Author name code: shibasaki
ADS astronomy entries on 2022-09-14
author:"Shibasaki, Kiyoto"
------------------------------------------------------------------------
Title: Comparative Study of Microwave Polar Brightening, Coronal
Holes, and Solar Wind over the Solar Poles
Authors: Fujiki, Ken'ichi; Shibasaki, Kiyoto; Yashiro, Seiji; Tokumaru,
Munetoshi; Iwai, Kazumasa; Masuda, Satoshi
Bibcode: 2019SoPh..294...30F
Altcode: 2019arXiv190210951F
We compared the long-term variation (1992 - 2017) in solar polar
brightening observed with the Nobeyama Radioheliograph, the polar
solar-wind velocity with interplanetary scintillation observations
at the Institute for Space-Earth Environmental Research, and the
coronal-hole distribution computed by potential-field calculations
of the solar corona using synoptic magnetogram data obtained at the
National Solar Observatory/Kitt Peak. First, by comparing the solar-wind
velocity [V ] and the brightness temperature [Tb] in the
polar region, we found good correlation coefficients (CCs) between
V and Tb in the polar regions, CC = 0.91 (0.83) for the
northern (southern) polar region, and we obtained the V -Tb
relationship as V =12.6 (Tb−10 ,667 ) 1 /2+432
. We also confirmed that the CC of V -Tb is higher than
those of V -B and V -B /f , where B and f are the polar magnetic-field
strength and magnetic-flux expansion rate, respectively. These results
indicate that Tb is a more direct parameter than B or B /f
for expressing solar-wind velocity. Next, we analyzed the long-term
variation of the polar brightening and its relation to the area of
the polar coronal hole [A ]. As a result, we found that the polar
brightening matches the probability distribution of the predicted
coronal hole and that the CC between Tb and A is remarkably
high, CC = 0.97. This result indicates that the polar brightening is
strongly coupled to the size of the polar coronal hole. Therefore,
the reasonable correlation of V - Tb is explained by V -
A . In addition, by considering the anti-correlation between A and
f found in a previous study, we suggest that the V - Tb
relationship is another expression of the Wang-Sheeley relationship
(V - 1 /f ) in the polar regions.
Title: Unusual Polar Conditions of the Sun during Solar Cycle 24
and its Iplications for Cycle 25
Authors: Gopalswamy, Nat; Masuda, Satoshi; Yashiro, Seiji; Akiyama,
Sachiko; Shibasaki, Kiyoto
Bibcode: 2018cosp...42E1250G
Altcode:
Polar field strength in one solar cycle is known to indicate the
strength (e.g., Sunspot number) and phase of the next cycle. In
particular the polar field strength (or its proxies such as the
polar coronal hole area and microwave polar brightness) during the
minimum phase of a given cycle seem to be well correlated with the
maximum sunspot number of the next cycle. Polar prominence eruptions
and coronal mass ejections have also been found to be indicators
of low polar field; their cessation signals the time of polarity
reversal. While these indicators are present in the current cycle,
significant differences are found regarding the phase lag between the
two hemispheres and the duration of polar eruptions. We use data from
the Nobeyama Radioheliograph, the Solar Dynamics Observatory, SOLIS,
and Wilcox Solar Observatory to highlight these differences. We find
that the north polar region of the Sun has near-zero field strength for
more than three years. This is unusually long and caused by surges of
both polarities heading toward the north pole that prevent the buildup
of the polar field. This seems to be due to anti-Hale active regions
that appeared around the 2012 peak sunspot activity in the northern
hemisphere. The unusual condition is consistent with (i) the continued
high-latitude prominence eruption, (ii) the extended period of high
tilt angle of the heliospheric current sheet, (iii) the weak microwave
polar brightness, and (iv) the lack of north polar coronal hole. On
the other hand, the south polar field has started building up and the
coronal hole has appeared in early 2015 because of large active regions
of the correct tilt in the southern hemisphere during the 2014 peak of
sunspot activity. The extended period of near-zero field in the north
polar region should result in very weak and delayed sunspot activity
in the northern hemisphere in cycle 25. On the other hand the south
polar field has already increased significantly, suggesting that the
activity in the southern hemisphere should start early; the amplitude
will depend on how the south polar fields will evolve in the declining
phase of cycle 24.
Title: Preflight Calibration Test Results for Optical Navigation
Camera Telescope (ONC-T) Onboard the Hayabusa2 Spacecraft
Authors: Kameda, S.; Suzuki, H.; Takamatsu, T.; Cho, Y.; Yasuda, T.;
Yamada, M.; Sawada, H.; Honda, R.; Morota, T.; Honda, C.; Sato, M.;
Okumura, Y.; Shibasaki, K.; Ikezawa, S.; Sugita, S.
Bibcode: 2017SSRv..208...17K
Altcode: 2016SSRv..tmp...23K
The optical navigation camera telescope (ONC-T) is a telescopic framing
camera with seven colors onboard the Hayabusa2 spacecraft launched
on December 3, 2014. The main objectives of this instrument are to
optically navigate the spacecraft to asteroid Ryugu and to conduct
multi-band mapping the asteroid. We conducted performance tests of the
instrument before its installation on the spacecraft. We evaluated the
dark current and bias level, obtained data on the dependency of the dark
current on the temperature of the charge-coupled device (CCD). The bias
level depends strongly on the temperature of the electronics package
but only weakly on the CCD temperature. The dark-reference data,
which is obtained simultaneously with observation data, can be used
for estimation of the dark current and bias level. A long front hood
is used for ONC-T to reduce the stray light at the expense of flatness
in the peripheral area of the field of view (FOV). The central area in
FOV has a flat sensitivity, and the limb darkening has been measured
with an integrating sphere. The ONC-T has a wheel with seven bandpass
filters and a panchromatic glass window. We measured the spectral
sensitivity using an integrating sphere and obtained the sensitivity
of all the pixels. We also measured the point-spread function using
a star simulator. Measurement results indicate that the full width
at half maximum is less than two pixels for all the bandpass filters
and in the temperature range expected in the mission phase except for
short periods of time during touchdowns.
Title: Microwave observations of a large-scale coronal wave with
the Nobeyama radioheliograph
Authors: Warmuth, A.; Shibasaki, K.; Iwai, K.; Mann, G.
Bibcode: 2016A&A...593A.102W
Altcode:
Context. Large-scale globally propagating waves in the solar corona
have been studied extensively, mainly using extreme ultraviolet (EUV)
observations. In a few events, corresponding wave signatures have
been detected in microwave radioheliograms provided by the Nobeyama
radioheliograph (NoRH). Several aspects of these observations seem to
contradict the conclusions drawn from EUV observations.
Aims:
We investigate whether the microwave observations of global waves are
consistent with previous findings.
Methods: We revisited the wave
of 1997 Sep. 24, which is still the best-defined event in microwaves. We
obtained radioheliograms at 17 and 34 GHz from NoRH and studied the
morphology, kinematics, perturbation profile evolution, and emission
mechanism of the propagating microwave signatures.
Results:
We find that the NoRH wave signatures are morphologically consistent
with both the associated coronal wave as observed by SOHO/EIT and
the Moreton wave seen in Hα. The NoRH wave is clearly decelerating,
which is typically found for large-amplitude coronal waves associated
with Moreton waves, and its kinematical curve is consistent with the
EIT wavefronts. The perturbation profile shows a pronounced decrease
in amplitude. Based on the derivation of the spectral index of the
excess microwave emission, we conclude that the NoRH wave is due to
optically thick free-free bremsstrahlung from the chromosphere.
Conclusions: The wavefronts seen in microwave radioheliograms are
chromospheric signatures of coronal waves, and their characteristics
support the interpretation of coronal waves as large-amplitude fast-mode
MHD waves or shocks.
Title: Unusual Polar Activity of the Sun in the Northern Hemisphere
and Its Implications for Solar Cycle 25
Authors: Gopalswamy, Nat; Masuda, Satoshi; Yashiro, Seiji; Akiyama,
Sachiko; Shibasaki, Kiyoto
Bibcode: 2016cosp...41E.712G
Altcode:
Polar field strength in one solar cycle is known to indicate the
strength (e.g., Sunspot number) and phase of the next cycle. In
particular the polar field strength (or its proxies such as the
polar coronal hole area and microwave polar brightness) during the
minimum phase of a given cycle seem to be well correlated with the
maximum sunspot number of the next cycle. Polar prominence eruptions
and coronal mass ejections have also been found to be indicators
of low polar field; their cessation signals the time of polarity
reversal. While these indicators are present in the current cycle,
significant differences are found regarding the phase lag between the
two hemispheres and the duration of polar eruptions. We use data from
the Nobeyama Radioheliograph, the Solar Dynamics Observatory, SOLIS,
and Wilcox Solar Observatory to highlight these differences. We find
that the north polar region of the Sun has near-zero field strength for
more than three years. This is unusually long and caused by surges of
both polarities heading toward the north pole that prevent the buildup
of the polar field. This seems to be due to anti-Hale active regions
that appeared around the 2012 peak sunspot activity in the northern
hemisphere. The unusual condition is consistent with (i) the continued
high-latitude prominence eruption, (ii) the extended period of high
tilt angle of the heliospheric current sheet, (iii) the weak microwave
polar brightness, and (iv) the lack of north polar coronal hole. On
the other hand, the south polar field has started building up and the
coronal hole has appeared in early 2015 because of large active regions
of the correct tilt in the southern hemisphere during the 2014 peak of
sunspot activity. The extended period of near-zero field in the north
polar region should result in very weak and delayed sunspot activity
in the northern hemisphere in cycle 25. On the other hand the south
polar field has already increased significantly, suggesting that the
activity in the southern hemisphere should start early; the amplitude
will depend on how the south polar fields will evolve in the declining
phase of cycle (24).
Title: Coronal Magnetic Fields Derived from Simultaneous Microwave
and EUV Observations and Comparison with the Potential Field Model
Authors: Miyawaki, Shun; iwai, Kazumasa; Shibasaki, Kiyoto; Shiota,
Daikou; Nozawa, Satoshi
Bibcode: 2016ApJ...818....8M
Altcode: 2015arXiv151204198M
We estimated the accuracy of coronal magnetic fields derived from radio
observations by comparing them to potential field calculations and the
differential emission measure measurements using EUV observations. We
derived line-of-sight components of the coronal magnetic field from
polarization observations of the thermal bremsstrahlung in the NOAA
active region 11150, observed around 3:00 UT on 2011 February 3
using the Nobeyama Radioheliograph at 17 GHz. Because the thermal
bremsstrahlung intensity at 17 GHz includes both chromospheric and
coronal components, we extracted only the coronal component by measuring
the coronal emission measure in EUV observations. In addition, we
derived only the radio polarization component of the corona by selecting
the region of coronal loops and weak magnetic field strength in the
chromosphere along the line of sight. The upper limits of the coronal
longitudinal magnetic fields were determined as 100-210 G. We also
calculated the coronal longitudinal magnetic fields from the potential
field extrapolation using the photospheric magnetic field obtained from
the Helioseismic and Magnetic Imager. However, the calculated potential
fields were certainly smaller than the observed coronal longitudinal
magnetic field. This discrepancy between the potential and the observed
magnetic field strengths can be explained consistently by two reasons:
(1) the underestimation of the coronal emission measure resulting from
the limitation of the temperature range of the EUV observations, and
(2) the underestimation of the coronal magnetic field resulting from
the potential field assumption.
Title: Depressed emission between magnetic arcades near a sunspot
Authors: Ryabov, B. I.; Shibasaki, K.
Bibcode: 2016BaltA..25..225R
Altcode: 2016OAst...25..225R
The locations of the depressed emission in microwaves, EUV and soft
X-rays are compared with each other and with the location of the
plasma outflow in the active region (AR) 8535 on the Sun. We found
that two open-field regions overlap the regions of depressed emission
near the AR's sunspot. These two open-field regions are simulated
with the potential-field source-surface (PFSS) model under radial
distances of RSS = 1.8 R⊙ and RSS
= 2.5 R⊙. Each open-field region is located between
the arcades of the loops of the same magnetic polarity. The former
open-field region covers the region of the plasma outflow, which is
thus useful for the tests on connection to the heliosphere. The utmost
microwave depression of the intensity in the ordinary mode (the Very
Large Array 15 GHz observations) also overlaps the region of the plasma
outflow and thus indicates this outflow. The lasting for eight days
depression in soft X-rays and the SOHO EIT 2.84× 10-8
m images are attributed to the evacuation of as hot coronal plasma
as T≥ 2× 106 K from the extended in height (``open")
magnetic structures. We conclude that the AR 8535 presents the sunspot
atmosphere affected by the large-scale magnetic fields.
Title: Chromospheric Sunspots in the Millimeter Range as Observed
by the Nobeyama Radioheliograph
Authors: Iwai, Kazumasa; Koshiishi, Hideki; Shibasaki, Kiyoto; Nozawa,
Satoshi; Miyawaki, Shun; Yoneya, Takuro
Bibcode: 2016ApJ...816...91I
Altcode: 2015arXiv151108991I
We investigate the upper chromosphere and the transition region
of the sunspot umbra using the radio brightness temperature at
34 GHz (corresponding to 8.8 mm observations) as observed by the
Nobeyama Radioheliograph (NoRH). Radio free-free emission in the
longer millimeter range is generated around the transition region,
and its brightness temperature yields the region's temperature and
density distribution. We use the NoRH data at 34 GHz by applying the
Steer-CLEAN image synthesis. These data and the analysis method enable
us to investigate the chromospheric structures in the longer millimeter
range with high spatial resolution and sufficient visibilities. We
also perform simultaneous observations of one sunspot using the NoRH
and the Nobeyama 45 m telescope operating at 115 GHz. We determine
that 115 GHz emission mainly originates from the lower chromosphere
while 34 GHz emission mainly originates from the upper chromosphere
and transition region. These observational results are consistent with
the radio emission characteristics estimated from current atmospheric
models of the chromosphere. On the other hand, the observed brightness
temperature of the umbral region is almost the same as that of the quiet
region. This result is inconsistent with current sunspot models, which
predict a considerably higher brightness temperature of the sunspot
umbra at 34 GHz. This inconsistency suggests that the temperature of
the region at which the 34 GHz radio emission becomes optically thick
should be lower than that predicted by the models.
Title: Ballooning Instability: A Possible Mechanism for Impulsive
Heating of Plasma Trapped in a Loop
Authors: Shibasaki, K.
Bibcode: 2015AGUFMSH13B2436S
Altcode:
Plasma confined in curved magnetic field are unstable when the plasma
beta (= gas pressure / magnetic pressure) exceeds a critical value
determined mainly by the loop geometry (~ loop thickness / curvature
radius). In TOKAMAK (one type of fusion experiment device), sudden
disruption of confined plasma are observed when plasma beta is high
and is called high-beta disruption. The main cause of the disruption
is ballooning instability (or localized interchange instability). This
instability can happen also in the solar atmosphere when conditions
are satisfied. Not only high gas pressure but also plasma flow along
curved magnetic field triggers ballooning instability. The most probable
location of the instability is around the loop top where the magnetic
field is the weakest. Impulsive heating of confined plasma and particle
acceleration can be expected by discharge process of the space charge
which is created by drift motion of plasma particles perpendicular
to the magnetic field. Associated with disruption, shock waves and
turbulences will be generated due to sudden expansion of plasma. Recent
high-resolution, high-cadence and multiple wavelength (visible-UV-EUV)
observations by SDO show many of these events.
Title: Detectability of hydrous minerals using ONC-T camera onboard
the Hayabusa2 spacecraft
Authors: Kameda, S.; Suzuki, H.; Cho, Y.; Koga, S.; Yamada, M.;
Nakamura, T.; Hiroi, T.; Sawada, H.; Honda, R.; Morota, T.; Honda,
C.; Takei, A.; Takamatsu, T.; Okumura, Y.; Sato, M.; Yasuda, T.;
Shibasaki, K.; Ikezawa, S.; Sugita, S.
Bibcode: 2015AdSpR..56.1519K
Altcode:
The Hayabusa2 spacecraft has three framing cameras (ONC-T, ONC-W1,
and ONC-W2) for optical navigation to asteroid 1999 JU3. The
ONC-T is a telescopic camera with seven band-pass filters in the visible
and near-infrared range. These filters are placed on a wheel, which
rotates to put a selected filter for different observations, enabling
multiband imaging. Previous ground-based observations suggesting that
hydrous materials may be present on the surface of 1999 JU3
and distributed in relatively limited areas. The presence of hydrous
minerals indicates that this asteroid experienced only low to moderate
temperatures during its formation, suggesting that primordial materials
are preserved. In order to find the best sampling sites, we will perform
reflectance spectroscopic observations using the ONC-T near the asteroid
after arrival. Finding regions rich in hydrous minerals is the key for
this remote sensing observation. In preparation for this, we conducted
ground-based experiments for the actual ONC-T flight model to confirm
the detectability of the absorption band of Fe-rich serpentine. As a
result, we detected the absorption band near 0.7 μm by reflectance
spectroscopy of CM2 chondrites, such as Murchison and Nogoya, which
are known to contain the Fe-rich serpentine, and did not detect any
0.7 μm absorption in Jbilet Winselwan CM2 chondrite with decomposed
Fe-rich serpentine.
Title: Calibration and First Light of Optical Navigation Camera
(ONC) of Hayabusa 2
Authors: Sugita, S.; Kameda, S.; Sawada, H.; Suzuki, H.; Yamada,
M.; Honda, C.; Ogawa, K.; Shirai, K.; Iijima, Y.; Cho, Y.; Takei,
A.; Sato, M.; Okumura, Y.; Yasuda, T.; Shibasaki, K.; Ikezawa, S.;
Nakamura, T.; Hiroi, T.; Kamata, S.; Koga, S. C.; ONC Team
Bibcode: 2015LPI....46.2169S
Altcode: 2015LPICo1832.2169S
We report the results of optical calibration, end-to-end tests with
meteorite samples, and the first light of the visible multi-band camera
on Hayabusa 2.
Title: Multi-mode quasi-periodic pulsations in a solar flare
Authors: Kolotkov, D. Y.; Nakariakov, V. M.; Kupriyanova, E. G.;
Ratcliffe, H.; Shibasaki, K.
Bibcode: 2015A&A...574A..53K
Altcode:
Context. Quasi-periodic pulsations (QPP) of the electromagnetic
radiation emitted in solar and stellar flares are often detected
in microwave, white light, X-ray, and gamma-ray bands. Mechanisms
for QPP are intensively debated in the literature. Previous studies
revealed that QPP may manifest non-linear, non-stationary and, perhaps,
multi-modal processes operating in flares.
Aims: We study QPP
of the microwave emission generated in an X3.2-class solar flare on
14 May, 2013, observed with the Nobeyama Radioheliograph (NoRH),
aiming to reveal signatures of the non-linear, non-stationary,
and multi-modal processes in the signal.
Methods: The NoRH
correlation signal obtained at the 17 GHz intensity has a clear QPP
pattern. The signal was analysed with the Hilbert-Huang transform
(HHT) that allows one to determine its instant amplitude and frequency,
and their time variation.
Results: It was established that the
QPP consists of at least three well-defined intrinsic modes, with the
mean periods of 15, 45, and 100 s. All the modes have quasi-harmonic
behaviour with different modulation patterns. The 100 s intrinsic
mode is a decaying oscillation, with the decay time of 250 s. The 15
s intrinsic mode shows a similar behaviour, with the decay time of
90 s. The 45 s mode has a wave-train behaviour.
Conclusions:
Dynamical properties of detected intrinsic modes indicate that the
100 s and 15 s modes are likely to be associated with fundamental
kink and sausage modes of the flaring loop, respectively. The 100 s
oscillation could also be caused by the fundamental longitudinal mode,
while this interpretation requires the plasma temperature of about 30
million K and hence is not likely. The 45 s mode could be the second
standing harmonics of the kink mode.
Title: Solar Cycle Indices from the Photosphere to the Corona:
Measurements and Underlying Physics
Authors: Ermolli, Ilaria; Shibasaki, Kiyoto; Tlatov, Andrey; van
Driel-Gesztelyi, Lidia
Bibcode: 2015sac..book..105E
Altcode:
No abstract at ADS
Title: Reduced Coronal Emission Above Large Isolated Sunspots
Authors: Ryabov, B. I.; Gary, D. E.; Peterova, N. G.; Shibasaki, K.;
Topchilo, N. A.
Bibcode: 2015SoPh..290...21R
Altcode: 2014SoPh..tmp..192R
We analysed specific regions of reduced soft X-ray and microwave
emission in five large isolated sunspots. The Nobeyama Radioheliograph
17 GHz observations reveal a local depression of microwave brightness
in the peripheral area of the sunspots. The depression regions appear
light (weak absorption) in the He 10830 Å line in areas with extended
(open) field lines, as indicated by potential field source surface
model (PFSS) extrapolations up to 1.5 R⊙. The observed
depressions of 3 - 8 % in ordinary mode at 17 GHz are interpreted as
resulting from free-free emission when the plasma density is lower
by 5 - 10 %. Our model estimates show that the decrease in density
in both the coronal and the lower layers above the depression region
accounts for the depression. These depression regions lend themselves
well to marking the location of outward plasma motions.
Title: Solar Cycle Indices from the Photosphere to the Corona:
Measurements and Underlying Physics
Authors: Ermolli, Ilaria; Shibasaki, Kiyoto; Tlatov, Andrey; van
Driel-Gesztelyi, Lidia
Bibcode: 2014SSRv..186..105E
Altcode: 2017arXiv170507054E; 2014SSRv..tmp...48E
A variety of indices have been proposed in order to represent the
many different observables modulated by the solar cycle. Most of these
indices are highly correlated with each other owing to their intrinsic
link with the solar magnetism and the dominant eleven year cycle,
but their variations may differ in fine details, as well as on short-
and long-term trends. In this paper we present an overview of the
indices that are often employed to describe the many features of the
solar cycle, moving from the ones referring to direct observations
of the inner solar atmosphere, the photosphere and chromosphere, to
those deriving from measurements of the transition region and solar
corona. For each index, we summarize existing measurements and typical
use, and for those that quantify physical observables, we describe
the underlying physics.
Title: Coronal magnetic field and the plasma beta determined from
radio and multiple satellite observations
Authors: Iwai, Kazumasa; Shibasaki, Kiyoto; Nozawa, Satoshi; Takahashi,
Takuya; Sawada, Shinpei; Kitagawa, Jun; Miyawaki, Shun; Kashiwagi,
Hirotaka
Bibcode: 2014EP&S...66..149I
Altcode: 2014arXiv1411.1913I
We derived the coronal magnetic field, plasma density, and temperature
from the observation of polarization and intensity of radio thermal
free-free emission using the Nobeyama Radioheliograph (NoRH) and extreme
ultraviolet (EUV) observations. We observed a post-flare loop on the
west limb on 11 April 2013. The line-of-sight magnetic field was derived
from the circularly polarized free-free emission observed by NoRH. The
emission measure and temperature were derived from the Atmospheric
Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO). The
derived temperature was used to estimate the emission measure from
the NoRH radio free-free emission observations. The derived density
from NoRH was larger than that determined using AIA, which can be
explained by the fact that the low-temperature plasma is not within
the temperature coverage of the AIA filters used in this study. We
also discuss the other observation of the post-flare loops by the EUV
Imager onboard the Solar Terrestrial Relations Observatory (STEREO),
which can be used in future studies to reconstruct the coronal magnetic
field strength. The derived plasma parameters and magnetic field were
used to derive the plasma beta, which is a ratio between the magnetic
pressure and the plasma pressure. The derived plasma beta is about
5.7 × 10-4 to 7.6 × 10-4 at the loop top region.
Title: Effect of solar cycle 23 in foF2 trend estimation
Authors: Elias, Ana G.; de Haro Barbas, Blas F.; Shibasaki, Kiyoto;
Souza, Jonas R.
Bibcode: 2014EP&S...66..111E
Altcode:
The effect of including solar cycle 23 in foF2 trend estimation is
assessed using experimental values for Slough (51.5°N, 359.4°E) and
Kokobunji (35.7°N, 139.5°E), and values obtained from two models:
(1) the Sheffield University Plasmasphere-Ionosphere model, SUPIM, and
(2) the International Reference Ionosphere, IRI. The dominant influence
on the F2 layer is solar extreme ultraviolet (EUV) radiation, evinced
by the almost 90% variance of its parameters explained by solar EUV
proxies such as the solar activity indices Rz and F10.7. This makes
necessary to filter out solar activity effects prior to long-term trend
estimation. Solar cycle 23 seems to have had an EUV emission different
from that deduced from traditional solar EUV proxies. During maximum
and descending phase of the cycle, Rz and F10.7 seem to underestimate
EUV solar radiation, while during minimum, they overestimate EUV
levels. Including this solar cycle in trend estimations then, and using
traditional filtering techniques, may induce some spurious results. In
the present work, filtering is done in the usual way considering the
residuals of the linear regression between foF2 and F10.7, for both
experimental and modeled values. foF2 trends become less negative as
we include years after 2000, since foF2 systematically exceeds the
values predicted by a linear fit between foF2 and F10.7. Trends become
more negative again when solar cycle 23 minimum is included, since
for this period, foF2 is systematically lower than values predicted
by the linear fit. foF2 trends assessed with modeled foF2 values are
less strong than those obtained with experimental foF2 values and more
stable as solar cycle 23 is included in the trend estimation. Modeled
trends may be thought of as a `zero level' trend due to the assumptions
made in the process of trend estimation considering also that we are
not dealing with ideal conditions or infinite time series.
Title: Direct interlink of plasma in the convection zone and in
the corona
Authors: Shibasaki, K.
Bibcode: 2014AGUFMSH44A..07S
Altcode:
Thermal plasma particles in a magnetic field have a magnetic moment
due to Lorentz force. The magnetic moment is anti-parallel to the
field direction (diamagnetic) and is inversely proportional to the
field strength. It does not disappear even under highly collisional
condition. The magnetic flux density (or magnetic field, B) in a
magnetized media is determined as B = μ0(H+M), where μ0 is the
magnetic permeability of the vacuum, H is the magnetic intensity, and
M is the magnetic moment per unit volume. This means that the magnetic
field in a plasma is a self-consistent field (B is a function of B
itself) and has some restrictions. Under high plasma beta condition,
this restriction results in spontaneous formation of magnetic flux
tubes. Hence, in the solar convection zone where the gas pressure is
high, the magnetic field can exists as concentrated flux tubes. Plasma
particles inside and outside the tube are rather independent even in
a low ionization degree plasma due to frequent collisions. Plasma
particles inside the flux tube are pushed upwards along the field
due to the diamagnetic moment (mirror force) against the gravity
force. The hot coronal plasma can be supplied directly from below
through magnetic flux tubes. Coronal heating and other important
questions can be understood by this simple mechanism.
Title: Erratum: "Spatial Structure of Sunspot Oscillations Observed
with SDO/AIA" (2012, ApJ, 756,
35)
Authors: Reznikova, V. E.; Shibasaki, K.
Bibcode: 2014ApJ...792...82R
Altcode:
No abstract at ADS
Title: Erratum: "Three-minute Oscillations above Sunspot Umbra
Observed with the Solar Dynamics Observatory/Atmospheric
Imaging Assembly and Nobeyama Radioheliograph" (2012, ApJ, 746, 119)
Authors: Reznikova, V. E.; Shibasaki, K.; Sych, R. A.; Nakariakov,
V. M.
Bibcode: 2014ApJ...792...81R
Altcode:
No abstract at ADS
Title: The 17 GHz Active Region Number
Authors: Selhorst, C. L.; Costa, J. E. R.; Giménez de Castro, C. G.;
Valio, A.; Pacini, A. A.; Shibasaki, K.
Bibcode: 2014ApJ...790..134S
Altcode: 2014arXiv1406.2252S
We report the statistics of the number of active regions (NAR) observed
at 17 GHz with the Nobeyama Radioheliograph between 1992, near the
maximum of cycle 22, and 2013, which also includes the maximum of cycle
24, and we compare with other activity indexes. We find that NAR minima
are shorter than those of the sunspot number (SSN) and radio flux at
10.7 cm (F10.7). This shorter NAR minima could reflect the presence of
active regions generated by faint magnetic fields or spotless regions,
which were a considerable fraction of the counted active regions. The
ratio between the solar radio indexes F10.7/NAR shows a similar
reduction during the two minima analyzed, which contrasts with the
increase of the ratio of both radio indexes in relation to the SSN
during the minimum of cycle 23-24. These results indicate that the
radio indexes are more sensitive to weaker magnetic fields than those
necessary to form sunspots, of the order of 1500 G. The analysis of
the monthly averages of the active region brightness temperatures shows
that its long-term variation mimics the solar cycle; however, due to the
gyro-resonance emission, a great number of intense spikes are observed
in the maximum temperature study. The decrease in the number of these
spikes is also evident during the current cycle 24, a consequence of
the sunspot magnetic field weakening in the last few years.
Title: Long-period pulsations of the thermal microwave emission of
the solar flare of June 2, 2007 from data with high spatial resolution
Authors: Kupriyanova, E. G.; Melnikov, V. F.; Puzynya, V. M.;
Shibasaki, K.; Ji, H. S.
Bibcode: 2014ARep...58..573K
Altcode:
Data from the Nobeyama Radioheliograph at 17 GHz with high spatial and
temporal resolution are used to detect quasi-periodic pulsations with
periods from 55 to 250 s in the thermal component of the microwave
emission of a solar flare loop observed on June 2, 2007. Observed
pulsations with periods of about 110-120 s are co-phased along the
entire loop axis. The observed periodicity is most likely due to
modulation of the radio emission by slow magnetoacoustic waves trapped
in the filamentary flare loop.
Title: Plasma Upflows and Microwave Emission in Hot Supra-arcade
Structure Associated with an M1.6 Limb Flare
Authors: Kim, S.; Shibasaki, K.; Bain, H. -M.; Cho, K. -S.
Bibcode: 2014ApJ...785..106K
Altcode:
We have investigated a supra-arcade structure associated with an
M1.6 flare, which occurred on the south-east limb on 2010 November
4. It is observed in EUV with the Atmospheric Imaging Assembly (AIA)
on board the Solar Dynamics Observatory, microwaves at 17 and 34 GHz
with the Nobeyama Radioheliograph (NoRH), and soft X-rays of 8-20
keV with RHESSI. Interestingly, we found exceptional properties of
the supra-arcade thermal plasma from the AIA 131 Å and the NoRH: (1)
plasma upflows along large coronal loops and (2) enhancing microwave
emission. RHESSI detected two soft X-ray sources, a broad one in the
middle of the supra-arcade structure and a bright one just above the
flare-arcade. We estimated the number density and thermal energy for
these two source regions during the decay phase of the flare. In the
supra-arcade source, we found that there were increases of the thermal
energy and the density at the early and last stages, respectively. On
the contrary, the density and thermal energy of the source on the top
of the flare-arcade decreases throughout. The observed upflows imply
that there is continuous energy supply into the supra-arcade structure
from below during the decay phase of the flare. It is hard to explain
by the standard flare model in which the energy release site is located
high in the corona. Thus, we suggest that a potential candidate of the
energy source for the hot supra-arcade structure is the flare-arcade,
which has exhibited a predominant emission throughout.
Title: Synoptic radio observations as proxies for upper atmosphere
modelling
Authors: Dudok de Wit, Thierry; Bruinsma, Sean; Shibasaki, Kiyoto
Bibcode: 2014JSWSC...4A..06D
Altcode: 2014arXiv1402.3946D
The specification of the upper atmosphere strongly relies on solar
proxies that can properly reproduce the solar energetic input in the
UV. Whilst the microwave flux at 10.7 cm (also called F10.7 index)
has been routinely used as a solar proxy, we show that the radio flux
at other wavelengths provides valuable complementary information that
enhances their value for upper atmospheric modelling. We merged daily
observations from various observatories into a single homogeneous data
set of fluxes at wavelengths of 30, 15, 10.7, 8 and 3.2 cm, spanning
from 1957 to today. Using blind source separation (BSS), we show that
their rotational modulation contains three contributions, which can
be interpreted in terms of thermal bremsstrahlung and gyro-resonance
emissions. The latter account for 90% of the rotational variability
in the F10.7 index. Most solar proxies, such as the MgII index, are
remarkably well reconstructed by simple linear combination of radio
fluxes at various wavelengths. The flux at 30 cm stands out as an
excellent proxy and is better suited than the F10.7 index for the
modelling the thermosphere-ionosphere system, most probably because
it receives a stronger contribution from thermal bremsstrahlung. This
better performance is illustrated here through comparison between
the observed thermospheric density, and reconstructions by the Drag
Temperature Model.
Title: Spatial Structure of Multimode Oscillations in a Solar Flare
on 14 May 2013 in EUV and Radio Bands
Authors: Kolotkov, Dmitry; Nakariakov, Valery; Nisticò, Giuseppe;
Shibasaki, Kiyoto; Kupriyanova, Elena
Bibcode: 2014cosp...40E1558K
Altcode:
Quasi-periodic pulsations and coronal loop oscillations in an X-class
solar flare on 14 May 2013 are considered. Rapidly decaying kink
oscillations of coronal loops with periods of several minutes in the
flaring active region detected in the EUV band with SDO/AIA after
the impulsive phase of the flare. Oscillations of neighbouring loops
are excited simultaneously, but get rapidly out of phase. In the
impulsive phase, observations in the radio band with the Nobeyama
Radioheliograph and Radiopolarimeter show quasi-periodic pulsations
that are most pronounced in the 17 GHz band. In the correlation plots
and the integrated flux the pulsations have a symmetric triangular
shape. The period of pulsations is about 1 min. Analysis of the spatial
locations of the radio sources reveal that the triangularity is likely
to be caused by superposition of several harmonic modes.
Title: Spatially resolved minute periodicities in flaring microwave
emission
Authors: Kupriyanova, Elena; Shibasaki, Kiyoto; Melnikov, Victor
Bibcode: 2014cosp...40E1696K
Altcode:
Spatially resolved quasi-periodic pulsations (QPPs) with minute
periodicities in microwave emission during solar flare on May 14,
2013 are studied. Data of Nobeyama Radioheliograph (NoRH) and
Radio Polarimeters (NoRP) at 17 GHz and 34 GHz are used. Metods of
correlation, Fourier and wavelet analyses are applied to time profiles
of the microwave fluxes. The following interesting properties of QPPs
have been found. The QPPs with the same period of 50 s originate from
two different flaring loops of different sizes during the impulsive
phase of the flare. Moreover, the larger loop has lower brightness
than the smaller one. Another interesting property is that the QPPs
of the flux integrated over the first loop are in antiphase with the
QPPs from the second loop. Such contradictory properties can not be in
correspondence with properties of the standing slow magnetoacoustic
waves trapped in magnetic loops of different sizes. Possible origin
of the QPPs properties are disscussed.
Title: Long-period oscillations of sunspots according to simultaneous
ground-based and space observations
Authors: Abramov-Maximov, V. E.; Efremov, V. I.; Parfinenko, L. D.;
Solov'ev, A. A.; Shibasaki, K.
Bibcode: 2013Ge&Ae..53..909A
Altcode:
An analysis of oscillatory processes with periods not shorter than
several tens of minutes in three isolated sunspots, which were
observed during identical periods in the optical and radio bands, is
illustrated. SDO/HMI magnetograms at an interval of 45 s and radio maps
at a wavelength of 1.76 cm, obtained using a Nobeyama radioheliograph
(NoRH), have been used. The time profiles, which were constructed based
on the NoRH and SDO/HMI data, indicate that the oscillations of the
radioemission correlate with those of the sunspot magnetic field. The
wavelet spectra and cross-wavelet transform reveal common oscillation
periods of 30-40, 70-100, and 150-200 min. The identical oscillation
periods, found using fundamentally different methods from ground-based
and space observations, confirm the solar nature of these oscillations,
which can be interpreted as oscillations of a sunspot as a whole.
Title: Long-Term Oscillations of Sunspots from Simultaneous
Observations with the Nobeyama Radioheliograph and Solar Dynamics
Observatory
Authors: Abramov-maximov, Vladimir E.; Efremov, Vyacheslav I.;
Parfinenko, Leonid D.; Solov'ev, Alexander A.; Shibasaki, Kiyoto
Bibcode: 2013PASJ...65S..12A
Altcode:
We present an investigation of oscillatory processes with periods in the
range of several tens of minutes for some single sunspots of a new solar
cycle, observed in 2010-2011 at the same time intervals in the optical
and radio ranges. We used magnetograms from SDO/HMI with a cadence of 45
s, and radio images at a frequency of 17 GHz obtained with the Nobeyama
Radioheliograph (NoRH). Radio images in intensity (Stokes parameter I )
and circular polarization (Stokes parameter V ) were synthesized with a
cadence of ten seconds and ten-second averaging. Time profiles obtained
with NoRH and SDO/HMI show a correlation between the radio emission
of sunspots and a magnetic field. Wavelet spectra and cross-wavelet
transforms give similar oscillation periods: 30-40 min, 60-70 min,
100-110 min, and 150-200 min. The same periods found by fundamentally
different methods from ground-based and space observations confirm the
solar nature of these oscillations. One of the possible interpretations
of our results is that detected oscillations reflect eigen oscillations
of a sunspot as a whole predicted by the shallow sunspot model.
Title: Evolution of the Source of Quasi-Periodic Microwave Pulsations
in a Single Flaring Loop
Authors: Kupriyanova, Elena G.; Melnikov, Victor F.; Shibasaki, Kiyoto
Bibcode: 2013PASJ...65S...3K
Altcode:
Quasi-periodic pulsations (QPP) of the microwave emission of a solar
flare on 2002 July 3, observed with the Nobeyama Radioheliograph
(Japan), were investigated with emphasise on the spatial structure
of the emission source. It was shown that the time profiles of the
variation of the distance between two main sources of the emission and
the microwave flux are similar, with a common quasi-periodicity. The
most significant QPP is found to be at 30 s. The increase in the
microwave emission flux from the Northern source, as well as the
increase in the spatially-integrated signal, is accompanied by a
decrease in the distance between the sources. In contrast, the decrease
in the flux corresponds to the decrease in the source separation. This
behaviour, together with the observed spatial localisation of the QPP,
is very consistent with the vertically polarised global kink mode of
the flaring loop.
Title: Long-Term Global Solar Activity Observed by the Nobeyama
Radioheliograph
Authors: Shibasaki, Kiyoto
Bibcode: 2013PASJ...65S..17S
Altcode:
The Nobeyama Radioheliograph has been observing the Sun at a frequency
of 17 GHz regularly since 1992, providing synthesized full-disk
images. This long period of continuous and consistent operation,
providing well-calibrated data of a uniform standard, makes possible
long-term studies of solar activity, from full-disk down to the
angular resolution of the instrument. By using about 7200 daily,
full-disk images, it has been possible to generate a radio version of
the butterfly diagram, which differs significantly from the sunspot
butterfly diagram. The polar regions are bright at 17 GHz, with their
brightness well-correlated with the polar magnetic field strengths. Both
are anti-correlated with activity at low latitudes, such as active
regions and solar flares. The 17 GHz butterfly diagram shows both high
and low-latitude activity. The brightness of both these facets of solar
activity shows a significant decline over the 20+ years observations
that have been made. In the northern hemisphere, the radio brightnesses
at low and high latitudes are strongly anti-correlated. However,
this anti-correlation is weak in the southern hemisphere. We find a
weakening of the synchronization of activity between the northern and
southern hemispheres, and also between high and low latitude activity
in the southern hemisphere. Possible causes of polar brightening and
the meaning with respect to the general scenario of solar activity
are discussed.
