[show abstract][hide abstract] ABSTRACT: We report a detailed examination of the "red asymmetry" of H-alpha emission
line seen during the 2001 April 10 solar flare by using a narrowband
filtergram. We investigated the temporal evolution and the spatial distribution
of the red asymmetry by using the H-alpha data taken with the 60cm Domeless
Solar Telescope at Hida Observatory, Kyoto University. We confirmed that the
red asymmetry clearly appeared all over the flare ribbons, and the strong red
asymmetry is located on the outer narrow edges of the flare ribbons, with the
width of about 1.5" - 3.0" (1000 - 2000 km), where the strong energy releases
occur. Moreover, we found that the red asymmetry, which also gives a measure of
the Doppler shift of the H-alpha emission line concentrates on a certain value,
not depending on the intensity of the H-alpha kernels. This implies not only
that the temporal evolutions of the red asymmetry and those of the intensity
are not in synchronous in each flare kernel, but also that the peak asymmetry
(or velocity of the chromospheric condensation) of individual kernel is not a
strong function of their peak intensity.
Publications- Astronomical Society of Japan 12/2011; · 2.44 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present the temporal and statistical relations between the mechanical energies of disappearing solar filaments and the thermal energies of the associated flare arcades in soft X-rays. Measuring the 3-D velocity fields of 10 eruptive filaments, we calculated their mechanical energy gain rate, εmc, per unit volume and compared it to the thermal energy release rate per unit volume, εth, derived with Yohkoh/SXT data. For the statistical relation, we found a relation that can be approximated as εth ∝ ε1.9mc. This relation can be explained by interpreting the energy input to an arcade via the Poynting flux in the magnetic reconnection process and the acceleration of a filament by the Lorentz force. This explanation is also supported by the strong dependence of the observed increase rates of both the thermal and mechanical energy densities on the mean magnetic field strength of the source region. We also investigated their temporal variations, and found that the start time of increase in the mechanical energy of a filament preceded that of the thermal energy of the coronal arcade in some cases. These relations imply that the basic mechanisms that accelerate a filament and create a hot plasma are different, and both energy increase rates are determined primary by the magnetic field strengths.
Publications- Astronomical Society of Japan 01/2010; 62. · 2.44 Impact Factor
[show abstract][hide abstract] ABSTRACT: We compared high-resolution images of an emerging flux region in Hα and in soft X-ray, using two types of coalignments. Hα images were taken at Hida Observatory. Soft X-ray images were taken by the Soft X-ray telescope onboard Yohkoh. These data were obtained through coordinated observations by Hida Observatory and Yohkoh. Soft X-ray brightenings were found above most of the emerging Hα arch filaments, which are traces of rising magnetic flux tubes. The released energies in the soft X-ray brightenings were found to be ~1027 ergs, which is consistent with an estimate of energy release through magnetic reconnection between coronal fields and rising flux tubes as an Hα arch filament. These observational results indicate that an arch filament or rising magnetic flux tube itself is not heated up to coronal temperature as soon as it has reached coronal heights, but it can induce a change of magnetic structure through magnetic reconnection in the overlying corona. We also studied the structure of an arch filament in detail at its birth stage. Its morphological feature and evolutionary characteristics can be well explained by the asymmetric rising of a flux tube.
The Astrophysical Journal 01/2009; 517(2):964. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report a detailed examination of the fine structure inside flare ribbons and the temporal evolution of such structure during an X2.3 solar flare, which occurred on 2001 April 10. We examined fine structures, such as systems of conjugate footpoints, inside flare ribbons by using the Hα images obtained with the Sartorius telescope at Kwasan Observatory, Kyoto University. We identified the conjugate footpoints of each Hα kernel in both flare ribbons by a new method that uses cross-correlation functions of the light curves. We also compared the sites of the Hα kernels with the spatial configurations of flare loops seen in the extreme-ultraviolet images obtained with the Transition Region and Coronal Explorer. We found that the highly correlated pairs of Hα kernels were connected by flare loops seen in the 171 Å images. Investigating such fine structures inside the flare ribbons, we can follow the history of energy release and perhaps acquire key information about particle acceleration.
