We performed statistical and event studies of linear polarization in the H line during solar flares. The statistical study revealed that, among 71 H flares analyzed, including 64 GOES flares, only ...one event shows significant linear polarization signals. Such an infrequent occurrence of significant linear polarization in solar flares is consistent with the result by Bianda et al., who studied 30 flares and found no polarization signals. In the event showing the significant polarization, the maximum degree of linear polarization was 1.16% 0.06%, and the average direction of the polarization deviated by −142 5 6 0 from the solar north. The observed polarization degrees and the directions are consistent with the preceding reports. These strong linear polarization signals did not appear at major flare ribbons, nor did they correlate with either hard or soft X-ray emissions temporally or spatially. Instead, they appeared at a minor flare kernel, which corresponds to one of the footpoints of a coronal loop. The active region caused coronal dimming after the soft X-ray peak. The observed flare shows no direct evidence that the linear polarization is produced by high-energy particles, which are often considered to generate the polarization. On the other hand, our study suggests the possibility that coronal mass ejections, which have been often observed in flares showing linear polarization signals, play an important role for exciting linear polarization at H flare kernels.
A statistical analysis of radio flare events was conducted by using the event list of Nobeyama Radioheliograph in the years 1996–2009. We examined center-to-limb variations of 17 GHz and 34 GHz ...fluxes by dividing the flare events into different groups according to the ``thermal plasma richness'' (ratio of the peak flux of soft X-ray to nonthermal radio emissions) and the duration of radio bursts. It was found that the peak flux at 17 and 34 GHz tended to be higher toward the limb for thermal-rich flares with short durations. We propose that the thermal-rich flares, which are supposed to be associated with an efficient precipitation of high-energy particles into the chromosphere, have a pitch-angle distribution of nonthermal electrons with a higher population along the flare loop.
Internal Fine Structure of Ellerman Bombs Hashimoto, Yuki; Kitai, Reizaburo; Ichimoto, Kiyoshi ...
Publications of the Astronomical Society of Japan,
08/2010, Letnik:
62, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We conducted coordinated observations of Ellerman bombs (EBs) between Hinode Satellite and Hida Observatory (HOP12). Ca II H broad-band filter images of NOAA 10966 on 2007 August 9 and 10 were ...obtained with the Solar Optical Telescope (SOT) aboard the Hinode Satellite, and many bright points were observed. We identified a total of 4 bright points as EBs, and studied the temporal variation of their morphological fine structures and spectroscopic characteristics. With high-resolution Ca II H images of SOT, we found that the EBs, thus far thought of as single bright features, are composed of a few of fine subcomponents. Also, by using Stokes
$I$
/
$V$
filtergrams with Hinode/SOT, and Ca II H spectroheliograms with Hida/Domeless Solar Telescope (DST), our observation showed: (1) The mean duration, the mean width, the mean length, and the mean aspect ratio of the subcomponents were 390 s, 170 km, 450 km, and 2.7, respectively. (2) Subcomponents started to appear on the magnetic neutral lines, and extended their lengths from the original locations. (3) When the Ca II H line of EBs showed the characteristic blue asymmetry, they are associated with the appearance or re-brightening of subcomponents. Summarizing our results, we obtained an observational view that elementary magnetic reconnections take place one by one successively and intermittently in EBs, and that their manifestation is the fine subcomponents of the EB phenomena.
A high-speed imaging system for observing solar flares in the continuum and H
$ \alpha$
wavelengths was installed on a
$ \phi$
25 cm telescope of the Solar Magnetic Activity Research Telescope ...(SMART) at Hida observatory of Kyoto University. The aim of this system is to diagnose the spatio-temporal evolution of high-energy particles in solar flares by capturing the explosive evolution of chromospheric and photospheric flare kernels. The system acquires flare images covering a field of view of 344
$ ''$
$ \times$
258
$ ''$
with a spatial sampling of 0
$ \hskip1pt''\!\!\!.\hskip1pt$
215 pixel
$ ^{-1}$
and a frame rate of 25 frames s
$ ^{-1}$
. Initial data, including two white-light flares, demonstrate the diffraction-limited performance of the system. Observations have been in regular operation since 2011 November. The system is expected to provide a data set that is highly complementary with Hinode/SOT, SDO/AIA, and other ground-based instruments for upcoming solar-flare research.
Spicule Dynamics over a Plage Region Anan, Tetsu; Kitai, Reizaburo; Kawate, Tomoko ...
Publications of the Astronomical Society of Japan,
08/2010, Letnik:
62, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We studied spicular jets over a plage area and derived their dynamic characteristics using Hinode Solar Optical Telescope (SOT) high-resolution images. A target plage region was near to the west limb ...of the solar disk. This location permitted us to study the dynamics of spicular jets without any overlapping effect of spicular structures along the line of sight. In this work, to increase the ease with which we could identify spicules on the disk, we applied the image processing method ‘MadMax’ developed by Koutchmy et al. (1989). It enhances fine, slender structures (like jets), over a diffuse background. We identified 169 spicules over the target plage. This sample permited us to derive statistically reliable results regarding spicular dynamics. The properties of plage spicules can be summarized as follows: (1) In a plage area, we clearly identified spicular jet features. (2) They were shorter in length than the quiet region limb spicules, and followed a ballistic motion under constant deceleration. (3) The majority (80%) of the plage spicules showed a cycle of rise and retreat, while 10% of them faded out without a complete retreat phase. (4) The deceleration of the spicule was proportional to the velocity of ejection (i.e., the initial velocity).