Title: Systematic Microwave Source Motions along a Flare-Arcade
Observed by Nobeyama Radioheliograph and AIA/SDO
Authors: Kim, Sujin; Masuda, Satoshi; Shibasaki, Kiyoto; Bong, Su-Chan
Bibcode: 2013PASJ...65S...2K
Altcode: 2013arXiv1310.2792K
We found systematic microwave source motions along a flare-arcade
using Nobeyama Radioheliograph (NoRH) 17 GHz images. The motions were
associated with an X-class disk flare that occurred on 2011 February
15. For this study, we also used EUV images from Atmospheric Imaging
Assembly (AIA) and magnetograms from Helioseismic and Magnetic Imager
(HMI) onboard Solar Dynamics Observatory, and multi-channel microwave
data from Nobeyama Radio Polarimeters (NoRP) and Korean Solar Radio
Burst Locator (KSRBL). We traced centroids of the microwave source
observed by NoRH 17 GHz during the flare, and found two episodes of
the motion based on several facts: (1) The microwave source moved
systematically along the flare-arcade, which was observed by the
AIA 94 Å channel, in a direction parallel to the neutral line. (2)
The period of each episode was 5 min and 14 min, respectively. (3)
Estimated parallel speed was 34 km s-1 for the first episode
and 22 km s-1 for the second episode. The spectral slope of
the microwave flux above 10 GHz obtained by NoRP and KSRBL was negative
for both episodes, and for the last phase of the second episodes it was
flat with a flux of 150 sfu. The negative spectrum and the flat with
high flux indicate that the gyrosynchrotron emission from accelerated
electrons was dominant during the source motions. The sequential
images from the AIA 304 Å and 94 Å channels revealed that there were
successive plasma eruptions, and each eruption was initiated just before
the start time of the microwave sources motion. Based on the results,
we suggest that the microwave source motion manifests the displacement
of the particle acceleration site caused by plasma eruptions.
Title: Measurements of Coronal and Chromospheric Magnetic Fields
using Polarization Observations by the Nobeyama Radioheliograph
Authors: Iwai, Kazumasa; Shibasaki, Kiyoto
Bibcode: 2013PASJ...65S..14I
Altcode: 2013arXiv1308.2283I
Coronal and chromospheric magnetic fields are derived from polarization
and spectral observations of the thermal free-free emission using
the Nobeyama Radioheliograph (NoRH). In magnetized plasma, the
ordinary and extraordinary modes of free-free emission have different
optical depths. This creates a circularly polarized component in an
atmosphere with a temperature gradient. We observed an active region
on 2012 April 13 to derive its coronal and chromospheric magnetic
fields. The observed degree of circular polarization was between 0.5%
and 1.7%. The radio circular polarization images were compared with
ultraviolet images observed by the Atmospheric Imaging Assembly and the
photospheric magnetic field observed by the Helioseismic and Magnetic
Imager, both on board the Solar Dynamic Observatory. At the edge of
the active region, the radio circular polarization was emitted mainly
from coronal loops, and the coronal magnetic field was derived to be
about 70 G. At the center of the active region, the chromospheric and
coronal components cannot be separated. The derived magnetic field is
about 20% to 50% of the corresponding photospheric magnetic field,
which is an emission-measure-weighted average of the coronal and
chromospheric magnetic fields.
Title: Long-Period Oscillations of Sunspots by NoRH and SSRT
Observations
Authors: Bakunina, Irina A.; Abramov-maximov, Vladimir E.; Nakariakov,
Valery M.; Lesovoy, Sergei V.; Soloviev, Alexander A.; Tikhomirov,
Yurii V.; Melnikov, Victor F.; Shibasaki, Kiyoto; Nagovitsyn, Yurii
A.; Averina, Elena L.
Bibcode: 2013PASJ...65S..13B
Altcode:
Long-term oscillations of microwave emission generated in sunspot
magnetospheres are detected with the Nobeyama Radioheliograph (NoRH)
at a frequency of 17 GHz, and the Siberian Solar Radio Telescope
(SSRT) at 5.7 GHz. Significant periodicities in the range of 22-170
min are found in the variation of the emission intensity, polarisation
and the degree of circular polarisation. Periods of the oscillations
are not stable: they are different in different sunspots and in the
same sunspot on different days. A cross-correlation analysis shows the
presence of common significant periods in both NoRH and SSRT data. The
cross-correlation coefficients are typically lower than 0.5, which
can be attributed to the different heights of the emission formation,
and different mechanisms for the emission generation (gyroresonance
and thermal bremstrahlung at 17 GHz, and pure gyroresonance at 5.7
GHz). The observational results are consistent with the global sunspot
oscillation model.
Title: Spatially Resolved Microwave Observations of Multiple
Periodicities in a Flaring Loop
Authors: Kupriyanova, E. G.; Melnikov, V. F.; Shibasaki, K.
Bibcode: 2013SoPh..284..559K
Altcode: 2012SoPh..tmp..245K
Quasi-periodic pulsations (QPPs) with at least three simultaneously
existing spectral components with periods P≥30 s, P≈20 s, and
about P≈10 s were detected during the decay phase of a solar flare
on 3 July 2002, observed with the Nobeyama Radioheliograph (NoRH). A
detailed study of the spatial structure of the Fourier amplitudes of
QPPs along a flaring loop has revealed different spatial distributions
of the three components. It is shown that the source of the QPPs
with period P≥30 s has its maximum amplitude in the inner region
of the loop, between the footpoints. QPPs with period P≈20 s are
localized at the periphery of the loop, mainly in the outer parts of
the footpoints. The spatial distribution of oscillations with period
about P≈10 s contains three regions of high QPP amplitudes: two
near the footpoints and one in the middle of the flaring region. It is
shown that the observed properties of the spectral components are most
accurately described by the fundamental, second, and third harmonics of
the kink mode standing waves. This is the first identification of the
kink mode in flare loops which is based on strict limitations derived
from data on the spatial structure of a pulsating flare region.
Title: Erratum: "Behavior of Solar Cycles 23 and 24 Revealed by
Microwave Observations" (2012,
ApJ, 750, L42)
Authors: Gopalswamy, N.; Yashiro, S.; Mäkelä, P.; Michalek, G.;
Shibasaki, K.; Hathaway, D. H.
Bibcode: 2013ApJ...763L..24G
Altcode:
No abstract at ADS
Title: Two Episodes of Systematic Microwave Source Motions Parallel
to Neutral Line during Two-ribbon Flare
Authors: Kim, S.; Masuda, S.; Shibasaki, K.
Bibcode: 2012AGUFMSH43B2175K
Altcode:
We present two episodes of systematic microwave source motions
associated with a two-ribbon solar flare occurred on 2011 February
15. For this work, we mainly used 17 GHz microwave imaging data from
Nobeyama Radioheliograph. In addition, we used EUV imaging data from
Atmospheric Imaging Assembly (AIA) and longitudinal magnetograms
from Heliosiesmic and Magnetic Imager (HMI) onboard Solar Dynamic
Observatory (SDO), and multi-channels microwave fluxes from Nobeyama
Radiopolarimeters (NoRP). During the flare, we traced the position of
the peak of brightness temperature (Tb) observed by NoRH 17 GHz and
examined the alpha index of the microwave spectrum, which is given as
the flux ratio between 17 and 35 GHz ln[Flux35/Flux17]/ln[35/17]. The
results are as follows: 1) we found two episodes of the systematic
source motion parallel to the neutral line. 2) It appears from the onset
time to the decay phase of the flare, for 22 mins. 3) Estimated parallel
speeds showed two distinct section for each episode: 180 and 60 km/s
for the first episode, and 50 and 20 km/s for the second episode. 4)
The propagation path and the directionality of two episodes were in
close proximity to each other. 5) The alpha index changed from -2 to
around 0 during these motions. Considering that accelerated electrons
by energy release process of flares readly emit microwave emissions
where they are trapped, observed microwave source motions imply the
displacement of the acceleration site. Based on the results, the
generation mechanisms of the microwave source motions are discussed.
Title: Hot Plasma Flows in the Solar Corona
Authors: Shibasaki, K.
Bibcode: 2012AGUFMSH33D2259S
Altcode:
The Solar Corona is a non-equilibrium open system. Energy and mass are
supplied from the lower atmosphere and flow upwards through the corona
into the interplanetary space. Steady state could be possible but not
equilibrium state. Temperature of the corona varies depending on solar
activities. However, even under very quite state, coronal temperature
is still kept around million degrees. Coronal heating mechanisms have
to work under such condition. Temperature of plasma is an averaged
kinetic energy of random motion of particles. Motion of charged
particles in magnetic field generates Lorenz force and particles gyrate
around magnetic field lines. Gyration of charged particles generates
magnetic moment which is directed anti-parallel to the surrounding
magnetic field. This is the origin of diamagnetism of plasma. Each
particle can be considered as a small magnet directed opposite to the
surrounding magnetic field. When these magnets are put in inhomogeneous
magnetic field, they are pushed toward weak field region. In case of
open magnetic field region in the solar corona, plasma particles are
pushed upwards. If this force (diamagnetic or mirror force) exceeds
the gravity force, plasma flows upwards. Magnetic moment of each
charged particle in thermal plasma is proportional to temperature and
inversely proportional to magnetic field strength. The condition for
plasma to flow upwards in an open magnetic field is that the scale
length of the change of magnetic field strength is shorter than the
hydrostatic scale length, which is determined by temperature and the
gravity acceleration. This can be a mechanism to regulate the coronal
temperature around million degree. The solar corona is filled with
magnetic field, which is rooted at the photosphere in the form of flux
tubes. Flux tubes connect directly the corona and the sub-photospheric
layer where temperature is higher than the photosphere. Hot plasma,
trapped in the flux tubes when they are generated around the bottom of
the convection zone, will be pushed upwards through the flux tubes due
to weakening of magnetic field strength upwards and are fed into the
corona. This scenario can explain why the solar corona is kept around
million degree independent of solar activity. This mechanism can be
applied to explain 1) temperature dependent plasma upflows found in
the solar atmosphere, 2) solar wind acceleration, 3) loop-top plasma
concentration in post flare loops, and 4) various eruptive phenomena,
including some of solar flares, caused by flows along curved magnetic
field. The MHD equation does not include this force along the field.
Title: Spatial Structure of Sunspot Oscillations Observed with SDO/AIA
Authors: Reznikova, V. E.; Shibasaki, K.
Bibcode: 2012ApJ...756...35R
Altcode:
The spatial structure of sunspot oscillations and its variation with
frequency and height have been studied using data from SDO/AIA for two
well-developed sunspots observed in 2010. Computation of potential
magnetic fields together with line-of-sight and vector magnetograms
from SDO/HMI allowed us to interpret discovered features of spatial
structure. Namely, we have found that (1) expansion of the magnetic
field lines above the sunspot causes a gradual broadening of the area
occupied by the 3 minute oscillations with height, and (2) variation
of magnetic field inclination across the sunspot causes a decrease in
the pulsation frequency with distance from the center of the umbra. We
have shown that the transformation from 3 minute umbral oscillations to
5 minute penumbral waves can be explained by variation of the acoustic
cutoff frequency across the sunspot.
Title: Slow Magnetoacoustic Oscillations in the Microwave Emission
of Solar Flares
Authors: Kim, S.; Nakariakov, V. M.; Shibasaki, K.
Bibcode: 2012ApJ...756L..36K
Altcode: 2013arXiv1310.2796K
Analysis of the microwave data, obtained in the 17 GHz channel of the
Nobeyama Radioheliograph during the M1.6 flare on 2010 November 4,
revealed the presence of 12.6 minute oscillations of the emitting
plasma density. The oscillations decayed with the characteristic time
of about 15 minutes. Similar oscillations with the period of about
13.8 minutes and the decay time of 25 minutes are also detected in the
variation of EUV emission intensity measured in the 335 Å channel
of the Solar Dynamics Observatory/Atmospheric Imaging Assembly. The
observed properties of the oscillations are consistent with the
oscillations of hot loops observed by the Solar and Heliospheric
Observatory/Solar Ultraviolet Measurement of Emitted Radiation (SUMER)
in the EUV spectra in the form of periodic Doppler shift. Our analysis
presents the first direct observations of the slow magnetoacoustic
oscillations in the microwave emission of a solar flare, complementing
accepted interpretations of SUMER hot loop oscillations as standing
slow magnetoacoustic waves.
Title: The Flare on December 13, 2006 and the Standard Solar Flare
Model
Authors: Shibasaki, K.
Bibcode: 2012ASPC..454..315S
Altcode:
The solar flare on December 13, 2006 was well observed by Hinode,
Nobeyama Radioheliograph and other instruments. In this work, these
observations are used to test applicability of the standard solar
flare model. This flare contains various elements (Neupert effect, two
ribbons, cusp structure, etc.) which are expected from the standard
model. Each element is tested whether it really supports the model
or not using high cadence multi-wavelength datasets. It is shown that
these elements do not necessarily support the model.
Title: Constraints for Electron Acceleration Models in Solar Flares
from Microwave Observations with High Spatial Resolution
Authors: Melnikov, V. F.; Pyatakov, N. P.; Shibasaki, K.
Bibcode: 2012ASPC..454..321M
Altcode:
In this study we show that different locations of acceleration/injection
sites in flaring loops may produce different types of pitch-angle
distributions of accelerated electrons and, as a consequence, very
different spatial, spectral and polarization properties of the loop
microwave emission. These properties can be detected using spatially
resolved microwave observations of specific flaring loops and be used
to choose the most suitable electron acceleration model.
Title: Microwave Diagnostics of the Acceleration Site Position and
Pitch-Angle Anisotropy of Energetic Electrons in the Flare 24 Aug 2002
Authors: Reznikova, V. E.; Melnikov, V. F.; Shibasaki, K.
Bibcode: 2012ASPC..454..325R
Altcode:
Model simulations with making use of the non-stationary Fokker-Planck
equation and calculation of gyrosynchrotron radiation have allowed us to
find a location of the injection site, electron pitch-angle anisotropy
type and to explain physical reasons of the observed microwave
brightness distribution and dynamics in the event of 2002 August 24.
Title: Microwave Emission of Supra-arcade Structure associated with
M1.6 Limb Flare
Authors: Kim, Sujin; Bain, Hazel; Shibasaki, Kiyoto; Reznikova,
Veronika
Bibcode: 2012arXiv1208.3535K
Altcode:
We have investigated a supra-arcade structure, associated with an M1.6
flare, which occurred on the south-east limb on 4th of November 2010. It
is observed in microwaves at 17 GHz with the Nobeyama Radioheliograph
(NoRH), soft X-rays in the range of 8-20 keV with the Reuven Ramaty High
Energy Solar Spectroscopic Imager (RHESSI), and EUV with the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). As
reported by Reeves & Golub (2011), the supra-arcade structure
is observed predominantly in the AIA 131 Å channel, which contains
a hot 11 MK component from Fe XIX (Boerner et al. 2011). While this
hot flare plasma lasts over the decay phase of the flare, it shows
some interesting characteristics in microwaves and soft X-rays: 1)
In the supra-arcade structure, the brightness temperature (TB) of the
microwave emission increases gradually up to 2\times10^4 K, and 2)
two soft X-ray sources appear: one cospatial with the supra-arcade
structure and another above the post-flare arcade. We have derived the
variation of emission measure, density, and energy of the supra-arcade
structure using the TB obtained from 17 GHz microwave observations.
Title: Inferences on the Behavior of Solar Cycle 24 from the Polar
Coronal Hole Enhancement and the Rate of Prominence Eruptions Observed
by the Nobeyama Radioheliograph
Authors: Gopalswamy, Nat; Yashiro, Seiji; Akiyama, Sachiko; Shibasaki,
Kiyoto
Bibcode: 2012cosp...39..651G
Altcode: 2012cosp.meet..651G
After a prolonged minimum at the end of the solar cycle 23, solar
activity picked up, but generally at low levels. One of the indicators
of the level of activity is the rate of prominence eruptions (PEs)
automatically detected in the images obtained by the Nobeyama
Radioheliograph (NoRH). The relation between PEs and coronal mass
ejections (CMEs) has a specific characteristic during solar minima:
The PE latitude is generally higher than that of the associated CME nose
indicating a general equatorward deflection of CMEs. The overall extent
of the offset seems to be similar during the rise phases of cycle 23
and 24, but there are far fewer PEs during cycle 24. The open field
lines emanating from the polar coronal hole are thought to deflect
CMEs away from the polar region. It is found that the offset starts
in the year 2007, roughly two years before the deepest solar minimum
and continued into the rise phase of the solar cycle 24. A significant
north-south asymmetry is observed in the deflection process, which can
be explained by the different behavior of the north and south polar
coronal holes. We also constructed NoRH microwave butterfly diagram
using 17 GHz images, which reveal that the solar activity has reached
the maximum phase in the north pole. This is further confirmed by the
latitudes of prominence eruptions reminiscent of the maximum phase.
Title: Behavior of Solar Cycles 23 and 24 Revealed by Microwave
Observations
Authors: Gopalswamy, N.; Yashiro, S.; Mäkelä, P.; Michalek, G.;
Shibasaki, K.; Hathaway, D. H.
Bibcode: 2012ApJ...750L..42G
Altcode: 2012arXiv1204.2816G
Using magnetic and microwave butterfly diagrams, we compare the
behavior of solar polar regions to show that (1) the polar magnetic
field and the microwave brightness temperature during solar minimum
substantially diminished during the cycle 23/24 minimum compared to
the 22/23 minimum. (2) The polar microwave brightness temperature
(Tb) seems to be a good proxy for the underlying magnetic field
strength (B). The analysis indicates a relationship, B = 0.0067Tb -
70, where B is in G and Tb in K. (3) Both the brightness temperature
and the magnetic field strength show north-south asymmetry most of
the time except for a short period during the maximum phase. (4) The
rush-to-the-pole phenomenon observed in the prominence eruption (PE)
activity seems to be complete in the northern hemisphere as of 2012
March. (5) The decline of the microwave brightness temperature in the
north polar region to the quiet-Sun levels and the sustained PE activity
poleward of 60oN suggest that solar maximum conditions have
arrived at the northern hemisphere. The southern hemisphere continues
to exhibit conditions corresponding to the rise phase of solar cycle 24.
Title: Frequency drifts of 3-min oscillations in microwave and EUV
emission above sunspots
Authors: Sych, R.; Zaqarashvili, T. V.; Nakariakov, V. M.;
Anfinogentov, S. A.; Shibasaki, K.; Yan, Y.
Bibcode: 2012A&A...539A..23S
Altcode: 2011arXiv1110.2556S
Aims: We analysed 3-min oscillations of microwave and extreme
ultraviolet (EUV) emission generated at different heights of a sunspot
atmosphere, studied the amplitude and frequency modulation of the
oscillations, and its relationship with the variation of the spatial
structure of the oscillations.
Methods: High-resolution data
obtained with the Nobeyama Radioheliograph, TRACE and SDO/AIA were
analysed with pixelised wavelet filtering (PWF) and wavelet skeleton
techniques.
Results: Three-minute oscillations in sunspots
appear in the form of recurring trains of 8-20 min duration (13 min
in average). The typical interval between the trains is 30-50 min. The
oscillation trains are transient in frequency and power. The relative
amplitude of 3-min oscillations was about 3-8% and sometimes reached
17%. Recurring frequency drifts of 3-min oscillations were detected
during the development of individual trains, with the period varying
in the range 90-240 s. A wavelet analysis showed that there are three
types of oscillation trains: with positive drifts (to high frequencies),
negative drifts, and without a drift. Negative drifts, i.e., when
the 3-min oscillation period gradually increases, were found to occur
more often. The start and end of the drifts coincides with the start
time and end of the train. Sometimes two drifts co-exist, i.e. during
the end of the previous drift, a new drift appears near 160 s, when
the frequency is in the low-frequency part of the 3-min spectrum,
near 200 s. This behaviour is seen at all levels of the sunspot
atmosphere. The speed of the drift is 4-5 mHz/h in the photosphere,
5-8 mHz/h in the chromosphere, and 11-13 mHz/h in the corona. There
were also low-frequency peaks in the spectrum, corresponding to the
periods of 10-20 min, and 30-60 min. The comparative study of the
spatial structure of 3-min oscillations in microwave and EUV shows
the appearance of new sources of the sunspot oscillations during the
development of the trains.
Conclusions: These structures can
be interpreted as waveguides that channel upward propagating waves,
which in turn are responsible for the 3-min oscillations. A possible
explanation of the observed properties are two simultaneously operating
factors: dispersive evolution of the upward propagating wave pulses
and the non-uniformity of the oscillation power distribution over
the sunspot umbra with different wave sources that correspond to
different magnetic flux tubes with different physical conditions and
line-of-sight angles.
Title: Three-minute Oscillations above Sunspot Umbra Observed with
the Solar Dynamics Observatory/Atmospheric Imaging Assembly and
Nobeyama Radioheliograph
Authors: Reznikova, V. E.; Shibasaki, K.; Sych, R. A.; Nakariakov,
V. M.
Bibcode: 2012ApJ...746..119R
Altcode: 2011arXiv1109.5434R
Three-minute oscillations over a sunspot's umbra in AR 11131 were
observed simultaneously in UV/EUV emission by the Solar Dynamics
Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and in radio
emission by the Nobeyama Radioheliograph (NoRH). We use 24 hr series of
SDO and 8 hr series of NoRH observations to study spectral, spatial,
and temporal variations of pulsations in the 5-9 mHz frequency range
at different layers of the solar atmosphere. High spatial and temporal
resolution of SDO/AIA in combination with long-duration observations
allowed us to trace the variations of the cutoff frequency and
spectrum of oscillations across the umbra. We found that higher
frequency oscillations are more pronounced closer to the umbra's
center, while the lower frequencies concentrate on the peripheral
parts. We interpreted this discovery as a manifestation of variation
of the magnetic field inclination across the umbra at the level of
temperature minimum. Possible implications of this interpretation for
the diagnostics of sunspot atmospheres are discussed.
Title: Radio Emission of the Quiet Sun and Active Regions (Invited
Review)
Authors: Shibasaki, K.; Alissandrakis, C. E.; Pohjolainen, S.
Bibcode: 2012esrs.book....3S
Altcode:
Solar radio emission provides valuable information on the structure
and dynamics of the solar atmosphere above the temperature minimum. We
review the background and most recent observational and theoretical
results on the quiet Sun and active region studies, covering the entire
radio range from millimeter to decameter wavelengths. We examine
small- and large-scale structures, at short and long time scales,
as well as synoptic aspects. Open questions and challenges for the
future are also identified.
Title: Quasi-periodic Oscillations of Solar Active Regions in
Connection with Their Flare Activity - NoRH Observations
Authors: Abramov-Maximov, V. E.; Gelfreikh, G. B.; Shibasaki, K.
Bibcode: 2012esrs.book...97A
Altcode:
The sunspot-associated sources at the frequency of 17 GHz give
information on plasma parameters in the regions of magnetic field
about B=2000 G at the level of the chromosphere-corona transition
region. The observations of short period (from one to ten minutes)
oscillations in sunspots reflect propagation of magnetohydrodynamic
(MHD) waves in the magnetic flux tubes of the sunspots. We investigate
the oscillation parameters in active regions in connection with
their flare activity. We confirm the existence of a link between the
oscillation spectrum and flare activity. We find differences in the
oscillations between pre-flare and post-flare phases. In particular, we
demonstrate a case of powerful three-minute oscillations that start just
before the burst. This event is similar to the cases of the precursors
investigated by Sych et al. (Astron. Astrophys. 505, 791, 2009). We
also found well-defined eight-minute oscillations of microwave emission
from sunspot. We interpret our observations in terms of a relationship
between MHD waves propagating from sunspots and flare processes.
Title: Isolated Sunspot with a Dark Patch in the Coronal Emission
Authors: Bezrukov, D. A.; Ryabov, B. I.; Shibasaki, K.
Bibcode: 2012BaltA..21..509B
Altcode: 2012OAst...21..509B
On the base of the 17 GHz radio maps of the Sun taken with the Nobeyama
Radio Heliograph we estimate plasma parameters in the specific region
of the sunspot atmosphere in the active region AR 11312. This region
of the sunspot atmosphere is characterized by the depletion in coronal
emission (soft X-ray and EUV lines) and the reduced absorption in
the a chromospheric line (He I 1.083 μ m). In the ordinary normal
mode of 17 GHz emission the corresponding dark patch has the largest
visibility near the central solar meridian. We infer that the reduced
coronal plasma density of about ∼ 5× 108 cm-3
is the characteristic feature of the dark patch.
Title: Radio Imaging Observations of Solar Activity Cycle and
Its Anomaly
Authors: Shibasaki, K.
Bibcode: 2011AGUFMSH33A2035S
Altcode:
The 24th solar activity cycle has started and relative sunspot
numbers are increasing. However, their rate of increase is rather
slow compared to previous cycles. Active region sizes are small,
lifetime is short, and big (X-class) flares are rare so far. We study
this anomalous situation using data from Nobeyama Radioheliograph
(NoRH). Radio imaging observations have been done by NoRH since
1992. Nearly 20 years of daily radio images of the Sun at 17 GHz are
used to synthesize a radio butterfly diagram. Due to stable operation
of the instrument and a robust calibration method, uniform datasets are
available covering the whole period of observation. The radio butterfly
diagram shows bright features corresponding to active region belts and
their migration toward low latitude as the solar cycle progresses. In
the present solar activity cycle (24), increase of radio brightness
is delayed and slow. There are also bright features around both poles
(polar brightening). Their brightness show solar cycle dependence but
peaks around solar minimum. Comparison between the last minimum and
the previous one shows decrease of its brightness. This corresponds to
weakening of polar magnetic field activity between them. In the northern
pole, polar brightening is already weakened in 2011, which means it is
close to solar maximum in the northern hemisphere. Southern pole does
not show such feature yet. Slow rise of activity in active region belt,
weakening of polar activity during the minimum, and large north-south
asymmetry in polar activity imply that global solar activity and its
synchronization are weakening.
Title: Multi-wavelength Observations of Supra-Arcade Structure
associated with M1.6 Limb Flare
Authors: Kim, S.; Bain, H. M.; Shibasaki, K.
Bibcode: 2011AGUFMSH33A2032K
Altcode:
We have investigated supra-arcade structure produced by M1.6 flare
that occurs in east-north limb on 2010 Nov 4th. For this work,
we have used multi-wavelength observations from microwave at 17
and 34 GHz with Nobeyama Radioheliograph (NoRH), Hard X-rays at
the range of 8-20 keV with Ramaty High Energy Solar Spectroscopic
Imager (RHESSI), EUV with Atmospheric Imaging Assembly (AIA) onboard
Solar Dynamic Observatory (SDO), and X-ray telescope (XRT) onboard
Hinode. As reported by Reeves & Golub (2011), this supra-arcade
structure comes into sight predominantly on AIA 131 Å channel,
one of AIA multi-channel, that contain a contribution from Fe XIX
formed at 11 MK (Boerner et al. 2011). While this hot flare plasma
lasts over the decay phase of the flare, we found two separated Hard
X-ray sources in the high corona inside of the hot flare plasma as
well as above the top of the flare loop. For these two HXR sources,
we have estimated the plasma temperature using filter ratio with a
pair of XRT thick filter and derived the emission measure, density,
and thermal energy using brightness temperature obtained by 17 GHz
microwave observation. Based on the results, we discuss the physical
mechanism to generate the supra-arcade structure.
Title: Quasi-periodic Oscillations of Solar Active Regions in
Connection with Their Flare Activity - NoRH Observations
Authors: Abramov-Maximov, V. E.; Gelfreikh, G. B.; Shibasaki, K.
Bibcode: 2011SoPh..273..403A
Altcode: 2011SoPh..tmp..280A; 2011arXiv1107.1620A; 2011SoPh..tmp..305A;
2011SoPh..tmp..330A
The sunspot-associated sources at the frequency of 17 GHz give
information on plasma parameters in the regions of magnetic field
about B=2000 G at the level of the chromosphere-corona transition
region. The observations of short period (from one to ten minutes)
oscillations in sunspots reflect propagation of magnetohydrodynamic
(MHD) waves in the magnetic flux tubes of the sunspots. We investigate
the oscillation parameters in active regions in connection with
their flare activity. We confirm the existence of a link between the
oscillation spectrum and flare activity. We find differences in the
oscillations between pre-flare and post-flare phases. In particular,
we demonstrate a case of powerful three-minute oscillations that
start just before the burst. This event is similar to the cases of
the precursors investigated by Sych et al. (Astron. Astrophys.505,
791, 2009). We also found well-defined eight-minute oscillations of
microwave emission from sunspot. We interpret our observations in
terms of a relationship between MHD waves propagating from sunspots
and flare processes.
Title: Radio Emission of the Quiet Sun and Active Regions (Invited
Review)
Authors: Shibasaki, K.; Alissandrakis, C. E.; Pohjolainen, S.
Bibcode: 2011SoPh..273..309S
Altcode: 2011SoPh..tmp..313S; 2011SoPh..tmp..246S; 2011SoPh..tmp..122S;
2011SoPh..tmp..288S; 2011SoPh..tmp..177S
Solar radio emission provides valuable information on the structure
and dynamics of the solar atmosphere above the temperature minimum. We
review the background and most recent observational and theoretical
results on the quiet Sun and active region studies, covering the entire
radio range from millimeter to decameter wavelengths. We examine
small- and large-scale structures, at short and long time scales,
as well as synoptic aspects. Open questions and challenges for the
future are also identified.
Title: The slow magnetoacoustic mode in the flaring loop
Authors: Reznikova, Veronika; Shibasaki, Kiyoto
Bibcode: 2011arXiv1110.1136R
Altcode:
We studied long duration flare observed with Nobeyama Radioheliograph
at frequencies 17 and 34 GHz and with Ramaty High Energy Solar
Spectroscopic Imager at 25-50 keV. We found that microwave and hard
X-ray emission variation contain well-pronounced periodicity with the
oscillation period growing from 2.5 to 5 min. Analysis of the loop
length and plasma temperature evolution during the flare allowed to
interpret the quasi-periodic pulsations in terms of the second standing
harmonics of the slow magnetoacoustic mode. This mode can be generated
by the initial impulsive energy release and work as a trigger for the
repeated energy releases.
Title: The Behavior of the 17 GHz Solar Radius and Limb Brightening
in the Spotless Minimum XXIII/XXIV
Authors: Selhorst, C. L.; Giménez de Castro, C. G.; Válio, A.;
Costa, J. E. R.; Shibasaki, K.
Bibcode: 2011ApJ...734...64S
Altcode:
The current solar minimum has surprised the entire solar community
because the spotless period is presently almost 2-3 years longer than
the usual minima. To better understand this, we studied the variation
of the solar radius and the polar limb brightening at 17 GHz, comparing
the results from the minimum at the end of cycle XXIII with those of
the previous one. Daily maps obtained by the Nobeyama Radioheliograph
(NoRH) from 1992 through 2010 were analyzed. Whereas the variation of
the solar radius at radio frequencies indicates the heating of the solar
atmosphere due to solar activity, the limb brightening intensity depends
on the organization of the polar magnetic field of the Sun, including
the global dipole and the features formed around it. These features are
more prominent during minima periods. As a common result, researchers
have observed a decrease in both radius and limb brightness intensity
at 17 GHz during the present minimum when compared with the previous
one. The mean solar radius is 0farcs9 ± 0farcs6 smaller and the limb
brightening reduced its intensity by around 20%. Both decrements are
interpreted in terms of the weaker solar chromospheric activity of
the present cycle. Measurement of the radius and limb brightening at
17 GHz can be used as an alternative solar activity index and should
be included in the set of parameters used to predict future cycles.
Title: Multilevel Analysis of Oscillation Motions in Active Regions
of the Sun
Authors: Abramov-Maximov, V. E.; Gelfreikh, G. B.; Kobanov, N. I.;
Shibasaki, K.; Chupin, S. A.
Bibcode: 2011SoPh..270..175A
Altcode: 2011arXiv1102.1074A; 2011SoPh..tmp...26A
The nature of the three-minute and five-minute oscillations
observed in sunspots is considered to be an effect of propagation
of magnetohydrodynamic (MHD) waves from the photosphere to the solar
corona. However, the real modes of these waves and the nature of the
filters that result in rather narrow frequency bands of these modes
are still far from being generally accepted, in spite of a large amount
of observational material obtained in a wide range of wave bands. The
significance of this field of research is based on the hope that local
seismology can be used to find the structure of the solar atmosphere
in magnetic tubes of sunspots. We expect that substantial progress can
be achieved by simultaneous observations of the sunspot oscillations in
different layers of the solar atmosphere in order to gain information on
propagating waves. In this study we used a new method that combines
the results of an oscillation study made in optical and radio
observations. The optical spectral measurements in photospheric and
chromospheric lines of the line-of-sight velocity were carried out at
the Sayan Solar Observatory. The radio maps of the Sun were obtained
with the Nobeyama Radioheliograph at 1.76 cm. Radio sources associated
with the sunspots were analyzed to study the oscillation processes in
the chromosphere - corona transition region in the layer with magnetic
field B=2000 G. A high level of instability of the oscillations in the
optical and radio data was found. We used a wavelet analysis for the
spectra. The best similarities of the spectra of oscillations obtained
by the two methods were detected in the three-minute oscillations inside
the sunspot umbra for the dates when the active regions were situated
near the center of the solar disk. A comparison of the wavelet spectra
for optical and radio observations showed a time delay of about 50
seconds of the radio results with respect to the optical ones. This
implies an MHD wave traveling upward inside the umbral magnetic tube
of the sunspot. For the five-minute oscillations the similarity in
spectral details could be found only for optical oscillations at the
chromospheric level in the umbral region or very close to it. The time
delays seem to be similar. Besides three-minute and five-minute ones,
oscillations with longer periods (8 and 15 minutes) were detected
in optical and radio records. Their nature still requires further
observational and theoretical study for even a preliminary discussion.
Title: Period persistence of long period oscillations in sunspots
Authors: Chorley, N.; Foullon, C.; Hnat, B.; Nakariakov, V. M.;
Shibasaki, K.
Bibcode: 2011A&A...529A.123C
Altcode:
Long period oscillations in the microwave radiation intensity
generated over the sunspot of NOAA AR 10330 are studied with the
Nobeyama Radioheliograph as the sunspot passes over the solar disk,
over the course of 9 days (06-15 April 2003). Periodogram, Fourier
and global wavelet analyses reveal the presence of a significant
oscillatory component in the range P ≈ 50-120 min over the course of
the observations. The spectral amplitudes of five significant Fourier
components in the range P = 50-150 min are also seen to be stable over
the observations, when the data are not affected by changes in magnetic
configuration in the region. The ground-based nature of the instrument
naturally introduces long data gaps in such long duration observations
and the presence of the gaps does not allow any conclusion as to the
stability of the phases of the oscillations. As a model to explain the
persistence of the dominant long periods, a simple oscillator with a
nonlinear driving term is proposed. The spectral difference between
distinct peaks within, e.g. the 3 min spectral band, is expected to
be able to resonate with the long period one hour oscillations.
Title: Imaging Observations of Coronal Magnetic Field by Nobeyama
Radioheliograph
Authors: Shibasaki, K.; Narukage, N.; Yoshimura, K.
Bibcode: 2011ASPC..437..433S
Altcode:
Coronal magnetic field in a post flare arcade of loops above the solar
limb is mapped by the Nobeyama Radioheliograph. Post flare loops are
filled with hot and dense plasma threaded by magnetic field. Thermal
free-free microwave emission from these plasma is bright enough to
carefully measure circular polarization degree. As circular polarization
is the result of gyration of electrons around magnetic field, inversion
of circular polarization degree to magnetic field strength is simple. We
successfully measured the circular polarization degree distribution
at 17 GHz and got a magnetic field map in a post flare arcade of loops
above the solar limb.
Title: Flare quasi-periodic pulsations with growing periodicity
Authors: Reznikova, V. E.; Shibasaki, K.
Bibcode: 2011A&A...525A.112R
Altcode:
We conducted a wavelet analysis of the flare intensity variations
for the long duration flare on 2005 August 22 observed with the
Nobeyama Radioheliograph at frequencies 17 and 34 GHz and with the
Ramaty High Energy Solar Spectroscopic Imager at 25-50 keV. We found
that the signals contain a well-pronounced periodicity in which the
oscillation period grows from 2.5 to 5 min. An analysis of the loop
length and plasma temperature evolution during the flare allowed us to
interpret the quasi-periodic pulsations in terms of the second standing
harmonics of the slow magnetoacoustic mode. This mode can be generated
by the initial impulsive energy release and work as a trigger for the
repeated energy releases.
Title: Types of Microwave Quasi-Periodic Pulsations in Single
Flaring Loops
Authors: Kupriyanova, E. G.; Melnikov, V. F.; Nakariakov, V. M.;
Shibasaki, K.
Bibcode: 2010SoPh..267..329K
Altcode: 2010SoPh..tmp..179K
Quasi-periodic pulsations (QPP) of microwave emission generated
in single flaring loops observed with the Nobeyama Radioheliograph
(NoRH) and Nobeyama Radio Polarimeters (NoRP) are studied. Specific
features of the time profiles, i.e. the visible presence or absence
of QPPs, are not accounted for in the selection. The time evolution
of the periods of the QPPs is examined using wavelet and correlation
analyses. In ten out of twelve considered events, at least one or more
significant spectral components with periods from 5 - 60 s have been
found. The quality of the oscillations is rather low: Q=πN, where
N is the number of cycles, mostly varies in the range 12 to 40, with
an average of 25. We suggest that the detected QPPs can be classified
into four types: i) those with stable mean periods (e.g. of 15 - 20
s or 8 - 9 s, the prevailing type); ii) those with spectral drift to
shorter periods (mostly in the rise phase of the microwave emission);
iii) those with drift to longer periods (mostly in the decay phase);
iv) those with multiple periods showing an X-shaped drift (e.g. in
the range from 20 - 40 s in the rise phase).
Title: Dynamics of the Flaring Loop System of 2005 August 22 Observed
in Microwaves and Hard X-rays
Authors: Reznikova, V. E.; Melnikov, V. F.; Ji, H.; Shibasaki, K.
Bibcode: 2010ApJ...724..171R
Altcode:
We studied the spatial dynamics of the flaring loop in the 2005 August
22 event using microwave (NoRH) and hard X-ray (RHESSI) observations
together with complementary data from SOHO/MDI, SMART at Hida, SOHO/EIT,
and TRACE. We have found that (1) the pre-flare morphology of the
active region exhibits a strongly sheared arcade seen in Hα and
the J-shape filament seen in EUV; (2) energy release and high-energy
electron acceleration occur in a sequence along the extensive arcade;
(3) the shear angle and the parallel (to the magnetic neutral line)
component of the footpoint (FP) distance steadily decrease during the
flare process; (4) the radio loop shrinks in length and height during
the first emission peak, and later it grows; after the fourth peak the
simultaneous descending of the brightest loop and formation of a new
microwave loop at a higher altitude occur; (5) the hard X-ray coronal
source is located higher than the microwave loop apex and shows faster
upward motion; (6) the first peak on microwave time profiles is present
in both the loop top and FP regions. However, the emission peaks that
follow are present only in the FP regions. We conclude that after the
first emission peak the acceleration site is located over the flaring
arcade and particles are accelerated along magnetic field lines. We
make use of the collapsing magnetic trap model to understand some
observational effects.
Title: Polar Chromospheric Signatures of the Subdued Cycle 23/24
Solar Minimum
Authors: Gopalswamy, N.; Yashiro, S.; Makela, P.; Shibasaki, K.;
Hathaway, D.
Bibcode: 2010AAS...21640103G
Altcode: 2010BAAS...41..857G
Coronal holes appear brighter than the quiet Sun in microwave images,
with a brightness enhancement of 500 to 2000 K. The brightness
enhancement corresponds to the upper chromosphere, where the
plasma temperature is about 10000 K. We constructed a microwave
butterfly diagram using the synoptic images obtained by the Nobeyama
radioheliograph (NoRH) showing the evolution of the polar and low
latitude brightness temperature. While the polar brightness reveals the
chromospheric conditions, the low latitude brightness is attributed to
active regions in the corona. When we compared the microwave butterfly
diagram with the magnetic butterfly diagram, we found a good correlation
between the microwave brightness enhancement and the polar field
strength. The microwave butterfly diagram covers part of solar cycle
22, whole of cycle 23, and part of cycle 24, thus enabling comparison
between the cycle 23/24 and cycle 22/23 minima. The microwave brightness
during the cycle 23/24 minimum was found to be lower than that during
the cycle 22/23 minimum by 250 K. The reduced brightness temperature
is consistent with the reduced polar field strength during the cycle
23/24 minimum seen in the magnetic butterfly diagram. We suggest that
the microwave brightness at the solar poles is a good indicator of
the speed of the solar wind sampled by Ulysses at high latitudes.