The Astrophysical Journal 12/2008; 586(1):624. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present the relation of the spatial distribution of Hα kernels with the distribution of hard X-ray (HXR) sources seen during the 2001 April 10 solar flare. This flare was observed in Hα with the Sartorius telescope at Kwasan Observatory, Kyoto University, and in HXRs with the hard X-ray telescope (HXT) on board Yohkoh. We compared the spatial distribution of the HXR sources with that of the Hα kernels. While many Hα kernels are found to brighten successively during the evolution of the flare ribbons, only a few radiation sources are seen in the HXR images. We measured the photospheric magnetic field strengths at each radiation source in the Hα images and found that the Hα kernels accompanied by HXR radiation have magnetic strengths about 3 times larger than those without HXR radiation. We also estimated the energy release rates based on the magnetic reconnection model. The release rates at the Hα kernels with accompanying HXR sources are 16-27 times larger than those without HXR sources. These values are sufficiently larger than the dynamic range of HXT, which is about 10, so that the difference between the spatial distributions of the Hα kernels and the HXR sources can be explained.
The Astrophysical Journal 12/2008; 578(1):L91. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have recently developed a new method for automatic detection of solar surges and other dark dynamic features. For the first time we find that some filaments can be quickly formed by trapping the cold material supplied by surges originating from the chromosphere. Two clear examples are presented in this Letter, showing the special process for new filament formation by surge injection. The data used here were taken from Hida Observatory and the Global Hα Network operated by Big Bear Solar Observatory. Both the filaments existed on the solar surface for not less than 20 hr, with an average length about 200'', and had obvious helical structures and barbs. The surge material was injected from one terminal along the main axis of the filaments or the filament channels. We conclude that there are two necessary conditions for new filament formation by surges at one location: (1) an "empty" filament channel, or magnetic trap, and (2) enough mass supplied by surge activity. In most other surge-filament events, apart from our two examples, the surges are observed moving toward and acting on a preexisting nearby filament. The close relationship between surge activity and filament formation and maintenance suggests that there should be a direct link between the filament axial fields and the large-scale background fields along which the surge material can be driven into the filament channel. On the other hand, it also supports the idea that the frequent injection of flow from below is an important way to convey mass and energy into the corona through magnetic reconnections driven by successive emerging flux and converging flow.
The Astrophysical Journal 12/2008; 631(1):L93. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We discovered three successive Moreton waves generated by a single solar flare on 2005 August 3. Although this flare was not special in magnitude or configuration, Moreton waves (shock waves) successively occurred three times. Multiple shock waves generated during a single flare have not been reported before. Furthermore, the faster second-generated Moreton wave caught up and merged with the slower first-generated one. This is the first report of shock-shock interaction associated with a solar flare. The shock-plasma interaction was also detected. When the third-generated Moreton wave passed through an erupting filament, the filament was accelerated by the Moreton wave. In this event, filaments also erupted three times. On the basis of this observation, we consider that filament eruption is indispensable to the generation of Moreton waves.
The Astrophysical Journal 12/2008; 684(1):L45. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have examined the relation between the evolution of the Hα flare ribbons and the released magnetic energy in a solar flare that occurred on 2001 April 10. Based on the magnetic reconnection model, the released energy was quantitatively calculated by using the photospheric magnetic field strengths and separation speeds of the fronts of the Hα flare ribbons. We compared the variation of the released energy with the temporal and spatial fluctuations in the nonthermal radiation observed in hard X-rays and microwaves. These nonthermal radiation sources indicate when and where large energy releases occur. We also estimated the magnetic energy released during the flare. The estimated energy release rates in the Hα kernels associated with the hard X-ray sources are locally large enough to explain the difference between the spatial distributions of the Hα kernels and the hard X-ray sources. We also reconstructed the peaks in the nonthermal emission by using the estimated energy release rates.
