
Authors: Sakurai, T.; Suematsu, Y.; Ichimoto, K.; Kurokawa, H.; Kitai,
R.; Akioka, M.; Tohmura, I.; Soltau, D.; Mickey, D. L.; Zhang, H.;
Li, W.; Zirin, H.; Tang, F.
1994ESASP.373..337S Altcode: 1994soho....3..337S
No abstract at ADS
---------------------------------------------------------
Title: Yohkoh observations of the creation of high-temperature plasma
in the flare of 16 December 1991
Authors: Culhane, J. L.; Phillips, A. T.; Inda-Koide, M.; Kosugi,
T.; Fludra, A.; Kurokawa, H.; Makishima, K.; Pike, C. D.; Sakao, T.;
Sakurai, T.; Doschek, G. A.; Bentley, R. D.
1994SoPh..153..307C Altcode:
Yohkoh observations of an impulsive solar flare which occurred on 16
December, 1991 are presented. This flare was a GOES M2.7 class event
with a simple morphology indicative of a single flaring loop. X-ray
images were taken with the Hard X-ray Telescope (HXT) and soft X-ray
spectra were obtained with the Bragg Crystal Spectrometer (BCS)
on board the satellite. The spectrometer observations were made at
high sensivity from the earliest stages of the flare, are continued
throughout the rise and decay phases, and indicate extremely strong
blueshifts, which account for the majority of emission in CaXIX during
the initial phase of the flare. The data are compared with observations
from other space and ground-based instruments. A balance calculation
is performed which indicates that the energy contained in non-thermal
electrons is sufficient to explain the high temperature plasma which
fills the loop. The cooling of this plasma by thermal conduction
is independently verified in a manner which indicates that the loop
filling factor is close to 100%. The production of `superhot' plasma
in impulsive events is shown to differ in detail from the morphology
and mechanisms appropriate for more gradual events.
---------------------------------------------------------
Title: Red Asymmetries of Optical Lines at the Impulsive Phase of
Solar Flares
Authors: Shoji, M.; Kurokawa, H.
1994kofu.symp..409S Altcode:
Impulsive phase spectra of two chromospheric flares were obtained
with high temporal resolution. H_alpha, Ca II K, He I D_3, and other
metallic lines were observed simultaneously and their red asymmetries
were studied. Velocities derived from K and D_3 line emissions are found
to be as large as H_alpha velocity, contrary to the previous works.
---------------------------------------------------------
Title: A Morphological Study of Magnetic Shear Development in a
Flare-Productive Region NOAA 7270
Authors: Kurokawa, H.; Kitai, R.; Kawai, G.; Shibata, K.; Yaji, K.;
Ichimoto, K.; Nitta, N.; Zhang, H.
1994kofu.symp..283K Altcode:
The evolutional changes of a flare-productive region NOAA 7270 were
examined in details with high resolution H_alpha images, magnetograms
and soft X-ray images to study the process of the magnetic shear
development and its relation to the strong flare activity of the
region. This study led us to the following results and a conclusion:(1)
Several new bipolar pairs simultaneously and or successively emerged in
NOAA 7270 from 5 through 7 September. (2) Magnetic shear configurations
developed at three locations, where most of flares occurred from 5
through 7 , September. (3)These magnetic shear configurations were
formed by successive emergences of twisted magnetic ropes from below
the photosphere.
---------------------------------------------------------
Title: Thermal and Density Structure of the Inner Corona Observed
at the 1991 Total Solar Eclipse
Authors: Takeda, A.; Kurokawa, H.; Kitai, R.; Ishiura, K.
1994kofu.symp..381T Altcode:
We observed the total solar eclipse on 11 July, 1991 with the
multi-channel telescope at Lapaz,Mexico, and successfully obtained
high-resolution pictures of the innermost corona at the wavelength
shown in Table 1. This is a brief summary of preliminary results
obtained from the photometric mesurement of the photographic pictures
and their image processing.
---------------------------------------------------------
Title: Flares on September 6, 1992
Authors: Kitai, R.; Kurokawa, H.; Funakoshi, Y.; Nakai, Y.; Shibata,
K.; Yaji, K.; Nitta, N.; YOHKOH Team; NAOJ Flare Telescope Team
1994kofu.symp..147K Altcode:
We present some preliminary results of our observational
study of typical eruptive flares in NOAA7270 on September 6,
1992. (1)Magnetic shear and flux emergence are strongly related to
flare production. (2)Observed flares showed a common temporal relation
between cool plasma dynamics seen in H_alpha and coronal energy releases
seen in YOHKOH data. (3)At the pre-heating stage of flares, there were
some indications of slow reconnection of adjacent magnetic loops.