Title: Topology Dynamics of the Flaring Loop System on 2005 August
22 Observed in Microwaves and Hard X-Rays
Authors: Reznikova, Veronika; Melnikov, Victor; Ji, Haisheng;
Shibasaki, Kiyoto
Bibcode: 2010cosp...38.3032R
Altcode: 2010cosp.meet.3032R
Microwaves generated by mildly relativistic electrons allow us to
trace magnetic flaring loops in their full length including their upper
parts. We take advantage of this property and study the spatial dynamics
of the system of flaring loops in the 2005 August 22 flare using high
res-olution microwave observations of Nobeyama Radioheliograph (NoRH)
along with hard X-ray observations of RHESSI. As complimentary data,
magnetograms from SOHO/MDI, Hα images from SMART at Hida Observatory,
as well as EUV images from SOHO/EIT and TRACE were analyzed. The flare
consisted of six temporal emission peaks. During all the emission
peaks, the evolution of sizes, footpoint positions and orientations
of the observed microwave loop(s) were analyzed. We have found that
the Northern footpoint of the apparent bright loop moves along the
magnetic neutral line, and the position of Southern footpoint is almost
invariable so that the shear angle of the loop steadily decreases during
the flare process. The corresponding contraction of the distance between
the footpoints parallel to the magnetic neutral line is from 25 Mm to 13
Mm. After the first emission peak, the length and altitude of the loop
are growing continuously. During the fifth emission peak we observe a
jump in the loop height which re-lates to the formation of a new loop
at higher altitude. The microwave loops characteristics are compared
with corresponding properties of the hard X-ray emission for the period
of RHESSI observations (after the first microwave peak). Diagnostics
of parameters of accelerated electrons and other flare parameters are
fulfilled. Possible theoretical models explaining the behavior of the
observed flaring loop system are considered.
Title: The subdued solar cycle 23/24 minimum revealed by microwave
butterfly diagram
Authors: Gopalswamy, N.; Yashiro, S.; Makela, P. A.; Shibasaki, K.
Bibcode: 2009AGUFMSH13C..02G
Altcode:
The 17 GHz microwave brightness temperature in coronal holes
is typically enhanced by 500 to 2000 K with respect to the quiet
Sun. This is considered to be a property of the upper chromosphere,
where the plasma temperature is ~10000 K. We constructed a microwave
butterfly diagram using the synoptic images obtained by the Nobeyama
Radioheliograph and compared it with the magnetic butterfly diagram. We
found a good correlation between the microwave brightness enhancement
and the polar field strength. We also performed a rotation-by-rotation
comparison between the two data sets to obtain the correlation
between the magnetic field strength and the microwave brightness
temperature. The microwave butterfly diagram covers part of cycle
22, whole of cycle 23, and part of cycle 24, thus enabling comparison
between the cycle 23/24 and cycle 22/23 minima. The microwave brightness
during the cycle 23/24 minimum was found to be lower than that during
the cycle 22/23 minimum by ~250 K. The reduced brightness temperature
is consistent with the reduced polar field strength during the cycle
23/24 minimum seen e.g., in the SOHO/MDI magnetic butterfly diagram. We
suggest that the microwave brightness at the solar poles is a good
indicator of the speed of the solar wind sampled by Ulysses at high
latitudes.
Title: 2002 August 24 Limb Flare Loop: Dynamics of Microwave
Brightness Distribution
Authors: Reznikova, V. E.; Melnikov, V. F.; Shibasaki, K.; Gorbikov,
S. P.; Pyatakov, N. P.; Myagkova, I. N.; Ji, H.
Bibcode: 2009ApJ...697..735R
Altcode:
High-resolution radio observation of Nobeyama Radioheliograph at
17 and 34 GHz allowed studying the dynamics of microwave brightness
distribution along the giant limb flaring loop in the event of 2002
August 24. It is found that on the rising phase of the radio burst
the brightness distribution was highly asymmetric, with a strong
maximum near the southern footpoint (SFP) and much weaker brightness
enhancements near the loop top (LT) and northern footpoint. On the
decay phase, the LT gradually became most bright. The similar dynamics
of brightness distribution are shown to happen for all major temporal
subpeaks of the burst. Results of our diagnostics show two important
properties: (1) the number density of mildly relativistic electrons
in the LT is much higher than near the footpoints (FPs) during rise,
maximum and decay of each major peak; and (2) the ratio of the electron
number densities in the LT and an FP increases from the maximum to
decay phase. Model simulations with making use of the nonstationary
Fokker-Planck equation have allowed us to find the model explaining
the major properties of the microwave brightness distribution and
dynamics. The model is characterized by a compact source of electrons
located near the center of an asymmetric magnetic loop; the source
is nonstationary, long lasting, and injecting high-energy electrons
with the pitch-angle distribution mostly directed toward the SFP but
also having a very weak isotropic component. This easily explains the
observed brightness asymmetry. The observed dynamics comes due to two
reasons: faster precipitation of electrons having their mirror points
near the ends of the magnetic trap, and relatively faster decay of the
lower energy electrons responsible for the gyrosynchrotron emission
near the FPs with higher magnetic field.
Title: Nonlinear and Diamagnetic Nature of Plasma and Activities in
the Solar Atmosphere
Authors: Shibasaki, Kiyoto
Bibcode: 2009SPD....40.3001S
Altcode:
Plasma is a nonlinear and diamagnetic media. Magnetic moment of
each charged particle in thermal plasma is μ=-kT/B, where k is
the Boltzmann constant, T is the plasma temperature and B is the
magnetic flux density. It does not depend on mass or charge. Negative
value means that the magnetic moment is anti-parallel to B, or
diamagnetic. This nonlinear and diamagnetic nature of plasma is
often not explicitly treated due to low plasma beta assumption. The
plasma beta is the ratio between magnetic moment per unit volume
and the magnetic flux density. However, if the plasma beta exceeds
several percent, nonlinear nature becomes important. This is one of
the reasons why nuclear fusion experiment in magnetically confined
plasmas is difficult. This condition should be the same in the solar
atmosphere. Particles with magnetic moment anti-parallel to B are
pushed toward weak field region along the field. This force (mirror
force, f = μ dB/dr = -kT/L) is proportional to the plasma temperature
and is inversely proportional to the magnetic scale length L (=1/ (1/B
dB/dr)). Generally, magnetic field strength decreases upwards, hence the
force is directed upwards. At higher temperature, this force exceeds
the gravity force and generates temperature dependent up-flows. If
the magnetic field is closed, plasma will be accumulated around the
top where magnetic field is the weakest and they suppress B further
due to their diamagnetism, hence a high beta region spontaneously
appears around the loop top. High-beta plasma around the loop top is
unstable against the interchange mode or the ballooning mode due to
convex outward curvature (or bad curvature) of B. High-beta disruption
will be expected from the outer surface of the loop top.
Title: A comparison of parameters of 3-minute and 5-minute
oscillations in sunspots from synchronous microwave and optical
observations
Authors: Abramov-Maximov, V. E.; Gelfreikh, G. B.; Kobanov, N. I.;
Shibasaki, K.
Bibcode: 2009IAUS..257...95A
Altcode:
The observations of 3 and 5 minute oscillations in sunspots present
information on propagation of MHD waves in the magnetic tubes of
sunspots. We present a comparison of wavelet spectra of radio flux
oscillations at λ = 1.76 cm and oscillations of longitudinal component
of the velocity at the chromosphere in sunspot umbra and penumbra in
AR 10661 (2004, Aug 18). The radio maps of the Sun obtained with the
Nobeyama Radioheliograph were used. The spatial resolution of the
radio data was about 10-15 arcsec, and 10 sec cadence was used. On
the radio maps sunspot-associated sources were identified and time
profiles of their maximum brightness temperatures for each radio source
were calculated. Radio data consists of information of oscillations
of plasma parameters (in the regions with magnetic field B = 2000
G) at the level of the chromosphere-corona transition region. The
optical observations were carried out at Sayan observatory. These data
included information on longitude component of the magnetic field at
the photosphere (line Fe I 6569 Å) and longitudinal component of the
velocity at the chromosphere (line Hα was used). Comparing the wavelet
diagrams covering the same periods of observations at radio and optics
showed that some wave trains of time profiles are very similar in both
kinds of observations (similar oscillation frequencies and their drifts,
variations of amplitudes), however, some significant differences were
also registered. The best similarity in optical and radio oscillations
was found when the active region (AR) was near the center of the solar
disk. The phase shifts between the two kinds of observations reflecting
the propagation of MHD waves were also analyzed.
Title: Long period oscillations of microwave emission of solar active
regions: observations with NoRH and SSRT
Authors: Bakunina, I. A.; Abramov-Maximov, V. E.; Lesovoy, S. V.;
Shibasaki, K.; Solov'ev, A. A.; Tikhomirov, Yu. V.
Bibcode: 2009IAUS..257..155B
Altcode:
In this work we present the first results of study and comparison
of the parameters of quasi-periodic long-term oscillations of
microwave emission of large (>0.7 arcmin) sunspots as a result of
simultaneous observations with two radioheliographs - NoRH (17 GHz)
and Siberian Solar Radio Telescope (SSRT) (5.7 GHz) with 1 minute
cadence. Radioheliographs have been working with quite large time
overlap (about 5 hours) and have the high spatial resolution: 10 arcsec
(NoRH) and 20 arcsec (SSRT). We have found that quasi-periodic long-term
oscillations are surely observed at both frequencies with the periods
in the range of 20-150 min. We detected common periods for common time
of observations with two radioheliographs and interpret this as the
consequence of the vertical-radial quasi-periodic displacements of
sunspot as a whole structure.
Title: Dynamics of microwave brightness distribution in the giant
24 August 2002 flare loop
Authors: Reznikova, Veronika E.; Melnikov, Victor F.; Shibasaki,
Kiyoto; Gorbikov, Sergey P.; Pyatakov, Nikolai P.; Myagkova, Irina N.;
Ji, Haisheng
Bibcode: 2009IAUS..257..345R
Altcode:
We have found a similar tendency of the spatial dynamics at 34 GHz for
all major temporal sub-peaks of the burst with the re-distribution of
the brightness from the footpoints (on the rising phase of each peak)
to the upper part of the loop (on the decay phase). Observed dynamics
is interpreted by the re-distribution of accelerated electrons number
density with their relative enhancement in the loop top. Results of
diagnostics show that the ratio of non-thermal electron number density
in the loop top and in the footpoint changes 7 times from the peak to
decay phase. Model simulations by solving the Fokker-Planck equation
allowed to determine an injection type which is able to result in
necessary dynamics of energetic electrons.
Title: Ballooning Instability in Coronal Flare Loops
Authors: Tsap, Y. T.; Kopylova, Y. G.; Stepanov, A. V.; Melnikov,
V. F.; Shibasaki, K.
Bibcode: 2008SoPh..253..161T
Altcode: 2008SoPh..tmp...98T
Within the framework of ideal magnetohydrodynamics the excitation of
the ballooning instability in a toroidal coronal loop with a radius of
cross section a and a radius of curvature R is analyzed by using the
energy method. Kink oscillations are able to excite the ballooning
instability when the plasma beta parameter β>2a/R. It has been
suggested that this can result in the formation of cusp-shaped
coronal loops. Modulation of gyrosynchrotron emission caused by
kink oscillations is considered. The intensity of gyrosynchrotron
emission for optically thin sources is the most sensitive to Alfvén
disturbances. The obtained theoretical results are discussed in the
light of Yohkoh, SOHO, TRACE, RHESSI, and Nobeyama observations.
Title: Absorption Phenomena and a Probable Blast Wave in the 13 July
2004 Eruptive Event
Authors: Grechnev, V. V.; Uralov, A. M.; Slemzin, V. A.; Chertok,
I. M.; Kuzmenko, I. V.; Shibasaki, K.
Bibcode: 2008SoPh..253..263G
Altcode: 2008arXiv0811.0899G; 2008SoPh..tmp..154G
We present a case study of the 13 July 2004 solar event, in which
disturbances caused by eruption of a filament from an active region
embraced a quarter of the visible solar surface. Remarkable are the
absorption phenomena observed in the SOHO/EIT 304 Å channel, which
were also visible in the EIT 195 Å channel, in the Hα line, and
even in total radio flux records. Coronal and Moreton waves were also
observed. Multispectral data allowed reconstructing an overall picture
of the event. An explosive filament eruption and related impulsive flare
produced a CME and blast shock, both of which decelerated and propagated
independently. Coronal and Moreton waves were kinematically close and
both decelerated in accordance with an expected motion of a coronal
blast shock. The CME did not resemble a classical three-component
structure, probably because some part of the ejected mass fell back
onto the Sun. Quantitative evaluations from different observations
provide close estimates of the falling mass, ∼3×1015 g,
which is close to the estimated mass of the CME. The falling material
was responsible for the observed large-scale absorption phenomena,
in particular, shallow widespread moving dimmings observed at 195
Å. By contrast, deep quasi-stationary dimmings observed in this
band near the eruption center were due to plasma density decrease in
coronal structures.
Title: Leakage of Sub-Photospheric Hot Plasma through Magnetic
Flux Tube
Authors: Shibasaki, K.
Bibcode: 2008AGUFMSH41A1614S
Altcode:
The solar corona has million degree temperature even though it is
located above the cooler chromosphere and the photosphere. Also, coronal
plasma is constantly flowing out as the solar wind. So the mechanism
of coronal heating needs to include a mechanism of constant plasma
supply. Most of the proposed coronal heating mechanisms are by waves
or nano-flares. Both mechanisms are to carry energy of photospheric
convection motion into the corona and dissipate there. Plasma supply
is assumed to be through evaporation (or ablation) from the lower
atmosphere due to steep temperature gradient. In these mechanisms,
tenuous coronal plasma receives large amount of energy to heat and
evaporate low temperature plasma into the corona. Hence the temperature
of the initially heated plasma should be much higher than the million
degree corona. Charged particles with such high temperature in the
tenuous corona cannot reach the lower atmosphere due to their strong
diamagnetic moment. They will be pushed upwards where magnetic field is
weak rather than downwards where magnetic field is strong. Hence, the
evaporation mechanism will not work. I will propose a quite different
mechanism of million-degree plasma supply in more direct manner. The
solar corona is filled with magnetic fields. They are generated at the
base of the convection zone and lifted by the convection motion. The
standard model of the Sun shows that the temperature at the base of the
convection zone is about 2 million degree. So the plasmas trapped in the
magnetic flux tube must have temperature there. Plasma particles have
diamagnetic moments and they will be pushed along the flux tube toward
weaker magnetic field region. As the result, the solar atmosphere which
is filled with magnetic field, generated at the base of the convection
zone, must have million degree temperature.
Title: Vertical Temperature Structures of the Solar Corona Derived
with the Hinode X-Ray Telescope
Authors: Kano, Ryouhei; Sakao, Taro; Narukage, Noriyuki; Tsuneta,
Saku; Kotoku, Jun'ichi; Bando, Takamasa; Deluca, Edward; Lundquist,
Loraine; Golub, Leon; Hara, Hirohisa; Matsuzaki, Keiichi; Shimojo,
Masumi; Shibasaki, Kiyoto; Shimizu, Toshifumi; Nakatani, Ichiro
Bibcode: 2008PASJ...60..827K
Altcode:
We obtained temperature structures in faint coronal features
above and near the solar limb with the X-Ray Telescope aboard the
Hinode satellite by accurately correcting the scattered X-rays
from surrounding bright regions with occulted images during
the solar eclipses. Our analysis yields a polar coronal hole
temperature of about 1.0MK and an emission measure in the range of
1025.5-1026.0cm-5. In addition,
our methods allow us to measure the temperature and emission
measure of two distinct quiet-Sun structures: radial (plume-like)
structures near the boundary of the coronal-hole and diffuse quiet
Sun regions at mid-latitudes. The radial structures appear to have
increasing temperature with height during the first 100Mm, and
constant temperatures above 100Mm. For the diffuse quiet-Sun region
the temperatures are the highest just above the limb, and appear
to decrease with height. These differences may be due to different
magnetic configurations.
Title: The Hinode X-Ray Telescope (XRT): Camera Design, Performance
and Operations
Authors: Kano, R.; Sakao, T.; Hara, H.; Tsuneta, S.; Matsuzaki, K.;
Kumagai, K.; Shimojo, M.; Minesugi, K.; Shibasaki, K.; DeLuca, E. E.;
Golub, L.; Bookbinder, J.; Caldwell, D.; Cheimets, P.; Cirtain, J.;
Dennis, E.; Kent, T.; Weber, M.
Bibcode: 2008SoPh..249..263K
Altcode:
The X-ray Telescope (XRT) aboard the Hinode satellite is a grazing
incidence X-ray imager equipped with a 2048×2048 CCD. The XRT has
1 arcsec pixels with a wide field of view of 34×34 arcmin. It is
sensitive to plasmas with a wide temperature range from < 1 to 30
MK, allowing us to obtain TRACE-like low-temperature images as well as
Yohkoh/SXT-like high-temperature images. The spacecraft Mission Data
Processor (MDP) controls the XRT through sequence tables with versatile
autonomous functions such as exposure control, region-of-interest
tracking, flare detection, and flare location identification. Data are
compressed either with DPCM or JPEG, depending on the purpose. This
results in higher cadence and/or wider field of view for a given
telemetry bandwidth. With a focus adjust mechanism, a higher resolution
of Gaussian focus may be available on-axis. This paper follows the
first instrument paper for the XRT (Golub et al., Solar Phys.243, 63,
2007) and discusses the design and measured performance of the X-ray
CCD camera for the XRT and its control system with the MDP.
Title: Heating and Kinematics of an Eruptive Prominence Associated
with a Fast Coronal Mass Ejection
Authors: Gopalswamy, N.; Yashiro, S.; Shibasaki, K.
Bibcode: 2008AGUSMSH31C..07G
Altcode:
The fast (1800 km/s) coronal mass ejection (CME) on 2005 July 27
had a bright bubble-shaped prominence core observed by the Nobeyama
Radioheliograph (NoRH) in microwaves (17 and 34 GHz), TRACE at 171 A,
and the Extreme-ultraviolet Imaging Telescope (EIT) on board SOHO. NoRH
has the largest field of view among the non- white light instruments,
so the prominence could be tracked until it reached a height of about
0.75 solar radii from the limb. The prominence remained optically thick
at both 17 and GHz, even though it was significantly heated. Comparison
with TRACE observations suggest that the prominence was heated in
individual fibers within the prominence, making it multi-thermal
plasma. The prominence maintained its overall shape as it entered into
the field of view of SOHO/LASCO coronagraphs with a speed of about 1400
km/s, so the height-time history could be studied over a distance of
more than 20 solar radii from the Sun. NoRH data indicated that the
initial acceleration was extremely high (about1.4 km/s/s). During the
slow-rise phase of the prominence, EUV loops overlying the prominence
also moved out, which when combines with CME leading-edge measurements
from LASCO/C2 yielded an acceleration of about 300 m/s/s. This was
comparable to the average acceleration of the prominence over the same
height range. When we consider the just the LASCO field of view, both
the prominence core and the CME leading edge showed deceleration, but to
vastly different extents (-32 m/s/s for the CME leading edge compared to
-3 m/s/s for the prominence core). Our preliminary conclusion is that
the prominence was insulated from interacting with the non-CME ambient
medium, which might explain the weaker slowing down of the prominence.
Title: Multi-Wavelength Imaging of Solar Plasma - High-Beta Disruption
Model of Solar Flares -
Authors: Shibasaki, Kiyoto
Bibcode: 2008PFR.....2S1012S
Altcode:
Solar atmosphere is filled with plasma and magnetic field. Activities in
the atmosphere are due to plasma instabilities in the magnetic field. To
understand the physical mechanisms of activities / instabilities, it is
necessary to know the physical conditions of magnetized plasma, such
as temperature, density, magnetic field, and their spatial structures
and temporal developments. Multi-wavelength imaging is essential for
this purpose. Imaging observations of the Sun at microwave, X-ray,
EUV and optical ranges are routinely going on. Due to free exchange of
original data among solar physics and related field communities, we can
easily combine images covering wide range of spectrum. Even under such
circumstances, we still do not understand the cause of activities in the
solar atmosphere well. The current standard model of solar activities
is based on magnetic reconnection: release of stored magnetic energy
by reconnection is the cause of solar activities on the Sun such as
solar flares. However, recent X-ray, EUV and microwave observations
with high spatial and temporal resolution show that dense plasma is
involved in activities from the beginning. Based on these observations,
I propose a high-beta model of solar activities, which is very similar
to high-beta disruptions in magnetically confined fusion experiments.
Title: Evidence for Alfvén Waves in Solar X-ray Jets
Authors: Cirtain, J. W.; Golub, L.; Lundquist, L.; van Ballegooijen,
A.; Savcheva, A.; Shimojo, M.; DeLuca, E.; Tsuneta, S.; Sakao, T.;
Reeves, K.; Weber, M.; Kano, R.; Narukage, N.; Shibasaki, K.
Bibcode: 2007Sci...318.1580C
Altcode:
Coronal magnetic fields are dynamic, and field lines may misalign,
reassemble, and release energy by means of magnetic reconnection. Giant
releases may generate solar flares and coronal mass ejections and,
on a smaller scale, produce x-ray jets. Hinode observations of polar
coronal holes reveal that x-ray jets have two distinct velocities:
one near the Alfvén speed (~800 kilometers per second) and another
near the sound speed (200 kilometers per second). Many more jets were
seen than have been reported previously; we detected an average of
10 events per hour up to these speeds, whereas previous observations
documented only a handful per day with lower average speeds of 200
kilometers per second. The x-ray jets are about 2 × 103 to
2 × 104 kilometers wide and 1 × 105 kilometers
long and last from 100 to 2500 seconds. The large number of events,
coupled with the high velocities of the apparent outflows, indicates
that the jets may contribute to the high-speed solar wind.
Title: Continuous Plasma Outflows from the Edge of a Solar Active
Region as a Possible Source of Solar Wind
Authors: Sakao, Taro; Kano, Ryouhei; Narukage, Noriyuki; Kotoku,
Jun'ichi; Bando, Takamasa; DeLuca, Edward E.; Lundquist, Loraine L.;
Tsuneta, Saku; Harra, Louise K.; Katsukawa, Yukio; Kubo, Masahito;
Hara, Hirohisa; Matsuzaki, Keiichi; Shimojo, Masumi; Bookbinder, Jay
A.; Golub, Leon; Korreck, Kelly E.; Su, Yingna; Shibasaki, Kiyoto;
Shimizu, Toshifumi; Nakatani, Ichiro
Bibcode: 2007Sci...318.1585S
Altcode:
The Sun continuously expels a huge amount of ionized material into
interplanetary space as the solar wind. Despite its influence on the
heliospheric environment, the origin of the solar wind has yet to
be well identified. In this paper, we report Hinode X-ray Telescope
observations of a solar active region. At the edge of the active region,
located adjacent to a coronal hole, a pattern of continuous outflow of
soft-x-ray emitting plasmas was identified emanating along apparently
open magnetic field lines and into the upper corona. Estimates of
temperature and density for the outflowing plasmas suggest a mass
loss rate that amounts to ~1/4 of the total mass loss rate of the
solar wind. These outflows may be indicative of one of the solar wind
sources at the Sun.
Title: Response of the Solar Atmosphere to Magnetic Flux Emergence
from Hinode Observations
Authors: Li, Hui; Sakurai, Takashi; Ichimito, Kiyoshi; Suematsu,
Yoshinori; Tsuneta, Saku; Katsukawa, Yukio; Shimizu, Toshifumi; Shine,
Richard A.; Tarbell, Theodore D.; Title, Alan M.; Lites, Bruce; Kubo,
Masahito; Nagata, Shin'ichi; Kotoku, Jun; Shibasaki, Kiyoto; Saar,
Steven H.; Bobra, Monica
Bibcode: 2007PASJ...59S.643L
Altcode:
No abstract at ADS
Title: A Study of Polar Jet Parameters Based on Hinode XRT
Observations
Authors: Savcheva, Antonia; Cirtain, Jonathan; Deluca, Edward E.;
Lundquist, Loraine L.; Golub, Leon; Weber, Mark; Shimojo, Masumi;
Shibasaki, Kiyoto; Sakao, Taro; Narukage, Noriyuki; Tsuneta, Saku;
Kano, Ryouhei
Bibcode: 2007PASJ...59S.771S
Altcode:
Hinode/SOHO campaign 7197 is the most extensive study of polar jet
formation and evolution from within both the north and south polar
coronal holes so far. For the first time, this study showed that the
appearance of X-ray jets in the solar coronal holes occurs at very high
frequency - about 60 jets d-1 on average. Using observations
collected by the X-Ray Telescope on Hinode, a number of physical
parameters from a large sample of jets were statistically studied. We
measured the apparent outward velocity, the height, the width and
the lifetime of the jets. In our sample, all of these parameters show
peaked distributions with maxima at 160kms-1 for the outward
velocity, 5 × 104 km for the height, 8 × 103
km for the width, and about 10min for the lifetime of the jets. We
also present the first statistical study of jet transverse motions,
which obtained transverse velocities of 0-35kms-1. These
values were obtained on the basis of a larger (in terms of frequency)
and better sampled set of events than what was previously statistically
studied (Shimojo et al. 1996, PASJ, 48, 123). The results were made
possible by the unique characteristics of XRT. We describe the methods
used to determine the characteristics and set some future goals. We
also show that despite some possible selection effects, jets preferably
occur inside the polar coronal holes.
Title: Hinode Observations of the Onset Stage of a Solar Filament
Eruption
Authors: Sterling, Alphonse C.; Moore, Ronald L.; Berger, Thomas
E.; Bobra, Monica; Davis, John M.; Jibben, Patricia; Kano, Ryohei;
Lundquist, Loraine L.; Myers, D.; Narukage, Noriyuki; Sakao, Taro;
Shibasaki, Kiyoto; Shine, Richard A.; Tarbell, Theodore D.; Weber, Mark
Bibcode: 2007PASJ...59S.823S
Altcode:
We used Hinode X-Ray Telescope (XRT) and Solar Optical Telescope (SOT)
filtergraph (FG) Stokes-V magnetogram observations, to study the
early onset of a solar eruption that includes an erupting filament
that we observe in TRACE EUV images. The filament undergoes a slow
rise for at least 20min prior to its fast eruption and strong soft
X-ray (SXR) flaring; such slow rises have been previously reported,
and the new Hinode data elucidate the physical processes occurring
during this period. XRT images show that during the slow-rise phase,
an SXR sigmoid forms from apparent reconnection low in the sheared core
field traced by the filament, and there is a low-level intensity peak
in both EUV and SXRs during the slow rise. MDI and SOT FG Stokes-V
magnetograms show that the pre-eruption filament is along a neutral
line between opposing-polarity enhanced network cells, and the SOT
magnetograms show that these opposing fields are flowing together
and canceling for at least six hours prior to eruption. From the MDI
data we measured the canceling network fields to be ∼ 40G, and we
estimated that ∼ 1019 Mx of flux canceled during the
five hours prior to eruption; this is only ∼ 5% of the total flux
spanned by the eruption and flare, but apparently its tether-cutting
cancellation was enough to destabilize the sigmoid field holding the
filament and resulted in that field's eruption.
Title: Fine Structures of Solar X-Ray Jets Observed with the X-Ray
Telescope aboard Hinode
Authors: Shimojo, Masumi; Narukage, Noriyuki; Kano, Ryohei; Sakao,
Taro; Tsuneta, Saku; Shibasaki, Kiyoto; Cirtain, Jonathan W.;
Lundquist, Loraine L.; Reeves, Katherine K.; Savcheva, Antonia
Bibcode: 2007PASJ...59S.745S
Altcode:
The X-Ray Telescope (XRT) aboard Hinode has revealed the fine structure
of solar X-ray jets. One of the fine structures observed by XRT is an
expanding loop. The loop appeared near the footpoint of the jet when
footpoint brightening was observed. Additionally, we have found that the
X-ray jets began just after the expanding loop ``breaks''. Other fine
structures discovered by XRT are thread-like features along the axis
of the jets. XRT has shown that these thread structures compose the
cross-section of jets. The fine structures and their motions strongly
support an X-ray jet model based on magnetic reconnection, and also
suggest that we must consider the three-dimensional configuration of the
magnetic field to understand the jet phenomenon. We also investigated
the reverse jet associated with the X-ray jet in the quiet Sun, and
propose that the reverse jet is produced by heat conduction, or a MHD
wave subsequent to the main jet.
Title: An On-Orbit Determination of the On-Axis Point Spread Function
of the Hinode X-Ray Telescope
Authors: Weber, Mark; Deluca, Edward E.; Golub, Leon; Cirtain,
Jonathan; Kano, Ryouhei; Sakao, Taro; Shibasaki, Kiyoto; Narukage,
Noriyuki
Bibcode: 2007PASJ...59S.853W
Altcode:
The Hinode X-ray Telescope provides unprecedented observations of
the solar corona in X-rays, due in part to its fine resolution. The
X-ray point spread function (PSF) was measured before launch at the
NASA X-ray Calibration Facility to have a FWHM of 0.8''. This paper
describes the work to verify the PSF measurements using on-orbit
observations of planetary transits and solar eclipses. Analysis of a
Mercury transit gives a PSF FWHM = 1.0" ± 0.12".
Title: The X-Ray Telescope (XRT) for the Hinode Mission
Authors: Golub, L.; DeLuca, E.; Austin, G.; Bookbinder, J.; Caldwell,
D.; Cheimets, P.; Cirtain, J.; Cosmo, M.; Reid, P.; Sette, A.; Weber,
M.; Sakao, T.; Kano, R.; Shibasaki, K.; Hara, H.; Tsuneta, S.; Kumagai,
K.; Tamura, T.; Shimojo, M.; McCracken, J.; Carpenter, J.; Haight,
H.; Siler, R.; Wright, E.; Tucker, J.; Rutledge, H.; Barbera, M.;
Peres, G.; Varisco, S.
Bibcode: 2007SoPh..243...63G
Altcode:
The X-ray Telescope (XRT) of the Hinode mission provides an
unprecedented combination of spatial and temporal resolution in solar
coronal studies. The high sensitivity and broad dynamic range of XRT,
coupled with the spacecraft's onboard memory capacity and the planned
downlink capability will permit a broad range of coronal studies over
an extended period of time, for targets ranging from quiet Sun to
X-flares. This paper discusses in detail the design, calibration, and
measured performance of the XRT instrument up to the focal plane. The
CCD camera and data handling are discussed separately in a companion
paper.
Title: Continuous Upflow of Plasmas at the Edge of an Active Region
as Revealed by the X-ray Telescope (XRT) aboard Hinode
Authors: Sakao, Taro; Kano, R.; Narukage, N.; Kotoku, J.; Bando, T.;
DeLuca, E. E.; Lundquist, L. L.; Golub, L.; Kubo, M.; Katsukawa, Y.;
Tsuneta, S.; Hara, H.; Matsuzaki, K.; Shimojo, M.; Shibasaki, K.;
Shimizu, T.; Nakatani, I.
Bibcode: 2007AAS...210.7205S
Altcode: 2007BAAS...39Q.179S
We present X-ray imaging observations with Hinode X-Ray Telescope (XRT)
of an active region NOAA AR 10942 made in the period of 20-22 February
2007. A prominent feature that drew our particular attention is that
there revealed continuous upflow of soft-X-ray-emitting plasmas along
apparently-open field lines towards the outer corona emanating from the
edge of the active region. The field lines are originated from
an ensamble of small spots of following polarity, and are located at
a border between the active region and an adjacent equatorial coronal
hole(s) located to the east. The upflow was observed to be continuous
throughout the three days of observation intervals with projected
velocity of 140 km/s, accompanied with undulating motion of the field
lines. We assert that these upflowing plasmas would be a possible
source of slow solar wind material, which supports a foresighted
notion which grew out of interplanetary scintillation observations
that slow solar wind most likely has its origin in the vicinity of
active regions with large flux expansion (Kojima et al. 1999). A
preliminaty analysis indicates that the temperature of the upflowing
material near the base of the field lines is 1.3 MK with number density
of 2 × 109 /cm3. Assuming that all the material
is to escape to the interplanetary space, this leads to a mass loss
rate of 2 × 1011 g/s which amounts to a good fraction of
the total mass loss rate for solar wind. It is noteworthy that, even
apart from this unique upflow, we see continuous (up)flows of plasmas
anywhere around (surrounding) the active region. Details of the
upflow will be presented and their possible implication to slow solar
wind discussed.
Title: Temperature Structures Above Coronal Hole and Quiet Sun
Authors: Kano, Ryouhei; Sakao, T.; Narukage, N.; Kotoku, J.; Bando,
T.; DeLuca, E. E.; Lundquist, L.; Golub, L.; Tsuneta, S.; Hara, H.;
Shibasaki, K.; Shimojo, M.
Bibcode: 2007AAS...210.9436K
Altcode: 2007BAAS...39..223K
The X-ray Telescope (XRT) on board Hinode satelite has the capability
to derive the temperature structure in the solar corona. We present
the hieght dependence of the temperature above the limb. Because X-ray
intensity above the limb is so faint, it is important to estimate the
scattered light from disk corona. The eclipses happened on February 17
and March 19 in 2007 at Hinode orbit. On February 17, we took X-ray
images above the south polar coronal hole, while Moon passed it. On
March 19, we took the data for quiet Sun in the same way. We
can estimated the scattered light from the eclipse data, and derived
the scatter-free X-ray images above the solar limb. In this meeting,
we will present the temperatures above coronal hole and quiet Sun,
based on the eclipse data.
Title: Particle Acceleration in the X3 Event on Dec. 13, 2007
Authors: Shibasaki, Kiyoto; Koshiishi, H.; Shimojo, M.; Minoshima,
T.; Imada, S.; Sakao, T.; Hinode Team
Bibcode: 2007AAS...210.9435S
Altcode: 2007BAAS...39..223S
Even during the solar minimum period, the active region NOAA 10930 had
a complex magnetic configuration especially around the main sunspot
and produced a couple of X-class events. The one on Dec. 13, 2007 was
well observed by Nobeyama Radioheliograph (NoRH) and Polarimeters
(NoRP). Microwave emission associated with this event has several
interesting characteristics: 1. Long lasting non-thermal phase 2. Very large decimetric flux (several thousand times of the quiet
sun flux) and quite different time development of decimetric emission
compared to shorter wavelengths 3. Very high turn-over frequency
(around 35 GHz) This event was also well observed by HINODE
satellite and partially by RHESSI satellite. Optical telescope (SOT) and
Soft X-ray telescope (XRT) onboard HINODE showed that the flare started
around the polarity reversal line which divides the main sunspot and
the closely associated small sunspot with opposite polarity. This line
is the interface of the penumbrae of both sunspots. The flare ribbons
started in the penumbrae and entered into umbrae of both sunspots. Microwave images of the event at 17 and 34 GHz are synthesized
and compared with optical and soft X-ray images taken by SOT and XRT
respectively. Based on these overlays, frequency spectral information
(NoRP) and RHESSI images in the later phase of the event, we try to
locate particle acceleration site and discuss possible mechanisms of
acceleration. Hinode is an international project supported by JAXA,
NASA, PPARC and ESA. We are grateful to the Hinode team for all their
efforts in the design, development and operation of the mission. NoRH
and NoRP are operated by Nobeyama Solar Radio Observatory, NAOJ. RHESSI
is a NASA project.
Title: Turbulent propagation of high-energy electrons in a solar
coronal loop
Authors: Stepanov, A. V.; Yokoyama, T.; Shibasaki, K.; Melnikov, V. F.
Bibcode: 2007A&A...465..613S
Altcode:
Aims:We study the solar flare on 28 August 1999 observed by the Nobeyama
Radioheliograph at 17 and 34 GHz and analyze the unusual behavior of
microwave source (a coronal loop) after injections of high-energy
electrons. The observations reveal a propagation velocity of the
emission front along the loop of about 104 km s-1,
which is 30 times less than the velocity of high-energy electrons
generating gyrosynchrotron emission at 17 and 34 GHz. The main goal is
to understand the physical origin of this electron propagation.
Methods: We interpret this anomalous propagation in terms of the
collective effects of relativistic electrons interacting with plasma
turbulence. A cloud of highly energetic electrons responsible for
microwave emission generates low-frequency whistler waves, and a
turbulent "wall" in the loop is formed.
Results: The electrons
undergo strong resonant scattering due to wave-particle interaction,
and the emission front propagates with the wave phase velocity, which
is much lower than the particle velocity.
Title: Solar Physics with the Nobeyama Radioheliograph -- Nobeyama
Symposium 2004 --
Authors: Shibasaki, K.
Bibcode: 2006spnr.conf....1S
Altcode:
The Nobeyama Radioheliograph (NoRH) has been in operation since 1992 and
well covered one solar cycle. Many user groups of NoRH have been formed
in the world and we have organized three symposiums related to NoRH in
the past. 1. "Symposium on Nobeyama Radioheliograph" November 26-28,
1990 at Nobeyama 2. "New Look at the Sun with Emphasis on Advanced
Observations of Coronal Dynamics and Flares" September 6-10, 1993 at
Kofu (jointly with Yohkoh) 3. "Solar Physics with Radio Observations"
October 27-30, 1998 at Kiyosato We are glad to know that more and more
data from NoRH are used and scientific outputs are still increasing. In
this symposium, we would like to summarize recent development of solar
physics using NoRH and discuss future direction of NoRH.
Title: MHD-Oscillations of Coronal Loops and Diagnostics of Flare
Plasma
Authors: Stepanov, A. V.; Shibasaki, K.; Kopylova, Y. G.; Tsap, Y. T.
Bibcode: 2006spnr.conf...23S
Altcode:
Effects of ballooning and radial oscillations of coronal magnetic
loops on the modulations of microwave and X-ray emission from flare
loops are considered. The damping mechanisms of loop MHD modes are
analyzed. The method for diagnostics of flare plasma parameters using
peculiarities of the microwave and X-ray pulsations is proposed. The
diagnostic method was applied for two solar flares: on May 8, 1998
and August 28, 1999 observed with the Nobeyama Radioheliograph.
Title: Electron Spatial Distribution in Microwave Flaring Loops
Authors: Melnikov, Victor F.; Reznikova, Veronika E.; Gorbikov,
Sergei P.; Shibasaki, Kiyoto
Bibcode: 2006AIPC..848..123M
Altcode:
In this paper we review recent studies of Nobeyama Radioheliograph
observations concerning 1) spatial distribution of microwave brightness
along flaring loops; 2) peculiarities ofits temporal dynamics in
different parts of a loop; 3) consequences of the obtained findings
on spatial and pitch-angle distributions of high energy electrons.
Title: A Statistical Study of Microwave Flare Morphologies
Authors: Tzatzakis, V.; Nindos, A.; Alissandrakis, C. E.; Shibasaki, K.
Bibcode: 2006AIPC..848..248T
Altcode:
Using Nobeyama Radioheliograph (NoRH) high spatial resolution images
at 17 and 34 GHz, we study the morphology of several flare events that
occured relatively close to the limb. Our study has been motivated by
the recent detection of a small number of optically thin flares whose
maximum emission peaks close to the loop top. These events may show
significant anisotropy of the density and pitch angle distribution
of the nonthermal electrons. However, we do not know how often they
occur. Our sample consists of 104 flare events. Using data from the
Nobeyama Polarimeter we were able to determine whether the 17 and 34
GHz emissions are optically thin or thick. Almost half of our events
appear unresolved in the NoRH images. Among the resolved events,
special attention is paid to those with circular polarization (V)
showing two distinct sources. Such V sources are considered proxies to
the flaring loop footpoints if the total intensity (I) morphology is
consistent with a single flaring loop configuration. A small number of
events, as expected at such high frequencies, are optically thick with
I maximum between the loop footpoints. The number of optically thin
events showing I maxima co-spatial with the V sources is approximately
the same as the number of those optically thin resolved events showing
emission peak between the V sources. Our future plans concerning the
study of our database are also outlined.
Title: MHD-Oscillation Modes of a Flaring Loop Using Microwave
Observations With High Spatial Resolution
Authors: Reznikova, Veronika E.; Melnikov, Victor F.; Nakariakov,
Valery M.; Shibasaki, Kiyoto
Bibcode: 2006AIPC..848..133R
Altcode:
Study of an oscillating loop observed with high spatial resolution
(NoRH) shows the presence of two Fourier spectral peaks: P1 = 14-17
s, which is more pronounced at the loop apex and P2 = 8-11 s, that is
stronger at the loop legs. We found the phase shift, P2/4, between the
pulsations at the northern leg and at the loop top for the P2 spectral
component and a lack of the phase shift between different parts of the
flare loop for the P1 component. The computed phase speeds and periods
of MHD modes of a coronal loop confirm identification of the first
periodicity P1 as the global (fundamental) sausage mode. The second
periodicity can be associated with several modes: the second and the
third longitudinal harmonics of the kink mode, the third harmonics of
the sausage mode and the second harmonics of ballooning mode.