Abstract
Aiming at the quantitative diagnostics of boron monohydryde, BH, in fusion plasmas, we present elastic, electronic excitation, and ionization cross sections of BH for the first time. The ...calculations were performed by the
R
-matrix and Born Encounter Bethe methods utilized by Quantemol-EC software. To examine the uncertainty due to the calculation conditions, we compared the results by different basis sets and internuclear distances of the target model. We found that the uncertainties are typically within ∼10%. Rate coefficients were derived and fitted to an Arrhenius function. The derived decay rate per photon,
S
/
X
B
, agreed with the value presented by Lieder
et al
(the ASDEX-Upgrade Team) (1994
Eur. Phys. Soc. Conf. Plasma Phys.
2
722).
Abstract
Solar filaments are dense, cool plasma clouds in the solar corona. They are supposed to be supported in a dip of the coronal magnetic field. However, the models still disagree between two ...types of field configuration; one is the normal polarity model proposed by Kippenhahn and Schlueter (1957, Z. Astrophys., 43, 36), and the other is the reverse polarity model proposed by Kuperus and Raadu (1974, A&A, 31, 189). To understand the mechanism that makes the filaments become unstable before eruption, it is critical to know the magnetic structure of solar filaments. We performed spectropolarimetric observation in the He i (10830 Å) line to investigate the magnetic field configuration of dark filaments. The observation was carried out with the Domeless Solar Telescope at Hida Observatory with a polarization sensitivity of 3.0 × 10−4. We obtained eight samples of filaments in a quiet region. As a result of the analysis of full Stokes profiles of filaments, we found that the field strengths were estimated as 8–35 G. By comparing the direction of the magnetic field in filaments and the global distribution of the photospheric magnetic field, we determined the magnetic field configuration of the filaments, and we concluded that one out of the eight samples has normal polarity configuration, and seven out of the eight have reverse polarity configuration.
Abstract
We performed statistical and event studies of linear polarization in the H
α
line during solar flares. The statistical study revealed that, among 71 H
α
flares analyzed, including 64
GOES
...flares, only one event shows significant linear polarization signals. Such an infrequent occurrence of significant linear polarization in solar flares is consistent with the result by Bianda et al., who studied 30 flares and found no polarization signals. In the event showing the significant polarization, the maximum degree of linear polarization was 1.16% ± 0.06%, and the average direction of the polarization deviated by −142.°5 ± 6.°0 from the solar north. The observed polarization degrees and the directions are consistent with the preceding reports. These strong linear polarization signals did not appear at major flare ribbons, nor did they correlate with either hard or soft X-ray emissions temporally or spatially. Instead, they appeared at a minor flare kernel, which corresponds to one of the footpoints of a coronal loop. The active region caused coronal dimming after the soft X-ray peak. The observed flare shows no direct evidence that the linear polarization is produced by high-energy particles, which are often considered to generate the polarization. On the other hand, our study suggests the possibility that coronal mass ejections, which have been often observed in flares showing linear polarization signals, play an important role for exciting linear polarization at H
α
flare kernels.
In the Large Helical Device (LHD), a high-performance plasma has been obtained at the inwardly shifted magnetic axis position of R
ax
= 3.60 m in which a spatial distance between the first wall on ...the vacuum vessel and the outermost edge boundary of the stochastic magnetic field layer existing outside the last closed flux surface takes a minimum value of ~12 mm at the inboard side. In order to investigate contact between the edge plasma boundary and the inboard first wall, a radial profile of Hβ line emissions at 4861 Å has been measured using a Czerny-Turner visible spectrometer and a 40-channel optical fiber array. All Hβ profiles measured at different magnetic axis positions of R
ax
= 3.60, 3.75, and 3.90 m showed a centrally peaked profile except for a few fiber channels observing the outboard edge plasma. The Hβ emission near the inboard first wall was negligibly weak, in particular, in the case of R
ax
= 3.60 m, suggesting no significant contact between the edge boundary plasma and the vacuum vessel first wall. The radial Hβ profile was then analyzed in detail using the EMC3-EIRENE edge plasma simulation code. The simulation well reproduced the measured profiles, including the extremely weak Hβ emission around the inboard first wall in the R
ax
= 3.60 m configuration. The centrally peaked profiles are found to originate in the Hβ emissions around X-points, while hydrogen neutrals are dominantly localized near the divertor plates. These results confirm the formation of a complete open divertor configuration in the LHD discharge without significant contact with the first wall. The presence of a region with extremely short magnetic field connection lengths (L
c
< 5 m) between the inboard first wall and the outermost edge boundary is a key point to eliminate the strong plasma-wall interaction because sustainment of a significant edge plasma is entirely difficult in such a low L
c
region.
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