---------------------------------------------------------
Title: Simultaneous Observations of a Prominence Eruption Followed
by a Coronal Arcade Formation in Radio, Soft X-Rays, and Hα
Authors: Hanaoka, Yoichiro; Kurokawa, Hiroki; Enome, Shinzo; Nakajima,
Hiroshi; Shibasaki, Kiyoto; Nishio, Masanori; Takano, Toshiaki; Torii,
Chikayoshi; Sekiguchi, Hideaki; Kawashima, Susumu; Bushimata, Takeshi;
Shinohara, Noriyuki; Irimajiri, Yoshihisa; Koshiishi, Hideki; Shiomi,
Yasuhiko; Nakai, Yoshihiro; Funakoshi, Yasuhiro; Kitai, Reizaburo;
Ishiura, Kiyomi; Kimura, Goro
1994PASJ...46..205H Altcode:
A prominence eruption followed by a coronal brightening was
simultaneously observed in radio (17 GHz), soft X-rays, and Hα on
1992 July 30--31. The observations were performed by newly developed
high-performance instruments: the Nobeyama Radioheliograph, the SXT
on the Yohkoh satellite, the Flare Monitoring Telescope of the Hida
Observatory, and some other Hα telescopes. This event gives us a
much more detailed picture of this type of phenomena than previously
observed. The erupting prominence, which occurred in a quiet region and
was observed in Hα and radio, ascended with a velocity of about 100 km
s(-1) . The general structure of the erupting prominence seen at 17 GHz
is very similar to that at Hα . While the prominence expanded rapidly,
the total radio flux of the erupting prominence did not change very
much. Since a prominence consists of fine threads, this fact means that
each thread did not expand while the prominence expanded. Consequently,
the surface filling factor of the prominence must have decreased during
the eruption. The high-resolution pictures of a clear coronal arcade
structure were taken in soft X-rays and radio after the prominence
eruption; the physical parameters of the arcade were derived from these
pictures. The mean temperature was 3.5*E(6) K in the early phase, and
decreased to 2.6*E(6) K within seven hours. The total emission measure
reached a maximum value of 1.6*E(48) cm(-3) after three hours from the
beginning of the arcade brightening, when the electron density at the
ridge of the arcade is estimated as 2.4*E(9) cm(-3) . The temporal and
spatial relationship between the erupting prominence and the coronal
arcade is shown. It gives an observational restriction to the magnetic
field configuration of the models of such events.
---------------------------------------------------------
Title: Attempt to Observe the Sodium Exosphere of Mercury During
the 1993 Solar Transit
Authors: Potter, A. E.; Talent, D.; Kurokawa, H.; Kawakami, S.;
Morgan, T. H.
1994LPI....25.1099P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High-Resolution Spectral Observation during the Impulsive
Phase of a Flare
Authors: Ji, G. P.; Kurokawa, H.; Fang, C.; Huang, Y. R.
1994SoPh..149..195J Altcode:
High-resolution observations of the flare on October 21, 1989 were
made with the Domeless Solar Telescope of the Hida Observatory. The
following new results have been obtained: (a) during the impulsive phase
of the flare, the spectral line asymmetry has spatial fine structures of
1″-2″; (b) for several points in the flare region the line profile
alternatively changes between blue asymmetry and red asymmetry within
a few seconds. A possible explanation has been suggested.
---------------------------------------------------------
Title: Fine Structures of the Inner Corona Observed at the 1991
Total Solar Eclipse
Authors: Takeda, A.; Kurokawa, H.; Kitai, R.; Ishiura, K.
1994scs..conf..565T Altcode: 1994IAUCo.144..565T
No abstract at ADS
---------------------------------------------------------
Title: Filament Tether Cutting Before a Major Eruptive Flare
Authors: Canfield, R. C.; Blais, K. A.; Reardon, K. P.; Acton, Loren;
Kurokawa, H.
1994ASPC...68..411C Altcode: 1994sare.conf..411C
No abstract at ADS
---------------------------------------------------------
Title: The X Flare of 15 November, 1991: Preflare Flux Emergence,
Heating and Filament Eruption
Authors: Canfield, R. C.; Blais, K. A.; McClymont, A. N.; Metcalf,
T. R.; Reardon, K. P.; Wülser, J. -P.; Acton, L. W.; Kurokawa, H.;
Hirayama, T.
1994xspy.conf..153C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transient Brightenings of Soft X-Ray Loops in Emerging
Flux Regions
Authors: Kurokawa, H.; Kawai, G.; Tsuneta, S.; Ogawara, Y.
1994xspy.conf...59K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Diagnostics of Twisted Flux Emergence (noaa AR7260)
Authors: Leka, K. D.; van Driel-Gesztelyi, L.; Anwar, B.; Canfield,
R. C.; Hudson, H. S.; Metcalf, T. R.; Mickey, D. L.; Nitta, N.;
Kurokawa, H.
1994xspy.conf...25L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Prominenece Eruption Followed by a Coronal Arcade Formation
on July 30-31, 1992
Authors: Hanaoka, Y.; Kurokawa, H.; Enome, S.; Nakajima, H.; Shibasaki,
K.; Nishio, M.; Takano, T.; Torii, C.; Sekiguchi, H.; Kawashima, S.;
Bushimata, T.; Shinohara, N.; Irimajiri, Y.; Koshiishi, H.; Shiomi,
Y.; Nakai, Y.; Funakoshi, Y.; Kitai, R.; Ishiura, K.; Kimura, G.
1994xspy.conf..193H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Prominence Eruption in NOAA7125 on April 6, 1992
Authors: Kitai, R.; Kawai, G.; Anwar, B.; Kurokawa, H.; Funakoshi,
Y.; Nakai, Y.; Tsuneta, S.
1994xspy.conf..287K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Filament Tether Cutting Before a Major Eruptive Flare
Authors: Canfield, R. C.; Blais, K. A.; McClymont, A. N.; Metcalf,
T. R.; Reardon, K. P.; Wuelser, J. -P.; Acton, L. W.; Kurokawa, H.
1993BAAS...25.1188C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flares on 1992 September 6
Authors: Shibata, K.; Nitta, N.; Kitai, R.; Kurokawa, H.; Yaji, K.;
Kato, T.; Zarro, D. M.