Title: Microwave Measurements of Coronal Magnetic Field
Authors: Shibasaki, K.
Bibcode: 2006IAUJD...3E..48S
Altcode:
Magnetic field measurements of the solar corona using microwave
observation are reviewed. The solar corona is filled with highly
ionised plasma and magnetic field. Moving charged particles interact
with magnetic field due to Lorentz force. This results in gyration
motion perpendicular to the magnetic field and free motion along the
magnetic field. Circularly polarized electro-magnetic waves interact
with gyrating electrons efficiently and the interaction depends on the
sense of circular polarization (right-handed or left-handed). This is
the reason why we can measure magnetic field strength through microwave
observations. This process does not require complicated quantum
physics but the classical treatment is enough. Hence the inversion
of measured values to magnetic field strength is simpler than in the
case of optical and infrared measurements. There are several methods to
measure magnetic field strength through microwave observations. We can
divide them into two categories: one is based on emission mechanisms
and the other is based on wave propagation. In the case of emission
mechanisms, thermal f-f emission, thermal gyro-resonance emission and
non-thermal gyro-synchrotron emission can be used to measure magnetic
field strength. In the case of wave propagation, polarization reversal
due to propagation through quasi-transverse magnetic field region can
be used. Examples of distribution of magnetic field strength in the
solar corona measured by Nobeyama Radioheliograph will be presented.
Title: Nobeyama radio heliograph observations of RHESSI microflares
Authors: Kundu, M. R.; Schmahl, E. J.; Grigis, P. C.; Garaimov, V. I.;
Shibasaki, K.
Bibcode: 2006A&A...451..691K
Altcode:
Aims.We present a summary of the analysis of thirty microflares,
observed simultaneously by the Ramaty High Energy Solar Spectroscopic
Imager (RHESSI) in hard X-rays and by Nobeyama RadioHeliograph (NoRH)
in microwaves (17 GHz).
Methods: .We used microflares observed
by RHESSI in the energy range 3-25 keV, and for larger events, up
to 35 keV. The observations were made 2002, May 2-6.
Results:
.We describe the imaging characteristics of these microflares including
their locations in hard X-rays and microwaves and the relative positions
of the micro-flaring sources. We discuss the brightness temperatures,
emission measures and their hard X-ray spectral properties. We see
small (mini) flaring loops clearly in NoRH and RHESSI images. The
microwave emission often seems to come from the RHESSI foot points
(for higher energies), and from the entire small (mini) flaring loop
(for lower energies). Sometimes the two (microwave and hard X-ray)
sources coincide, at other times they are at opposite ends of a mini
flaring loop. Typically, the hard X-ray spectrum of the microwave
associated RHESSI microflares can be fit by an isothermal component at
low energies (below 10 or 12 keV) and a nonthermal component at higher
energies (above 12 keV).
Conclusions: .Microflares in hard X-rays
and in microwaves behave like normal flares in many respects. They can
have both thermal and nonthermal components appearing in bremsstrahlung
and gyrosynchrotron radiation.
Title: Plasma Parameters in a Post-Eruptive Arcade Observed with
CORONAS-F/SPIRIT, Yohkoh/SXT, SOHO/EIT, and in Microwaves
Authors: Grechnev, Victor V.; Uralov, Arkadiy M.; Zandanov, Vasily G.;
Rudenko, George V.; Borovik, Valery N.; Grigorieva, Irina Y.; Slemzin,
Vladimir A.; Bogachev, Sergey A.; Kuzin, Sergei V.; Zhitnik, Igor'a.;
Pertsov, Andrey A.; Shibasaki, Kiyoto; Livshits, Moisey A.
Bibcode: 2006PASJ...58...55G
Altcode:
The SPectroheliographIc X-Ray Imaging Telescope (SPIRIT) aboard the
CORONAS-F spacecraft sometimes observes in the Mg XII 8.42Å line
(Tmax ∼ 9 MK) large, bright features existing for many
hours high in the corona. This fact suggests that plasma beta there
might not be small. We identify such a feature observed on 2001 October
22 at a height of 100Mm with a hot part of a post-eruptive arcade. Using
multi-spectral data and radio astronomy methods, we estimate the
plasma parameters in the arcade and reveal the coronal magnetic
configuration. Several hours after the eruption, the temperature
in the arcade was 6-8MK, and the plasma density was (5-10) \cdot
109 cm-3. We confirm the results by the accord
of the quantities obtained from different observations using different
methods and by the extrapolation of the photospheric magnetograms into
the corona, from which we have obtained a magnetic field strength of
about 7G at that height. Hence, indeed β ≥ 1 in the post-eruptive
arcade. The high-beta possibility had previously been stated, e.g.,
by Ichimoto et al. (1994), but still not investigated. We address this
issue in terms of the ``standard flare model'' elaborated by Shibata
and Yokoyama. During this event, Yohkoh/SXT observed McKenzie-Hudson
dark moving features. Those features are filled with cold material,
if they are not empty, and may affect the arcade.
Title: Observations of Prominence Eruptions with Two Radioheliographs,
SSRT, and NoRH
Authors: Grechnev, Victor V.; Uralov, Arkadiy M.; Zandanov, Vasily G.;
Baranov, Nikolai Y.; Shibasaki, Kiyoto
Bibcode: 2006PASJ...58...69G
Altcode:
We address simultaneous observations of eruptive prominences with
two radioheliographs, SSRT at 5.7GHz and NoRH at 17 and 34GHz. Three
events are presented: 1997 September 27, 2000 September 4, and 2001
January 14. We analyze them using images observed in microwaves, Hα,
images from Extreme ultraviolet Imaging Telescope on board Solar and
Heliospheric Observatory (SOHO), and white-light images from Large Angle
and Spectrometric Coronagraph (SOHO/LASCO). We address three stages of
the eruptive process: 1) pre-eruptive ascent, 2) rapid acceleration, 3)
free expansion, and the overall kinematics of the ejecta. We estimate
the densities and kinetic temperatures of prominences, and also the
velocities and accelerations of ejecta. The main body of a prominence
is surrounded by low-density cool extensions mixed with the coronal
plasma, but the transition from the cool prominence to the hot plasma
is sharp. >From microwave and LASCO observations with overlapping
fields of view we identify a radio prominence and a core of a coronal
mass ejection (CME). Their temperature remains at about 5000K, while
the brightenings observed in extreme ultraviolet are probably due
to only skin-heating. We discuss the observations in terms of our
Dual-Filament CME initiation model.
Title: One Solar-Cycle Observations of Prominence Activities Using
the Nobeyama Radioheliograph 1992-2004
Authors: Shimojo, Masumi; Yokoyama, Takaaki; Asai, Ayumi; Nakajima,
Hiroshi; Shibasaki, Kiyoto
Bibcode: 2006PASJ...58...85S
Altcode:
We newly developed a method of limb-event detection for the Nobeyama
Radiograph, and show the results over one solar-cycle, 1992 July-2004
December. We detected 785 prominence activities and 31 flares on the
limb by this method. We investigated the relationship between the
distributions of the prominence activities and the solar cycle. As a
result, we found the following facts: 1) The variation in the number of
prominence activities is similar to that of sunspots during one solar
cycle. 2) There are differences between the peak times of prominence
activities and sunspots. 3) The frequency distribution as a function
of the magnitude of the prominence activities (the size of activated
prominences) at each phase shows a power-law distribution. The power-law
index of the distribution does not change, except around the solar
minimum. 4) The number of prominence activities has a dependence on the
latitude. On the other hand, the average magnitude is independent of the
latitude. 5) During the rise phase of the solar cycle, the location of
the high-latitude prominence activities migrates to the pole region. 6)
After a solar polarity reversal, the location of the prominence
activities in the northern hemisphere migrates to the equator. On
the other hand, the prominence activities in the southern hemisphere
occurred in the high-latitude region until the decay phase of Cycle 23.
Title: On the Relation of Brightness Temperatures in Coronal Holes
at 5.7 and 17 GHz
Authors: Maksimov, Vladimir P.; Prosovetsky, Dmitry V.; Grechnev,
Victor V.; Krissinel, Boris B.; Shibasaki, Kiyoto
Bibcode: 2006PASJ...58....1M
Altcode:
From the analysis of simultaneous observations with the Siberian Solar
Radio Telescope and Nobeyama Radioheliograph we show that coronal
holes are not uniform. In particular, in coronal holes small-scale
features exist with anticorrelating brightness temperatures at 5.7
and 17GHz. The features are disposed radially, which suggests radial
heat transfer in them. We propose that the favorable heating mechanism
within those features is dissipation of Alfvén waves.
Title: Sunspot Gyroresonance Emission at 17 GHz: A Statistical Study
Authors: Vourlidas, Angelos; Gary, Dale E.; Shibasaki, Kiyoto
Bibcode: 2006PASJ...58...11V
Altcode:
We investigate the sunspot gyroresonance emission at 17 GHz using the
synoptic database of the Nobeyama Radioheliograph. Our statistical
study is based on full disk observations obtained during the maximum
of Cycle 22 (1992-94). We study the center-to-limb variation of the
brightness and polarization of the sunspot radio emission and present
some cases of polarization reversal. We find that the radio emission
is most likely 3rd-harmonic gyroresonance emission arising from 2000
G fields in transition region, or low corona temperatures.
Title: One solar-cycle observations of prominence activities using
the Nobeyama Radioheliograph 1992--2004
Authors: Shimojo, M.; Yokoyama, T.; Asai, A.; Nakajima, H.;
Shibasaki, K.
Bibcode: 2006cosp...36..417S
Altcode: 2006cosp.meet..417S
We newly developed a method of limb-event detection for the Nobeyama
Radiograph and show the results over one solar-cycle 1992 July --
2004 December We detected 785 prominence activities and 31 flares on
the limb by this method We investigated the relationship between the
distributions of the prominence activities and the solar cycle As a
result we found the following facts 1 The variation in the number of
prominence activities is similar to that of sunspots during one solar
cycle 2 There are differences between the peak times of prominence
activities and sunspots 3 The frequency distribution as a function
of the magnitude of the prominence activities the size of activated
prominences at each phase shows a power-law distribution The power-law
index of the distribution does not change except around the solar
minimum 4 The number of prominence activities has a dependence on the
latitude On the other hand the average magnitude is independent of the
latitude 5 During the rise phase of the solar cycle the location of the
high-latitude prominence activities migrates to the pole region 6 After
a solar polarity reversal the location of the prominence activities
in the northern hemisphere migrates to the equator On the other hand
the prominence activities in the southern hemisphere occurred in the
high-latitude region until the decay phase of Cycle 23
Title: Diagnostics of Mhd-Oscillation Modes of a Flaring Loop Using
Microwave Observations with High Spatial Resolution
Authors: Reznikova, V. E.; Nakariakov, V. M.; Melnikov, V. F.;
Shibasaki, K.
Bibcode: 2005ESASP.600E.140R
Altcode: 2005ESPM...11..140R; 2005dysu.confE.140R
No abstract at ADS
Title: Dissipation of Diamagnetic Currents and Plasma Heating in
Coronal Magnetic Loops
Authors: Zaitsev, V. V.; Shibasaki, K.
Bibcode: 2005ARep...49.1009Z
Altcode:
SOHO and TRACE data have shown that the coronal plasma is heated most
actively near sunspots, in magnetic loops that issue from the penumbral
region. The source of heating is nonuniform in height, and its power is
maximum near the footpoints of the magnetic loops. The heating process
is typically accompanied by the injection of dense chromospheric
plasma into the coronal parts of the magnetic loops. It is important
that the radiative losses cannot be compensated for via electron
thermal conduction in the loops, which have temperatures of 1.0 1.5 MK;
therefore, some heating source must operate throughout the entire length
of the loop, balancing radiative losses and maintaining a quasi-steady
state of the loop over at least several hours. As observations show,
the plasma density inside the loops exceeds the density of the ambient
plasma by more than an order of magnitude. It is supposed that the
enhanced plasma density inside the loops results from the development of
the ballooning mode of a flute-type instability in the sunspot penumbra,
where the plasma of the inner sunspot region, with β i ≪ 1, comes
into contact with the dense chromospheric plasma, which has β e ≫
β i (β is the gas-to-magnetic pressure ratio). As the chromospheric
plasma penetrates into the potential field of the sunspot, the generated
diamagnetic currents balance the excess gas pressure. These currents
efficiently decay due to the Cowling conductivity. Even if neutrals
are few in number in the plasma (accounting for less than 10-5 of
the total mass density), this conductivity ensures a heating rate
that exceeds the rate of the normal Joule dissipation of diamagnetic
currents by 7 8 orders of magnitude. Helium is an important factor in
the context of plasma heating in magnetic loops. Its relatively high
ionization potential, while not forbidding dielectronic recombination,
ensures a sufficiently high number of neutrals in the coronal plasma and
maintains a high heating rate due to the Cowling conductivity, even at
coronal temperatures. The heating results from the “burning-out”
of the nonpotential component of the magnetic field of the coronal
magnetic loops. This mechanism provides the necessary heating rate
for the plasma inside the loops if the loops are thin enough (with
thickness of the order of 105 106 cm). This may imply that the observed
(1 5) × 108-cm-thick loops consist of numerous hot, thin threads. For
magnetic loops in hydrostatic equilibrium, the calculated heating
function exponentially decreases with height on characteristic scales a
factor of 1.8 smaller than the total-pressure scale height, since the
scale heights for the total pressure and for the 4He partial pressure
are different. The heating rate is proportional to the square of the
plasma pressure in the loop, in agreement with observational data.
Title: Dynamics of Electron Spatial Distribution in Microwave
Flaring Loops
Authors: Melnikov, V. F.; Gorbikov, S. P.; Reznikova, V. E.;
Shibasaki, K.
Bibcode: 2005ESASP.600E.132M
Altcode: 2005ESPM...11..132M; 2005dysu.confE.132M
No abstract at ADS
Title: Spatially resolved microwave pulsations of a flare loop
Authors: Melnikov, V. F.; Reznikova, V. E.; Shibasaki, K.; Nakariakov,
V. M.
Bibcode: 2005A&A...439..727M
Altcode:
A microwave burst with quasi-periodic pulsations was studied with high
spatial resolution using observations with the Nobeyama Radioheliograph
(NoRH). We found that the time profiles of the microwave emission at
17 and 34 GHz exhibit quasi-periodic (with two well defined periods
P_1= 14-17 s and P_2= 8-11 s) variations of the intensity at different
parts of an observed flaring loop. Detailed Fourier analysis shows the
P1 spectral component to be dominant at the top, while the
P2 one near the feet of the loop. The 14-17 s pulsations
are synchronous at the top and in both legs of the loop. The 8-11 s
pulsations at the legs are well correlated with each other but the
correlation is not so obvious with the pulsations at the loop top. For
this P2 spectral component, a definite phase shift, P_2/4≈
2.2~s, between pulsations in the northern leg and loop top parts of
the loop have been found. The length of the flaring loop is estimated
as L = 25 Mm (≈ 34 arcsec) and its average width at half intensity
at 34 GHz as about 6 Mm (≈ 8 arcsec). Microwave diagnostics shows
the loop to be filled with a dense plasma with the number density
n0 ≈ 1011 cm-3, penetrated by the
magnetic field changing from B0 ≈ 100 G near the loop top
up to B0 ≈ 200 G near the north footpoint. A comparative
analysis of different MHD modes of the loop demonstrates the possibility
of the simultaneous existence of two modes of oscillations in the loop:
the global sausage mode, with the period P_1= 14-17 s and the nodes at
the footpoints, and a higher harmonics mode (possibly with the radial
wave number l>1), with P_2= 8-11 s.
Title: Coronal Magnetography of Solar Active Region 8365 with the
SSRT and NoRH Radio Heliographs
Authors: Ryabov, B. I.; Maksimov, V. P.; Lesovoi, S. V.; Shibasaki,
K.; Nindos, A.; Pevtsov, A.
Bibcode: 2005SoPh..226..223R
Altcode:
Microwave maps of solar active region NOAA 8365 are used to derive
the coronal magnetograms of this region. The technique is based on
the fact that the circular polarization of a radio source is modified
when microwaves pass through the coronal magnetic field transverse to
the line of sight. The observations were taken with the Siberian Solar
Radio Telescope (SSRT) on October 21 - 23 and with the Nobeyama Radio
Heliograph (NoRH) on October 22 - 24, 1998. The known theory of wave
mode coupling in quasi-transverse (QT) region is employed to evaluate
the coronal magnetograms in the range of 10 - 30 G at the wavelength 5.2
cm and 50 - 110 G at 1.76 cm, taking the product of electron density and
the scale of coronal field divergence to be constant of 1018
cm−2. The height of the QT-region is estimated from the
force-free field extrapolations as 6.2 × 109 cm for the
20 G and 2.3 × 109 cm for 85 G levels. We find that on
large spatial scale, the coronal magnetograms derived from the radio
observations show similarity with the magnetic fields extrapolated
from the photosphere.
Title: Observations of a Post-Eruptive Arcade on October 22, 2001
with CORONAS-F, other Spaceborne Telescopes, and in Microwaves
Authors: Borovik, V. N.; Rudenko, G. V.; Slemzin, V. A.; Stepanov,
A. I.; Shibasaki, K.; Uralov, A. M.; Zandanov, V. G.; Zhitnik, I. A.;
Grechnev, V. V.; Bugaenko, O. I.; Bogachev, S. A.; Grigorieva, I. Y.;
Kuzin, S. V.; Lesovoi, S. V.; Livshits, M. A.; Pertsov, A. A.
Bibcode: 2005IAUS..226..108B
Altcode:
Using multi-spectral data, we estimate plasma parameters in the
post-eruptive arcade observed on October 22, 2001 at 100 Mm above
the limb: the temperature is 6 MK and the plasma density is (5-9)
\cdot 109 cm-3. We state a problem of the
long-term equilibrium of the hot top of the arcade high in the corona:
either the magnetic field surrounding the arcade well exceeds that
one extrapolated in the potential approximation, or β > 1 both
inside and outside the arcade. A downflow observed in soft X-rays can
contribute to the equilibrium.
Title: The first build-up of the Solar-B flight models
Authors: Hara, Hirohisa; Ichimoto, Kiyoshi; Otsubo, Masashi; Katsukawa,
Yukio; Kato, Yoshihiro; Kano, Ryohei; Kumagai, Kazuyoshi; Shibasaki,
Kiyoto; Shimizu, Toshifumi; Shimojo, Masumi; Suematsu, Yoshinori;
Tamura, Tomonori; Tsuneta, Saku; Noguchi, Motokazu; Nakagiri, Masao;
Miyashita, Masakuni; Watanabe, Tesuya; Kosuchi, Takeo; Sakao, Taro;
Matsuzaki, Keiichi; Kitakoshi, Yasunori; Kubo, Masahito; Sakamoto,
Yasushi
Bibcode: 2005ARAOJ...7...46H
Altcode:
No abstract at ADS
Title: Science of the X-ray Sun: The X-ray telescope on Solar-B
Authors: DeLuca, E. E.; Weber, M. A.; Sette, A. L.; Golub, L.;
Shibasaki, K.; Sakao, T.; Kano, R.
Bibcode: 2005AdSpR..36.1489D
Altcode:
The X-Ray Telescope (XRT) on Solar-B is designed to provide high
resolution, high cadence observations of the X-ray corona through
a wide range of filters. The XRT science team has identified four
general problems in coronal physics as the primary science goals for our
instrument. Each of these goals will require collaborative observations
from the other Solar-B instruments: EUV Imaging Spectrograph (EIS)
and Solar Optical Telescope Focal Plane Package (SOT). We will discuss
the science goals and observations needed to address those goals.
Title: Focal plane CCD camera for the X-Ray Telescope (XRT) aboard
SOLAR-B
Authors: Sakao, Taro; Kano, Ryouhei; Hara, Hirohisa; Matsuzaki,
Keiichi; Shimojo, Masumi; Tsuneta, Saku; Kosugi, Takeo; Shibasaki,
Kiyoto; Kumagai, Kazuyoshi; Sawa, Masaki; Tamura, Tomonori; Iwamura,
Satoru; Nakano, Mitsuhiko; Du, Zhangong; Hiyoshi, Kenji; Horii,
Michihiro; Golub, Leon; Bookbinder, Jay A.; Cheimets, Peter C.; Hill,
Lawrence D.; Owens, Jerry K.
Bibcode: 2004SPIE.5487.1189S
Altcode:
We present scientific as well as engineering overview of the X-Ray
Telescope (XRT) aboard the Japanese Solar-B mission to be launched in
2006, with emphasis on the focal plane CCD camera that employs a 2k
x 2k back-thinned CCD. Characterization activities for the flight CCD
camera made at the National Astronomical Observatory of Japan (NAOJ)
are discussed in detail with some of the results presented.
Title: A new solar flare scenario
Authors: Shibasaki, Kiyoto
Bibcode: 2004AstHe..97..509S
Altcode:
A new solar flare scenario is proposed based on high-beta plasma
disruption. It is also proposed to interpret solar atmospheric
structures and activities as "dissipative structure". In the standard
model, the origin of solar activities is magnetic energy and of the
mechanism of releasing magnetic energy is magnetic reconnection. In
the present article, roles of plasma are stressed and the instability
of plasma confined in the magnetic field in the solar atmosphere
is attributed to the solar surface activities, especially solar
flares. Nuclear fusion experiments in TOKAMAKs show that when the
plasma density and temperature are higher, the plasma in the loop are
disrupted due to ballooning instability. The same mechanism can be
applied to magnetic loops in the solar atmosphere.
Title: Pulsations of Microwave Emission and Flare Plasma Diagnostics
Authors: Stepanov, A. V.; Kopylova, Yu. G.; Tsap, Yu. T.; Shibasaki,
K.; Melnikov, V. F.; Goldvarg, T. B.
Bibcode: 2004AstL...30..480S
Altcode:
We consider the modulation of nonthermal gyrosynchrotron emission from
solar flares by the ballooning and radial oscillations of coronal
loops. The damping mechanisms for fast magnetoacoustic modes are
analyzed. We suggest a method for diagnosing the plasma of flare loops
that allows their main parameters to be estimated from peculiarities of
the microwave pulsations. Based on observational data obtained with the
Nobeyama Radioheliograph (17 GHz) and using a technique developed for
the event of May 8, 1998, we determined the particle density n ~ 3.7 x
1010 cm-3, the temperature T ~ 4 x 107
K, and the magnetic field strength B ~ 220 G in the region of flare
energy release. A wavelet analysis for the solar flare of August 28,
1999, has revealed two main types of microwave oscillations with
periods P1 = 7, 14 s and P2 = 2.4 s, which we attribute to the
ballooning and radial oscillations of compact and extended flare
loops, respectively. An analysis of the time profile for microwave
emission shows evidence of coronal loop interaction. We determined
flare plasma parameters for the compact (T ~ 5.3 x 107 K,
n ~ 4.8 x 1010 cm-3, B ~ 280 G) and extended (T ~
2.1 x 107 K, n ~ 1.2 x 1010 cm-3, B ~
160 G) loops. The results of the soft X-ray observations are consistent
with the adopted model.
Title: A new solar flare scenario: - High-beta plasma disruption -
Authors: Shibasaki, Kiyoto
Bibcode: 2004IAUS..223..485S
Altcode: 2005IAUS..223..485S
The solar corona is believed to be generally low beta. In a low-beta
plasma, energy is mainly stored as magnetic energy or current. To
dissipate the stored magnetic energy in the highly conductive
corona, anomalous resistivity is needed. Activities of outer layers
of X-ray loops in solar flares have been interpreted as the result
of reconnection of magnetic field due to anomalous resistivity in a
current sheet located above the flaring loop.
Title: Prominence eruptions and coronal mass ejection: a statistical
study using microwave observations
Authors: Gopalswamy, N.; Lu, W.; Yashiro, S.; Shimojo, M.; Shibasaki,
K.
Bibcode: 2004naoj.book...18G
Altcode:
No abstract at ADS
Title: On coronal streamer changes
Authors: Gopalswamy, N.; Shimojo, M.; Lu, W.; Yashiro, S.; Shibasaki,
K.; Howard, R. A.
Bibcode: 2004AdSpR..33..676G
Altcode:
Coronal streamer represents one of the pre-eruption configurations
of coronal mass ejections (CMEs), because they overlie prominences
and often possess all the substructures of CMEs. In this paper,
we report on a study of streamer changes associated with prominence
eruptions. The prominence eruptions and streamer changes were observed
by the Nobeyama radioheliograph and Solar and Heliospheric Observatory
(SOHO), respectively. Multiwavelength data showed that at least one of
the streamer events involved heating and small-scale material ejection
that subsequently stalled. After presenting illustrative examples,
we compare the properties of the streamer-related events with those of
general population of prominence events. We find that the properties
of streamer-related prominence events are closer to those of prominence
eruptions with transverse trajectories.
Title: Analysis of quasi-periodic oscillations of position and
brightness of details of the radio sources of the solar active
regions based on observations made with the radio heliograph Nobeyama
Authors: Gelfreikh, G. B.; Shibasaki, K.; Nagovitsyna, E. Yu.;
Nagovitsyn, Yu. A.
Bibcode: 2004IAUS..223..245G
Altcode: 2005IAUS..223..245G
As based on analysis of radio maps at the wavelength of 1.76 cm
obtained from observations at the radio heliograph Nobeyama the
parameters of oscillation processes in solar active regions were
studied. As a technique for data processing wavelet analysis was
used. The inherent periodicity in oscillations submits the existence
of a resonance structure for some kinds of MHD waves in the plasma of
the solar atmosphere.
Title: Microwave imaging observation of high-energy electron
propagation in a solar flare
Authors: Shibasaki, Kiyoto; Nakajima, Hiroshi; Yokoyama, Takaaki;
Melnikov, V. F.; Stepanov, A. V.
Bibcode: 2004naoj.book...15S
Altcode:
No abstract at ADS
Title: Observations of sausage mode oscillations in a flaring loop
Authors: Melnikov, V. F.; Reznikova, V. E.; Shibasaki, K.; Nakariakov,
V. M.
Bibcode: 2004IAUS..223..647M
Altcode: 2005IAUS..223..647M
We provide an observational proof of the existence of the global sausage
mode oscillations in a flaring loop studying a microwave burst with
quasi-periodical pulsations observed with the Nobeyama Radioheliograph
(NoRH).
Title: Coronal Radio Magnetography of Solar Active Region 8365
Authors: Ryabov, B. I.; Nindos, A.; Shibasaki, K.; Maksimov, V. P.;
Lesovoi, S. V.; Pevtsov, A. A.
Bibcode: 2003AGUFMSH42B0508R
Altcode:
Using the microwave radio observations with Siberian Solar Radio
Telescope (SSRT) and Nobeyama Radio Heliograph (NoRH) we derived 2D
coronal magnetograms of solar active region NOAA 8365. The circular
polarization (CP) of radio source is modified, when the radiation
passes through the overlying magnetic field transverse to the
line-of-sight. This change in CP was used to study the properties of
coronal fields. We employed the known theory of wave-mode coupling
in quasi-transverse (QT) region to evaluate the distribution of the
field strength at the level of transformation of 5.2 cm radiation
(SSRT, field strength ∼ 10-30 G) and 1.76 cm (NoRH, ∼ 50-110
G). The magnetic field strength was derived under the assumption
N~Lα = 1018 cm-2, where N is electron
density and Lα is the scale of coronal field divergence
along line-of-sight. The height of QT-region (HQTR) was
estimated using force free field extrapolations, HQRT =
6.3 x 109 cm (2.3 x 109 cm) for 20 G (85 G). We
then compared the coronal radio magnetograms and the force free field
extrapolation of photospheric magnetic field, and we found close
similarity between them on large spatial scale.
Title: Radio and Hard X-Ray Images of High-Energy Electrons in an
X-Class Solar Flare
Authors: White, S. M.; Krucker, S.; Shibasaki, K.; Yokoyama, T.;
Shimojo, M.; Kundu, M. R.
Bibcode: 2003ApJ...595L.111W
Altcode:
We present the first comparison between radio images of high-energy
electrons accelerated by a solar flare and images of hard X-rays
produced by the same electrons at photon energies above 100 keV. The
images indicate that the high-energy X-rays originate at the footpoints
of the loops dominating the radio emission. The radio and hard X-ray
light curves match each other well and are quantitatively consistent
with an origin in a single population of nonthermal electrons with
a power-law index of around 4.5-5. The high-frequency radio spectral
index suggests a flatter energy spectrum, but this is ruled out by the
X-ray spectrum up to 8 MeV. The preflare radio images show a large
hot long-lived loop not visible at other wavelengths. Flare radio
brightness temperatures exceed 109 K, and the peak in the
radio spectrum is as high as 35 GHz: both these two features and the
hard X-ray data require very high densities of nonthermal electrons,
possibly as high as 1010 cm-3 above 20 keV at
the peak of the flare.
Title: A Microwave Imaging Observation of an Electron Stream in a
Solar Flare by Nobeyama Radioheliograph
Authors: Yokoyama, T.; Nakajima, H.; Shibasaki, K.; Melnikov, V. F.;
Stepanov, A. V
Bibcode: 2003ICRC....6.3359Y
Altcode: 2003ICRC...28.3359Y
We report a Nob eyama Radioheliograph microwave observation in a flare
of a propagating feature of non-thermal emission to propagate from
one end of the loop to the other with a speed of 9 × 104 km s-1 . We
interpret this microwave is emitted from streaming electrons. From the
comparison of energies of the electrons that should emit the microwave
with their observed apparent speed, we suggest that the high energy
electrons possibly have large (> 70 degree) pitch angles when they
are injected.
Title: A Multi-wavelength Analysis of a Solar Limb Flare on 2002
April 15
Authors: Sui, L.; Holman, G. D.; Gary, D. E.; Shibasaki, K.
Bibcode: 2003SPD....34.1807S
Altcode: 2003BAAS...35..840S
A detailed analysis of a limb flare on 2002 April 15 was carried out
using RHESSI X-ray images and spectra, Nobeyama microwave images,
Owens Valley Solar Array (OVSA) microwave spectra, and SOHO EIT &
LASCO images. This M1.2 flare lasted about 40 minutes in GOES soft
X-rays. RHESSI missed part of the decay phase of the flare. RHESSI
images show a thermal flare loop at 6-25 keV and a bright thermal
looptop source within the loop throughout the flare. At the peak of
the flare, a coronal source 6 arcseconds above the flare loop and
two clear-cut footpoints appear at 25-50 keV. Another coronal source
above the loop at 10-25 keV ejected outward at about 600 km/s after the
peak. By fitting the RHESSI spectra, we found that a low-energy cut-off
at about 22 keV is required in order to get a consistent evolution of
the thermal plasma parameters with time. After the hard X-ray peak,
the flare loop moves outward in both the SOHO/EIT 195 Å band and the
Nobeyama microwave images. It precedes an expanding coronal anomaly
observed in SOHO/LASCO C2 images. We will show images and movies of
our results, and a comparison of the microwave images and spectra with
the RHESSI observations. This project was supported in part by
the RHESSI Project and the NASA Sun-Earth Connection Program.
Title: Temporal and angular variation of the solar limb brightening
at 17 GHz
Authors: Selhorst, C. L.; Silva, A. V. R.; Costa, J. E. R.;
Shibasaki, K.
Bibcode: 2003A&A...401.1143S
Altcode:
In order to better understand the atmosphere structure of the Sun,
we have analyzed over 3000 daily maps of the Sun taken at 17 GHz from
the Nobeyama Radioheliograph (NoRH) from 1992 through 2001, focusing on
the excess brightness temperature observed near the limb. The purpose
of this work is to characterize the limb brightness in two ways:
(i) study the temporal variation of the intensity and radial width of
polar brightening; and (ii) measure the brightness distribution along
the limb as a function of position angle and compare it with data at
other wavelengths throughout the solar cycle. The mean intensity of the
polar regions were found to be approximately 13% and 14% above quiet
Sun levels at the North and South poles, respectively. Moreover, the
polar brightenings are strongly anti-correlated with solar activity (as
measured by sunspot number). The radial width of the excess brightness
is slightly over 1 arcmin for both polar regions. Only a small variation
with the solar cycle was observed during the decline of last maximum,
that is, the Southern polar brightening was found to be both wider and
brighter than the Northern one for the 23rd cycle. As for the angular
variation of the limb brightening, for a month during a period of
minimum activity, it reaches 25% above quiet Sun levels at the poles,
~ 15% near the equator, and 10% at intermediate regions. Hα images
also show brightening enhancements at the polar regions for the same
period. We also found a strong anti-correlation between the radio
polar brightenings and the coronal holes seen in soft X-ray images
from 1992 to 2001. There seems to be a strong association of the radio
limb brightening at 17 GHz with faculae. The implications of these
correlations are discussed.
Title: Prominence Eruptions and Coronal Mass Ejection: A Statistical
Study Using Microwave Observations
Authors: Gopalswamy, N.; Shimojo, M.; Lu, W.; Yashiro, S.; Shibasaki,
K.; Howard, R. A.
Bibcode: 2003ApJ...586..562G
Altcode:
We present the results of a statistical study of a large
number of solar prominence events (PEs) observed by the Nobeyama
Radioheliograph. We studied the association rate, relative timing,
and spatial correspondence between PEs and coronal mass ejections
(CMEs). We classified the PEs as radial and transverse, depending on
whether the prominence moved predominantly in the radial or horizontal
direction. The radial events were faster and attained a larger height
above the solar surface than the transverse events. Out of the 186
events studied, 152 (82%) were radial events, while only 34 (18%)
were transverse events. Comparison with white-light CME data revealed
that 134 (72%) PEs were clearly associated with CMEs. We compare our
results with those of other studies involving PEs and white-light CMEs
in order to address the controversy in the rate of association between
CMEs and prominence eruptions. We also studied the temporal and spatial
relationship between prominence and CME events. The CMEs and PEs seem
to start roughly at the same time. There was no solar cycle dependence
of the temporal relationship. The spatial relationship was, however,
solar cycle dependent. During the solar minimum, the central position
angle of the CMEs had a tendency to be offset closer to the equator
as compared to that of the PE, while no such effect was seen during
solar maximum.
Title: Signature of Energy Release and Particle Acceleration Observed
by the Nobeyama Radioheliograph
Authors: Shibasaki, K.
Bibcode: 2003LNP...612...96S
Altcode: 2003ecpa.conf...96S
Microwave imaging observations of solar flares are presented and a
new scenario for solar flares is proposed. Microwaves are effectively
emitted by high-energy electrons gyrating in active region magnetic
fields. Higher harmonics (10 - 100) of the gyro-frequency in active
regions, excited by mildly relativistic electrons, correspond
to microwaves. Imaging observations of strong microwave emission
associated with solar flares make it possible to study where and how
the high-energy electrons are crreated in solar flares, which is one
of the long-standing questions of solar flares. Hot and dense plasma
created by solar flares also emits microwaves by the free-free mechanism
although usually weak compared to the non-thermal emission. It is
shown that flares start in a small loop and also shown that hot plasmas
and high-energy electrons are fed into a nearby larger loop from the
small one. Based on these and other observations, it is proposed that
"high-beta disruption" is the cause of solar flare phenomena.
Title: Microwave imaging observation of an electron stream in a
solar flare
Authors: Yokoyama, T.; Nakajima, H.; Shibasaki, K.; Melnikov, V. F.;
Stepanov, A. V.
Bibcode: 2003AdSpR..32.2517Y
Altcode:
We report a Nobeyama Radioheliograph (NoRH) microwave observation of a
propagating feature of non thermal emission in a solar flare. The flare
had a very extended source well resolved by NoRH. In the rising phase of
the microwave burst, a non-thermal gyrosynchrotron source was observed
by the high-rate (10 images per second) observations to propagate from
one end of the loop to the other with a speed of 9 × 10 4
km s -1. We interpret this non-thermal propagating source
is emitted from streaming electrons.
Title: High-beta disruption in the solar atmosphere
Authors: Shibasaki, Kiyoto
Bibcode: 2003naoj.book...33S
Altcode:
No abstract at ADS
Title: Spectral dynamics of mildly relativistic electrons in extended
flaring loops
Authors: Melnikov, V. F.; Reznikova, V. E.; Yokoyama, T.; Shibasaki, K.
Bibcode: 2002ESASP.506..339M
Altcode: 2002ESPM...10..339M; 2002svco.conf..339M
The specific task of this work is an analysis of the microwave spectral
dynamics of several well-resolved loop-like radio sources with the
Nobeyama Radioheliograph (NoRH) at 17 and 34 GHz. The flares were
detected as well with the Yohkoh/HXT and the BATSE/CGRO hard X-ray
spectrometer. Their hard X-ray spectral index evolution follows to the
classical "soft-hard-soft" behavior, typical for most of impulsive
flares with simple time profiles. On the contrary, the temporal
evolution of the microwave spectral index derived from the emission at
17 and 34 GHz in different portions of the loop-like sources displays
"soft-hard-harder" behavior: decrease of its value from the rise
phase to the decay phase. These results indicate on the different
spectral evolutions of low and high energy electrons in a flaring
loop. Some possibilities for such a difference, including processes
of acceleration/injection, trapping and scattering, are considered.
Title: Observational constraints on short-wave turbulence in flares
Authors: Fleishman, G. D.; Melnikov, V. F.; Shibasaki, K.
Bibcode: 2002ESASP.506..283F
Altcode: 2002ESPM...10..283F; 2002svco.conf..283F
Decimetric counterparts of microwave bursts are analyzed. A few radio
bursts (in particular, recorded by Nobeyama Radioheliograph with high
spatial resolution) are discussed within the framework of available
theories of nonthermal radio emission. The study yields important
observational constraints on short-wave turbulence in flares.
Title: A new solar flare scenario: high-beta plasma disruption
Authors: Shibasaki, Kiyoto
Bibcode: 2002ESASP.506..749S
Altcode: 2002svco.conf..749S; 2002ESPM...10..749S
A new solar flare scenario is proposed based on a high-beta plasma
instability. Plasma confined in a curved magnetic field (magnetic loop)
has free energy. This free energy will be converted to other forms
explosively under certain conditions through localized quasi-interchange
instability called "ballooning instability". Relations between solar
flare phenomena and ballooning instability phenomena are discussed.
Title: Constraints on electron acceleration/injection from NoRH
observations
Authors: Melnikov, V. F.; Shibasaki, K.; Reznikova, V. E.
Bibcode: 2002ESASP.506..257M
Altcode: 2002ESPM...10..257M; 2002svco.conf..257M
Nobeyama Radioheliograph microwave data provide us with unique
information about radio brightness distribution along flaring loops. In
particular it has been found for several events that the brightness
maximum at 17 and 34 GHz is located at the top of extended flaring
loops. The detailed analysis of these events strongly suggests that
the distribution of mildly relativistic electrons along an extended
flaring loop must be highly inhomogeneous: accelerated electrons
are concentrated in the upper part of the loop. This finding impose
important new constraints on the acceleration/injection mechanisms
and kinetics of high energy particles in solar flares.
Title: Loop-Top Nonthermal Microwave Source in Extended Solar
Flaring Loops
Authors: Melnikov, V. F.; Shibasaki, K.; Reznikova, V. E.
Bibcode: 2002ApJ...580L.185M
Altcode:
Nobeyama Radioheliograph (NoRH) microwave data provide us with unique
information about the radio brightness distribution along flaring
loops. In particular, it has been found that for several events with
extended looplike sources well resolved with NoRH, the brightness
maximum at 17 and 34 GHz is located at the top of the corresponding
flaring loops. The detailed analysis of these events strongly suggests
that the distribution of mildly relativistic electrons along an extended
flaring loop must be highly inhomogeneous: accelerated electrons
are concentrated in the upper part of the loop. This finding imposes
important new constraints on the acceleration/injection mechanisms
and on the kinetics of high-energy particles in solar flares.
Title: Radio observations of the July 13, 2000 transequatorial
eruptive prominence
Authors: Karlický, M.; Shibasaki, K.