The Astrophysical Journal 12/2008; 611(1):557. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this paper we compare EUV Imaging Telescope (EIT) waves with simultaneous phenomena seen in Hα in order to address the question of what an EIT wave is. We surveyed the events associated with solar flares larger than GOES M-class in 1999-2002. The Hα data are taken with the Flare-monitoring Telescope (FMT) at the Hida Observatory of Kyoto University. Among 14 simultaneous observations of EIT waves and Hα, 11 were found to have filament eruptions, three were associated with Moreton waves, and one was found to have only filament oscillations. This shows that we cannot see clear wave fronts in Hα even if EIT waves exist, but that it is possible to recognize invisible waves by means of filament oscillations. The nature of filament oscillations and Moreton waves associated with EIT waves is examined in detail, and it is found that the filament oscillations were caused by EIT waves.
The Astrophysical Journal 12/2008; 608(2):1124. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: In order to obtain an overall view of the flow structure of convective gas in emerging flux regions (EFRs), we studied three EFRs in two solar active regions, NOAA 8218 and NOAA 10774. Using the Local Correlation Tracking method, we found several horizontally divergent flow structures, which were stable over a period of 1 hour, in 2 EFRs in NOAA 8218. The horizontal flow velocities and the sizes of the structures were around 500m s-1 and about 4Mm in radius, respectively. We analyzed another dataset of NOAA 10774 using spectroscopic methods and found temporarily stable up-ward gas flows in the central part of the EFR. The line-of-sight velocities were around 150m s-1 and the size of the flow patch was 2 to 5Mm in radius. These results support our previous findings that convective-cell-like flow appears in the central part of an EFR. We estimated from these results that the depth of the flow cell in EFRs is about 600km, and the turn-over time of the cell is about 2 hours.
Publications of The Astronomical Society of Japan - PUBL ASTRON SOC JPN. 01/2006; 58:407-421.
[show abstract][hide abstract] ABSTRACT: It is unclear whether it is possible for magnetic helical fields of
opposite signs to co-exist in a coronal mass ejection (CME). During
filament eruption with high-cadence observations for the initial stage,
evidence is found for the formation of right-handed helical fields in a
rising dextral filament that is embedded in a CME with helical fields in
a left-handed sense. The data include Mees multi-off-band Hα
observations with 16s cadence and TRACE 1600Å observations of 2s
cadence. The filament material is ejected outward and is associated with
the expanding CME, suggesting that both of the opposite-sign helical
fields are injected into interplanetary space. In this paper, we
consider the key observational features, including the formation of a
coil-like structure (due to barb reconnections) and the alignment of
reconnected field lines with the primary axis of the filament. It is
found that they are consistent with the predicted changes during
filament eruption by the filament model of Martin and McAllister.
However, our results do not reject the filament model of Rust and Kumar.
Moreover, a model that reconciles both of them seems to be more
convenient for understanding the complicated observations. Therefore,
the formation of opposite-sign helicity in an eruptive flux rope should
be common for such types of filament eruptions.
Publications- Astronomical Society of Japan 05/2004; 56:497-507. · 2.44 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report on the simultaneous observation of a Moreton wave in Hα
and two kinds of coronal expanding features in soft X-rays near the
solar limb. We consider the faster X-ray feature and the slower one as
being an ``X-ray wave'' and ``ejecta'', respectively. The chromospheric
Moreton wave propagated on the solar disk at a speed of 1040 ±
100 km s-1 whereas the coronal X-ray wave propagated outside
of the disk toward the outer corona at 1400 ± 250 km
s-1. We identified the X-ray wave as MHD fast-mode shock. The
fast-mode Mach number (Mf) of the X-ray wave was also
estimated to be about 1.13-1.31, which decreases during propagation. The
timing when the Mf became ``1'' is consistent with that of
the disappearance of the Moreton wave. Moreover, we discuss the
3-dimensional structure of the shock wave and the relation between the
shock wave and the ejecta (and Hα filament eruptions).