1993BAAS...25R1187S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: H alpha Surge Activity at the First Stage of Magnetic Flux
Emergence
Authors: Kurokawa, H.; Kawai, G.
1993ASPC...46..507K Altcode: 1993IAUCo.141..507K; 1993mvfs.conf..507K
No abstract at ADS
---------------------------------------------------------
Title: Comparison between YOHKOH Soft X-ray Images and 3D MHD
Simulations of Solar Emerging Flux Regions
Authors: Matsumoto, R.; Tajima, T.; Kaisig, M.; Shibata, K.; Ishido,
Y.; Tsuneta, S.; Shimizu, T.; Kawai, G.; Kurokawa, H.; Akioka, M.;
Acton, L.; Strong, K.; Nitta, N.
1992AAS...181.8109M Altcode: 1992BAAS...24.1253M
The soft X-ray telescope on the Yohkoh mission enabled us to observe
the evolution of emerging flux regions (EFR) in coronal X-rays with
high spatial and temporal resolution. Furthermore, we now have enough
computing capability to perform three-dimensional MHD simulation
of EFRs with sufficient spacial resolution to study details of the
flux emergence process. These new tools provide the opportunity to
investigate the physics involved in the formation of coronal loops
in much more detail. We carried out 3D MHD simulations of emerging
magnetic flux regions under various intial conditions; (1) a horizontal
magnetic flux sheet, (2) a bundle of horizontal flux tubes, and (3)
a flux sheet with sheared magnetic fields. Numerical results show that
coronal magnetic loops are formed due to the enhanced buoyancy resulting
from gas precipitating along magnetic field lines. The interchange modes
help to produce a fine fibrous structure perpendicular to the magnetic
field direction in the linear stage, while the undular modes determine
the overall loop structure. We observe in 3D simulations that during the
ascendance of loops the bundle of flux tubes, or even the flux sheet,
developes into dense filaments pinched between magnetic loops. We
also find that magnetic field lines are twisted by the vortex motion
produced by the horizontal expansion of magnetic loops. Our numerical
results may explain the observed signatures such as (1) the spacial
relation between soft X-ray loops and Hα arch filaments obtained by
coordinated observation between Yohkoh and ground-based observatories
(Kawai et al. 1992), (2) the rate of increase in size of soft X-ray
loops in EFRs (Ishido et al. 1992), (3) emergence of twisted magnetic
loops, and (4) the threshold flux for formation of chromospheric arch
filament systems (AFS).
---------------------------------------------------------
Title: Detailed Comparison between Hα and YOHKOH Soft X-Ray Images
of a Confined Two-Ribbon Flare
Authors: Kurokawa, Hiroki; Kawai, Goro; Kitai, Reizaburo; Funakoshi,
Yasuhiro; Nakai, Yoshihiro; Tsuneta, Saku; Kosugi, Takeo; Enome,
Shinzo; Acton, Loren W.; Ogawara, Yoshiaki
1992PASJ...44L.129K Altcode:
The spatial and temporal relationships between soft X-ray loops
and Hα flare Kernels were studied for the 1B (M2.6) flare of 1991
December 5. Most of flare energy was released inside three soft X-ray
loops whose footpoints were bright as Hα Kernels. We suggest that the
interaction among pre-existing or emerging magnetic loops is essential
for the successive energy release in a confined two-ribbon flare.
---------------------------------------------------------
Title: Comparison between Hα and YOHKOH Soft X-Ray Images of Emerging
Flux Regions
Authors: Kawai, Goro; Kurokawa, Hiroki; Tsuneta, Saku; Shimizu,
Toshifumi; Shibata, Kazunari; Acton, Loren W.; Strong, Keith T.;
Nitta, Nariaki
1992PASJ...44L.193K Altcode:
We carried out a detailed comparison between Hα and Yohkoh Soft X-ray
(SXR) images of three emerging flux regions. The main results are:
(1) In general, SXR bright features coincide well in space with Hα
arch filament systems in the emerging flux regions (EFR). (2) Some
young and active parts of EFRs are especially bright in SXR. (3)
The SXR structures related to EFR show fairly rapid changes in both
brightness and shape. These results are consistent with the model that
the emerging cool loops of EFRs evolve into hot coronal loops through
some heating processes.
---------------------------------------------------------
Title: Fine Structures of Chromospheric Magnetic Field and Material
Flow in a Solar Active Region
Authors: Zhang, Hongqi; Ai, Guoxiang; Sakurai, T.; Kurokawa, H.
1991SoPh..136..269Z Altcode:
In this paper, we analyze the relations between photospheric vector
magnetic fields, chromospheric longitudinal magnetic fields and velocity
fields in a solar active region. Agreements between the photospheric and
chromospheric magnetograms can be found in large-scale structures or in
the stronger magnetic structures, but differences also can be found in
the fine structures or in other places, which reflect the variation of
the magnetic force lines from the photosphere to the chromosphere. The
chromospheric superpenumbral magnetic field, measured by the Hβline,
presents a spoke-like structure. It consists of thick magnetic fibrils
which are different from photospheric penumbral magnetic fibrils. The
outer superpenumbral magnetic field is almost horizontal. The direction
of the chromospheric magnetic fibrils is generally parallel to the
transverse components of the photospheric vector magnetic fields. The
chromospheric material flow is coupled with the magnetic field
structure. The structures of the Hβ chromospheric magnetic fibrils
in the network are similar to Hβ dark fibrils, and the feet of the
magnetic fibrils are located at the photospheric magnetic elements.