Bibcode: 2002ESASP.506..657K
Altcode: 2002ESPM...10..657K; 2002svco.conf..657K
Using the 17 and 34 GHz Nobeyama Radioheliograph observations the
July 13, 2000 transequatorial eruptive prominence was studied. It
was found that the eruption started near the bright equatorial
feature, which reappeared in the post-eruption phase. During 7
hours of observations of this feature periodic variations of its
brightness temperature were recognized, e.g. in the initial phase of
the prominence eruption their characteristic period was about of 12
minutes. Circular loops and helical structures of different scales,
indicating the presence of electric currents were observed during the
whole prominence eruption. The velocity of the upper boundary of the
prominence in the image plane, along the chosen line was estimated as
24 km s-1 in the first 15 minutes of the eruption and about
of 66 km s-1 in following times. Finally, the observations
are shortly discussed.
Title: Microwave Observations of the Rapid Propagation of Nonthermal
Sources in a Solar Flare by the Nobeyama Radioheliograph
Authors: Yokoyama, T.; Nakajima, H.; Shibasaki, K.; Melnikov, V. F.;
Stepanov, A. V.
Bibcode: 2002ApJ...576L..87Y
Altcode:
We report a Nobeyama Radioheliograph (NoRH) microwave observation
of propagating features of nonthermal emission in a solar flare on
1999 August 28, an M2.8 event for the GOES soft X-ray class. The
flare had a very extended source (~4.5×104 km) that was
well resolved by the NoRH, and it is confirmed to be a magnetic loop
by comparison with the photospheric magnetic field. In the rising
phase of the microwave burst, a nonthermal gyrosynchrotron source was
observed by the high-rate (10 images per second) observation of the
NoRH to propagate from one end of the loop to the other with a speed of
6×103 km s-1. We also found a 9×104
km s-1 propagation in the same apparent position, which is
the first imaging observation of streaming electrons.
Title: A study of the development of global solar activity in the
23rd solar cycle based on radio observations with the Nobeyama radio
heliograph. I. Latitude distribution of the active and dark regions
Authors: Gelfreikh, G. B.; Makarov, V. I.; Tlatov, A. G.; Riehokainen,
A.; Shibasaki, K.
Bibcode: 2002A&A...389..618G
Altcode:
Daily radio maps of the Sun at the wavelength of 1.76 cm were used to
analyze the parameters of solar activity at all heliographic latitudes
for the period 1992-2001. As a criterion of the level of solar activity,
we analyzed the area/number of regions with an excess of brightness
above a certain fixed level as well as regions with brightness below a
certain level. The distribution of such ``bright'' and ``dark'' regions
with heliographic latitude as function of time was found. Special
attention was paid to the high latitude polar regions where the ways
of analyzing solar activity are rather limited and have no generally
accepted methods. The results are compared with some other indices
of high latitude solar activity, such as polar faculae and magnetic
field measurements. They appear to be in general agreement with the
radio observations. The advantage of using radio observations is a
more homogeneous database and a stable method of analysis.
Title: A study of development of global solar activity in the 23rd
solar cycle based on radio observations with the Nobeyama radio
heliograph. II. Dynamics of the differential rotation of the Sun
Authors: Gelfreikh, G. B.; Makarov, V. I.; Tlatov, A. G.; Riehokainen,
A.; Shibasaki, K.
Bibcode: 2002A&A...389..624G
Altcode:
An analysis of solar rotation as a function of heliographic latitude
and time is made using daily radio maps of the Sun at the wavelength
of 1.76 cm. Variations of the velocity as a function of the latitude
during the period 1992-2001 have been studied. The mean synodical
rotation rate of the intensity features is best fit by ω = 13.41 -
1.66\sin2 θ -2.19 \sin4 θ (deg/day) where
theta is the latitude. We have found alternating bands of faster and
slower rotation. They travel from higher latitudes towards the equator
during the current solar cycle. Radio observations with high accuracy
and reliability thus confirm the reality of torsional oscillations in
the higher levels of the solar atmosphere.
Title: Prominence Eruptions and CMEs: A Statistical Study
Authors: Gopalswamy, N.; Shimojo, M.; Yashiro, S.; Shibasaki, K.
Bibcode: 2002AAS...200.3705G
Altcode: 2002BAAS...34..695G
Prominence eruptions are thought to be an integral part of coronal mass
ejections. However, recent statistical studies obtained conflicting
conclusions regarding this relationship: a nearly one-to-one
correspondence to a poor association. We revisited this problem using
all the eruptive prominences detected automatically from the daily
images obtained by the Nobeyama Radioheliograph. The images were
made with a 10 min cadence so only slower eruptions could be detected
from these images. During January 1996 to December 2001, there were
226 prominence eruptions detected this way and 182 of them had white
light observations from the Solar and Heliospheric Observatory (SOHO)
mission. When we compared the radio and white light data, we found
that 76 CMEs, while only 16 remaining 8 suggesting partial eruption. We
conclude that there is good association between CMEs when the prominence
eruptions have a radial component of the velocity is dominant.
Title: Microwave Detection of Shock and Associated Electron Beam
Formation
Authors: Aurass, H.; Shibasaki, K.; Reiner, M.; Karlický, M.
Bibcode: 2002ApJ...567..610A
Altcode:
We use complementary European and Japanese solar radio ground-based
observations, together with Yohkoh soft X-ray and SOHO extreme-UV
images, to search for the signature of flare-related waves at different
heights above the Sun. The key data set for event selection is 40-800
MHz dynamic radio spectra from the Potsdam Astrophysical Institute,
whose radio spectral polarimeter is sensitive to the coronal shock
waves due to the associated type II radio bursts in the range between
0.2 and 1 Rsolar. Nobeyama Radio Heliograph images at 17
GHz show the chromosphere and the transition region to the corona with
unprecedented sensitivity and time resolution (1 s image cadence). Here
we focused on 17 GHz images in the time interval between flare onset
and the start of the metric type II burst. The decametric-hectometric
(Dm-Hm 1-14 MHz) radio experiment on board Wind completes the radio
spectral coverage. The spectra are used to check if the coronal shock
wave is also continuously visible in the range 3-8 Rsolar and
if the corona is open or closed for electron beams exciting hectometric
type III bursts. We selected two flare events that show metric type II
bursts, but with different associated 17 GHz features. For both events
we find flare disturbances in 17 GHz images that propagate earlier
than the type II bursts: a hot, dense blob (event 1; 1997 April 2)
or a cold, absorbing cloud (event 2; 1998 July 31). In event 1, the
hot and dense blob preceded the formation of a wave front segment that
appeared in SOHO/EIT images. In event 2, we observed the impact of
the 17 GHz absorbing cloud on a preexisting quiescent prominence far
out of the flaring active region after several minutes of propagation
without being disturbed. We demonstrate that the spectral pattern, as
well as the drift rate, of the given type II burst drastically changes
shortly before the cloud's impact. The Dm-Hm spectra in event 2 reveal
a typical shock-associated (SA) event in the outer corona during the
interaction between the absorbing cloud and the prominence. Finally,
we stress that there may be a common driver for the metric type II
bursts and simultaneous decimeter reverse-drift bursts between 1 and
2 GHz recorded on the radio spectrograph of Astronomical Observatory
Ondřejov.
Title: Energy and Mass Supply in the Decay Phase of Long-Duration
Solar Flare Events
Authors: Shibasaki, Kiyoto
Bibcode: 2002ApJ...567L..85S
Altcode:
A new mechanism is proposed to supply energy and mass in the decay
phase of long-duration solar flare events. The long-duration event
(LDE) flares are known to be caused by filament eruptions, and
bright arcade structures continue for several hours or even a day. To
overcome the short cooling time, continuous energy and mass supplies are
required. Continuous magnetic reconnection in the current sheet extended
above the arcade has been proposed to supply energy and mass. However,
no direct observations of the current sheet have been reported. The new
mechanism that we are proposing is based on the recent observations of
downflows onto the top of arcades along the vertical spiky features
observed by the Yohkoh soft X-ray telescope. We interpret these
downflows as free-falling plasma. Plasma falling from a high altitude
can convert its potential energy into thermal energy and heat itself
with an average temperature of several million kelvins. Observations
show that the downflows continue for several hours. Coronagraph
observations by the Solar and Heliospheric Observatory Large Angle
and Spectrometric Coronagraph also show many falling features after
coronal mass ejections. Instead of magnetic reconnection, we propose
that these falling plasmas are the source of the energy and mass supply
for LDEs in the long-lasting decay phase.
Title: Microwave observation of rapid propagation of a non-thermal
sources in a solar flare by Nobeyama Radioheligoraph
Authors: Yokoyama, T.; Nakajima, H.; Shibasaki, K.; Melnikov, V.;
Stepanov, A.
Bibcode: 2002cosp...34E2325Y
Altcode: 2002cosp.meetE2325Y
We report a Nobeyama Radioheliograph (NoRH) microwave observation of a
propagating feature of non-thermal emission in a solar flare on August
28, 1999 with GOES soft X-ray class M2.8. The flare had a very extended
source ( 105 km) well resolved by the NoRH, which is confirmed to be
a magnetic loop by comparing with the photospheric magnetic field. In
the rising phase of the microwave burst, a non-thermal gyrosynchrotron
source was observed by the high-rate (10 images per second) observation
of the NoRH to propagate from one end of the loop to the other with
a speed of 104 km s-1 . It is a first observation of such a rapid
propagating non-thermal microwave source inside a flaring loop. We
also found a nearly 105 km s-1 propagation in the same apparent
position. This is the first imaging observation of streaming electrons.
Title: Origin of coronal streamer distention
Authors: Gopalswamy, N.; Shimojo, M.; Lu, W.; Yashiro, S.; Shibasaki,
K.; Howard, R.
Bibcode: 2002cosp...34E1257G
Altcode: 2002cosp.meetE1257G
Distention of coronal streamers is considered to be one of the
pre-eruption evolution of coronal mass ejections (CMEs), although how
mass is added to the streamers is poorly understood. During our study
of eruptive prominences and their relation to CMEs, we observed a large
number of prominences associated with significant changes in the helmet
streamers overlying the prominences. We used the white light images of
the corona obtained by the Solar and Heliospheric Mission's Large Angle
and Spectrometric Coronagraph images and the microwave images from the
Nobeyama radioheliograph in Japan. We found that the streamer distention
is associated with prominence eruption with mostly horizontal motion
(parallel to the solar limb) or with eruptive prominences with most of
the mass falling back to the solar surface. We suggest that the physical
process which activates the prominences also add mass to the streamers.
Title: Ozone and Pollution Measuring Ultraviolet Spectrometer (OPUS):
an overview
Authors: Kuze, A.; Suzuki, M.; Sano, T.; Watanabe, M.; Yoshida, S.;
Yui, Y.; Okumura, S.; Shibasaki, K.; Ogawa, T.
Bibcode: 2002cosp...34E2231K
Altcode: 2002cosp.meetE2231K
Atmospheric composition measurements from space are essential
for monitoring earth's environment. Ozone and Pollution Measuring
Ultraviolet Spectrometer (OPUS) is a nadir-looking, cross-track
scanning ultraviolet spectrometer, which will be onboard Global
Change Observation Mission-A1 (GCOM-A1). It will be placed in a 650
km non-sun-synchronous orbit in 2007, with an inclination angle of
69 deg. OPUS consists of a mechanical scanner, a Fastie-Ebert type
polychromator with a one-dimensional UV Si-CMOS array detector, and
a radiometer for cloud detection using O2 A band. It will provide
information about cloud height and tropospheric O3 , SO2 , NO2 , BrO,
OClO, HCHO, as well as the global distribution of total O3 , surface
albedo, and aerosol in one day. This paper describes scientific
objectives, instrument design, and retrieval algorithm. Pre-launch
calibration, onboard calibration, and validation plan will be also
presented. In addition, the ground test results using laboratory models
will be discussed.
Title: Global Change Observation Mission-A1 (GCOM-A1): an overview
Authors: Suzuki, M.; Shimoda, H.; Kawanishi, T.; Ishida, C.; Sobue,
S.; Shibasaki, K.; Kuze, A.; Sano, T.; Ogawa, T.
Bibcode: 2002cosp...34E2237S
Altcode: 2002cosp.meetE2237S
GCOM-A1 is one of the satellite programs as follow-on of ADEOS and
ADEOS-II. GCOM-A1 is under planning, which is targeting for the
launch in 2007 (Jan.-Mar.). GCOM (Global Change Observation Mission)
is a Japan's new concept for systematic and long-term observation of
global environment and climate system from space. The mission concept
of GCOM covers 15 years: ADEOS-II (2002 to 2007), GCOM-A1 &-B1
(2007-2012), and GCOM-A2 &-B2 (2012-17). Within this mission period,
key geophysical parameters necessary to document and understand global
changes and climate variability will be measured continuously. GCOM-A1
will be a satellite dedicated to measure parameters related to
atmospheric chemistry and dynamics. It will carry three instruments:
OPUS (Ozone and Pollution measuring Ultraviolet Spectrometer) by
NASDA, SOFIS (Solar Occultation FTS for Inclined orbit Satellite)
by the Ministry of the Environment of Japan, and SWIFT (Stratospheric
Wind Interferometer For Transport studies) by ESA &CSA.
Title: Periodic Acceleration of Electrons in the 1998 November 10
Solar Flare
Authors: Asai, A.; Shimojo, M.; Isobe, H.; Morimoto, T.; Yokoyama,
T.; Shibasaki, K.; Nakajima, H.
Bibcode: 2001ApJ...562L.103A
Altcode: 2001astro.ph.11018A
We present an examination of the multiwavelength observation of
a C7.9 flare that occurred on 1998 November 10. This is the first
imaging observation of the quasi-periodic pulsations (QPPs). Four
bursts were observed with the hard X-ray telescope aboard Yohkoh
and the Nobeyama Radioheliograph during the impulsive phase of the
flare. In the second burst, the hard X-ray and microwave time profiles
clearly showed a QPP. We estimated the Alfvén transit time along
the flare loop using the images of the soft X-ray telescope aboard
Yohkoh and the photospheric magnetograms and found that the transit
time was almost equal to the period of the QPP. We therefore suggest,
based on a shock acceleration model, that variations of macroscopic
magnetic structures, such as oscillations of coronal loops, affect
the efficiency of particle injection/acceleration.
Title: High-Beta Disruption in the Solar Atmosphere
Authors: Shibasaki, Kiyoto
Bibcode: 2001ApJ...557..326S
Altcode:
The outer layers of X-ray loops in solar flares are known to be more
active: they are hotter than the lower loops and above the loop-top
hard X-ray sources are formed there. These phenomena are interpreted as
the result of the reconnection above the loop, which converts magnetic
energy into thermal and nonthermal energy of plasma. However, little
direct evidence for the reconnection has been presented so far. This
paper interprets the activity in the outer layer of flaring loops
on a different scenario. Coronal loops filled with hot and dense
plasma (high beta) or with fast plasma flow, surrounded by the
low-beta corona, are unstable at their outer boundary, where the
curvature is convex outward and the density gradient is inward. The
centrifugal force acting upward on the plasma in the loop can exceed
that of gravity. This condition is favorable for localized interchange
instability called ``ballooning instability,'' and the plasma in the
loop is ejected when the instability has developed into a nonlinear
phase (``high-beta disruption''). This is a natural consequence of
the high-beta (and/or the high-velocity) plasma confined in a curved
coronal loop. The high-beta disruption has many elements common to solar
flares. In this paper, importance of the high-beta plasma is stressed,
which is a neglected part of the solar activity so far.
Title: A Radio Study of the Evolution of Spatial Structure of an
Active Region and Flare Productivity
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Raulin, J. -P.
Bibcode: 2001ApJS..133..467K
Altcode:
We present the results of a radio study of the evolution of an active
region through its flare productivity. The radio study was carried out
with data obtained by the Nobeyama Radio Heliograph at 17 GHz. We chose
the active region AR 7515, which appeared at the east limb on 1993 May
23 and then evolved during its passage across the disk. We followed
its evolution until June 2. This region produced many small flares. We
consider this region to be a typical active region in the sense that it
did not produce any large flares, but a large number of weak flares. We
investigate the optical and magnetic development of the region and show
how this affects the locations of the flaring activity. We discuss
a number of events in detail in order to investigate the roles of
nonthermal and thermal radio emission in the flares. The nonthermal
gyrosynchrotron emission generally occurs in regions of strong magnetic
fields, is generally circularly polarized, and often varies rapidly in
time. On the other hand, gradual radio components tend to be thermal and
only weakly polarized, if at all. An interesting aspect of evolution
of the flares in this region is that many of the flares in the early
phase of the evolution show strong but brief nonthermal radio emission
in the impulsive phase followed by gradual thermal emission, whereas
in the last 3 days more gradual events without a strong spike of radio
emission in the impulsive phase tend to be seen. Correspondingly, the
flare images suggest that the radio sources are more compact during
the early phases and more extended in the last half of the period
covered. The most dominant component of the preflare region is often
not the component that undergoes immediate flaring. Sometimes a number
of components in the preflare region participate in the flare process
together. We speculate that these component sources are unresolved
compact bipolar loops that flare in sequence. Loop-loop interactions
occurring at many different sites at the same time seems to be a less
plausible explanation of these events.
Title: Microwave Detection of Umbral Oscillation in NOAA Active
Region 8156: Diagnostics of Temperature Minimum in Sunspot
Authors: Shibasaki, Kiyoto
Bibcode: 2001ApJ...550.1113S
Altcode:
A radio brightness oscillation of 3 minutes at 17 GHz was detected in
a compact radio source associated with a sunspot umbra in the NOAA
active region 8156. We interpret the radio brightness oscillation
by the density and temperature fluctuations due to upward-traveling
acoustic waves through the third harmonic gyroresonance layer (2000
G). SOHO/SUMER observed the same active region close to the time
of radio observations by the Nobeyama Radioheliograph. Transition
region line observations by SUMER showed both velocity and intensity
oscillations with the period of 3 minutes, and the oscillation was
interpreted as an upward-traveling acoustic wave. We applied the value
of the density and temperature fluctuations deduced from the SUMER
experiment to the gyroresonance emission in the transition region and
found good agreement with the detected radio brightness oscillation. The
origin of the 3 minute oscillation is attributed to the resonant
excitation of the cutoff frequency mode of the temperature plateau
around the temperature minimum without assuming the chromospheric
cavity. We can estimate the temperature of the temperature minimum
region in the umbra from the measured frequency.
Title: Spatial Structure of Simple Spiky Bursts at
Microwave/Millimeter Wavelengths
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Sakurai, T.;
Grechnev, V. V.
Bibcode: 2001ApJ...547.1090K
Altcode:
We present the results of a study of spatial structure of sources
of microwave and millimeter bursts with simple spiky time profiles
at 17 and 34 GHz, similar to those found to be common at 3 mm
wavelength. These bursts are of short duration, with fast 2-4 s rise
time to peak, followed by a rapid exponential decay. When mapped at
high spatial resolution with the Nobeyama Radio Heliograph (NoRH), the
radio images show direct evidence that the radio sources are compact
bipolar loops: source sizes are less than 5" and three of the five
events studied show closely spaced oppositely polarized components in
the circular polarization maps. All five events are located directly
over magnetic neutral lines in the photosphere. The soft X-ray behavior
is not entirely consistent with the Neupert effect in these events,
since all five events show a rise in the soft X-ray flux well before
any nonthermal electrons are present in the corona and the ratio of
peak soft X-ray flux to peak radio 17 GHz flux may vary by many orders
of magnitude from one event to the next. The abrupt time profiles
of these events and their physical properties are consistent with a
single-loop scenario in which magnetic energy release and acceleration
of nonthermal electrons are confined to a compact localized region.
Title: Nonthermal Flare Emission from MEV-Energy Electrons at 17,
34, and 86 GHZ
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Sakurai, T.
Bibcode: 2000ApJ...545.1084K
Altcode:
We present analyses of two solar flares observed with high spatial
resolution at 86 GHz with the BIMA millimeter-wavelength telescope
and at 17 and 34 GHz with the Nobeyama radioheliograph. The flares
were observed on 1998 November 24 and 1999 May 1. At millimeter
wavelengths these are impulsive events, and therefore they must be
produced by MeV-energy electrons. The present study using simultaneous
observations of two flares at 86, 34, and 17 GHz provides an excellent
opportunity to study high-energy electrons with high spatial resolution
observations at three optically thin frequencies. The morphology of
millimeter emission can reveal both the properties of the MeV-energy
electrons and the nature of the coronal magnetic field lines where they
radiate. One of the two events we present is the first clear case of a
λ=3 mm source in which both footpoints of a loop are detected. In the
second event the polarization image at 17 GHz also suggests a bipolar
or looplike morphology. Such morphological observations can be used
to constrain the nature of the magnetic field in the solar corona.
Title: High-resolution grazing incidence telescope for the Solar-B
observatory
Authors: Golub, Leon; DeLuca, Edward E.; Bookbinder, Jay A.; Cheimets,
Peter; Shibasaki, Kiyoto; Sakao, Taro; Kano, Ryouhei
Bibcode: 2000SPIE.4139..313G
Altcode:
The X-ray observations from the Yohkoh SXT provided the greatest
step forward in our understanding of the solar corona in nearly two
decades. We believe that the scientific objectives of the Solar-B
mission can best be achieved with an X-ray telescope (XRT) similar to
the SXT, but with significant improvements in spatial resolution and
in temperature response that take into account the knowledge gained
from Yohkoh. We present the scientific justification for this view,
discuss the instrumental requirements that flow from the scientific
objectives, and describe the instrumentation that will meet these
requirements. XRT is a grazing-incidence (GI) modified Wolter I X-ray
telescope, of 35 cm inner diameter and 2.7 m focal length. The 2048 X
2048 back-illuminated CCD has 13.5 (mu) pixels, corresponding to 1.0
arcsec and giving full Sun field of view. This will be the highest
resolution GI X-ray telescope ever flown for Solar coronal studies,
and it has been designed specifically to observe both the high and
low temperature coronal plasma.
Title: Soft X-Ray and Gyroresonance Emission above Sunspots
Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Shibasaki, K.;
Gopalswamy, N.
Bibcode: 2000ApJS..130..485N
Altcode:
Using Yohkoh SXT and Nobeyama 17 GHz data, we have studied the soft
X-ray and microwave emission above several stable, large sunspots
near central meridian passage. Our study confirms the well-known fact
that soft X-ray emission is depressed above sunspots. It also shows
that the distribution of their soft X-ray intensity is not uniform;
usually the darkest pixels are associated with the umbra or the far
edges of the leading part of the penumbra while the following part
of the penumbra may contain higher intensity pixels associated with
brighter loops. For the first time, we present a systematic survey
of the temperatures and emission measures of the soft X-ray material
above sunspots. Sunspots always contain the lowest temperatures and
emission measures in the active regions. The mean umbral temperature
is 1.8×106 K, and the mean penumbral temperature is
2.4×106 K. The mean umbral and penumbral emission measures
are logEM=26.60 cm-5 and logEM=27.00 cm-5,
respectively. The differences between the umbral and penumbral plasma
temperatures are physically significant. The higher penumbral values
imply that the loops associated with the penumbrae are generally hotter
and denser than the loops associated with the umbrae. The highest
sunspot temperatures and emission measures are still lower than the
average active region parameters but higher than the quiet-Sun plasma
parameters. The coronal radiative energy loss rate above the umbrae
is 15% higher than the radiative loss rate of the quiet-Sun plasma
but a factor of 8.3 lower than the typical active region radiative
loss rate. The radio emission comes from the gyroresonance mechanism,
and, as expected, it is sensitive to the magnetic field rather than
the soft X-ray-emitting plasma.
Title: Microwave Enhancement in Coronal Holes: Statistical Propeties
Authors: Gopalswamy, N.; Shibasaki, K.; Salem, M.
Bibcode: 2000JApA...21..413G
Altcode:
No abstract at ADS
Title: Microwave/Millimeter Wavelength Bursts with Simple Spiky
Time Profiles
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Sakurai, T.
Bibcode: 2000SPD....31.0242K
Altcode: 2000BAAS...32..818K
We report the detection at 17 and 34 GHz of microwave and millimeter
bursts which have simple spiky time profiles similar to those found to
be common at λ = 3 mm. These bursts are of short duration, with fast
2 - 4 sec rise time to peak, followed by an exponential decay. These
bursts can be of any intensity, from 1 sfu to 10's of sfu; they are
very strongly polarized (> 50%), and they have similar properties
regardless of the nature of the active region in which the bursts
originate. The bursts seem to originate in compact sources which are
generally unresolved with 15" and 7" resolution of the Nobeyama Radio
Heliograph at 17 and 34 GHz respectively. We provide both direct and
indirect evidence that these compact sources are low-lying bipolar
loops. The direct evidence follows from the physical appearance of
the loop as well as from the bipolar nature of the loop. The indirect
evidence follows from the offset in position of the footpoint emission
in microwaves and hard X-rays, implying a compact asymmetric loop with
microwaves originating from the stronger magnetic field foot point
and the hard X-rays originating from the weaker field foot point.
Title: Microwave tomography of solar magnetic fields
Authors: Grebinskij, A.; Bogod, V.; Gelfreikh, G.; Urpo, S.;
Pohjolainen, S.; Shibasaki, K.
Bibcode: 2000A&AS..144..169G
Altcode:
We present a new technique for the measurement of magnetic fields in
the solar chromosphere - corona through observations of its free-free
microwave emission in intensity and polarization. We derive the
decoupled radiation transfer equations for Stoke's parameters of I
and V for circular polarized emission in plane-layer inhomogeneous
atmospheres and present a model solutions of inversion problem. We
discuss the discrimination between contributions from the corona and
the chromosphere to the observed brightness spectra from the quiet
Sun and plage regions and propose a practical method of magnetic
field estimates, which was used both with single frequency (the
Nobeyama Radioheliograph at 17 GHz) and multi frequency (RATAN at 1 -
16 GHz) observations and discuss the preliminary results. The proposed
techniques may be useful as microwave magnetography at the corona base
and for checks and improvements in the current problem of extrapolating
magnetic fields from photosphere to corona.
Title: The X-ray telescope on Solar B.
Authors: Deluca, E. E.; Golub, L.; Bookbinder, J.; Cheimets, P.;
Shibasaki, K.; Sakao, T.; Kano, R.
Bibcode: 2000BAAS...32..827D
Altcode:
No abstract at ADS
Title: The X-Ray Telescope on Solar B
Authors: DeLuca, E. E.; Golub, L.; Bookbinder, J.; Cheimets, P.;
Shibasaki, K.; Sakao, T.; Kano, R.
Bibcode: 2000SPD....31Q0293D
Altcode:
The X-ray observations from the Yohkoh SXT provided the greatest
step forward in our understanding of the solar corona in nearly two
decades. We believe that the scientific objectives of the Solar-B
mission can best be achieved with an X-ray telescope (XRT) similar to
the SXT, but with significant improvements in spatial resolution and in
temperature response that take into account the knowledge gained from
Yohkoh. We present the scientific justification for this view, discuss
the instrumental requirements that flow from the scientific objectives,
and describe the instrumentation to meet these requirements. XRT is
a grazing-incidence (GI) modified Wolter I X-ray telescope, of 35cm
inner diameter and 2.7m focal length. The 2048x2048 back-illuminated
CCD has 13.5&mu pixels, corresponding to 1.0 arcsec and giving
full Sun field of view. This will be the highest resolution GI X-ray
telescope ever flown for Solar coronal studies, and it has been designed
specifically to observe both the high and low temperature coronal
plasma. A small optical telescope provide visibles light images for
coalignment with the Solar-B optical and EUV instruments. The US XRT
team is support by a NASA Contract from MSFC.
Title: Microwave Observation of Eruptive Solar Events with and
without Flare Activity
Authors: Hori, K.; Kosugi, T.; Fujiki, K.; Koshiishi, H.; Shibasaki, K.
Bibcode: 2000ApJ...533..557H
Altcode:
We present microwave (17 GHz) observations of eruptive activity in four
solar coronal events with the Nobeyama Radioheliograph. These are weak
events occurring at or near the solar limb associated with several
types of activity: polar crown activity, prominence eruptions, and
arcade flares. The morphological evolutions of the microwave sources in
these events show the following characteristic features in common. The
activity starts as a mound-shaped source (1.0-4.5×104
km in height), above which a compact blob (<=1.0×104
km in size) appears later and expands horizontally toward the top
of another low-lying mound. Finally a faint arch with a filamentary
structure is formed, bridging the two mounds (0.2-2.0×105
km in horizontal scale size). Thus, the activity seems to propagate
through the arch corridor from the initially activated mound to
the secondary. During this process, the activity level increases, as
indicated by an increase of the brightness temperature of the mound and
the blob as well as by the formation of the arch and the eruption of
the blob. These common features suggest that basically the same energy
buildup and release process takes place in all four events, in spite
of the large difference in the total released energy. Here we propose
magnetic reconnection progressing in between the blob and the mound
as the basic process, as indicated by high-temperature plasma there,
seen in soft X-rays. Our findings support a theoretically predicted
analogy between filament (or prominence) activity and flare onset.
Title: Magnetic Trapping and Electron Injection in Two Contrasting
Solar Microwave Bursts
Authors: Lee, J.; Gary, Dale E.; Shibasaki, K.
Bibcode: 2000ApJ...531.1109L
Altcode:
We study two microwave bursts (which occurred about 12 minutes apart
in the same active region) that show contrasting characteristics
in morphology and spectral variation in microwave data from the
Owens Valley Radio Observatory (OVRO) Solar Array and the Nobeyama
Radioheliograph (NoRH). The first flare (X-ray class C2.8, 23:22 UT)
shows radio morphology that changes from a single source at a low
frequency (5 GHz) to a double source at high frequencies (10-17 GHz),
and shows a total power spectrum that hardens in the decay phase. In
contrast, the second flare (X-ray class M1.0, 23:35 UT) shows a simple,
single-source morphology at 7-17 GHz. This source is located at one
of the two footpoints of a small loop identified in Yohkoh/HXT maps,
and its spectrum evolves in a typical soft-hard-soft pattern. We infer
the trap properties of these two loops from the microwave spectral
behaviors and a coronal field extrapolation from the vector magnetogram
of the active region obtained from Mees Solar Observatory, along
with X-ray maps obtained from Yohkoh/SXT. It is shown that the radio
characteristics of the first event are consistent with the hypothesis
in which Coulomb collisions dominate in a highly anisotropic loop with
low ambient electron density ~5x109 cm-3. The
second flare involves a small loop in which a more uniform field
strength allows rapid loss of electrons by precipitation, resulting
in a spectral variation mainly controlled by the energy dependence and
time profile of the injection. In spite of the significantly differing
decay times (~8 and ~1 minutes, respectively), very similar injection
times of ~30 s are inferred from the analysis of time profiles under
the above hypotheses. We therefore present a view that the largely
different morphologies and the corresponding spectral variations are
consequences of the differing trap properties rather than dissimilar
injection properties. The low trap density inferred for the first event
(~5x109 cm-3) as compared with the second event
(~8x1010 cm-3) also explains why this event
showed richer microwave output in spite of weaker GOES activity.
Title: Solar Microwave Large-Scale Bright Structures Observed with
the Nobeyama Radioheliograph
Authors: Chertok, I.; Shibasaki, K.
Bibcode: 2000AdSpR..25.1901C
Altcode:
The analysis of the Nobeyama radio heliograms at 17 GHz with
a restricted range of the brightness temperature revealed a
new phenomenon of the large-scale solar activity: microwave blob
chains with characteristic sizes comparable with the solar disk
diameter. The blobs consisting the chains have angular sizes of 30-60
arcseconds and the brightness temperature of Tb ~ (11 -
15) × 103 K. Long-living chains exist over many days and
may coincide with sharp boundaries of coronal holes, observed with
Yohkoh/SXT. Transient microwave chains with a time scale of tens of
hours appear to be associated with coronal mass ejections revealed by
long-duration events in the soft X-ray and microwave range
Title: Nonthermal Flare Emission from MeV-Energy Electrons at 17,
34, and 86, GHz
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.; Sakurai, T.
Bibcode: 2000ASPC..206..307K
Altcode: 2000hesp.conf..307K
No abstract at ADS
Title: The Roots of Sigmoidal Structures with SOHO - Microwave
Observations
Authors: Bogod, V. M.; Grebinskij, A. S.; Shibasaki, K.
Bibcode: 2000IAUJD...7E...8B
Altcode:
Sigmoidal patterns of soft X-ray coronal loops are often related with
CME's and eruptive activity. We study the origins of such structures
throughout photosphere to corona, with Stanford's magnetogram of
background photospheric fields, high resolution SOHO/MDI magnetography
of AR's, and combined RATAN-600 (1.5 - 16 GHz) and Nobeyama (17 GHz)
spectral-polarization microwave observations. We discovered, that most
of reported sigmoidal structures are closely related with presence of
chains of opposite polarity magnetic islands, displayed with Stanford's
magnetogram of background fields. Coronal sigmoidal loops are rooted at
such islands, and are energized with electric currents. We identified
small regions of intermixed fields at every sigmoid roots location with
SOHO/MDI and microwaves radio-magnetography, both at photosphere and
chromosphere levels as origin of vertical electic currents. Whirling
motions of photospheric magnetic islands may explain basic patterns of
observed sigmoidal loops twist. Combined optical-microwave observations
points on complicated nature of global and fine-scale structures in
sigmoid's associated magnetospheres, further study are needed to clarify
a possible relation of Stanford's magnetic chains with CME's onset.
Title: Microwave and Extreme Ultraviolet Observations of Solar
Polar Regions
Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Gary, D. E.;
Shibasaki, K.; Dere, K. P.
Bibcode: 1999ApJ...527..415N
Altcode:
The poles of the Sun are brighter than the rest of the quiet Sun's
emission in a limited range of radio frequencies from 17 GHz to 87
GHz. We have studied microwave images of the quiet Sun made with
the Nobeyama radioheliograph at 17 GHz. They show that the so-called
polar-cap brightening consists of two components: a diffuse component
of 1500 K excess brightness and patchy compact sources with localized
excess brightness of about 3500 K. We test the reality of the compact
sources using the maximum entropy method deconvolution. The total flux
and the number of compact polar sources as well as the north-south
extent of the diffuse polar emission are larger in the pole that is
closest to the Earth. We compared the microwave polar emission with
nearly simultaneous SOHO EIT images taken in the lines of He II at 304
Å and Fe XII at 195 Å. No one-to-one correlation between the compact
radio sources and the bright EUV features was found: most of the radio
emission arises between the plumes visible to EIT. The boundaries of
the polar-cap brightenings did not match exactly the boundaries of the
coronal holes as seen in either the Fe XII 195 Å images or the He II
304 Å images. The temporal variations of the compact microwave sources
did not correspond to any significant changes in EUV emission. On the
other hand, most He II 304 Å changing features were associated with the
diffuse polar microwave emission, which was practically constant. Our
data suggest that the origin of the polar brightening is not coronal;
it seems that the bulk of the patchy radio emission comes from heights
below the 80,000 K layer.
Title: A Microwave Study of Coronal and Chromospheric Ejecta
Authors: Nindos, A.; Kundu, M. R.; Raulin, J. -P.; Shibasaki, K.;
White, S. M.; Nitta, N.; Shibata, K.; Shimojo, M.
Bibcode: 1999spro.proc..135N
Altcode:
We have studied the radio properties of 18 X-ray coronal jets (observed
by the Yohkoh SXT) using Nobeyama 17 GHz data. We also searched for
chromospheric ejecta (Hα surges) during the time intervals that the
X-ray images were available. Microwave emission was associated with the
majority of the X-ray jets. The radio emission came from the base or
the lower part of the jets. We detected radio emission from almost all
jets which showed flare-like activity at their footpoints. The 17 GHz
time profiles were gradual and unpolarized, implying that the emission
was thermal. When possible, we computed the physical properties of the
X-ray-emitting ejected plasma. In one two-sided-loop type jet and one
anemone-type jet, the observed microwave fluxes from the lower part of
the jets were well above the fluxes predicted from the computed electron
temperatures and emission measures of the soft X-ray-emitting material
on the basis of thermal free-free emission. We interpreted the large
discrepancies in terms of the presence of lower temperature material
which cannot be detected by the SXT but produces strong microwave
free-free emission. This is the first time that such material is
observed in two-sided-loop type jets. Thus our observations confirm the
theoretical prediction by Yokoyama and Shibata (1996). We detected no
cool material at the base of the jets. We also observed an Hα surge
which was not associated with an X-ray jet and showed no signatures on
the SXT images but was detected with the Nobeyama Radioheliograph. The
emission of the microwave surge-associated source was free-free from the
chromospheric plasma. Constraints for the surge density were derived.
Title: 17 GHz Mode Coupling in the Solar Corona
Authors: Lara, A.; Gopalswamy, N.; Pérez-Enríquez, R.; Shibasaki, K.
Bibcode: 1999spro.proc...83L
Altcode:
We studied the development of microwave polarization of a group
of active regions for a period of 10 days during April, 1993 using
data obtained by the Nobeyama radioheliograph. The observed sense
of polarization at 17 GHz changed with the active region position on
the solar disk. This change of polarization can be explained by the
mode coupling theory according to which a weak coupling between the
ordinary and extraordinary electromagnetic modes takes place when the
radiation crosses a region of transverse magnetic field and results in
a polarization reversal. Since the strength of the mode coupling depends
on the physical parameters (and their gradients) of the quasi-transverse
region, observations of polarization changes can be used to obtain key
values of the magnetic field and field gradient in the active region
corona. Using the intensity and polarization images of active regions,
we found that the coupling constant is typically > 103
corresponding to a weak coupling regime. We determined the mean
value of the transition frequency to be ~ 5.3 × 1011
Hz, below which the weak coupling effect is important. For all the
active regions studied in this paper, there seems to be a similarity
in the position on the solar disk where the mode coupling effects
become important. The polarization reversal always occurred when the
active regions were farther than the 500 arc sec mark from the disk
center. Using this fact and extrapolated photospheric magnetic field
we are able to estimate heights of both the quasi-transverse layer
and the source region. Assuming a value of ~ 70 G, we obtain a value
of 2.2 × 104 km for the Q-T layer height.
Title: Microwave Measurements of the Solar Magnetic Fields at
Chromosphere-Corona
Authors: Grebinskij, A.; Shibasaki, K.; Zhang, H.
Bibcode: 1999spro.proc...59G
Altcode:
We present new techniques for measurements of magnetic fields in
solar chromosphere - corona by observations its free-free microwave
emission in intensity and polarization. We discuss the results of
such measurements with Nobeyama imaging at ν =17 GHz and Beijing
vector magnetograph for typical photospheric active region structures
(isolated spots, plages, bipolar active regions). We discovered strong
differences of photospheric and chromospheric field patterns and discuss
possible explanations. These results may be useful for problems of 3D
reconstruction of magnetic fields through its photospheric boundary
values extrapolations.
Title: Solar Physics with Radio Observations
Authors: Bastian, T. S.; Gopalswamy, N.; Shibasaki, K.
Bibcode: 1999spro.proc.....B
Altcode:
Radio observations contribute a unique perspective on the many physical
phenomena, which occur on the Sun. From thermal bremsstrahlung emission
in the quiet solar atmosphere and filaments, to thermal gyroresonance
emission in strongly magnetized solar active regions, to the nonthermal
emission from MeV electrons accelerated in flares, observations of radio
emission provide a powerful probe of physical conditions on the Sun and
provide an additional means of understanding the myriad phenomena which
occur there. Moreover, radio observing techniques have led the way in
developing and exploiting Fourier synthesis imaging techniques. The
Nobeyama Radioheliograph, commissioned in June, 1992, soon after the
launch of Yohkoh satellite in August, 1991, is the most powerful,
solar-dedicated Fourier synthesis in the world, now capable of imaging
the full disk of the Sun simultaneously at frequencies of 17 and 34
GHz, with an angular resolution as much as 10" and 5", respectively,
and with a time resolution as fine as 100 msec. Between 27-30 October,
1998, the Nobeyama Radio Observatory and the National Astronomical
Observatory of Japan hosted the Nobeyama Symposium on Solar Physics
with Radio Observations, an international meeting bringing more than
sixty participants together at the Seisenryo Hotel in Kiyosato, for a
meeting devoted to reviewing recent progress in outstanding problems
in solar physics. Emphasis was placed on radio observations and,
in particular, radio observations from the very successful Nobeyama
Radioheliograph. These results were compared and contrasted with those
that have emerged from the Yohkoh mission. In addition, looking forward
to the next solar maximum, new instruments, upgrades, and collaborative
efforts were discussed. The result is the more than seventy invited
and contributed papers that appear in this volume.