Publications- Astronomical Society of Japan 03/2004; 56:L5-L8. · 2.44 Impact Factor
[show abstract][hide abstract] ABSTRACT: Moreton waves are flare-associated waves observed to propagate across the solar disk in Halpha, especially in the wing of Halpha. The Flare Monitoring Telescope at Hida Observatory of Kyoto University observed 12 events associated with flare waves (i.e., Moreton waves and/or filament oscillations) in Halpha from 1997 to 2002. We review our studies of Moreton waves based on these observations; relation between EIT wave and Moreton wave (Eto et al. 2002),simultaneous observation with X-ray wave (Narukage et al. 2002),three dimensional structure of flare-associated wave (Narukage et al. 2004),relation between Moreton waves and filament eruptions.
Proceedings of the International Astronomical Union 01/2004; 223:367-370.
[show abstract][hide abstract] ABSTRACT: A detailed study of the evolution and cooling process of post-flare loops is presented for a large X9.2 solar flare of 2 November 1992 by using H images obtained with Domeless Solar Telescope at Hida Observatory and soft X-ray images of Yohkoh Soft X-ray Telescope (SXT). The detailed analysis with a new method allows us to determine more precise values of the cooling times from 107K to 104K plasma in the post-flare loops than in previous works. The subtraction of sequential images shows that soft X-ray dimming regions are well correlated to the H brightening loop structure. The cooling times between 107K and 104K are defined as the time difference between the start of soft X-ray intensity decrease and the end of H intensity increase at a selected point, where the causal relation between H brightening and soft X-ray dimming loops is confirmed. The obtained cooling times change with time; about 10min at the initial stage and about 40min at the later stage. The combined conductive and radiative cooling times are also calculated by using the temperature and density obtained from SXT data. Calculated cooling times are close to observed cooling times at the beginning of the flare and longer in the later stage.
Solar Physics 06/2003; 215(1):127-146. · 3.26 Impact Factor
[show abstract][hide abstract] ABSTRACT: Surge activities were observed at the edge of an emerging flux region.
We studied the relations between the features around the surges in
various data sets: magnetogram, Hα, G-band, UV, EUV, and soft
X-rays. We showed that the surge activities in Hα and the
brightenings in TRACE 1600Å images correlate well in both time and
space with the cancellation of magnetic fluxes around an emerging flux
region. In particular, at the onset of surge activity, a close
correlation among them was clearly found. These facts are consistent
with the magnetic reconnection model. The released energy through
magnetic reconnection, which is estimated to be 1028 erg, is
sufficiently large to produce surge activities. No prominent
brightenings were observed in soft X-ray and EUV images during the surge
activities. This may suggest that the energy releases occurred at a
layer of high densities.
Publications- Astronomical Society of Japan 01/2003; 55:313-320. · 2.44 Impact Factor
[show abstract][hide abstract] ABSTRACT: The 3-D velocity fields of disappearing filaments (Disparition Brusques: DBs) on the solar disk were extensively studied in order to determine their 3-D velocity fields. Applying Beckers' cloud model to 5 DB events observed in the Halpha line center and Halpha ± 0.8 Å with the Flare Monitoring Telescope (FMT) at Hida Observatory, we developed a method to derive the complete 3-D velocity field of DBs. The line-of-sight velocity is obtained (i) by calculating the Halpha line profile of the filament, and (ii) by measuring the Doppler shift which best fits to the observed temporal variations of contrasts of the filament. The tangential velocity is obtained by tracing the motions of the internal structures on the successive images. In this method, corrections for the effective filter bandwidths of the instrument, stray lights, and Doppler brightening effect are performed. We also discuss the velocity errors which arise from the intrinsic variations of the filament plasma during its activation, the fluctuations in intensities of the background chromosphere, and the choice of different forms of the spread function for estimating the stray light. It is emphasized that the calculation of three-dimensional vector trajectories of a disappearing filament with our method can enhance the quality of a space weather forecast with better certainty.