---------------------------------------------------------
Title: Optical Observations of Flare-Productive Flux Emergence
Authors: Kurokawa, H.
1991LNP...387...39K Altcode: 1991LNP...387...37K; 1991fpsa.conf...39K
The optical observations of the relationship between emerging magnetic
fluxes and flares are reviewed and the characteristics essential to
the flare-productive emerging flux regions are studied. Examining
several essential parameters, i.e. location of emergence, orientation
of bipolar axis, growth rate and magnetic shear development, we conclude
that the emergence of twisted magnetic flux ropes is the most important
factor for the major flare activities. Some observational evidence of
the emergence of the twisted magnetic flux ropes is demonstrated with
high resolution H pictures.
---------------------------------------------------------
Title: High resolution observations of active phenomena obtained at
Hida Observatory
Authors: Kurokawa, H.; Nakai, Y.; Funakoshi, Y.; Kitai, R.
1991AdSpR..11e.233K Altcode: 1991AdSpR..11..233K
Samples of high-resolution observations of solar active regions and
flares obtained with the 60-cm Domeless Solar Telescope (DST) at
Hida Observatory, Kyoto University are presented. What gives rise to
the twist and shear in the magnetic loop structures is the essential
question for the study of solar active phenomena. Several examples
showing the development of twisted or sheared magnetic structures
are demonstrated and morphologically studied. Two examples of
high-resolution spectra of a flare and spicules are also demonstrated.
---------------------------------------------------------
Title: High-Resolution Observation and Detailed Photometry of a
Great Hα Two-Ribbon Flare
Authors: Kitahara, T.; Kurokawa, H.
1990SoPh..125..321K Altcode:
A great Hα two-ribbon flare of 12 October, 1981 was observed with
the Domeless Solar Telescope at the Hida Observatory and its detailed
photometry was made with a two dimensional microdensitometer. The
principal results are as follows: (1) The impulsive phase of the flare
started with the progressive brightenings of flare points forming
the front lines of the Hα two ribbons at both sides of the magnetic
neutral line. These are followed by the explosive expansion of Hα
two ribbons at the main impulsive phase. (2) Three typical shapes of
Hα light curves were found. The type 1 light curve is characterized
by the primary impulsive rise and rapid fall of intensity. The light
curve of type 3 has no impulsive component but has a very gradual
maximum. The type 2 profile attains the main gradual maximum with a
few small impulsive peaks. These different types of light curves are
made by different heating mechanisms, those are electron precipitation,
heat conduction and soft X-ray radiation respectively. (3) The light
curve of total intensity, which was made by integrating Hα - 1.0
Å intensities of the whole main Hα flare region, shows a primary
impulsive peak and a later gradual maximum. The former peak coincides
in time with that of the hard X-ray emission. The latter maximum is
well correlated with the soft X-ray maximum. (4) The brightest flare
points with time profiles of type 1 are closely related to the impulsive
hard X-ray emissions of highest energy.
---------------------------------------------------------
Title: High-Resolution Observations of Hα Flare Regions
Authors: Kurokawa, Hiroki
1989SSRv...51...49K Altcode:
This paper gives a review of the recent high-resolution Hα observations
of solar flares and flare-productive active regions. From studies
of the morphological and evolutional features of Hα flare emitting
regions, two types of two-ribbon flares, which are termed separating
two-ribbon flare and confined two-ribbon flare, are discussed. The
former is characterized by conspicuous separating motions or expanding
motions of the Hα two ribbons, whereas the latter shows only a short
range of or no separating motions of the two ribbons. The explosive
compact flares, which occur in some compact newly-emerging flux
regions, are also discussed. Attention is paid to the successive
and impulsive brightenings of Hα flare points which form the Hα
flare kernels and the front lines of Hα two ribbons at the impulsive
phases of flares. Temporal relationships between Hα line intensities
or profiles and hard X-ray or microwave emissions are discussed to
discriminate the energy transport mechanisms in the flare loops. Hα
monochromatic image of high spatial resolution, at the present time,
is the most sensitive detector for finding the first appearance of
newly-emerging magnetic flux region and the developing features of
sheared configuration of magnetic field, both of which are the key
factors in flare energy build-up processes. It is suggested that the
successive emergence of a twisted magnetic flux rope might be essential
for the production of a major flare.
---------------------------------------------------------
Title: Mass Motions in Active Region Filaments
Authors: Hanaoka, Yoichiro; Kurokawa, Hiroki
1989SoPh..124..227H Altcode:
Mass motions in active region filaments of regions NOAA 4171 and McMath
16208 are analyzed. Both regions were continuously observed with the
Zeiss Lyot filter for about a week at the Hida Observatory. As for NOAA
4171, Dopplergrams are made from the Hα filtergrams of 7 wavelengths
for the qualitative study of the velocity fields in the filament, and
Beckers' cloud model analysis is employed for a quantitative study of
them. Dopplergrams of McMath 16208 are also constructed for qualitative
analyses to determine whether the results derived from the analysis
of NOAA 4171 are applicable to this region.