Title: Radio Magnetography of Solar Active Regions Using Radio
Observations
Authors: Gelfreikh, G. B.; Shibasaki, K.
Bibcode: 1999ESASP.448.1339G
Altcode: 1999ESPM....9.1339G; 1999mfsp.conf.1339G
No abstract at ADS
Title: Microwave Observations of the Quiet Sun
Authors: Shibasaki, K.
Bibcode: 1999spro.proc....1S
Altcode:
Recent quiet sun observations in microwave regions are reviewed. In the
review, the mechanism of radio emission (thermal free-free) from the
quiet sun and atmosphere models of the quiet sun are summarized. The
models are compared with the observations of the frequency spectrum
of the disk center brightness temperature and of the center-to-limb
variations. Then the performances and limitations of the Nobeyama
Radioheliograph (NoRH) for studies of the quiet sun are summarized. By
stressing the results from the NoRH, several observational features
of the quiet sun are summarized. Coronal holes and the polar cap
brightening are particularly interesting subjects. It is shown that
the NoRH is a powerful tool for quiet sun studies.
Title: Observations of Oscillations in Solar Active Regions using
Radio Observations
Authors: Gelfreikh, G. B.; Shibasaki, K.
Bibcode: 1999ESASP.448..197G
Altcode: 1999ESPM....9..197G; 1999mfsp.conf..197G
No abstract at ADS
Title: Observational Evidence of Ballooning Instabilities in a
Solar Flare
Authors: Shibasaki, K.
Bibcode: 1999spro.proc..419S
Altcode:
Radio imaging observation of a solar flare on January 2, 1993, showed
the formation isolated radio sources over the loop top of a flaring
loop at several times during the flare development. In this paper, it
is suggested that these isolated loop-top radio sources are magnetic
islands or balloons produced by nonlinear ballooning instabilities
due to the high β plasma in the loop. The plasma β is estimated by
combining the total flux soft X-ray data, and radio brightness and
circular polarization data. The upper boundaries of magnetic loops
with high β plasma are unstable against the ballooning instability
because of unfavorable curvature (convex outward). A new energy
transfer scenario in flares is proposed based on this ballooning
instability. It is also pointed out that the centrifugal acceleration
caused by thermal motion in the curved magnetic line of force far
exceeds the surface gravity and can sustain hot and dense plasma at
the top of the elongated loop.
Title: Nobeyama Radioheliograph Data on Dynamics of Microwave
Counterparts of Giant Post-Eruptive Soft X-ray Arches
Authors: Chertok, I. M.; Fomichev, V. V.; Gorgutsa, R. V.; Hildebrandt,
J.; Krüger, A.; Shibasaki, K.
Bibcode: 1999spro.proc..203C
Altcode:
The dynamics of a number of giant post-eruptive arches in several
near-the-limb events is studied using the Nobeyama Radioheliograph
data at 17 GHz in comparison with observations of the Yohkoh Soft X-ray
Telescope. It is found that the leading front and the brightest part of
some microwave arches rise in the corona with a characteristic speed
of 1--4 km/s, coinciding with that of soft X-ray arches, and lift to
altitudes of at least about of 140,000 of km.
Title: Large-Scale Shining Chains on the Solar Disk: Nobeyama
Radioheliograph Data
Authors: Chertok, I. M.; Shibasaki, K.
Bibcode: 1999spro.proc..175C
Altcode:
Consideration of the Nobeyama radioheliograms at 17 GHz with a
restricted range of the brightness temperature (Tb≈
(5-20)× 103 K) revealed a novel phenomenon of the
large-scale solar activity: long-living (days) and transient (hours)
microwave shining chains of characteristic sizes comparable with the
solar disk diameter and consisting of 30--60'' blobs.
Title: Temporal and Spatial Evolution of Microwave Spikes Observed
by Beijing and Nobeyama Observatories
Authors: Fu, Q.; Huang, G.; Shibasaki, K.; Nakajima, H.; Liu, Y.
Bibcode: 1999spro.proc..273F
Altcode:
Preliminary results of an analysis of data with high spatial
resolution and high temporal resolution are presented for the event
of May 14, 1993. Observations were made with the three-channel 10 cm
band radiotelescope of the Beijing Astronomical Observatory (BAO) and
simultaneously with the Nobeyama Radioheliograph (NoRH) at 17 GHz. The
results show that the microwave spike emission was produced in a region
with lower brightness temperature, high degree of polarization, high and
compact magnetic field and small dimension. The microwave spike emission
has a frequency drift rate of more than 30 GHz/s and in X-mode. These
results are consistent with the mechanism of electron cyclotron maser
(ECM) instability.
Title: Microwave Enhancement in Coronal Holes: Structure, Variability
and Magnetic Nature
Authors: Gopalswamy, N.; Shibasaki, K.
Bibcode: 1999STIN...0011601G
Altcode:
The microwave enhancement in coronal holes in comparison with the
quiet Sun is a distinct and easily observed signature related to the
magnetic activity. This has proven to be a new tool to study the
solar atmospheric layer where the fast solar wind originates. We
have developed a catalog of a large number of coronal holes using
images obtained by SOHO's Extreme-ultraviolet Imaging Telescope in
EUV and by the Nobeyama radioheliograph in microwaves. We also have
high resolution longitudinal magnetograms obtained by SOHO's Michelson
Doppler Imager. We present the statistical properties of the microwave
enhancements and discuss the small-scale dynamics as revealed by the
magnetograms and radioheliograms. We also discuss the geoeffectiveness
of these coronal holes.
Title: Multiple Components in the Millimeter Emission of a Solar Flare
Authors: Raulin, J. -P.; White, S. M.; Kundu, M. R.; Silva, A. V. R.;
Shibasaki, K.
Bibcode: 1999ApJ...522..547R
Altcode:
We analyze a small flare using imaging data at millimeter, microwave,
and soft X-ray wavelengths and microwave and hard X-ray spectral
observations. The remarkable aspect of this flare is evidence for
the presence of MeV-energy electrons, which are responsible for the
nonthermal millimeter emission, at a time when no hard X-rays from
lower energy electrons are detected. This occurs during a smoothly
varying phase, which is seen at radio wavelengths to last several
minutes and is the brightest phase at millimeter wavelengths but is
undetected in hard X-rays: it follows a brief spike of emission at
flare onset, which has the more usual properties of impulsive events and
features nonthermal microwave, millimeter, and hard X-ray emission. We
interpretthe phase that is brightest at millimeter wavelengths as being
due to efficient trapping of a relatively small number of nonthermal
electrons, whereas during the hard X-ray emission, trapping is much
less efficient, and the decay time is much shorter at all energies,
which leads to a larger ratio of hard X-ray flux to radio flux. As
in many previous events studied at millimeter wavelengths, there is a
discrepancy between the electron energy spectral indices inferred from
the milllimeter and hard X-ray data during the impulsive phase when both
are detected: again it appears that the energy spectrum at 1 MeV must be
significantly flatter than at several hundred keV and below. However,
there are problems in reconciling quantitatively the energy spectra
for the hard X-ray-emitting and radio-emitting components: based on
the most plausible parameters, the radio-emitting electrons should
produce most of the hard X-rays. One solution to this contradiction
is to invoke a coronal magnetic field stronger than seems likely based
on the photospheric magnetic field.
Title: A Microwave Study of Coronal Ejecta
Authors: Kundu, M. R.; Nindos, A.; Raulin, J. -P.; Shibasaki, K.;
White, S. M.; Nitta, N.; Shibata, K.; Shimojo, M.
Bibcode: 1999ApJ...520..391K
Altcode:
Using Nobeyama 17 GHz data, we have studied the radio properties of
19 coronal jets identified in Yohkoh soft X-ray imaging telescope
(SXT) X-ray observations. The radio data provide information on the
physical conditions in the jets, which complements the data from the
X-ray surveys. Microwave emission was associated with the majority of
the X-ray jets in our sample. The radio emission typically came from
the base or the base and lower part of the jets. We detected radio
emission from almost all jets that showed flarelike activity at their
bases. The jets that were not associated with radio emission did not
show any significant increase in X-ray emission at their bases. The
strongest radio emission came from two of the largest jets in our
sample. Our data show a general correlation between the X-ray jet
fluxes and the associated radio fluxes. The 17 GHz time profiles were
gradual and unpolarized, implying that the emission was thermal. In a
two-sided-loop jet (1992 July 22 event) and one anemone-type jet (1993
February 9 event), the observed microwave fluxes from the lower part
of the jets were well above the fluxes calculated from the computed
physical parameters of the soft X-ray-emitting material on the basis
of thermal free-free emission. We interpret the large discrepancies
in terms of the presence of lower temperature material, which cannot
be detected by the SXT (the SXT is most sensitive to hot plasma above
2×106 K), but which produces strong microwave free-free
emission. This is the first time that such material has been observed
in two-sided-loop-type jets. We also observed motion of a jet-associated
microwave source with a velocity of 55 km s-1. The microwave
motion occurred after the appearance of the X-ray jet. There is clear
evidence that the microwave emission of that source was associated
with the jet and not with the associated small flare.
Title: Is the chromosphere hotter in coronal holes?
Authors: Gopalswamy, N.; Shibasaki, K.; Thompson, B. J.; Gurman,
J. B.; Deforest, C. E.
Bibcode: 1999AIPC..471..277G
Altcode: 1999sowi.conf..277G
Coronal holes are brighter than the quiet Sun in microwaves. Microwave
emission from the quiet Sun is optically thick thermal bremsstrahlung
from the upper chromosphere. Therefore, the optically thick layer in the
coronal hole chromosphere must be hotter than the corresponding layer
in the quiet chromosphere. We present microwave and SOHO observations
in support of this idea. Because of the availability of simultaneous
EUV and microwave images it is now possible to obtain more details
of this enigmatic phenomenon. In this paper, we highlight the primary
properties of the microwave enhancement in coronal holes and point out
some related phenomena. Finally, we summarize the possible explanations
of the radio enhancement.
Title: Microwave and Extreme Ultraviolet Observations of Solar
Polar Regions
Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Gary, D. E.;
Shibasaki, K.; Dere, K. P.
Bibcode: 1999AAS...194.3207N
Altcode: 1999BAAS...31..871N
The radio emission of solar poles is brighter than the rest of the
quiet Sun's emission in a limited range of frequencies from 17 GHz to
87 GHz. We have studied microwave images of the quiet Sun made with
the Nobeyama Radioheliograph at 17 GHz. They show that the so-called
polar-cap brightening consists of two components: a diffuse component
of 1500 K excess brightness, and patchy compact sources with localized
excess brightness of about 3500 K. The total flux and the number of
compact polar sources as well as the North-South extent of the diffuse
polar emission are larger in the pole which is closest to the Earth. We
compared the microwave polar emission with nearly simultaneous SoHO EIT
images taken in the lines of He ii at 304 Angstroms and Fe xii at 195
Angstroms. No one-to-one correlation between the compact radio sources
and the bright EUV features was found: most of the radio emission arises
between the plumes visible to EIT. The boundaries of the polar-cap
brightenings did not match exactly the boundaries of the coronal holes
as seen in the Fe xii 195 Angstroms images. The temporal variations of
the compact microwave sources did not correspond to any significant
changes in EUV emission. On the other hand, most He ii 304 Angstroms
changing features were associated with the diffuse polar microwave
emission which was practically constant. Our data suggest that the
origin of the polar brightening is not coronal; it seems that the bulk
of the patchy radio emission comes from heights below the 80000 K layer.
Title: Microwave enhancement and variability in the elephant's trunk
coronal hole: Comparison with SOHO observations
Authors: Gopalswamy, N.; Shibasaki, K.; Thompson, B. J.; Gurman, J.;
DeForest, C.
Bibcode: 1999JGR...104.9767G
Altcode:
We report on an investigation of the microwave enhancement and its
variability in the elephant's trunk coronal hole observed during the
Whole Sun Month campaign (August 10 to September 9, 1996). The microwave
images from the Nobeyama radioheliograph were compared with magnetograms
and EUV images obtained simultaneously by the Michelson Doppler imager
and the extreme ultraviolet imaging telescope (EIT) on board the SOHO
spacecraft. The combined data set allowed us to understand the detailed
structure of the microwave enhancement in the spatial and temporal
domains. We find that the radio enhancement is closely associated
with the enhanced unipolar magnetic regions underlying the coronal
hole. The radio enhancement consists of a smooth component originating
from network cell interiors and a compact component associated with
network magnetic elements. When a minority polarity is present near
a majority polarity element, within the coronal hole, the resulting
mixed polarity region is associated with a bright-point-like emission
in coronal EUV lines such as the Fe XII 195 Å. These coronal bright
points are also observed distinctly in the EIT 304 Å band, but not
in microwaves. On the other hand, the lower-temperature line emission
(304 Å) and the microwave enhancement are associated with the unipolar
magnetic flux elements in the network. We found strong time variability
of the radio enhancement over multiple timescales, consistent with the
initial results obtained by SOHO instruments. The microwave enhancement
is most probably due to temperature enhancement in the chromosphere
and may be related to the origin of solar wind.
Title: A Microwave Study of Coronal Ejecta
Authors: Kundu, M. R.; Nindos, A.; Raulin, J. -P.; Shibasaki, K.;
White, S. M.; Nitta, N.; Shibata, K.; Shimojo, M.
Bibcode: 1999AAS...194.1704K
Altcode: 1999BAAS...31..853K
Using Nobeyama 17 GHz data, we have studied the radio properties
of 19 coronal jets identified in Yohkoh SXT X-ray observations. The
radio data provide information on the physical conditions in the jets
which complements the data from the X-ray surveys. Microwave emission
was associated with the majority of the X-ray jets in our sample. The
radio emission typically came from the base or the base and lower part
of the jets. We detected radio emission from almost all jets which
showed flare-like activity at their bases. The jets which were not
associated with radio emission did not show any significant increase
in X-ray emission at their bases. The strongest radio emission came
from two of the largest jets in our sample. Our data show a general
correlation between the X-ray jet fluxes and the associated radio
fluxes. The 17 GHz time profiles were gradual and unpolarized, implying
that the emission was thermal. In a two-sided-loop jet (July 22, 1992
event) and one anemone-type jet (February 9, 1993 event), the observed
microwave fluxes from the lower part of the jets were well above the
fluxes calculated from the computed physical parameters of the soft
X-ray-emitting material on the basis of thermal free-free emission. We
interpret the large discrepancies in terms of the presence of lower
temperature material which cannot be detected by the SXT (the SXT is
most sensitive to hot plasma above 2 x 10(6) K) but which produces
strong microwave free-free emission. This is the first time that
such material has been observed in two-sided-loop type jets. We also
observed motion of a jet-associated microwave source with a velocity
of 55 km/sec. The microwave motion occurred after the appearance of
the X-ray jet. There is clear evidence that the microwave emission of
that source was associated with the jet and not with the associated
small flare.
Title: Detection of Periodic Oscillations in Sunspot-Associated
Radio Sources
Authors: Gelfreikh, G. B.; Grechnev, V.; Kosugi, T.; Shibasaki, K.
Bibcode: 1999SoPh..185..177G
Altcode:
Using microwave observations made with the Nobeyama radioheliograph
(λ=1.76 cm), we have studied temporal variations of sunspot-associated
sources in the circularly polarized component. For all three cases
of well-developed and rather stable sunspots we found nearly harmonic
oscillations with periods in a range of 120-220 s. In one case of an
unstable and quickly devolving active region, the fluctuations appear
to be irregular with no dominant period. Sunspot-associated solar radio
sources are known to be generated by cyclotron radiation of thermal
electrons in magnetic tubes of sunspots at the level of the lower
solar corona or chromosphere-corona transition region (CCTR). At the
wavelength of 1.76 cm, the polarized emission arises in a layer where
the magnetic field is B=2000 G (assuming the emission generated at the
third harmonic of electron gyrofrequency). We suggest that the observed
effect is a manifestation of the well-known 3-min oscillations observed
in the chromosphere and photosphere above sunspots. The observed
effects are believed to be a result of resonance oscillation of MHD
waves inside a magnetic tube. Radio observations of this phenomenon
open a new tool for studying regions of reflection of MHD waves near
CCTR level. The method is very sensitive both to the height of the CCTR
and magnetic fields above sunspots. Thus, detection of oscillations
of the height of the transition region even with an amplitude of a
few km are possible. The use of a spectrum of one of the observed
sources obtained with the radio telescope RATAN-600 allows us to
conclude that oscillations in magnetic field strength of about 4 G
could be responsible for the effect and are reliably registered. The
appearance of the famous 5-min oscillations in the solar atmosphere
was also registered in some spectra of radio oscillations.
Title: Coronal Magnetography of an Active Region From Microwave
Polarization Inversion
Authors: Ryabov, B. I.; Pilyeva, N. A.; Alissandrakis, C. E.;
Shibasaki, K.; Bogod, V. M.; Garaimov, V. I.; Gelfreikh, G. B.
Bibcode: 1999SoPh..185..157R
Altcode:
The microwave circular polarization of the active region (AR) NOAA 7260
on 21-23 August 1992 is analyzed. Two-dimensional images at 1.76 cm
with spatial resolution of θ=10'' from the Nobeyama radioheliograph
and one-dimensional scans at 9 wavelengths in the range of 1.81-3.43
cm and θ=16.3''-31.1'' from the radio telescope RATAN-600 were
used. An inversion of the sense of circular polarization through
the wavelength range was recorded on 22 August. It is shown that
both the wavelength and the time dependence of the inversion are
consistent with quasi-transverse (QT) propagation of the radiation
in the solar corona. From this, the strength of the coronal magnetic
field in the active region was found to be H=20-65 G at a height of h=
(5.7-8.7)×109 cm above the photosphere on 22 and 30 August and 125
G at the lower height of (3.7-6.4)×109 cm on 23 August. We present a
new technique, based on the radio mapping (in both Stokes I and V) of
an AR undergoing circular polarization inversion; applying this method
to the Nobeyama data we obtained, for the first time, a magnetogram of
the coronal magnetic field. For AR 7260 we found values in the range of
70-100 G at heights of (4-6)×109 cm on 23 August, adopting a constant
value of N Lα (where N is the electron density and Lα is the scale
of the coronal field divergence) of 2.5×1018 cm−2. We compare our
results with force-free extrapolations of the photospheric magnetic
field from a MSFC magnetogram obtained on 20 August.
Title: Mesospheric Nitric Oxide and Ozone Measurements in Polar
Winter at 69°N
Authors: Iwagami, N.; Yamamoto, H.; Sekiguchi, H.; Watanabe, T.;
Suzuki, K.; Shibasaki, K.
Bibcode: 1999AdSpR..24.1665I
Altcode:
Two rocket experiments were carried out just before and after the polar
night at Andoya (69°N), Norway to investigate transport of nitric
oxide produced by auroral processes into the middle atmosphere and
its influence on the ozone chemistry. Nitric oxide densities of (2-5)
× 108cm-3 found in the 70-90 km region are one
to two orders of magnitude larger than those at middle latitudes. The
influence on ozone densities in the 70-90 km region due to such enhanced
nitric oxide abundance is found to be insignificant as compared to
that due to transport in the middle of February. The larger ozone
densities found in February (in spite of longer sunlit duration)
than in November in the 40-60 km region again support predominance of
transport over photochemical loss
Title: Measurements of O3 and N2O in Alaska
with a Tunable Diode Laser Heterodyne Spectrometer
Authors: Murata, I.; Fukuma, N.; Ohtaki, Y.; Fukunishi, H.; Kanzawa,
H.; Nakane, H.; Shibasaki, K.
Bibcode: 1999AdSpR..24.1623M
Altcode:
Total column amounts and vertical profiles of O3 and
N2O have been observed with a tunable diode laser heterodyne
spectrometer at Poker Flat, Alaska (65°N, 147°W) from February 17 to
March 10, 1997 and from April 1 to May 8, 1997. Poker Flat was usually
located outside the polar vortex during these early to late spring
periods, but sometimes located inside the vortex as in the cases of
March 10 and April 17. The correlation plots between O3 and
N2O show that O3 amount in the lower stratosphere
was chemically depleted inside the polar vortex
Title: Chromosphere magnetic field measurements by a microwave
free-free emission polarization, theory and observations.
Authors: Grebinskij, A.; Bogod, V.; Gelfreikh, G.; Shibasaki, K.;
Urpo, S.; Pohjolainen, S.
Bibcode: 1999joso.proc...95G
Altcode:
The authors present new techniques for measurements of solar magnetic
fields in solar chromosphere-corona by observations its microwave
emission in intensity and polarization. They discuss the results of
such measurements with Nobeyama imaging at λ = 1.76 cm for several
ARs on August 1992, December 13, 1992, August 1993 and June 9, 1995,
and compare results with Huairou vector magnetograph observations for
same ARs. The authors show close relations of peculiar microwave sources
and underlining magnetic structures at photosphere-chromosphere levels.
Title: Images of Gradual Millimeter Emission and Multi-Wavelength
Observations of the 17 august 1994 Solar Flare
Authors: Silva, Adriana V. R.; Lin, R. P.; de Pater, Imke; White,
Stephen M.; Shibasaki, K.; Nakajima, H.
Bibcode: 1998SoPh..183..389S
Altcode:
We present a comprehensive analysis of the 17 August 1994 flare,
the first flare imaged at millimeter (86 GHz) wavelengths. The
temporal evolution of this flare displays a prominent impulsive peak
shortly after 01:02 UT, observed in hard X-rays and at microwave
frequencies, followed by a gradual decay phase. The gradual phase was
also detected at 86 GHz. Soft X-ray images show a compact emitting
region (≲20''), which is resolved into two sources: a footpoint and
a loop top source. Nonthermal emissions at microwave and hard X-ray
wavelengths are analyzed and the accelerated electron spectrum is
calculated. This energy spectrum derived from the microwave and hard
X-ray observations suggests that these emissions were created by the
same electron population. The millimeter emission during the gradual
phase is thermal bremsstrahlung originating mostly from the top of
the flaring loop. The soft X-rays and the millimeter flux density
from the footpoint source are only consistent with the presence of a
multi-temperature plasma at the footpoint.
Title: Microwave measurements of solar magnetic fields at chromosphere
- corona.
Authors: Grebinskij, A.; Bogod, V.; Gelfrejkh, G.; Shibasaki, K.;
Fu, Qijun; Zhang, Hongqi
Bibcode: 1998ArBeS...4..101G
Altcode:
The authors present new techniques for measurements of solar magnetic
fields in solar chromosphere - corona by observations of its microwave
emission in intensity and polarization. They discuss the results with
Nobeyama imaging at λ = 1.76 cm for several ARs on Dec. 13, 1992,
Aug. 1993 and June 9, 1995, and compare the results with Huairou
vector magnetograph observations for the same ARs. The authors show
close relations of peculiar microwave sources and underlying magnetic
structures at photosphere - chromosphere levels.
Title: Polar thermosphere-stratosphere photochemical coupling
experiment: Two rocket measurements in polar winter at 69°N
Authors: Iwagami, N.; Yamamoto, H.; Yajima, K.; Sekiguchi, H.;
Watanabe, T.; Suzuki, K.; Shibasaki, K.; Amemiya, H.; Yamamoto, M.;
Ono, T.
Bibcode: 1998EP&S...50..745I
Altcode:
Two rocket experiments were carried out just before and after the polar
night at Andoya (69°N), Norway to investigate transport of nitric
oxide produced by auroral processes into the middle atmosphere and
its influence on the ozone chemistry. Nitric oxide densities of (2-5)
× 108 cm-3 found in the 70-90 km region are one
to two orders of magnitude larger than those at middle latitudes. The
measured density profiles appear to agree semi-quantitatively with
model simulations which includes auroral processes. The influence on
ozone densities in the 70-90 km region due to such enhanced nitric
oxide abundance is found to be still insignificant as compared to
that due to transport in the middle of February, one month after the
end of polar night and one month before the spring equinox. The larger
ozone densities found in February (in spite of longer sunlit duration)
than in November in the 40-60 km region again support predominance of
transport over photochemical destruction.
Title: The Filament Disappearance of 7 May 1992 (the Ebi)
Authors: Mouradian, Z.; Soru-Escaut, I.; Hiei, E.; McAllister, A. H.;
Shibasaki, K.; Ohyama, M.; Khan, J. I.; Uchida, Y.
Bibcode: 1998SoPh..180..313M
Altcode:
The 7 May 1992 filament disappearance in the low corona is analyzed. The
cool and hot components of this event are studied, using Hα, soft X-ray
and radio data. We first show the general effect of the disparition
brusque (DB) on the life of the filament, which was a quiescent filament
in the vicinity of an active region, and then give the history of the
development of the 7 May event. The main stages of the event are: (i)
the formation of hot arches spanning the cool filament; (ii) rise of
the filament, with plasma ejection into the corona, in which we note
some spreading of loops from the main body, with two distinct rising
velocity phases of the Hα filament; (iii) formation of X-ray arches
below the filament, the foot points of the arcades being two-ribbon
Hα flare patches. The dynamics of Hα and X-rays features are given.
Title: Solar radio emission, January - December 1988.
Authors: Shibasaki, K.
Bibcode: 1998QBSA...30....1S
Altcode:
The preparation of this Part V has been edited by Nobeyama Solar Radio
Observatory. Daily and monthly means of flux density are given for
the period January to December 1988.
Title: Solar radio emission, January - December 1987.
Authors: Shibasaki, K.
Bibcode: 1998QBSA...29....1S
Altcode:
The preparation of this Part V has been edited by Nobeyama Solar Radio
Observatory. Daily and monthly means of flux density are given for
the period January to December 1987.
Title: Multiwavelength Observations of a Coronal Hole
Authors: Gopalswamy, N.; Shibasaki, K.; Deforest, C. E.; Bromage,
B. J. I.; Del Zanna, G.
Bibcode: 1998ASPC..140..363G
Altcode: 1998ssp..conf..363G
No abstract at ADS
Title: Comparison of Microwave and SOHO Synoptic Maps of the Sun
During the Whole Sun Month, 1996
Authors: Gopalswamy, N.; Thompson, B. J.; Shibasaki, K.
Bibcode: 1998ASPC..140..401G
Altcode: 1998ssp..conf..401G
No abstract at ADS
Title: Microwave large-scale shining chains and their relation to
CME/LDE events
Authors: Chertok, I. M.; Shibasaki, K.
Bibcode: 1998cee..workE..29C
Altcode:
The analysis of the Nobeyama Radio Heliograph (NRH) data at 17 GHz
have revealed a new remarkable feature: an existence of large-scale
(comparable with the size of the solar disk) chains shining at
microwaves. Such chains can be seen clearly at the NRH images with
a restricted range of the brightness temperature (for example,
for Tb <= 2 times 104 K) when the most
intense sources are suppressed. The blobs consisting the chains
are characterized by the angular sizes of 30-60 arcseconds and
the brightness temperature of about Tb ~(11-15) times
103 K. At least two types of the microwave chains should
be distinguished. Firstly, there are so-called long-living chains
which exist and keep their general form during many days, stretch
from one active region to another remote active region/plage and
rotate together with these formations. The microwave chains of the
second type with a characteristic time scale of tens of hours appear
to be associated with coronal mass ejections (CMEs) and post-CME energy
release that are revealed, in particular, by long-duration events (LDEs)
in the soft X-ray and microwave ranges. In some cases, such events
are accompanied by strong changes of the form and location of the
pre-existing chains, especially near the LDE source. In other cases,
new chains and cells arise also in an extended region around the LDE
source. The comparison with other solar images and maps shows that
the form and location of the microwave chains (particularly, of the
long-living ones) may coincide with sharp boundaries of coronal holes,
observed with Yohkoh/SXT. They may outline also footpoint lines of some
large X-ray arcades and correspond to the general picture of large-scale
magnetic fields and filaments. In the latter case, the chains repeat
the form of the corresponding filaments but are located at considerable
distance from these filaments. These features mean that some large-scale
structures shine at microwaves as a result of energy release associated
either with long-term evolution of large-scale magnetic fields or with
disturbances of extended magnetic fields identified with CMEs. The
most probable mechanism responsible for the radio emission of the
blobs forming the chains is the thermal free-free emission. The more
detailed study of this phenomenon and especially detailed comparisons
with other solar images and magnetograms are in progress.
Title: Coronal magnetic-field changes of a strong, very fast
developing compact solar active region and related processes
Authors: Shibasaki, K.; Kosugi, T.; Bogod, V.; Garaimov, V.; Gelfreikh,
G.; Stepanov, A. V.; Kliem, B.; Hildebrandt, J.; Kruger, A.; Hofmann,
A.; Urpo, S.
Bibcode: 1998cee..workE..49S
Altcode:
We have studied the development of the large active region NOAA AR
7321, which suddenly appeared near the central meridian of the Sun,
during the first days of its remarkably fast evolution. To analyse the
structural and evolutional features of the magnetosphere of the active
region spatially resolved spectral-polarization observations of the
large Radioheliograph at Nobeyama (Japan), the RATAN-600 telescope at
Zelenchuk (Russia), and mm-wave data of the Metsahovi Radio Research
Station (Finland) have been used and compared with model calculations
of the radio emission. Our main goals concern the evolution of the
magnetic scale height above the sunspots centre deduced from the
gyromagnetic emission and its relation to the flare activity, as well
as the nature of the energy release responsible for the source of
long-duration coronal mm-wave radiation.
Title: Radio Synoptic Maps and Polar CAP Brightening
Authors: Shibasaki, Kiyoto
Bibcode: 1998ASPC..140..373S
Altcode: 1998ssp..conf..373S
No abstract at ADS
Title: Observational Evidences of Ballooning Instability in Solar
Flares
Authors: Shibasaki, K.
Bibcode: 1998cee..workE..62S
Altcode:
Radio imaging observation of the solar flare on January 2, 1993 showed
a formation process of radio sources over the flare loop (Shibasaki,
1996). In the present paper, we interpret this overtopping radio
sources as magnetic islands (or balloons) produced by a ballooning
instability due to high pressure (or high beta value) in the flare
loop. The overtopping radio sources appeared several moments in the
flare: 1) When a rising plasma cloud hit the apex of the loop, 2) when
the growing flare loop reached at its maximum height, and 3) a couple
of times after the well developed bright flare loop was formed. At
these moments, the plasma beta value was high, due to local enhancement
of the pressure by the collision of the rising plasma cloud with the
curved magnetic field at the loop apex 1), and by the collision of the
evaporated plasma flow through both legs of the loop at the loop top
2). After the formation of the bright flare loop, the loop was filled
with the evaporated high density plasma 3). Extensive studies have been
done of the stability of plasma loops in the solar corona (e.g. Bray
et al., 1991). In the field of fusion in magnetically confined plasma
such as Tokamak, detailed studies of the stability of the confined
plasma have been developed. Main difference between these two cases
is line-tying of the solar coronal magnetic fields. They are anchored
at the photosphere. Instabilities with low wave numbers (large scale)
are suppressed due to line-tying effect. However, instabilities with
high wave numbers can develop. Outer boundary of high density (beta)
flare loops are unstable against localized interchange instability
(ballooning mode) because the outer boundary has unfavorable magnetic
field curvature (convex outwards). Appearances of overtopping microwave
sources satisfy the above condition of the ballooning instability. The
overtopping sources are interpreted as magnetic islands (or balloon)
produced by the ballooning instability. Recent development of numerical
simulation made it possible to simulate nonlinear full 3D behavior of
the plasma in Tokamak machines under various conditions. The growth
of the ballooning mode under high beta condition was simulated and was
compared with the experiment by Park et al.(1995). In the experiment,
a strong local pressure bulge destroyed the flux surface and most of
the confined plasma escaped. During the disruption, nonthermal emission
was observed. Large magnetic islands were formed after the recovery of
the magnetic surface. This scenario is very attractive to solar flare
scenario, although the physical conditions are very different between
the two. It is necessary to do similar MHD simulation (nonlinear,
full 3D, resistive) for loops in the corona with high beta. With this
scenario, high temperature regions above flare loops, loop top hard
X-ray sources and high density plasmoid ejections which were found by
YOHKOH could be explained without reconnection above the flare loop.
Title: Radio magnetography of the solar active regions
Authors: Gelfreikh, G. B.; Shibasaki, K.
Bibcode: 1998cee..workE..39G
Altcode:
The observations of the solar magnetic fields is one of the most
important basics for study of all important processes in structuring
the solar atmosphere and most kinds of the release of the energy. The
radio methods are of the special interest here because they gain the
information on the magnetic field strength in the solar corona and
upper chromosphere where traditional optical methods do not work. The
construction of the Nobeyama radio heliograph opens a new era in
usage radio methods for solar radio magnetography due to some unique
property of the instrument: - The 2D mapping of the whole disk of the
sun both in I and V Stokes parameters with resolution of 10 arcsec. -
Regular observations (without breaks due to weather conditions),
eight hours a day, already for seven years. The most effective and
representative radio method of measuring the solar magnetic fields
is to use polarization measurements of the thermal bremsstrahlung
(free-free emission). It is applicable both to analysis of chromospheric
and coronal magnetic fields and presents information on longitude
component of the magnetic field strength in solar active regions. Three
problems are met, however: (i) One needs to measure very low degree of
polarization (small fraction of a percent); (ii) To get the real value
of the field the spectral data are necessary. (iii) While observing
an active region on the disk we have got the overlapping effects on
polarized signal of the chromospheric and coronal magnetic fields. To
get higher sensitivity the averaging of the radio maps over periods of
about ten minutes were used with the results of sensitivity on V-maps of
the order 0.1%. Observations for a number of dates have been analysed
(August 22, 1992, October 31, 1992; June 30, 1993, July 22,1994,
June 15, 1995 and some more). In all cases a very good similarity was
found of the polarized regions (V-maps) with the Ca^ + plages in form
and total coincidence with the direction of the magnetic fields on the
optical magnetograms of the same active regions. For rough estimation of
the magnetic field strength an a priory value of spectral index (n ~1)
was used with more or less reasonable result. The value of the longitude
component of the magnetic field is obtained using the solution of the
equation of transfer of the radio waves in thermal plasma, which can
be written in the form: B_l = frac{107}{lambda cdot n}cdot P%, where
spectral index n and degree of polarization P% are to be found from
observations. In case of coronal magnetic fields n = 2 for optically
thin structure, so the spectral data can be omitted. To make a more
detailed analysis including separate estimation for both chromospheric
and coronal magnetic field distributions we may use some additional
information from spectral (but one dimensional) observation made with
the RATAN-600 or Pulkovo radio telescope. Also methods of stereoscopy
are in some cases effective (in this case we need observations of a
stable active regions for several days). However, these methods will
be discussed in another paper. This work is supported by RFBR Grant
No. 96-02-16268 and GKNT 1.5.4.6. - program ''Astronomy''.
Title: Plasma Motion in Solar Flares Observed by the Radio-Heliograph
Authors: Shibasaki, K.
Bibcode: 1998ASSL..229..175S
Altcode: 1998opaf.conf..175S
No abstract at ADS
Title: Non-thermal microwave solar radio emission from
plage-associated coronal loops and their 3D modelling.
Authors: Korzhavin, A. N.; Kaltman, T. I.; Stepanov, A. A.; Gelfreikh,
G. B.; Shibasaki, K.
Bibcode: 1998joso.proc...92K
Altcode:
On September 20-29, 1996, there was SOHO, Yohkoh and Meudon joint
Observations of Filaments and Chromospheric Activity. The target
active region was observed also with RATAN-600 radiotelescoope and
Nobeyama radioheliograph in the frames of the SOHO ground-based support
program. This active region was very stable and its radio emission was
observed at least during five solar rotations. The authors present
some results of observations and their modelling. The observation
combined with the model show that there are the non-thermal processes
continuously acting in the solar corona in the period of deep minimum
of solar activity.
Title: Microwave tomography study of quiet and active chromospheres
Authors: Urpo, S.; Pohjolainen, S.; Grebinskij, A.; Bogod, V.;
Gelfreikh, G. B.; Shibasaki, K.
Bibcode: 1998cee..workE..25U
Altcode:
In recent VLA - Yohkoh (SXT) observations of quiet sun regions with
high (several arcs) resolution in the shortest microwave band (at
lambda = 1.3, 2.0 and 3.6 cm) were measured brightness contrasts above
magnetic network (Benz et al., 1996). Model simulations of observed
contrasts with current optical reference atmospheres (FAL, 1993) were
inconclusive. We use here the technique of multy frequency tomography
(Bogod and Grebinskij, 1997) in a wide range mm - cm band microwave
brightness observations for a quiet sun, plages and spots regions,
but with middle spatial resolution. Metsahovi observations at shortest
microwave band at lambda = 0.34, 0.39, 0.82, 1.35 and 2.59 cm (Urpo
et al, 1987) together with RATAN-600 observations at cm waves lambda =
1.8 - 30 cm gives a strong additional restrictions to atmosphere model
simulations from deep chromosphere to corona. We discuss the results
of such simulations, which leads to some common features of microwave
emissitivity of solar atmosphere at different scales of spatial
average. We show, that main contribution to microwave brightness
gives an optically thin hot plasma (with coronal temperatures), and
the chromosphere temperatures plasma, without transitional temperature
contribution. Such models, with a power-law temperature distribution in
chromosphere, gives good fit with observations at all microwaves range
at lambda = 0.3 - 30 cm. We use these results for study of polarization
radiation transfer in solar atmosphere and discuss observational results
with Nobeyama radio heliograph images of AR 7877 on June 1995 both
in intensity and polarization. This work is supported by INTAS Grant
No.95-0316 and partially by RFBR Grants No. 96-02-16598, 96-02-16268.
Title: The Filament Disappearance of may 7, 1992
Authors: Hiei, E.; Mouradian, Z.; Soru-Escaut, I.; McAllister, A. H.;
Shibasaki, K.; Ohyama, M.
Bibcode: 1998ASSL..229...95H
Altcode: 1998opaf.conf...95H
No abstract at ADS
Title: Microwave counterparts of rising soft X-ray post-flare
giant arches
Authors: Chertok, I. M.; Fomichev, V. V.; Gorgutsa, R. V.; Hildebrandt,
J.; Kruger, A.; Shibasaki, K.
Bibcode: 1998cee..workE..30C
Altcode:
Basing on Yohkoh/SXT images, v. Svestka et al. (1995) and v. Svestka
(1996) described a number of giant post-flare arches rising sometimes
with a constant speed of 1.1--2.4 km/s during more than 24 hours
up to altitudes of (250-300) times 103 km above the solar
limb. As a rule, these arches are associated with gradual long-duration
soft X-ray events (LDE) being a signature of coronal mass ejections
(CME). An analysis of the Nobeyama Radioheliograph (NRH) images at 17
GHz reveals the microwave counterparts of such soft X-ray arches. Some
so-called coronal millimeter wave sources (CMMS) appear to belong to the
same phenomenon (e.g., Urpo, Pohjolainen, and Kruger, 1994). We used
high-spatial-resolution (~10^{' '}) NRH data to study the dynamics of
a number of such radio arches. The analysis shows that their evolution
is rather complex reflecting particularly a three-dimensional character
of these structures. In the course of their development, the microwave
arches are extended also along the solar limb. They change their
internal structure and location of individual components. Some of these
components seem to remain approximately at fixed altitudes. However,
the leading front and the brightest part of some microwave arches rises,
especially during the initial phase of the events, with a characteristic
speed of 1--4 km/s that coincides with that of soft X-ray arches. At
some restricted time intervals, lifting of the arches in the microwave
and soft X-ray ranges display a good correspondence. The radio arches
at 17 GHz rise to altitudes of at least about 140 times 103
km. It should be added, that according to the modeling of Hanaoka
(1994), the observed microwave emission and spatial structure of
the arches corresponds as a whole to thermal free-free radiation of
optically thin plasma at 17 GHz with temperature and emission measure
derived from the Yohkoh/SXT images, although some differences take
place due to the multi-temperature plasma in the arches and different
emission conditions in the microwave and soft X-ray ranges.
Title: Detection of Microwave Emission from Coronal X-Ray Jets
Authors: Kundu, M. R.; Shibasaki, K.; Nitta, N.