Publications of The Astronomical Society of Japan - PUBL ASTRON SOC JPN. 01/2003; 55:505-520.
[show abstract][hide abstract] ABSTRACT: We consider the relationship between two flare-associated waves, a
chromospheric Moreton wave and a coronal EIT wave, based on an analysis
of an X-class flare event in AR 8100 on 1997 November 4. A Moreton wave
was observed in Hα + 0.8 Å, and Hα - 0.8 Å with
the Flare-Monitoring Telescope (FMT) at the Hida Observatory. An EIT
wave was observed in EUV with the Extreme ultraviolet Imaging Telescope
(EIT) on board SOHO. The propagation speeds of the Moreton wave and the
EIT wave were approximately 715 km s-1 and 202 km
s-1, respectively. The times of visibility for the Moreton
wave did not overlap those of the EIT wave, but the continuation of the
former is indicated by a filament oscillation. Data on the speed and
location clearly show that the Moreton wave differed physically from the
EIT wave in this case. The Moreton wave preceded the EIT wave, which is
inconsistent with an identification of the EIT wave with a fast-mode MHD
Publications- Astronomical Society of Japan 05/2002; 54:481-491. · 2.44 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present a detailed study of coronal loop brightenings observed in an active region on the solar limb. These brightening
loops show expanding and shrinking motions in EUV coronal line images and also show downflow along the loops in Lα and Hα
images. By means of time-slice analysis of the images, we found that both the expanding and shrinking motions of the loops
are not real motions of plasma but apparent motions like post-flare loops, where the loops at the different height are successively
heated and cooled. From a temperature analysis, the time delay between the brightenings of hot 195Å and cool Lα loops is
found to be nearly equal to the time-scale of the conduction cooling. We conclude that these loop brightenings are sources
of so called Hα coronal rains.
Solar Physics 02/2002; 206(1):133-142. · 3.26 Impact Factor
[show abstract][hide abstract] ABSTRACT: An emerging twisted flux rope model to explain the drastic evolution of a flare-productive NOAA Active Region 9026 is presented. The drastic changes in the -type sunspot configuration were found to start shortly before the big flares of 2000 June 6: (1) rapid proper motions of sunspots started at the both sides of the central sunspot about 7 hr prior to the strong flare activity, (2) the collapse of the central sunspot with its disintegration and partial disappearance started about 3 hr before the strong flare activity, (3) a switchback-shaped and strongly sheared magnetic neutral line was formed with intruding motions of sunspots into the opposite magnetic polarities, and (4) the direction of the neutral line rapidly rotated clockwise at the same time when the switchback neutral line was formed. To explain these outstanding features of the sunspot evo-lution, we constructed a schematic model of an emerging twisted flux rope in which the central writhe helicity of the flux rope could be formed by continuous transformation of the twist helicity by means of the kink instability in the course of its emergence through the convection zone.
The Astrophysical Journal 01/2002; 572(1). · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present conspicuous activities of plasma ejections along a light bridge of a stable and mature sunspot in NOAA 8971 on 2000 May 02. We found the ejections both in the H-alpha (10^4 K) images obtained with the Domeless Solar Telescope (DST) at Hida Observatory, and in the 171 A (Fe IX/X, ~10^6 K) images obtained with the Transition Region and Coronal Explorer (TRACE). Main characteristics of the ejections are as follows: (1)Ejections occur intermittently and recurrently, (2)The velocities and the timings of the 171 A-ejections are the same as those of H-alpha ejections, (3)The appearance of ejections are different from one another, i.e. the H-alpha ejections have jet-like appearance, while that of 171 A-ejections is like a loop. Comment: 6 pages, 1 table, 4 figures
The Astrophysical Journal 11/2001; · 6.73 Impact Factor