---------------------------------------------------------
Title: Detailed comparison of transverse magnetic fields of the sun
with H-alpha fine structures
Authors: Kawakami, Singo; Makita, Mitsugu; Kurokawa, Hiroki
1989PASJ...41..175K Altcode:
Vectormagnetograms obtained at the Okayama Astrophysical Observatory
are compared in detail with H-alpha filtergrams taken with the Domeless
Solar Telescope at Hida Observatory for three active regions. The
coincidence rate between the azimuth of transverse magnetic fields and
elongated H-alpha dark fine structures decreases as the active region
moves on the solar disk from the center to the limb. This center-to-limb
variation of the azimuthal coincidence rate can be explained by the
difference of elevation angle between the photospheric and chromospheric
magnetic fields. The analysis of three active regions shows that,
in a more active region, the magnetic field is more inclined in the
photosphere, and more sheared in the vertical direction. Three active
regions show different values of the azimuthal coincidence rate, and
these differences are discussed in connection with the magnetic field
configuration and the evolutional characteristics of the individual
active regions.
---------------------------------------------------------
Title: Plasma Motions in an Emerging Flux Region
Authors: Brueckner, G. E.; Bartoe, J. -D. F.; Cook, J. W.; Dere,
K. P.; Socker, D.; Kurokawa, H.; McCabe, M.
1988ApJ...335..986B Altcode:
Ultraviolet spectra of C IV show large nonthermal broadening in an
area of emerging flux. These nonthermal motions are observed at a very
early stage of reconnecting field lines. The spectra can be traced
to small, rapidly changing surge or filament-like features which
are seen in the center, blue, and red wing of H-alpha. They seem to
have the characteristics of macrospicules or explosive events. They
are precursors of the reconnection process. Plasma turbulence and/or
plasma waves in the reconnecting plasma may cause the broad C IV line
profiles. The activity in the transition zone precedes the formation
of a bright chromospheric loop system.
---------------------------------------------------------
Title: A coronal condensation observed at the total solar eclipse
of June 11, 1983 and a related transient prominence
Authors: Suematsu, Yoshinori; Saito, Sumisaburo; Funakoshi, Yasuhiro;
Kurokawa, Hiroki
1988SoPh..116..285S Altcode:
A coronal condensation was observed simultaneously with Fexiv λ5303,
Fex λ6374, Fe XI λ7892, and Hα filtergraphs. The size and shape
of the condensation in λ5303 are different from those in other
filtergrams. Hα filtergrams taken around the eclipse time show that a
small transient prominence exists in close proximity to the condensation
core and behaves like a post-flare loop system, though the appearance
is quite different and no flare-report exists. A small-scale energetic
phenomenon seems to have occurred at the top of magnetic loops.
---------------------------------------------------------
Title: Active region coronal loops observed at the total solar
eclipse of February 16, 1980
Authors: Hanaoka, Yoishiro; Kurokawa, Hiroki; Saito, Sumisaburo
1988PASJ...40..369H Altcode:
Coronal loop structures above an active region observed at the total
eclipse of February 16, 1980 in Kenya are analyzed. Temperatures and
densities of the loops are derived from three monochromatic images
of Fe X λ6374 (1×10<SUP>6</SUP>K or cool corona), Fe XIV λ5303
(2×10<SUP>6</SUP>K or hot corona), and continuum. These monochromatic
images are processed for the analyses, and pure images of the active
region corona are obtained. Results from a morphological diagnostics
are presented.
---------------------------------------------------------
Title: Close relationship between H-alpha and hard X-ray emissions
at the impulsive phase of a solar flare
Authors: Kurokawa, Hiroki; Takakura, Tatsuo; Ohki, Kenichiro
1988PASJ...40..357K Altcode:
High-resolution Hα images of the March 23, 1982 flare were obtained
with the 60-cm Domeless Solar Telescope at the Hida Observatory. The
mean temporal resolution of Hα - 1.0-Å images was about 1 s at
the impulsive phase of the flare and better than those of any other
observations which had been published. This enabled the authors to
study the close correlation between Hα light curves and hard X-ray time
profiles obtained by the Japanese satellite Hinotori. Main observational
results are presented and discussed.
---------------------------------------------------------
Title: Surge activity in an emerging magnetic region of the sun
Authors: Kurokawa, H.
1988VA.....31...67K Altcode:
From the morphological study of the earliest phase of an emerging
flux region, we found that the first manifestation of the emerging
flux region on the solar surface is a surge activity. Examining the
magnetic field configuration of the surge region, we suggest that
the surges in emerging flux regions are produced by the reconnection
between newly-emerging fields and older surrounding magnetic fields.
---------------------------------------------------------
Title: Rotating eruption of an untwisting filament triggered by the
3B flare of 25 April, 1984
Authors: Kurokawa, Hiroki; Hanaoka, Yoichiro; Shibata, Kazunari;
Uchida, Yutaka
1987SoPh..108..251K Altcode:
A great 3B flare, whose X-ray class was X13, occurred over a
delta-sunspot at 00: 01 UT on April 25, 1984. Before the flare, a strong
magnetic shear was found to be formed along the neutral line in the
delta-sunspot with shear motions of umbrae. The shear motions of the
umbrae were caused by the successive emergence of a magnetic flux rope.
---------------------------------------------------------
Title: Vapor compression distiller and membrane technology for
water revitalization
Authors: Ashida, A.; Mitani, K.; Ebara, K.; Kurokawa, H.; Sawada,
I.; Kashiwagi, H.; Tsuji, T.; Hayashi, S.; Otsubo, K.; Nitta, K.