Bibcode: 1997ApJ...491L.121K
Altcode:
We present evidence of the detection of microwave emission at 17 GHz in
association with coronal X-ray jets. We present two typical cases--one
on the disk (1995 March 31) and the other at the limb (1992 August
25). For the disk event we see 17 GHz emission from the upper part of
the jet base (active region loop or loops), but no emission from the
collimated X-ray jet itself, implying that it must be optically thin
at 17 GHz. For the limb event, we see the base of the jet as well as
the bottom part of the jet itself, implying that the optical depth is
higher at the bottom part (obviously because of higher electron density)
than at the top. We believe that the 17 GHz emission is thermal,
because it is gradual and unpolarized, and that the heating process
that gives rise to the jet X-ray plasma also results in the 17 GHz
emission. The calculated 17 GHz flux densities seem to agree with the
observed values within a factor of 2. We consider this disagreement
to be quite reasonable in view of the various uncertainties involved
in computing the emission in both radio and X-rays.
Title: Nobeyama/SOHO/BBSO Comparison of Solar Polar Coronal Holes
Authors: Gary, D. E.; Enome, S.; Shibasaki, K.; Gurman, J. B.; Shine,
R. A.
Bibcode: 1997SPD....28.0801G
Altcode: 1997BAAS...29..912G
Although it is not widely known outside the discipline of solar
radiophysics, a long-standing puzzle exists: the poles of the Sun
appear brighter than the rest of the quiet Sun in a restricted range
of wavelengths roughly from 15 GHz to about 48 GHz (cf. Kosugi et
al. 1986). At somewhat lower radio frequencies the poles appear darker
than the quiet Sun due to a deficit of coronal material, while at
mm-wavelengths the polar and non-polar quiet Sun appear quite uniform
due to the similarity of the atmospheric structure at lower heights
in the chromosphere. The excess brightness at the poles has also been
reported in coronal holes on the disk, and so is apparently related to
the phenomenon of coronal holes. The brightening likely corresponds to
an elevated temperature in the upper chromosphere in coronal holes
relative to normal quiet Sun. The phenomenon is especially well
suited to study via radio emission due to the unique sensitivity of
radio waves to this height range in the chromosphere. The possibility
exists that the different chromospheric structure for coronal holes
implied by the radio brightening may offer some clue to the origin of
the fast solar wind, which is now well established to arise in coronal
holes. Radio brightening of coronal holes is a difficult observational
problem because an instrument is needed that can image large areas of
the Sun at relatively high resolution. The Nobeyama Radioheliograph
has the required capability and operates at 17 and 34 GHz, nicely
within the frequency range where the brightening occurs. We compare
Nobeyama radio synthesis images on several days in 1996 with images
from the EIT, CDS, and MDI experiments on the Solar and Heliospheric
Observatory (SOHO) spacecraft, and with high resolution images from
the Big Bear Solar Observatory, with the aim of determining the spatial
and temporal characteristics of the brightening. We compare the extent
of the radio brightening with the boundaries of the coronal holes seen
from the SOHO data, to establish the previously suggested identity of
the polar brightening with coronal holes. We investigate whether the
brightening is primarily associated with network features, faculae,
or perhaps bipolar magnetic elements, or whether it is instead a
diffuse brightening more-or-less uniformly covering the coronal hole
area. We look for temporal variations, and their correlation with
changing features seen from SOHO. We conclude with some ideas for how
the chromospheric structure may be different in coronal holes than in
normal quiet Sun, and speculate on the implications for acceleration
of the fast solar wind.
Title: Microwave Radio Emission from Coronal X-ray Jets
Authors: Kundu, M. R.; Shibasaki, K.; Nitta, N.
Bibcode: 1997SPD....28.0142K
Altcode: 1997BAAS...29..887K
We report the first detection of microwave emission from coronal
X-ray jets using simultaneously obtained imaging data at 17 GHz
(Nobeyama Radioheliograph data) and in X-rays (Yohkoh/SXT data). We
present detailed results for one jet on the disk and another at the
limb. The 17 GHz emission in the disk event originates from the base
(a loop or a system of loops) of the jet, and for the limb jet the
microwave emission comes from the base as well as from a part of the
X-ray jet. We believe that the collimated jet is optically thin at 17
GHz in most cases. We have investigated more than two dozen jet events
and found 17 GHz emission in at least 70% of the cases. The 17 GHz
emission is unpolarized. We interpret the microwave emission as thermal,
related to the heating of the plasma responsible for the X-ray jet.
Title: Sunspot Gyroresonance Emission at 17 GHz: A Statistical Study
Authors: Vourlidas, A.; Gary, D. E.; Shibasaki, K.
Bibcode: 1997SPD....28.0134V
Altcode: 1997BAAS...29..885V
Our statistical study is based on a compilation of the daily Nobeyama
Radioheliograph full-disk maps obtained at 17 GHz between July 1992 --
December 1994. It includes 533 active regions, 20% of which appear to
have gyroresonance cores during some part of their disk crossing. At
least one of the regions reaches coronal temperatures (T>10(6)
K) while several others show a polarization reversal at the extreme
limb. Our study indicates that the gyroresonance cores are polarized
in the sense of the x-mode and are due to s=3 (B=2024 G) and/or s=4
(B=1518 G) gyroresonance absorption in the transition region and/or
corona. We also investigate the dependence between various physical
quantities such as brightness temperature, degree of polarization,
spot area, photospheric magnetic field and heliographic longitude and
comment on the polarization reversals at the limb. A more detailed
study of individual active regions, that have been also observed with
the Owens Valley Solar Array, will follow.
Title: An Upgrade of Nobeyama Radioheliograph to a Dual-Frequency
(17 and 34 GHz) System
Authors: Takano, Toshiaki; Nakajima, Hiroshi; Enome, Shinzo; Shibasaki,
Kiyoto; Nishio, Masanori; Hanaoka, Yoichiro; Shiomi, Yasuhiko;
Sekiguchi, Hideaki; Kawashima, Susumu; Bushimata, Takeshi; Shinohara,
Noriyuki; Torii, Chikayoshi; Fujiki, Kenichi; Irimajiri, Yoshihisa
Bibcode: 1997LNP...483..183T
Altcode: 1997cprs.conf..183T
The Nobeyama Radioheliograph, originally constructed as a 17 GHz
system, was upgraded into a dual-frequency system operating at 17
and 34 GHz on a time sharing basis. For each of the 84 antennas, a
frequency-selective sub-reflector, which reflects 17 GHz radio waves
into the Cassegrain focus while transmits 34 GHz waves into the primary
focus, was installed and a 34 GHz frontend receiver system was mounted
in parallel with the existing 17 GHz system. No major modification was
introduced to the backend system. Neither were antennas added nor their
arrangement changed. With this minimal modification, we have obtained
(1) an angular resolution of ∼5″ (at 34 GHz) and (2) a spectral
diagnostic capability of cm- to mm-wave emissions from solar flares
with temporal resolution up to 100 ms. Daily 8-hour (from ∼22:45
to ∼6:45 UT) operation at dual frequencies started late October,
1995. Final tuning of the new system, such as the calibration and
development of image synthesis software tools is still under way. Flare
images taken at the dual frequencies are presented and compared with
that from the Yohkoh SXT as an example.
Title: A Giant Prominence Eruption Observed by Nobeyama
Radioheliograph and YOHKOH Spacecraft
Authors: Gopalswamy, N.; Hanaoka, Y.; Kundu, M. R.; Shibasaki, K.;
Koshiishi, H.; Enome, S.; Lemen, J. R.
Bibcode: 1997IAUJD..19E...4G
Altcode:
The results of an investigation of a giant prominence which erupted from
the northwest limb of the Sun on 1994 April 05, will be reported. The
event could be traced back to a large prominence of March 19, 1994
above the east limb. The filament was located in the north-south
direction when it appeared on the disk. At about 23:00 UT on April 05,
the filament started slowly rising and then accelerated. The speed of
the prominence was was only 75 km s^{-1} when it reached a height of
about 0.5 R_ odot above the surface. Preliminary examination shows that
the eruption caused a geomagnetic storm on April 07 at 20:00 UT. We
study the dynamical and physical properties of the erupting prominence
and obtain physical parameters of the prominence plasma. In X-rays, the
region of eruption was relatively faint. After the eruption, however,
there was a large void at the previous location of the prominence and
an arcade formed progressively spreading from south to north along
the limb. Based on the X-ray and radio observations, we determine the
characteristics of the pre- and post-eruption structures.
Title: Coronal Magnetic Fields from Microwave Polarization
Observations
Authors: Alissandrakis, C. E.; Borgioli, F.; Chiuderi Drago, F.;
Hagyard, M.; Shibasaki, K.
Bibcode: 1996SoPh..167..167A
Altcode:
The solar active region (AR) 7530 was observed at 6 cm on July 3
and 4, 1993 with the Westerbork Synthesis Radio Telescope, using a
multi-channel receiver with very narrow bandwidth. We compare the
radio data with Yohkoh SXT observations and with the magnetic field
extrapolated from the Marshall vector magnetograms in the force-free
and current-free approximations. The comparison with soft X-rays shows
that, although a general agreement exists between the shape of the
radio intensity map and the X-ray loops, the brightness temperature,
Tb, obtained using the parameters derived from the SXT is
much lower than that observed. The comparison with the extrapolated
photospheric fields shows instead that they account very well for
the observed Tb above the main sunspots, if gyroresonance
emission is assumed. In the observation of July 4 an inversion and
strong suppression of the circular polarization was clearly present
above different portions of the AR, which indicates that particular
relationships exist between the electron density and the magnetic
field in the region where the corresponding lines of sight cross the
field quasi-perpendicularly. The extrapolated magnetic field at a
much higher level (∼ 1010 cm), satisfies the constraints
required by the wave propagation theory all over the AR. However,
a rather low electron density is derived.
Title: On the Spatial Directivity of Solar Radio Bursts
Authors: Pogodin, I. E.; Stupishin, A. G.; Shibasaki, K.
Bibcode: 1996SoPh..167..349P
Altcode:
In this paper, a new method of estimating the spatial directivity (in
the form of center-to-limb variation) of microwave burst emission is
proposed and derived. Estimations of radioemission directivity values
vs observation frequency are obtained. Results are compared to the
radio source model using an inhomogeneous magnetic field, source size
and particle density, and show a high degree of agreement. Values of
model parameters from earlier estimations are confirmed.
Title: Book reviews
Authors: Somov, B. V.; Shibasaki, K.; Moussas, X.
Bibcode: 1996SoPh..165..407S
Altcode:
No abstract at ADS
Title: Millimeter Observations of a B5.6 Flare
Authors: Raulin, J. -P.; White, S. M.; Kundu, M. R.; Silva, A. V. R.;
Shibasaki, K.
Bibcode: 1996AAS...188.4503R
Altcode: 1996BAAS...28..894R
We present millimeter imaging observations of a B5.6 flare which occured
on 1994 August 16 in the active region AR 7765. The BIMA interferometer
and the Nobeyama radioheliograph observed both the impulsive phase
and the thermal phase of the flare emission. The 3.5 mm maps obtained
with BIMA allowed us to determine the location of the radio source
and its properties at different phases of the flare evolution. In
X-ray wavelengths the impulsive phase was detected by the first two
channels of BATSE (25-50 keV, 50-100 keV); although YOHKOH/SXT did not
observe the impulsive phase, it was possible to image the post-flare
loop in soft X-rays. We compare the images of the flare at different
wavelengths and discuss the relevance of millimeter emission in the
context of flare models.
Title: Radio bursts above a sunspot
Authors: Shibasaki, K.
Bibcode: 1996AdSpR..17d.135S
Altcode: 1996AdSpR..17Q.135S
We have detected weak but frequent radio bursts above a major sunspot
in NOAA 7654 by the Nobeyama Radioheliograph at 17 GHz.
Title: First Images of a Solar Flare at Millimeter Wavelengths
Authors: Silva, Adriana V. R.; White, Stephen M.; Lin, Robert P.;
de Pater, Imke; Shibasaki, K.; Hudson, Hugh S.; Kundu, Mukul R.
Bibcode: 1996ApJ...458L..49S
Altcode:
We present the first high spatial resolution images of a solar flare
at millimeter wavelengths. On 1994 August 17, a GOES soft X-ray class
M1 flare was observed by the Berkeley-Illinois-Maryland Array at 86
GHz by the Nobeyama 17 GHz array and by the Yohkoh spacecraft. The
flare displayed both a prominent impulsive phase in microwaves and a
gradual phase that lasted over 30 minutes. The millimeter data were
taken only during the gradual phase. The millimeter images show a
source with a size of ~8", a peak brightness temperature of ~106 K,
and maximum optical depth of 0.09. At both X-ray and radio wavelengths,
the emitting region appeared to be compact (<~20"). In soft X-ray,
the images are resolved into two sources: one located at a footpoint
and the other at the top of the flaring loop. The millimeter emission
is consistent with the predicted free-free flux from an isothermal
temperature (~14 MK) loop-top source, a multitemperature footpoint
source with a hot (~22 MK), and a cold (~12 MK) component. Most (80%)
of the millimeter flux density originates from the top of the magnetic
loop, and the footpoint contribution is only 20%.
Title: Radio Source above a Flare Loop
Authors: Shibasaki, K.
Bibcode: 1996ASPC..111..171S
Altcode: 1997ASPC..111..171S
Faint radio sources were detected above the flare loop during the
M class event on 2 Jan 1993 by the Nobeyama radioheliograph. These
sources appeared several times during the flare associated with plasma
cloud motion. Flare loop and cusp shape formation processes were also
found. The energy transfer process in the flare is discussed in relation
to the appearance of the sources above the flare loop.
Title: Radio Imaging Observation of a Solar Flare Cusp
Authors: Shibasaki, K.
Bibcode: 1996mpsa.conf..205S
Altcode: 1996IAUCo.153..205S
No abstract at ADS
Title: Coronal Magnetic Fields from Polarization Observations at
Microwaves
Authors: Chiuderi Drago, F.; Borgioli, F.; Alissandrakis, C. E.;
Hagyard, M.; Shibasaki, K.
Bibcode: 1996mpsa.conf..443C
Altcode: 1996IAUCo.153..443C
No abstract at ADS
Title: Microwave and Hard X-Ray Observations of Footpoint Emission
from Solar Flares
Authors: Kundu, M. R.; Nitta, N.; White, S. M.; Shibasaki, K.; Enome,
S.; Sakao, T.; Kosugi, T.; Sakurai, T.
Bibcode: 1995ApJ...454..522K
Altcode:
We investigate radio and X-ray imaging data for two solar flares in
order to test the idea that asymmetric precipitation of nonthermal
electrons at the two ends of a magnetic loop is consistent with the
magnetic mirroring explanation. The events we present were observed in
1993 May by the HXT and SXT X-ray telescopes on the Yohkoh spacecraft
and by the Nobeyama 17 GHz radioheliograph. The hard X-ray images in
one case show two well-separated sources; the radio images indicate
circularly polarized, nonthermal radio emission with opposite polarities
from these two sources, indicating oppositely directed fields and
consistent with a single-loop model. In the second event there are
several sources in the HXT images which appear to be connected by
soft X-ray loops. The strongest hard X-ray source has unpolarized
radio emission, whereas the strongest radio emission lies over strong
magnetic fields and is polarized. In both events the strongest radio
emission is highly polarized and not coincident with the strongest
hard X-ray emission. This is consistent with asymmetric loops in
which the bulk of the precipitation (and hence the X-ray emission)
occurs at the weaker field footpoint.
Title: The Radio Properties of Solar Active Region Soft X-Ray
Transient Brightenings
Authors: White, S. M.; Kundu, M. R.; Shimizu, T.; Shibasaki, K.;
Enome, S.
Bibcode: 1995ApJ...450..435W
Altcode:
We present the results of a search for radio emission from active-region
transient brightenings identified in Yohkoh soft X-ray telescope
observations of active region AR 7260. We present detailed observations
of four events in which 17 GHz radio emission is clearly detected in
observations by the Nobeyama radioheliograph. The time profiles of
the 17 GHz data are very similar to those of the soft X-ray fluxes,
and the 17 GHz flux is very close to that expected from plasma with
the temperature and emission measure derived for the soft X-ray
emitting material from filter ratios. No impulsive nonthermal radio
emission was detected from any of the four events, although each was
at least GOES class B 1 in soft X-rays. Weak hard X-rays may have been
detected by GRO/BATSE from the strongest of the events, but not from
two others. These negative results leave open the possibility that
there is a difference between active region transient brightenings
and solar flares, in that the former do not convert a significant
amount of the released energy into accelerated electrons. However,
confirmation of this hypothesis will require a larger sample of events.
Title: Simultaneous Multifrequency Observations of an Eruptive
Prominence at Millimeter Wavelengths
Authors: Irimajiri, Yoshihisa; Takano, Toshiaki; Nakajima, Hiroshi;
Shibasaki, Kiyoto; Hanaoka, Yoichiro; Ichimoto, Kiyoshi
Bibcode: 1995SoPh..156..363I
Altcode:
Radio images and spectra of an eruptive prominence were obtained
from simultaneous multifrequency observations at 36 GHz, 89 GHz,
and 110 GHz on May 28, 1991 with the 45-m radio telescope at Nobeyama
Radio Observatory (NRO), the National Astronomical Observatory, Japan
(NAOJ). The radio spectra indicated that the optical depth is rather
thick at 36 GHz whereas it is thin at 89 and 110 GHz. The Hα data,
taken at Norikura Solar Observatory, NAOJ, suggest that the eruption of
an active region filament was triggered by an Hα flare. The shape and
position of the radio prominence generally coincided with those of Hα
images. The radio emission is explained with an isothermal cool thread
model. A lower limit for the electron temperature of the cool threads
is estimated to be 6100 K. The range of the surface filling factors
of the cool threads is 0.3-1.0 after the Hα flare, and 0.2-0.5 in the
descending phase of the eruptive prominence. The column emission measure
and the electron number density are estimated to be of the order of
1028 cm−5 and 1010 cm−3,
respectively. The physical parameters of a quiescent prominence are also
estimated from the observations. The filling factors of the eruptive
prominence are smaller than those of the quiescent prominence, whereas
the emission measures and the electron densities are similar. These
facts imply that each cool thread of the prominence did not expand
after the eruption, while the total volume of the prominence increased.
Title: New Nobeyama Radio Heliograph
Authors: Nakajima, H.; Nishio, M.; Enome, S.; Shibasaki, K.; Takano,
T.; Hanaoka, Y.; Torii, C.; Sekiguchi, H.; Bushimata, T.; Kawashima,
S.; Shinohara, N.; Irimajiri, Y.; Koshiishi, H.; Kosugi, T.; Shiomi,
Y.; Sawa, M.; Kai, K.
Bibcode: 1995JApAS..16..437N
Altcode:
No abstract at ADS
Title: Characteristics of Two Simple Microwave Bursts
Authors: Kundu, M. R.; White, S. M.; Nitta, N.; Shibasaki, K.;
Enome, S.
Bibcode: 1995LNP...444...75K
Altcode: 1995cmer.conf...75K
We present simultaneous microwave and X-ray data for two microwave
bursts with simple impulsive time profiles. The 17 GHz images show
compact sources, and in the one case for which we have simultaneous
soft and hard X-ray images, they also show compact sources coincident
with the radio source. One of the bursts is barely detected in soft
X-rays, yet has a moderate 17 GHz flux,.
Title: On the study of solar radio microbursts at 17 GHz
Authors: Pogodin, I. E.; Shibasaki, K.
Bibcode: 1995ARep...39...83P
Altcode:
No abstract at ADS
Title: Nobeyama Radio Observatory report, no. 361: The radio
properties of solar active region soft x-ray transient brightenings
Authors: White, S. M.; Kundu, M. R.; Shimizu, T.; Shibasaki, K.;
Enome, S.
Bibcode: 1995STIN...9529098W
Altcode:
We present the results of a search for radio emission from active-region
transient brightenings identified in Yohkoh Soft X-ray Telescope
observations of active region AR 7260. We present detailed observations
of four events in which 17 GHz radio emission is clearly detected in
observations by the Nobeyama Radioheliograph. The time profiles of
the 17 GHz data are very similar to those of the soft X-ray fluxes,
and the 17 GHz flux is very close to that expected from plasma with the
temperature and emission measure derived for the soft X-ray-emitting
material from filter ratios. No impulsive nonthermal radio emission
was detected from any of the 4 events, although each was at least
GOES class B1 in soft X-rays. Weak hard X-rays may have been detected
by GRO/BATSE from the strongest of the events, but not from two
others. These negative results leave open the possibility that there
is a difference between active region transient brightenings and solar
flares, in that the former do not convert a significant amount of the
released energy into accelerated electrons. However, confirmation of
this hypothesis will require a larger sample of events.
Title: Evolution of a Flare Source Inferred from Hard X-Ray and
Radio Observations: Solar Burst on 1992 October 27
Authors: Takakura, Tatsuo; Nishio, Masanori; Nakajima, Hiroshi; Enome,
Shinzo; Shibasaki, Kiyoto; Takano, Toshiaki; Hanaoka, Yoichiro; Kosugi,
Takeo; Sakao, Taro; Masuda, Satoshi; Makishima, Kazuo; Inda-Koide, Mika
Bibcode: 1994PASJ...46..653T
Altcode:
An impulsive burst which occurred on 1992 October 27 was observed
simultaneously with the hard X-ray telescope on board the Yohkoh
satellite and the Nobeyama Radioheliograph at 17 GHz. The hard X-ray
images show a double-source structure during the main phase. One
footpoint, A, shows a nonthermal spectrum, while another, B, shows
a better fit to the X-rays from extremely hot thermal electrons
with about 80 million degrees, flowing into the chromosphere. The
loop top also shows a better fit to a quasi-thermal spectrum of 75
million degrees at the main peak. On the other hand, the radio images
are a larger single source covering the X-ray source, and are highly
polarized in the L-sense. The larger single image is mainly ascribed
to the beamwidth, and the single polarization may be due to ``limiting
polarization". Consequently, the radio source at 17 GHz may be cospatial
with the X-ray source around the loop top. The radio emission at 17 GHz
and a part of the emission at 9.4 GHz are attributed to the thermal
gyro emissions from the extremely hot thermal electrons emitting the
X-rays. The rest of the radio emission at 9.4 GHz and the emission at
3.75 GHz are ascribed to thermal gyro emission at the outer layers
with smaller magnetic fields and lower electron temperatures. The
intense radio emission at 35 GHz at the main peak is ascribed to
gyro-synchrotron emission from the nonthermal electrons in footpoint A.
Title: Detection of 17 GHz Radio Emission from X-Ray--bright Points
Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.
Bibcode: 1994ApJ...431L.155K
Altcode:
Using observations made with the Nobeyama radio heliograph (NRH) at 17
GHz and the Yohkoh/SXT experiment, we report the first detection of 17
GHz signatures of coronal X-ray-bright points (XBPs). This is also the
first reported detection of flaring bright points in microwaves. We
have detected four BPs at 17 GHz out of eight identified in SXT data
on 1992 July 31, for which we looked for 17 GHz emission. For one
XBP located in a quiet mixed-polarity region, the peak times at 17
GHz and X-rays are very similar, and both are long-lasting-about 2
hr in duration. There is a second BP (located near an active region)
which is most likely flaring also, but the time profiles in the two
spectral domains are not similar. The other two 17 GHz BPs are quiescent
with fluctuations superposed upon them. For the quiet region XBP, the
gradual, long-lasting, and unpolarized emission suggests that the 17
GHz emission is thermal.
Title: Energy Transport and Dynamics
Authors: Schmieder, B.; Peres, G.; Enome, S.; Falciani, R.; Heinzel,
P.; Hénoux, J. C.; Mariska, J.; Reale, F.; Rilee, M. L.; Rompolt, B.;
Shibasaki, K.; Stepanov, A. V.; Wülser, J. P.; Zarro, D.; Zharkova, V.
Bibcode: 1994SoPh..153...55S
Altcode:
We report findings concerning energy transport and dynamics in flares
during the impulsive and gradual phases based on new ground-based and
space observations (notably fromYohkoh). A preheating sometimes occurs
during the impulsive phase. CaXIX line shifts are confirmed to be
good tracers of bulk plasma motions, although strong blue shifts are
not as frequent as previously claimed. They often appear correlated
with hard X-rays but, forsome events, the concept that electron beams
provide the whole energy input to the thermal component seems not
to apply. Theory now yields: new diagnostics of low-energy proton
and electron beams; accurate hydrodynamical modeling of pulse beam
heating of the atmosphere; possible diagnostics of microflares (based
on X-ray line ratio or on loop variability); and simulated images of
chromospheric evaporation fronts. For the gradual phase, the continual
reorganization of magnetic field lines over active regions determines
where and when magnetic reconnection, the mechanism favoured for energy
release, will occur. Spatial and temporal fragmentation of the energy
release, observed at different wavelengths, is considered to be a
factor as well in energy transport and plasma dynamics.
Title: The Nobeyama Radioheliograph Data Use
Authors: Shibasaki, K.; Enome, S.; Nakajima, H.; Nishio, M.; Takano,
T.; Hanaoka, Y.; Torii, C.; Sekiguchi, H.; Kawashima, S.; Bushimata,
T.; Shinohara, N.; Koshiishi, H.; Shiomi, Y.
Bibcode: 1994kofu.symp...45S
Altcode:
No abstract at ADS
Title: Morphological Development of Gradual Nonthermal Microwave
Flares
Authors: Nakajima, H.; Enome, S.; Shibasaki, K.; Nishio, M.; Takano,
T.; Hanaoka, Y.; Torii, C.; Shiomi, Y.; Sekiguchi, H.; Bushimata,
T.; Kawashima, S.; Shinohara, N.; Koshiishi, H.
Bibcode: 1994kofu.symp..185N
Altcode:
Provisional results are presented for three gradual microwave
bursts. Observations were made with the Nobeyama Radioheliograph
at 17 GHz and simultaneously with the Yohkoh /Soft X-ray Telescope
with partial coverage in time as well as radiometers at Nobeyama and
Toyokawa. 1993 March 23 flare shows a cusp-type structure in soft
X-ray images in late phase, where the 17GHz images show weak emission
in gradual phase. This new discovery is explained in terms of a simple
model of trapped electrons in a weak field.
Title: Evolution of an Active Region and Flare Productivity
Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.; Bruner,
M.; Sakao, T.; Kosugi, T.
Bibcode: 1994kofu.symp..353K
Altcode:
We have studied the evolution of an active region (AR 7515) in terms
of flare productivity. This region appears at the east limb on May 23,
1993 and then continues its onward march across the disk. We follow
its evolution until June 2. This region produces many small flares. We
study the topology, both magnetic and structural of the neighboring
regions as observed at 17 GHz by the Nobeyama Radio Heliograph (NRH)
and the Yohkoh/SXT to find their effects on the flare-producing AR. We
investigate the spatial structure of the flaring region from 17 GHz
and SXT maps during various times of the impulsive and decay phase,
to understand the difference in the flaring region spatial structure
during the preflare, impulsive and decay phases. In general, the maps
made during these phases show several loops. We try to relate these
flaring loops with the preflare active region structure.
Title: Processing of the Nobeyama Radioheliograph Data
Authors: Hanaoka, Y.; Shibasaki, K.; Nishio, M.; Enome, S.; Nakajima,
H.; Takano, T.; Torii, C.; Sekiguchi, H.; Bushimata, T.; Kawashima,
S.; Shinohara, N.; Irimajiri, Y.; Koshiishi, H.; Kosugi, T.; Shiomi,
Y.; Sawa, M.; Kai, K.
Bibcode: 1994kofu.symp...35H
Altcode:
The Nobeyama Radioheliograph is a dedicated interferometer to the
solar observations, which requires a high time-resolution and a long
observational time-coverage. It is important to extract the flare
activity during the observing time efficiently from the obtained
correlation data. For this purpose, the real-time calibration
and imaging are performed with the data processing system of the
radioheliograph. The real-time data processing and the CLEAN procedure
for the radioheliograph data are described here.
Title: Evolution and Radio Activity of a Flare Productive Active
Region NOAA7321
Authors: Nishio, M.; Takakura, T.; Ikeda, H.; Nakajima, H.; Enome,
S.; Shibasaki, K.; Takano, T.; Hanaoka, Y.; Choi, Y. -S.; Koshiishi, H.
Bibcode: 1994kofu.symp..151N
Altcode:
By the Nobeyama Radioheliograph, evolution of radio features in flare
productive active region NOAA7321 was observed. Delay of emergence
of radio feature was detected comparing with soft X-ray feature
observed by Yohkoh, which implied that coronal region above NOAA7321
had weak magnetic field strength and high temperature at initial phase
of evolution. During evolution of this region, many radio bursts are
observed by the radioheliograph and the radio polarimeters at Nobeyama
and Toyokawa. These bursts showed radio spectra with high turnover
frequency and steep lower frequency cutoff. Negative bursts were
observed during entire observation period of NOAA7321. These results
suggest that the radio bursts in NOAA7321 were caused by continuous
appearance of strong magnetic field regions to lower corona.
Title: Observation of 17 GHz Radio Emission from X-ray Bright Points
Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.
Bibcode: 1994kofu.symp...79K
Altcode:
Using observations made with the Nobeyama radio heliograph (NRH) at 17
GHz and the Yohkoh/SXT experiment, we report the first detection of 17
GHz signatures of coronal X-ray bright points (XBP's). This is also the
first reported detection of flaring bright points in microwaves. We
have detected four BP's at 17 GHz out of eight observed by SXT on
July 31, 1992, for which we looked for 17 GHz emission. For one XBP
located in a quiet mixed-polarity-region, the peak times at 17 GHz
and X-rays are very similar, and both are long lasting -- at least
6 hours in duration. There is a second BP (located near an active
region) which is most likely flaring also, but the time profiles in
the two spectral domains are not similar. The other two 17 GHz BPs
are quiescent with fluctuations superposed upon them. For the quiet
region XBP, we believe that the 17 GHz emission is thermal.
Title: Structural Change of Radio Sources During Early Phase of
Small Bursts
Authors: Shibasaki, K.; Enome, S.; Nakajima, H.; Nishio, M.; Takano,
T.; Hanaoka, Y.; Torii, C.; Sekiguchi, H.; Kawashima, S.; Bushimata,
T.; Shinohara, N.; Koshiishi, H.; Shiomi, T.
Bibcode: 1994kofu.symp..205S
Altcode:
Morphological developments of several small radio bursts are studied
using Nobeyama Radioheliograph. In some events, only one source is
involved in the event. In other events, more than two sources are
involved and they show different temporal developments especially in
the early phase. We studied the emission mechanism of each component
sources by considering temporal behavior, polarization degree and
also soft X-ray images taken simultaneously by Yohkoh satellite. We
identified thermal free-free and nonthermal gyrosynchrotron emissions
in the radio bursts and studied their relations.
Title: Alignment of Radio, Soft X-ray, Hard X-ray Images of Sources
in Impulsive and Gradual Phases of the Flare of 1992 August 17-18
Authors: Enome, S.; Nakajima, H.; Shibasaki, K.; Nishio, M.; Takano,
T.; Hanaoka, Y.; Torii, C.; Shiomi, Y.; Sekiguchi, H.; Bushimata,
T.; Kawashima, S.; Shinohara, N.; Irimajiri, Y.; Koshiishi, H.; Choi,
Y. -S.; Sakai, J.; Takahashi, M.; Takakura, T.; Sakao, T.; Kosugi, T.
Bibcode: 1994kofu.symp..141E
Altcode:
This is a preliminary report concerning an impulsive flare, which
occurred on 1992 August 17-18, and was observed with the Nobeyama
Radioheliograph, Yohkoh, and ground-based instruments. Emphasis is put
on the alignment of radio images as well as soft X-ray and hard X-ray
maps, which are compared in both impulsive and gradual phases. In the
impulsive phase, which continued for about 30 s, nonthermal emission
was most remarkable at 17 GHz, and was also seen in hard X-rays at the
southern part of the SXT source, which was about 14" width and 80"
long, extending in the north-east to south-west direction. Thermal
emission was detected in soft X-rays and possibly in hard X-rays at the
northern part. During the gradual phase, about 80 s after the onset of
the impulsive phase, thermal emission dominated and was located at the
northern part of the source over the entire energy range. Difficulties
are discussed concerning a possible simple topology of the magnetic
fields. Note:This is the abstract of the Letter published PASJ 46,
L27-31(1994)
Title: The Nobeyama Radioheliograph --- Hardware System ---
Authors: Nishio, M.; Nakajima, H.; Enome, S.; Shibasaki, K.; Takano,
T.; Hanaoka, Y.; Torii, C.; Shiomi, Y.; Sekiguchi, H.; Bushimata,
T.; Kawashima, S.; Shinohara, N.; Koshiishi, H.; Kosugi, T.; Sawa,
M.; Kai, K.; Irimajiri, Y.; Nohmi, H.; Honda, K.; Shinohara, H.; Ito,
T.; Miyawaki, M.; Imoto, A.; Takabayashi, T.; Nishikawa, K.; Futagawa,
N.; Tanaka, S.; Morikawa, H.; Kitahara, Y.; Harakawa, K.; Mishima, K.
Bibcode: 1994kofu.symp...19N
Altcode:
The Nobeyama Radioheliograph began routine observations in late June,
1992, and radio full-disk images of the Sun have been observed for 8h
every day. This instrument is a 17-GHz radio interferometer dedicated
for solar observations, which consists of eighty-four 80-cm-diameter
antennas arranged in a Tee-shaped array extending 490m in east-west
and 220m in north-south directions. The spatial resolution is 10" and
the temporal resolution is 1s and 50ms for selected events. The array
configuration is optimized to observe the whole sun with high spatial
and temporal resolution and a high dynamic range of images. Image
quality of better than 20dB is realized by incorporation of technical
advances in hardware and software, such as (1) low-loss phase-stable
optical fiber cables for local reference signal and IF signals,
(2) newly developed phase-stable local oscillators, (3) custom
CMOS gate-array LSIs of one-bit quadra-phase correlators for 4 x 4
combinations, (4) an expanded real-time self-calibration method of
gain and phase errors using redundant antenna combinations, and (5) new
image processing techniques to suppress large sidelobe effects due to
the solar disk and extended sources. A newly developed control system
with fully distributed computers enable us to continue observations
even in a condition where some portions of the radioheliograph are
malfunctioning. In this paper, a detailed description is given of the
radioheliograph's hardware, with particular emphasis on the stability
and accuracy of the total system.
Title: The Nobeyama radioheliograph.
Authors: Nakajima, H.; Nishio, M.; Enome, S.; Shibasaki, K.; Takano,
T.; Hanaoka, Y.; Torii, C.; Sekiguchi, H.; Bushimata, T.; Kawashima,
S.; Shinohara, N.; Irimajiri, Y.; Koshiishi, H.; Kosugi, T.; Shiomi,
Y.; Sawa, M.; Kai, K.
Bibcode: 1994IEEEP..82..705N
Altcode:
A new 17-GHz radio interferometer dedicated for solar observations was
constructed in 2 years at Nobeyama, Nagano. It consists of eighty-four
80-cm-diameter antennas arranged in a Tee-shaped array extending
490 m in east-west and 220 m in north-south directions. The array
configuration is optimized to observe the whole Sun with high spatial
and temporal resolution and a high dynamic range of images.
Title: Thermal and nonthermal flare emission observed with the
Nobeyama Radio Heliograph
Authors: Shibasaki, K.; Takano, T.; Enome, S.; Nakajima, H.; Nishio,
M.; Hanaoka, Y.; Torii, C.; Sekiguchi, H.; Bushimata, T.; Kawashima,
S.; Shinohara, N.; Koshiishi, H.; Shiomi, Y.
Bibcode: 1994SSRv...68..217S
Altcode:
The early phases of three flares, observed by the Nobeyama Radio
Heliograph, are studied. Nonthermal and thermal radio sources are
identified by comparison with soft X-ray images taken by the Soft
X-ray Telescope onboard the Yohkoh satellite. Two of the flares are
mainly of nonthermal origin and their location coincides with one of
the footpoints of soft X-ray loops. Another flare has both thermal and
nonthermal components which start to brighten simultaneously. This
suggests that particle acceleration and plasma compression develop
simultaneously.
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
Bibcode: 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: Radio Imaging Observations of the Evolution of Thermal and
Nonthermal Sources during a Gradual Solar Burst
Authors: Nishio, Masanori; Nakajima, Hiroshi; Enome, Shinzo; Shibasaki,
Kiyoto; Takano, Toshiaki; Hanaoka, Yoichiro; Torii, Chikayoshi;
Sekiguchi, Hideaki; Bushimata, Takeshi; Kawashima, Susumu; Shinohara,
Noriyuki; Irimajiri, Yoshihisa; Choi, Yong-Seok; Koshiishi, Hideki;
Shiomi, Yasuhiko; Metcalf, Thomas R.; Canfield, Richard C.
Bibcode: 1994PASJ...46L..11N
Altcode:
With the Nobeyama Radioheliograph, evolution of thermal and nonthermal
radio sources was observed during a gradual solar radio burst. Two
thermal sources were located near the top of an arcade-like soft X-ray
structure observed by the Yohkoh satellite, while a nonthermal source
was observed near the foot points of the arcade-like structure. During
the early phase of the burst, an elongated structure was observed
connecting one of the thermal sources and the nonthermal source. The
elongation started from the location of the nonthermal source and
gradually progressed to the thermal source placed just radially above
the nonthermal source with the velocity of about 170 km s(-1) . These
observations imply that the thermal source and the nonthermal source
are connected by a single magnetic loop, and that the elongation of
the source structure is an indication of chromospheric evaporation by
radio imaging observations. The energetics of the thermal and nonthermal
sources was analyzed using the radio and soft X-ray data. We suggest
that a continuous supply of accelerated electrons for about 1000 s
can maintain the hot plasma observed at the foot points of the loop.
Title: A Purely Polarized S-Component at 17 GHz
Authors: Shibasaki, Kiyoto; Enome, Shinzo; Nakajima, Hiroshi; Nishio,
Masanori; Takano, Toshiaki; Hanaoka, Yoichiro; Torii, Chikayoshi;
Sekiguchi, Hideaki; Kawashima, Susumu; Bushimata, Takeshi; Shinohara,
Noriyuki; Koshiishi, Hideki; Shiomi, Yasuhiko; Irimajiri, Yoshihisa;
Leka, K. D.; Canfield, Richard C.
Bibcode: 1994PASJ...46L..17S
Altcode:
A purely polarized bright radio source was found at 17 GHz by the
Nobeyama Radioheliograph. This source was associated with a large
sunspot. The source structure of this S-component was resolved due to
high spatial resolution of the radioheliograph. A soft X-ray image of
this active region taken by Yohkoh Satellite shows no counterpart for
the radio source. Emission mechanism of the radio source is identified
as gyroresonance. Magnetic field of the sunspot was measured by the
Haleakala Vector Magnetograph at Mees Solar Observatory. The field
strength at the half power level of the radio source was 2000 gauss
at the photospheric level. This corresponds to the third harmonic
layer. A bright soft X-ray loop, whose footpoint is at the penumbra
of the large sunspot, can also be seen in the radio map. This loop
is strongly curved, to form a part of spiral, which reflects strong
electric current. Vector magnetogram shows strong rotation of the
transverse field in the sunspot, which also corresponds to strong
electric current. Due to this current and also to the density and the
temperature enhancement near the X-ray loop, the radio peak is shifted
toward the loop and has no dip.
Title: Evaluation of the Imaging Performance of the Nobeyama
Radioheliograph
Authors: Koshiishi, Hideki; Enome, Shinzo; Nakajima, Hiroshi;
Shibasaki, Kiyoto; Nishio, Masanori; Takano, Toshiaki; Hanaoka,
Yoichiro; Torii, Chikayoshi; Sekiguchi, Hideaki; Kawashima, Susumu;
Bushimata, Takeshi; Shinohara, Noriyuki; Irimajiri, Yoshihisa;
Shiomi, Yasuhiko
Bibcode: 1994PASJ...46L..33K
Altcode:
The Nobeyama Radioheliograph is a radio interferometer dedicated to
solar observations at 17 GHz. Its imaging performance is concisely
described on the basis of the correlator outputs. Antenna-based
errors are removed by a self-calibration method. Possible causes of
correlator-based errors have been considered, respectively. Among them,
the important factors are: 1) unequal bandpass characteristics, 2)
antenna pointing errors, 3) delay errors, and 4) noise at correlator
outputs. The expected dynamic range of synthesized snap-shot images
is 30 dB based on these correlator-based errors. However, the actual
images have a 25 dB dynamic range, which may be mostly due to the
image-restoration procedure currently adopted.