1987AdSpR...7d..73A Altcode: 1987AdSpR...7...73A
Water revitalization for a space station can consist of membrane
filtration processes and a distillation process. Water recycling
equipment using membrane filtration processes was manufactured
for ground testing. It was assembled using commercially available
components. Two systems for the distillation are studied; one is an
absorption type thermopervaporation cell and the other is a vapor
compression distiller. Absorption type thermopervaporation able to
easily produce condensed water under zero gravity was investigated
experimentally and through simulated calculation. The vapor compression
distiller was studied experimentally and it offers significant energy
savings for evaporation of water.
---------------------------------------------------------
Title: Two distinct morphological types of magnetic shear development
and their relation to flares
Authors: Kurokawa, H.
1987SoPh..113..259K Altcode: 1982SoPh..113..259K
From a morphological study of the evolution of six active regions,
we found two types of processes for the development of magnetic shear
configurations between sunspots: (A) collision of two sunspots of
opposite magnetic polarities, and (B) successive emergence of twisted
magnetic flux ropes. We conclude that the process (B) might be essential
for the production of major flares.
---------------------------------------------------------
Title: The innermost corona observed at the 1973 June 30 eclipse
Authors: Hanaoka, Yoichiro; Kanno, Mitsuo; Kurokawa, Hiroki; Tsubaki,
Tokio
1986SoPh..106...95H Altcode:
Slitless flash spectrograms in heights below 8000 km above the solar
limb were obtained by the University of Kyoto Expedition at Atar,
Mauritania. The integrated intensities of FeXIVλ5303, FeXλ6374,
FeXIλ7892, and the continuum are measured as a function of height above
the solar limb at eleven points (P.A. = 284-300°) around the third
contact point. It is found that a significant amount of the emission in
FeXλ6374 originates in chromospheric levels well below 8000 km. This
implies that the interspicular region of the chromosphere is occupied
by coronal material. The average values of the electron temperature and
the electron density in the interspicular region are derived from the
FeXλ6374 and the FeXIλ7892 intensities on the assumption of spherical
symmetry: T<SUB>e</SUB> = 0.9-1.1 × 10<SUP>6</SUP> K and N<SUB>e</SUB>
= 9-10 × 10<SUP>8</SUP> cm<SUP>−3</SUP>. The intensity variations
of the coronal lines and the continuum with position angle are also
studied. Strong correlations between FeXIVλ5303 and the continuum
and between FeXλ6374 and FeXIλ7892 are found. From the FeXλ6374
intensities it is inferred that there is a density fluctuation in the
innermost corona by at least a factor of two.
---------------------------------------------------------
Title: The post flare loops observed at the total eclipse of February
16, 1980
Authors: Hanaoka, Y.; Kurokawa, H.; Saito, S.
1986SoPh..105..133H Altcode:
A post flare loop system was observed on the west limb at the total
solar eclipse of February 16, 1980 in Kenya. Analyzing the monochromatic
images and the flash spectra, we obtained the following results: (1)
the lower part of the post flare loop system is characterized mainly
by distinct cool loops of Hα and Fe x 6374. Fe x 6374 emitting plasma
(T<SUB>e</SUB> = 1.0 × 10<SUP>6</SUP> K) is highly concentrated in
the loops. The 6374 loops are broader in diameter and located very
close to but a little higher than the corresponding Hα loops. The
electron densities of the dense part in Hα and Fe x 6374 loops are
10<SUP>11</SUP> cm<SUP>-3</SUP> and 6 × 10<SUP>9</SUP>cm<SUP>-3</SUP>,
respectively; (2) the Ca xv emitting region (3.5 × 10<SUP>6</SUP> K) is
confined to the upper part of the post flare loops. The electron density
of this hot region is estimated as 8 × 10<SUP>9</SUP> cm<SUP>-3</SUP>
from the Ca xv line intensity ratio, I(λ5694)I(λ5445). These
observational results led us to construct an empirical model of the
post flare loop system which is consistent with the reconnection model
of Kopp and Pneuman (1976).
---------------------------------------------------------
Title: Observations of chromospheric flare dynamics at the next
solar maximum specific recommendations of the Chromospheric Flare
Dynamics Group.
Authors: Canfield, R. C.; Gaizauskas, V.; Kurokawa, H.; Martin, S. F.;
Svestka, Z.
1986lasf.conf..489C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High resolution observation of Hα solar flares and temporal
relation between Hα and X-ray, microwave emission
Authors: Kurokawa, H.; Kitahara, T.; Nakai, Y.; Funakoshi, Y.;
Ichimoto, K.
1986Ap&SS.118..149K Altcode:
We studied the evolutional characteristics of fine structures in
Hα flare emitting regions and their relation to X-ray and microwave
emissions for selected events observed with the 60 cm Domeless Solar
Telescope at Hida Observatory, University of Kyoto. The principal
conclusions of this investigation are: (1) Hα kernel consists of some
finer bright points or Hαflare points whose individual size is less
than 1 arc sec. (2) Impulsive brightnenings of Hα flare points occurred
simultaneously with the spikes of the hard X-ray and microwave bursts
within the time resolution of our Hα observations which varied from
1 to 10 s. (3) It is concluded that fast electron beams must be the
principal mechanism of heating Hα flares during the impulsive phase
of a flare.
---------------------------------------------------------
Title: Impulsive brightening of Hα flare points.
Authors: Kurokawa, Hiroki
1986lasf.conf...51K Altcode: 1986lasf.symp...51K
The authors showed clearly that flare points are elementary structures
of Hα flare emitting regions. Many flare points successively brighten
in the chromosphere to form Hα kernels or the front lines of Hα
flare ribbons at the impulsive phases of flares. The flare points
correspond to the chromospheric footpoints of flare loops and their
individual size is less than 1arcsec. Impulsive brightenings of flare
points closely synchronize with the hard X-ray or microwave spikes at
the early impulsive phases of flares.
---------------------------------------------------------
Title: Periodic behaviour of solar flare activity
Authors: Ichimoto, K.; Kubota, J.; Suzuki, M.; Tohmura, I.; Kurokawa,
H.
1985Natur.316..422I Altcode:
The periodic nature of solar activity has been studied using parameters
such as the sunspot Wolf numbers, calcium plage areas and flare
indices. The magnitude of the solar activity based on these parameters
reveals periodicities other than the most pronounced 11-yr one. Any
absolute detection of periodicity in active phenomena would have
fundamental significance for our understanding of solar activity. Here
we investigate the temporal variation of the flare activity of the Sun
using the data of 8,821 Hα flares which occurred during the period
January 1965 to February 1984, and show new evidence for 155-day and
17-month periodicities of the flare activity. The 155-day periodicity
is examined by taking into account the location of the flare on the
Sun. It is suggested that the 155-day period may be related to the
timescale for the storage and/or the escape of the magnetic field.
---------------------------------------------------------
Title: Hα Red Asymmetry of Solar Flares
Authors: Ichimoto, K.; Kurokawa, H.
1984SoPh...93..105I Altcode:
The evolutional characteristics of the red asymmetry of Hα flare
line profiles were studied by means of a quantitative analysis of
Hα flare spectra obtained with the Domeless Solar Telescope at Hida
Observatory. Red-shifted emission streaks of Hα line are found at the
initial phase of almost all flares which occur near the disk center,
and are considered to be substantial features of the red asymmetry. It
is found that a downward motion in the flare chromospheric region is the
cause of the red-shifted emission streak. The downward motion abruptly
increases at the onset of a flare, attains its maximum velocity of
about 40 to 100 km s<SUP>-1</SUP> shortly before the impulsive peak of
the microwave burst, and rapidly decreases before the intensity of Hα
line reaches its maximum. Referring to the numerical simulations made
by Livshits et al. (1981) and Somov et al. (1982), we conclude that
the conspicuous red-asymmetry or the red-shifted emission streak of
Hα line is due to the downward motion of the compressed chromospheric
flare region produced by the impulsive heating by energetic electron
beam or thermal conduction.
---------------------------------------------------------
Title: Solar active regions and flares.
Authors: Kurokawa, H.
1984AstHe..77..136K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A CMG attitude control system for balloon use
Authors: Kurokawa, H.; Yajima, N.; Usui, S.
1984spte.symp.1211K Altcode:
A plan for a balloon-borne platform for astronomical observation and
its control system is derived. For a control torquer, single-gimbal
control moment gyros (CMGs) with a pyramid configuration were chosen. A
new steering law is presented with its computer simulation results
for such CMGs.
---------------------------------------------------------
Title: The Height of Hα Flare Emitting Region
Authors: Kurokawa, Hiroki
1983SoPh...86..195K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of a compact solar flare on 1981 September 7 in
Hα, X-ray, and microwave radiations
Authors: Kanno, Mitsuo; Kurokawa, Hiroki; Hinotori Group
1983SoPh...86..193K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Morphological and Evolutional Features of Ellerman Bombs
Authors: Kurokawa, H.; Kawaguchi, I.; Funakoshi, Y.; Nakai, Y.
1982SoPh...79...77K Altcode:
Morphological and evolutional features of Ellerman bombs were studied
with Hα filtergrams of two active regions very close to the solar
limb. We quantitatively determined the elongated or spike-like shape
of the bomb. The mean apparent length of 174 bombs is 1.1 arc sec,
while 80% of 204 bombs have a diameter of less than 0.6 arc sec. The
mean lifetime of 77 bombs is about 12 min at Hα - 1.2 Å. The first
maximum brightness of a typical bomb is attained, on average in about
2 min. Bombs grow longer in the first brightening phase and their mean
upward velocity explains the blue asymmetry of Hα emission profiles
of moustaches.
---------------------------------------------------------
Title: Progressive Brightenings Observed in the Wing of Hα Line
Authors: Kawaguchi, I.; Kurokawa, H.; Funakoshi, Y.; Nakai, Y.
1982SoPh...78..101K Altcode:
In an active region, several points were observed to brighten
progressively on the monochromatic image of Hα - 1.2 Å formed by the
Domeless Solar Telescope installed recently at Hida Observatory. The
phenomena were interpreted as small flares or subflares. The propagation
velocity was measured in two cases and discussed in terms of the
multiple loop activation observed in EUV radiation.
---------------------------------------------------------
Title: Hα Fine Structures in the 1981SEP7 Flare and Their Relation
to X-Ray and Microwave Emission
Authors: Kurokawa, H.; Kanno, M.
1982sofl.symp..199K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Heterogeneous structures of the lower corona.
Authors: Saito, S.; Kurokawa, H.; Ogimachi, Y.
1981otse.conf...31S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Some Observational Results on Ellerman Bomb
Authors: Kurokawa, H.
1980jfss.conf..206K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Coronal Condensation Observed at the 1973 Eclipse
Authors: Kurokawa, H.