Title: Behavior of Accelerated Electrons in a Small Impulsive Solar
Flare on 1992 August 12
Authors: Takano, Toshiaki; Enome, Shinzo; Nakajima, Hiroshi; Shibasaki,
Kiyoto; Nishio, Masanori; Hanaoka, Yoichiro; Torii, Chikayoshi;
Sekiguchi, Hideaki; Bushimata, Takeshi; Kawashima, Susumu; Shinohara,
Noriyuki; Irimajiri, Yoshihisa; Koshiishi, Hideki; Kosugi, Takeo;
Shiomi, Yasuhiko; Sakurai, Takashi; Ichimoto, Kiyoshi
Bibcode: 1994PASJ...46L..21T
Altcode:
A GOES C1.0-class impulsive flare was observed by the new Nobeyama
Radioheliograph on 1992 August 12 with 1 s temporal and 10('') spatial
resolutions at 17 GHz. The radio flare consisted of an impulsive phase
of ~ 20 s and a decay phase of ~ 90 s. Radio images showed double
sources in the impulsive phase, whereas in the decay phase a single
elongated source appeared which connected the double sources. Soft
X-ray images with Yohkoh/SXT show that the radio double sources
correspond to foot points of newly appearing coronal loops and the
single source was located at the top of one of the loops. The radio
emission for both phases can be explained by gyrosynchrotron radiation
from accelerated electrons. These loops began to brighten at their
intersecting point ~ 1 min before the radio flare. All of these facts
suggest that the reconnection of magnetic fields heated up the coronal
loops and produced accelerated electrons, which ran through the loops,
precipitated onto the foot points, and caused the radio flare. Less
than 1% of the electrons were mirrored at the foot points and trapped
at the top of the loop. The lack of radio emission in the loop top area
during the impulsive phase implies that the accelerated electrons were
highly beamed.
Title: Alignment of Radio, Soft X-Ray, Hard X-Ray Images of Sources
in Impulsive and Gradual Phases of the Flare of 1992 August 17--18
Authors: Enome, Shinzo; Nakajima, Hiroshi; Shibasaki, Kiyoto; Nishio,
Masanori; Takano, Toshiaki; Hanaoka, Yoichiro; Torii, Chikayoshi;
Shiomi, Yasuhiko; Sekiguchi, Hideaki; Bushimata, Takeshi; Kawashima,
Susumu; Shinohara, Noriyuki; Irimajiri, Yoshihisa; Koshiishi, Hideki;
Choi, Yong-Seok; Sakai, Jun-Ichi; Takahashi, Masaaki; Takakura,
Tatsuo; Sakao, Taro; Kosugi, Takeo
Bibcode: 1994PASJ...46L..27E
Altcode:
This is a preliminary report concerning an impulsive flare, which
occurred on 1992 August 17--18, and was observed with the Nobeyama
Radioheliograph, Yohkoh, and ground-based instruments. Emphasis is put
on the alignment of radio images as well as soft X-ray and hard X-ray
maps, which are compared in both impulsive and gradual phases. In the
impulsive phase, which continued for about 30 s, nonthermal emission
was most remarkable at 17 GHz, and was also seen in hard X-rays at the
southern part of the SXT source, which was about 14'' width and 80''
long, extending in the north-east to south-west direction. Thermal
emission was detected in soft X-rays and possibly in hard X-rays at the
northern part. During the gradual phase, about 80 s after the onset of
the impulsive phase, thermal emission dominated and was located at the
northern part of the source over the entire energy range. Difficulties
are discussed concerning a possible simple topology of the magnetic
fields.
Title: Small Scale Activity Just Before the Onset of Radio Burst
Detected by the Nobeyama Radioheliograph
Authors: Shibasaki, K.; Enome, S.; Nakajima, H.; Nishio, M.; Takano,
T.; Hanaoka, Y.; Torii, C.; Sekiguchi, H.; Kawashima, S.; Bushimata,
T.; Shinohara, N.; Irimajiri, Y.; Kishiishi, H.; Shiomi, Y.
Bibcode: 1994xspy.conf...47S
Altcode:
No abstract at ADS
Title: The Next Plan of the Nobeyama Radioheliograph
Authors: Takano, T.; Enome, S.; Nakajima, H.; Shibasaki, K.; Nishio,
M.; Hanaoka, Y.; Torii, C.; Sekiguchi, H.; Bushimata, T.; Kawashima,
S.; Shinohara, N.; Irimajiri, Y.; Koshiishi, H.; Kosugi, T.; Shiomi,
Y.; Sawa, M.
Bibcode: 1994ASPC...59..430T
Altcode: 1994IAUCo.140..430T; 1994amsw.conf..430T
No abstract at ADS
Title: Microbursts Observed by the Nobeyama Radioheliograph
Authors: Pogodin, I.; Shibasaki, K.
Bibcode: 1994xspy.conf...43P
Altcode:
No abstract at ADS
Title: Coalignment of the Radioheliograph and the YOHKOH Images
Authors: Nishio, M.; Nakajima, H.; Nitta, N.; Enome, S.; Shibasaki,
K.; Takano, T.; Hanaoka, Y.
Bibcode: 1994xspy.conf..187N
Altcode:
No abstract at ADS
Title: Time Development of the 1992 June 28 X-Class Flare
Authors: Nakajima, H.; Enome, S.; Shibasaki, K.; Nishio, M.; Takano,
T.; Hanaoka, Y.; Torii, C.; Shiomi, Y.; Sekiguchi, H.; Bushimata,
T.; Kawashima, S.; Shinohara, N.; Irimajiri, Y.; Koshiishi, H.
Bibcode: 1994xspy.conf...63N
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.
Bibcode: 1994xspy.conf..193H
Altcode:
No abstract at ADS
Title: Evolution of a Solar Active Region and Flare Productivity
Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.; Bruner, M.
Bibcode: 1993AAS...183.6807K
Altcode: 1993BAAS...25.1396K
We have studied the evolution of an active region (AR 7515) in terms of
flare productivity. This region appeared on the east limb on May 23,
1993 and continued its onward march across the disk. We followed its
evolution until June 2. This region produced many small flares. We
studied the topology, both magnetic and structural of the flaring
region as observed at 17 GHz by the Nobeyama radio Heliograph (NRH)
with a spatial resolution of 10 arcsec and the Yohkoh SXT which has
a spatial resolution of 2.5 arcsec. Among other things, we find: (i)
Frequently a flare starts with the appearance of a new region/loop
which interacts with a pre-existing loop; this interaction acta as a
flare trigger. (ii) There appear to exist multiple sets of interacting
loops in the same active region. Different bursts on the same day
seem to come from diffrent sets of interacting loops. (iii) Sometimes
two or more sets of interacting loops can activate at the same time,
giving rise to different peaks in the same burst. In the decay phase
of some bursts there may appear a new or reactivated region/loop which
becomes the source of new burst emission. (iv) A simple spiky burst
in general originates from a narrow region and by implication from a
compact set of interacting loops.
Title: Preliminary results of observations of solar flares with
Nobeyama Radioheliograph.
Authors: Nakajima, H.; Enome, S.; Shibasaki, K.; Nishio, M.; Takano,
T.; Hanaoka, Y.; Torii, C.; Sekiguchi, H.; Bushimata, T.; Kawashima,
S.; Shinohara, N.; Irimajiri, Y.; Koshiishi, H.; Kosugi, T.; Shiomi,
Y.; Sawa, M.; Kai, K.
Bibcode: 1993ppcn.conf...85N
Altcode:
The new Nobeyama Radioheliograph, dedicated for solar observations
started routine observations since late June, 1992. It operates at 17
GHz and realizes high spatial and time resolution imaging capabilities
of the whole Sun with high image quality. From initial observations
of solar flares, the authors present four topics putting stress
on morphological development of the events, such as (1) a thermal
flare suggesting plasma heating through loop-loop interaction, (2)
prominence eruption followed by formation of arcade loops as evidence
of energy release through magnetic reconnection, (3) impulsive flares
interpreted as production of nonthermal electron beams, (4) an intense
flare initiated by preflare activities. Results of those observations
provide new insights on energy release mechanisms in solar flares. The
above topics are analyzed.
Title: Solar Activity Observed with the New Nobeyama Radioheliograph
Authors: Enome, S.; Nakajima, H.; Shibasaki, K.; Nishio, M.; Takano,
T.; Hanaoka, Y.; Torii, C.; Sekiguchi, H.; Kawashima, S.; Bushimata,
T.; Shinohara, N.; Irimajiri, Y.; Koshiishi, H.; Kosugi, T.; Shiomi,
Y.; Sawa, M.; Kai, K.
Bibcode: 1993ASPC...46..310E
Altcode: 1993mvfs.conf..310E; 1993IAUCo.141..310E
No abstract at ADS
Title: Ten Years of the Okayama Vector Magnetograph
Authors: Makita, M.; Sakurai, T.; Shibasaki, K.; Koyano, H.
Bibcode: 1993ASPC...46..180M
Altcode: 1993IAUCo.141..180M; 1993mvfs.conf..180M
No abstract at ADS
Title: The receiver system of Nobeyama radio heliograph
Authors: Nishio, M.; Nakajima, H.; Hanaoka, Y.; Takano, T.; Shibasaki,
K.; Enome, S.; Honda, K.; Nohmi, H.; Shinohara, H.; Ito, T.
Bibcode: 1992igrs.conf.1435N
Altcode:
A new radioheliograph has been constructed to explicate the mechanism
of solar flares. The radioheliograph is an interferometer with T-shaped
two-dimensional antenna arrays. In order to obtain high spatial and
high time resolution simultaneously, element antennas are allocated
more densely in the inner part of the T-shaped array and more sparsely
in the outer part. Correlations with all antenna combinations are
calculated by a multichannel 1-b correlator. The design principles
and performances of the radioheliograph receivers are described.
Title: The Hard X-ray Telescope (HXT) for the SOLAR-A mission
Authors: Kosugi, T.; Makishima, K.; Murakami, T.; Sakao, T.; Dotani,
T.; Inda, M.; Kai, K.; Masuda, S.; Nakajima, H.; Ogawara, Y.; Sawa,
M.; Shibasaki, K.
Bibcode: 1991SoPh..136...17K
Altcode:
The Hard X-ray Telescope (HXT) is a Fourier-synthesis imager; a set of
spatially-modulated photon count data are taken from 64 independent
subcollimators and are Fourier-transformed into an image by using
procedures such as the maximum entropy method (MEM) or CLEAN. The
HXT takes images of solar flares simultaneously in four energy bands,
nominally 15 (or 19)-24, 24-35, 35-57, and 57-100 keV, with an ultimate
angular resolution as fine as ∼ 5 arc sec and a time resolution 0.5
s. Each subcollimator has a field of view wider than the solar disk. The
total effective area of the collimator/detector system reaches ∼ 70
cm2, about one order of magnitude larger than that of the
HINOTORI hard X-ray imager. Thanks to these improvements, HXT will for
the first time enable us to take images of flares at photon energies
above ∼ 30 keV. These higher-energy images will be compared with
lower-energy ones, giving clues to the understanding of nonthermal
processes in solar flares, i.e., the acceleration and confinement of
energetic electrons. It is of particular importance to specify the
acceleration site with regard to the magnetic field figuration in a
flaring region, which will be achieved by collaborative observations
between HXT and the Soft X-ray Telescope on board the same mission.
Title: The relation between the spectrum and directivity of solar
radio emission bursts.
Authors: Shibasaki, K.; Moskovkina, V. M.; Pogodin, I. E.
Bibcode: 1991Ge&Ae..31..275S
Altcode:
It is demonstrated that the character of the spatial directivity of
solar-radio bursts is determined by the frequency of the spectral
maximum, which is due to the difference in the position of the source
and the orientation of the corresponding magnetic fields.
Title: A 17 GHz Radioheliograph Project: A High-Speed Radio Camera
Authors: Nishio, M.; Kai, K.; Enome, S.; Nakajima, H.; Shibasaki, K.;
Takano, T.; Nitta, N.; Torii, C.; Shiomi, Y.; Sekiguchi, H.; Sawa,
M.; Bushimata, T.; Kawashima, S.; Shinohara, N.; Irimajiri, Y.
Bibcode: 1991rst..work..161N
Altcode:
No abstract at ADS
Title: The relation between the spectrum and direction of solar
radio bursts.
Authors: Shibasaki, K.; Moskovkina, V. M.; Pogodin, I. E.
Bibcode: 1991Ge&Ae..31..357S
Altcode:
It is shown that the character of the spatial directivity of solar radio
bursts is determined by the frequency of the spectral maximum. This
is explained by differences in the locations of the sources and the
orientation of the corresponding magnetic fields. Specifically,
'low-frequency' 3-5 GHz bursts of a magnetobremsstrahlung nature
are generated in quasi-tangential fields near magnetic loop apexes
while 'high-frequency' 9-15 GHz bursts are generated in the stronger
quasi-radial field at loop bases.
Title: The SOLAR-A Hard X-ray Telescope (HXT)
Authors: Kosugi, T.; Makishima, K.; Inda, M.; Murakami, T.; Dotani,
T.; Inda, M.; Kai, K.; Masuda, S.; Nakajima, H.; Ogawara, Y.; Sakao,
T.; Sawa, M.; Shibasaki, K.
Bibcode: 1991AdSpR..11e..81K
Altcode: 1991AdSpR..11...81K
The Hard X-ray Telescope (HXT), now under fabrication for the SOLAR-A
mission (scheduled for launch in August 1991), is an advanced
Fourier-synthesis imager. An overview of the HXT instrument is
given together with its scientific objectives, that is, the electron
acceleration and confinement mechanisms in solar flares. Scientific
return from HXT will be greatly increased if worldwide collaboration
with other space and ground-based observations is well organized.
Title: Microwave observations of the sun during the 22nd solar
activity cycle - 17 GHz radio heliograph
Authors: Shibasaki, K.; Kai, K.; Enome, S.; Nakajima, H.; Nishio,
M.; Takano, T.; Torii, C.; Shiomi, Y.; Sekiguchi, H.; Sawa, M.
Bibcode: 1991ese..book..345S
Altcode:
For the study of high energy phenomena on the sun during the maximum
period of the 22nd solar activity cycle, we started to construct
a radio heliograph at Nobeyama Radio Observatory. The operating
frequency was selected to be 17 GHz to catch the emission from the
accelerated electrons in solar flares. The 17 GHz Radio Heliograph
consists of T-shaped array of 490 m in the E-W direction and 220 m in
N-S direction with 84 antenna elements. The heliograph can map the
whole sun with 10-arcsec spatial resolution and with 50-millisecond
temporal resolution.
Title: a New Radio Heliograph at Nobeyama
Authors: Nakajima, H.; Kai, H.; Enome, S.; Shibasaki, K.; Nishino, M.;
Takano, T.; Torii, C.; Shiomi, Y.; Sekiguchi, H.; Sawa, M.; Bushimata,
T.; Kawashima, S.; Shinohara, N.; Kosugi, T.
Bibcode: 1991nro..reptQ...1N
Altcode:
No abstract at ADS
Title: On the delay of microwave solar flux variations at different
frequencies.
Authors: Shibasaki, K.; Molchanov, A. P.; Pogodin, I. E.
Bibcode: 1989BSolD..11..115S
Altcode:
The delay of microwave flux variations at lower frequencies relative
to higher frequencies is found to be a common phenomenon. The delay
is interpreted to be due to different source positions at different
frequencies within active regions.
Title: Note on the Decay of Solar Microwave Flux Variations
Authors: Shibasaki, K.; Andrianov, S. A.; Korneeva, P. G.; Molchanov,
A. P.; Pogodin, I. E.
Bibcode: 1989BSolD..11..116S
Altcode:
No abstract at ADS
Title: A real-time image processor with multi-channel correlator
for solar radio observations
Authors: Nishio, M.; Tsukiji, Y.; Shibasaki, K.; Enome, S.;
Kobayashi, S.
Bibcode: 1988A&A...198..370N
Altcode:
A description is given of a new back-end processor for the λ 8-cm
radioheliograph at Toyokawa. By the introduction of this system, the
λ 8-cm radioheliograph is changed from the swept-lobe type to the
multi-correlator type. Two-dimensional and one-dimensional solar radio
images are displayed on a graphic terminal in real time at the rate
of 10 s/image. On the other hand, correlation data, that is spatial
frequency components of these images, are stored on a data storage
sytem at the rate of 0.1 s/image for off-line analysis. Comparing the
images obtained by using the new back-end and the original swept-lobe
typ back-end, it is confirmed that in two-dimensional observations the
improvement greater than 1000 times in the time resolution is achieved
without sacrificing the sensitivity.
Title: Lambda 8-CM solar maps observed with the RSIP, a real-time
multi-channel digital correlator backend installed to the
radioheliograph at Toyokawa
Authors: Enome, Shinzo; Shibasaki, Kiyoto; Nishio, Masanori
Bibcode: 1987NURIA..34...35E
Altcode:
The lambda 8-cm radioheliograph at Toyokawa has been improved with
respect to sensitivity and time resolution by the introduction of
a new real-time digital correlator backend, which is called RSIP
(Real-Time Solar Image Processor). Observations were started in late
February, 1986. Radio maps of the daily observations are shown in part,
and synoptic charts of total period of observations are illustrated
for solar rotations between Carrington rotation number 1773, which
started March 10, 1986, and 1783. Active regions are clearly seen on
these synoptic charts, some of which are at high latitude of the new
solar cycle and also absorption features are definitely recognized
corresponding to dark filaments. Quality of the images is estimated
to be 30 to 1 or 15 dB. Applied data processings are described briefly
to obtain present images from observed antenna output correlations.
Title: Dark filaments observed at 8.3 mm and 3.1 mm wavelengths.
Authors: Hiel, E.; Ishiguro, M.; Kosugi, T.; Shibasaki, K.
Bibcode: 1986NASCP2442..109H
Altcode:
Mapping of the sun was made at 3.1 mm (98 GHz) and 8.3 mm (36 GHz)
wavelengths with a 45 m dish radio telescope at the Nobeyama Cosmic
Radio Observatory. The depressions associated with large Hα filaments
are derived to be -0.2 at 8.3 mm and -0.05 at 3.1 mm, which are darker
than the values inferred by Raoult et al. (1979).
Title: Stratospheric nitrogen dioxide observed by ground-based and
balloon-borne techniques at Syowa Station (69.0°S, 39.6°E)
Authors: Shibasaki, K.; Iwagami, N.; Ogawa, T.
Bibcode: 1986GeoRL..13.1268S
Altcode:
Seasonal variation of vertical column density of stratospheric
NO2 was determined for the period of March 1983 to January
1984 by means of ground-based visible absorption spectroscopy at
Syowa Station (69.0°S, 39.6°E), Antarctica. The winter minimum of
about 1×1015 cm-2 and the summer maximum of
7×1015 cm-2 were observed. These values are
nearly equal to, or a little bit smaller than, those observed at
northern high latitudes. The nighttime decay of column density was
small from autumn to early spring. A rapid increase in column density
occurred at the end of September before the minimum of total ozone
content in mid-October. This behavior suggests that both dynamical
and photochemical processes may be involved in the Antarctic ozone
depletion. The vertical profile of stratospheric NO2 in early
summer in Antarctica was revealed by three balloon-borne measurements
over Syowa Station in November 1982 and 1983. Above 25 km altitude,
these profiles are basically identical to those observed at middle and
high latitudes in the northern hemisphere. In the lower stratosphere
below 25 km, variability in NO2 density seems to be large
due to dynamical effects.
Title: Polar-cap and coronal-hole-associated brightenings of the
Sun at millimeter wavelengths
Authors: Kosugi, T.; Ishiguro, M.; Shibasaki, K.
Bibcode: 1986sfcp.nasa..215K
Altcode:
Mapping observations of the Sun at millimeter wavelengths were made
on 16 to 22 July 1984 with the 45-m telescope of the Nobeyama Radio
Observatory. Seven 36-GHz (8.3-mm) maps and five 98-GHz (3.1-mm)
maps were taken with half-power beam widths of 46 arc sec and 17 arc
sec, respectively. Instead of the conventional rastering technique, a
radial-scan method was adopted in which every scan passes through the
disk center. Accordingly, the variation of the atmosphere attenuation
due to changes in the weather conditions can be easily estimated
and removed by using the brightness values at the disk center as
calibration data. Also, the pointing errors of the telescope due to
the high-speed scans can be corrected by using the solar limbs as
position references. The rms residual errors in relative brightness
and position after the corrections were estimated to be approx. 2%
and approx. 5 arc sec respectively. To further reduce these errors,
enabled us to make high-quality maps with with or approx. 1% uncertainty
in brightness. Here and in the following, brightness is expressed in
terms of the average brightness of the solar disk as a unit. Note
that the brightness temperature of the quiet Sun is approx. 8000 K
and approx. 6000 K at 36 GHz and 98 GHz, respectively.
Title: Height Measurements of S-Components
Authors: Shibasaki, K.
Bibcode: 1986Ap&SS.119...21S
Altcode:
The direct measurement of the height of the radio source above a solar
active region was done by the Westerbork Synthesis Radio Telescope
when the source crossed the west limb. The height of the brightest
part was 12000 km above the limb. The result of the disk observation
is also presented and the emission mechanisms of the observed sources
are discussed.
Title: Polar-cap and coronal-hole-associated brightenings of the
sun at millimeter wavelengths
Authors: Kosugi, T.; Ishiguro, M.; Shibasaki, K.
Bibcode: 1986PASJ...38....1K
Altcode:
Observations of the sun at 36 GHz (8.3 mm) and 98 GHz (3.1 mm) were made
on July 16 to 22, 1984 with the Nobeyama 45-m telescope. High quality
maps were obtained from 240 radial scans across the disk. Maps taken at
36 GHz provided evidence for 3-7 percent brightness enhancement near the
poles at latitudes greater than 65 deg, although no limb brightenings
above 1 percent were observed in the equatorial region. Also an
about 5 percent brightness enhancement was observed at 36 GHz in at
least one equatorial coronal hole region. On the other hand, no such
brightenings were detected at 98 GHz. It is suggested that the two
types of brightenings at 36 GHz are two aspects of one phenomenon,
associated with polar and equatorial coronal holes, respectively. Also,
it is suggested that the temperature and density structure of the
upper chromosphere in coronal holes differs from that outside holes.
Title: Polar-cap and coronal-hole-associated brightenings of the
sun at millimeter wavelengths.
Authors: Kosugi, T.; Ishiguro, M.; Shibasaki, K.
Bibcode: 1986NASCP2421..215K
Altcode:
No abstract at ADS
Title: Solar Vector Magnetograms of the Okayama Astrophysical
Observatory
Authors: Makita, Mitsugu; Hamana, Shigeo; Nishi, Keizo; Shimizu,
Minoru; Sakurai, Takashi; Shibasaki, Kiyoto
Bibcode: 1986Ap&SS.118..163M
Altcode:
The title instrument is mounted on the 65 cm solar Coudé telescope
at the Okayama observatory. Observation is usually of the Fe i 5250
Å line. The data obtained are briefly described.
Title: Observation of Magnetic Field Vector in Solar Active Regions
Authors: Sakurai, T.; Makita, M.; Shibasaki, K.
Bibcode: 1985tphr.conf..313S
Altcode:
The vector magnetograph at Okayama Astrophysical Observatory has been
in operation since 1982. The conversion from the observed polarization
degrees to the magnetic field components is made by using Unno's formula
(1956) applied to a homogeneous magnetic field.
Title: Spectrum S-component flux and active region magnetic field
Authors: Shibasaki, K.
Bibcode: 1985PRIAN..32....1S
Altcode:
Characteristics are examined of an active region magnetic field
structure whose spectral peak of an S-component source flux is of
a higher frequency than that of a normal source. The flux ratio at
3 cm and 8 cm wavelengths (F3/F8) is used as an indicator of the
peak frequency. The magnetic field structure of an active region
with a high flux ratio is compared with the structure of that with
a low flux ratio. It is shown that low-lying magnetic lines of
force are characteristic of active regions with high flux ratio. The
high-temperature and high-density plasma confined by low-lying magnetic
lines of force intensifies the flux at short wavelengths, thus the
flux peak shifts to a shorter wavelength.
Title: Realtime Solar Image Processor / Rsip / for the 8-CM
Radioheliograph AAT Toyokawa
Authors: Nishio, M.; Tsukuji, Y.; Kobayashi, S.; Shibasaki, K.;
Enome, S.
Bibcode: 1985PRIAN..32...45N
Altcode:
No abstract at ADS
Title: Real time solar image processor (RSIP) for the λ 8-cm
radioheliograph at Toyokawa.
Authors: Nishio, M.; Tsukiji, Y.; Kobayashi, S.; Shibasaki, K.;
Enome, S.
Bibcode: 1985isap....2..651N
Altcode:
No abstract at ADS
Title: Observation of magnetic field vector in solar active regions.
Authors: Sakurai, T.; Makita, M.; Shibasaki, K.
Bibcode: 1985MPARp.212..312S
Altcode:
The vector magnetograph at Okayama Astrophysical Observatory has been
in operation since 1982. The conversion from the observed polarization
degrees to the magnetic field components is made by using Unno's formula
(1956) applied to a homogeneous magnetic field.
Title: Earth-rotation synthesis of the radio sun by the 8-cm
wavelength radioheliograph at Toyokawa
Authors: Shibasaki, K.
Bibcode: 1984PRIAN..31...25S
Altcode:
Rotational synthesis method is proposed to make a two-dimensional
map from one-dimensional fan beam scans by the 8-cm wavelength
radioheliograph at Toyokawa Observatory. A preliminary map was
synthesized using the back projection method combined with the CLEAN
technique. S-components were successfully mapped but the quiet sun
was not able to be restored by the CLEAN technique. Some problems
associated with rotational synthesis by a fan beam scanning instrument
of the sun are discussed.
Title: The Improved Lambda 8-CM Radioheliograph at Toyokawa
Authors: Nishio, M.; Torii, C.; Enome, S.; Shibasaki, K.; Tsukiji, Y.;
Kobayashi, S.; Yoshimi, N.; Takata, S.; Takayanagi, T.; Ishiguro, M.
Bibcode: 1984PASJ...36..371N
Altcode:
The sensitivity and the phase stability of the &lambda 8-cm
radioheliograph have been improved by replacing the waveguide network
of the original system with low-noise and phase-stable front-end
receivers and low-loss and phase-stable coaxial cables. Receiver noise
temperatures of antennas are mostly around 800 K with a few exceptions
of 1000 K, and long-term relative phase variations of antennas are less
than 6° rms during a four-month period. The short-term phase variation
of each antenna is estimated to be less than 4° rms in 4 hr. In
addition, the operational performance of the system is improved by the
introduction of a new control system composed of two micro-processors,
which enable us to make a weekly check of gain and phase variations of
the system. By this improvement, observations can be made in stable
conditions for a few weeks without phase calibration, and it became
possible to observe radio bursts with a higher time resolution than
that of the original system. Some examples of the solar radio maps
observed by the improved system are presented.
Title: Microwave, ultraviolet, and soft X-Ray observations of hale
region 16898
Authors: Shibasaki, K.; Chiuderi-Drago, F.; Melozzi, M.; Slottje,
C.; Antonucci, E.
Bibcode: 1983SoPh...89..307S
Altcode:
Hale region 16898 was observed by the Westerbork Synthesis
Radio Telescope at 6 cm and by the Ultraviolet Spectrometer and
Polarimeter and the X-Ray Spectrometer on the Solar Maximum Mission
satellite. Optical pictures of the same active region were taken at
Sacramento Peak, Big Bear, and Meudon Observatories. The radio emission
mechanisms are identified by comparing radio data with ultraviolet
and soft X-ray data. The height of the radio sources and the magnetic
field strength at that height are deduced. A radio source above a large
sunspot shows a crescent shaped depression of circular polarization and
a high brightness temperature. The emission mechanism is identified
as gyroresonance at the second and the third harmonic layers and it
is found that the second harmonic layer, where the magnetic field
strength is 900 G, must be in the corona. An extended loop-like source
connecting the leading and the following part of the active region
as well as the sources associated with small spots are mainly due
to thermal free-free emission by hot and dense plasma which is also
observed in ultraviolet and soft X-ray radiation. The calculated radio
brightness temperature, using the physical parameters deduced from the
ultraviolet and soft X-ray line intensities, agrees with the observed
brightness temperature. The height of the low brightness temperature
sources above the small spots is 6000 ± 3000 km and that above the
large spot is less than 3000 km: the source above the large spot
does not show any shift relative to the sunspot due to the projection
effect. Very strong radio emission was found which was associated with
the merging of a group of small spots into the large sunspot. In the
same day, warm (≤ 106 K) and dense matter was present
above the large spot. Evidence for nonthermal emission is presented.
Title: Radio, X-ray, and optical observations of the flare of June
13, 1980, at 6h22m UT
Authors: Kattenberg, A.; Allaart, M.; de Jager, C.; Schadee, A.;
Schrijver, J.; Shibasaki, K.; Švestka, Z.; van Tend, W.
Bibcode: 1983SoPh...88..315K
Altcode:
A subflare of importance Sf was observed on June 13, 1980 simultaneously
by instruments aboard the Solar Maximum Mission (SMM) and various
ground based observatories. We describe and compare different kinds
of observations, with emphasis on the Hard X-Ray Imaging Spectrometer
(HXIS) images and spectra, and on the one-dimensional microwave images
with high time and spatial resolution, obtained with the Westerbork
Synthesis Radio Telescope (WSRT). The fast electrons causing the X-ray
and microwave impulsive bursts had a common acceleration source, but the
burst were produced at the opposite footpoints of the loops involved,
with microwaves emitted near to a sunspot penumbra. The flare (of a
`compact' type) was probably triggered by an emerging flux, and two
possible interpretations of this process are briefly discussed.
Title: Microwave heliograph of arcsecond resolution (a joint project
of solar radio astronomy in Japan).
Authors: Kai, K.; Nakajima, H.; Kosugi, T.; Enome, S.; Shibasaki,
K.; Nishio, M.; Kawabata, K.
Bibcode: 1983STERJ...7....4K
Altcode:
No abstract at ADS
Title: Multiple Wavelength Observations of a Solar Active Region
Authors: Chiuderi-Drago, F.; Bandiera, R.; Willson, R. F.; Slottje,
C.; Falciani, R.; Antonucci, E.; Lang, K. R.; Shibasaki, K.
Bibcode: 1982SoPh...80...71C
Altcode:
The Solar Maximum Mission Satellite, the Sacramento Peak Vacuum
Tower Telescope, the Very Large Array and the Westerbork Synthesis
Radio Telescope have been used to observe active region AR 2490 on
two consecutive days at soft X-ray, ultraviolet, optical and radio
wavelengths (2, 6, and 20 cm), with comparable angular resolution
(2″ to 15″) and field of view (4' × 4'). The radio emissions at
λ = 6 cm and 20 cm show a double structure in which one component is
associated with bright Hα plage, C IV and soft X-ray emission, and
the other component is associated only with sunspots. No radiation at
λ = 2 cm is detected in this latter component. Coronal temperature
and emission measure derived from X-ray lines indicate that the
dominant radiation mechanism of the plage-associated component is
due to thermal bremsstrahlung while the gyroresonance absorption
coefficient must be invoked to account for the high brightness
temperature (Tb≈2×106K) observed in the
sunspot associated component. The high magnetic field strength needed
(600 G at a level where T∼2×106K) is explained assuming
a thin transition zone, in order to reach a high electron temperature
close to the sunspot, where the magnetic fields are stronger. A higher
temperature gradient above sunspots is also consistent with the absence
of detectable C IV emission.
Title: A design study and some experiments of digital correlator
backed for lambda 8-cm radioheliograph at Toyokawa
Authors: Nishio, M.; Tsukiji, Y.; Enome, S.; Shibasaki, K.; Morita,
K. -I.
Bibcode: 1982NURIA..29...47N
Altcode: 1982nuri...29...47N
The design and results of testing of a digital correlator back end
intended to improve the time resolution characteristics and the
dynamic range of the 8-cm wavelength radioheliograph at Toyokawa are
presented. The back end frequency converts the signal transmitted from
the second IF stage to a video-band signal, then amplifies it to a level
acceptable to an analog/digital converter, which in turn transmits the
signal through a digital delay line to a one-bit correlator to produce
spatial frequency components of the solar brightness distribution which
is obtained through a Fourier transformation. Tests were conducted on
a circuit designed to produce the cross correlation of a pair of input
analog signals using a one-bit correlator composed of an exclusive OR
circuit and a synchronous counter associated with a Van Vleck correction
circuit, and have shown that true visibility for the solar brightness
distribution may be obtained.
Title: Observations of the Quiet Sun during the Solar Minimum Cycles
20-21 with the Toyokawa Lambda 8-CM Radioheliograph
Authors: Ishiguro, M.; Enome, S.; Shibasaki, K.; Tanaka, H.
Bibcode: 1980PASJ...32..533I
Altcode:
The radio quiet sun was observed during the solar minimum (cycles 20-21)
with the λ8-cm radioheliograph at Toyokawa. Daily radio maps were
statistically processed to obtain the monthly-averaged quiet sun. In
spite of the presence of the seasonal variation in these quiet-sun maps,
the differences between the E-W and N-S center-to-limb variations of
the brightness temperature showed a relatively coherent feature. This
center-to-limb effect of the quiet sun can be explained by a simple
coronal model with arches and holes.
Title: Solar Radio Acquisition and Communication System /SORDACS/
of Toyokawa Observatory
Authors: Shibasaki, K.; Ishiguro, M.; Enome, S.
Bibcode: 1979PRIAN..26..117S
Altcode:
Solar Radio Data Acquisition and Communication System (SORDACS)
is described on input data, hardware, software and operation. The
SORDAC system which presently handles data of the full-automatic
radiopolarimeters, is designed to be able to treat data of the
lambda 8-cm and 3-cm radioheliographs systematically. The system is
characterized in automatic operation to minimize the load of observers
and in very high speed of data transmission at 48 kilobaud. It is also
featured by a variety of backup subsystems to obtain full coverage of
data as complete as possible. Examples are shown for the latest data.
Title: A project to improve the sensitivity and the phase stability
of the lambda 8-cm radioheliograph at Toyokawa
Authors: Ishiguro, M.; Torii, C.; Shibasaki, K.; Enome, S.; Tanaka, H.
Bibcode: 1979PRIAN..26..145I
Altcode:
An improvement of the present system is suggested by replacing its
waveguide network with a combination of low noise, phase stable front
ends, and low loss, phase stable coaxial cables to transmit signals from
and to the front ends. The temperature inside the front end box is kept
within 0.1 C deg accuracy to achieve the required phase stability. It
is recommended to use a higher frequency as a reference signal to
minimize a phase error. Attention is given to the reference signal
cables rather than IF return cables. A polyethylene coaxial cable is
used as the transmission line to improve phase stability. At the second
IF stage, the transmission loss and front end gain for each channel
are equalized by computer controlled digital phase shifters. Each
channel can be operated as an independent radiometer to achieve the
better calibration of total errors in gain and phase.
Title: Sudden decrease of microwave solar radio emission
Authors: Shibasaki, K.; Ishiguro, M.; Enome, S.
Bibcode: 1979PRIAN..26...53S
Altcode:
Total flux observations on the microwave solar radio emission sometimes
show depressions after bursts or without bursts. These, classified as
'post burst decrease' or 'absorption', are gradual phenomena and the
duration is usually more than an hour. In contrast to these phenomena,
the authors found two sudden decreases of the total flux just before
the bursts of July 21, 1978 and September 7-8, 1978. The durations were
shorter than 10 minutes. The observational results are given which
were obtained by four microwave polarimeters and two interferometers
at Toyokawa. A preliminary interpretation is also given for the event
of September 7-8, 1978 using the data of optical, soft X-ray and
meter-wave observations.
Title: Microwave activities associated with McMath regions 14943
and 14979.
Authors: Shibasaki, K.; Ishiguro, M.; Enome, S.; Nakajima, H.
Bibcode: 1978STERJ...2...56S
Altcode:
The paper presents polarimetric and east-west scan data on microwave
burst activity associated with the solar McMath regions 14943 and
14979 for the period September and October 1977. It was found that the
latitude of the active region is low and its polarity is reversed from
what would be expected for cycle 21, while its activity is high and
caused several large bursts. The activity was divided into two phases
and the frequency spectra of the burst which occurred during these
two phases were divided into two groups. This division may be caused
by changes in the intensity and/or morphology of the magnetic field.
Title: V A Coronal Hole Observed with a 2 8-cm Radioheliograph
Authors: Shibasaki, K.; Ishiguro, M.; Énomé, S.; Tanaka, H.
Bibcode: 1978PASJ...30..589S
Altcode:
Around the end of 1975, a low-brightness region was detected with the
8-cm radioheliograph at Toyokawa and observed over a period of three
solar rotations. It was accompanied by a high-speed solar wind stream
and caused recurrent-type geomagnetic storms. This region was identified
as a coronal hole and its brightness temperature was 6000 K lower than
that of the normal quiet region. A simple model of the solar atmosphere
is used to calculate the brightness temperature at 8- cm wavelength in
the coronal hole and the normal quiet region. The electron pressure at
the base of the corona obtained by EUV and soft X-ray observations is
too high to explain the present radio observations of the coronal hole
and the normal quiet region. Key words: Coronal hole; Solar radio map.
Title: Solar radio emission in solar cycles 19 and 20
Authors: Tanaka, H.; Enome, S.; Ishiguro, M.; Shibasaki, K.
Bibcode: 1977STERJ...1...72T
Altcode:
Monthly mean values of the solar radio flux, adjusted to 1 AU,
are presented for solar cycles 19 and 20 (April, 1954 to March,
1976). Solar cycle 20, typical of a low-activity cycle, shows a low
but wide peak of activity; solar cycle 19, on the other hand, shows
a higher and narrower peak of activity. Correlations between emission
fluxes and sunspot numbers are also discussed.
Title: A coronal hole observed by 8-cm wavelength radioheliograph
Authors: Shibasaki, K.; Ishiguro, M.; Enome, S.; Tanaka, H.
Bibcode: 1977cosp.meetS....S
Altcode:
Around the end of 1975, a low brightness region was detected by an
8-cm radioheliograph at Toyokawa. It was observed over a period of
three solar rotations. It was accompanied by a high-speed solar wind
stream and caused recurrent-type geomagnetic storms. This region was
identified as a coronal hole. The brightness temperature of this coronal
hole was 6000 K lower than that of the normal quiet region. A simple
model of the solar atmosphere was used to calculate the brightness
temperature at 8-cm wavelength in the coronal hole and the normal quiet
region. The electron pressure at the base of the corona obtained by
EUV and soft X-ray observations is too high to explain the present
radio observations of the coronal hole and the normal quiet region.
Title: lambda 8 cm radioheliograms.
Authors: Shibasaki, K.; Ishiguro, M.; Enome, S.; Tanaka, H.; Torii,
C.; Tsukiji, Y.; Kobayashi, S.; Yoshimi, N.
Bibcode: 1976PRIAN..23...21S
Altcode:
No abstract at ADS
Title: Latitudinal distribution of solar wind velocity and its
relation to solar EUV corona
Authors: Watanabe, T.; Shibasaki, K.; Kakinuma, T.
Bibcode: 1974JGR....79.3841W
Altcode:
The solar wind velocity in high heliographic latitudes up to 64°N
is derived from the interplanetary scintillation of 3C48 in 1972 and
1973, and the relation between latitudinal distribution of the solar
wind velocity and of the brightness of solar EUV corona is examined. In
May-June 1972 the solar wind velocity tended to increase with increasing
heliographic latitude of the source of observed solar wind, while the
intensity of the EUV corona weakened with increasing latitude. In
May-June 1973 the solar wind velocity did not noticeably increase
with latitude, and average brightness of the EUV corona in low and
high latitudes was approximately the same. Hence it is suggested that
the latitudinal distribution of the solar wind velocity is inversely
related to the brightness distribution of the solar EUV corona.
Title: Solar wind disturbances detected by the interplanetary
scintillation of radio sources in early August 1972
Authors: Watanabe, T.; Kakinuma, T.; Kojima, M.; Shibasaki, K.
Bibcode: 1973JGR....78.8364W
Altcode:
No abstract at ADS