1975SoPh...43..385K Altcode:
The flash spectrograms obtained at the June 30, 1973 eclipse contain
the monochromatic images of a coronal condensation in three coronal
lines of FeXIV 5303, FeX 6374 and FeXI 7892 and Hα line. The
assumption of the axially-symmetric distribution of the emissivity
in the coronal lines allows us to find the density and temperature
structure of the coronal condensation. While the electron density in
the central axis of the condensation is about ten times as high as
that of the normal corona at each height, the temperature is not so
high (T⩽2.3×10<SUP>6</SUP>K). This seems to be a representative
nature of a coronal active region in the post maximum phase of
activity. It is found that there exists a cool and dense core (T =
10<SUP>6</SUP>K, N<SUB>e</SUB>=6 × 10<SUP>9</SUP> cm<SUP>-3</SUP>
at 17000 km) at the lower part of the coronal condensation, which is
in a close geometrical coincidence with the small active prominence
protruding from the underlying plage region.
---------------------------------------------------------
Title: Observations of the total solar eclipse of 7 March, 1970.
Authors: Kanno, M.; Tsubaki, T.; Kurokawa, H.
1974MmKyo..34..281K Altcode: 1974KyoMe..34..281K
No abstract at ADS
---------------------------------------------------------
Title: The Continuum of the Extreme Limb and the Chromosphere at
the 1970 Eclipse
Authors: Kurokawa, H.; Nakayama, K.; Tsubaki, T.; Kanno, M.
1974SoPh...36...69K Altcode:
The flash spectra of the partial Sun and the chromosphere were
obtained at the total solar eclipse on 7 March, 1970. We studied
the distributions of the surface brightness of the continuum
at six wavelengths in the visual region to compare them with the
previous observations and the existing model atmospheres. All of the
distributions show a shallow dip and a small hump similar to those of
Heintze's observation at the 1954 eclipse. But the hump in our results
is of quite a different type from that given by Heintze's revised
model. It was found that none of the existing model atmospheres can
reproduce this hump. The intensity distribution in the low chromosphere
was also examined.
---------------------------------------------------------
Title: A large flare of August 2, 1972.
Authors: Kubota, J.; Kurokawa, H.; Kureizumi, T.
1972RISRJ..26..288K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fine Structure in the Inner Corona Observed at the 1970 Eclipse
(Papers presented at the Proceedings of the International Symposium on
the 1970 Solar Eclipse, held in Seattle, U. S. A. , 18-21 June, 1971.)
Authors: Tsubaki, T.; Kurokawa, H.; Kanno, M.
1971SoPh...21..305T Altcode:
On the slit spectrogram obtained at the 1970 eclipse in Mexico, the
intensities of four coronal lines (NiXIII λ5116, FeXIV λ5303, FeX
λ6374, and NiXV λ6702) and the continuum were measured as a function
of distance along the slit. It is found that there exist a lot of
fine fluctuations both in the lines and in the continuum intensities
superposed on a large scale formation. The correspondence of such
fluctuations between the continuum and the lines is good, with the
exception of the line λ6374 which shows a peculiar fluctuation. It
is shown that the intensities of the three lines λλ5116, 5303, and
6702 seem to be proportional to the square of the continuum intensity
while the λ6374 line intensity may be proportional to the fourth
power or more.
---------------------------------------------------------
Title: On the Coronal Lines in the Chromosphere at the 1970 Eclipse
(Papers presented at the Proceedings of the International Symposium on
the 1970 Solar Eclipse, held in Seattle, U. S. A. , 18-21 June, 1971.)
Authors: Kanno, M.; Tsubaki, T.; Kurokawa, H.
1971SoPh...21..314K Altcode:
Spectrographic observations of the flash spectrum were made by
the Kwasan Observatory at the total solar eclipse on 7 March,
1970. The integrated intensities of FeXIV λ5303, FeX λ6374,
and the continuum were measured on the spectrograms as a function
of height above the Sun's limb. It was found that a large amount
of emission in the coronal lines originates in the interspicular
regions of the chromosphere. Analysis of the data yielded that the
interspicular regions consist of coronal material of T<SUB>e</SUB>
= 1.6 × 10<SUP>6</SUP>-1.2 × 10<SUP>6</SUP> and log N<SUB>e</SUB>
= 8.5-9.5, and that a decrease in T<SUB>e</SUB> and an increase in
N<SUB>e</SUB> occur with decreasing height.
---------------------------------------------------------
Title: The Flash Spectrum Observed at the Total Eclipse of February
5, 1962
Authors: Kurokawa, H.; Tominaga, S.; Kubota, J.; Kawaguchi, I.
1969PASJ...21..141K Altcode:
At the total solar eclipse of February 5, 1962, the flash spectrum
was observed at Lae, New Guinea. Logarithmic intensities of about
130 emission lines were obtained at several positions on the east
and west limbs of the sun in the wavelength range from 5850 A to 6563
A. A comparison of our intensities with those previously published is
made. Two types of abnormal intensity gradients of the Ha and D3 lines
were found in the active region very near the west limb and the observed
spectral features are described in some detail. A comparison between
the flash spectrograms and the whitelight or the monochromatic images
of the solar disk before the eclipse reveals that the emission line
intensities of Ha and D3 extend to large altitudes in the chromosphere
over the active region ex9ept in the close vicinities of the sunspot
where the intensities decrease rapidly.
