清水 敏文

HINODE, Japanese for "sunrise", is a spacecraft dedicated for observations of the Sun, and was launched in 2006 to study the Sun's magnetic fields and how their explosive energies propagate through the different atmospheric layers. The spacecraft carries the Solar Optical Telescope (SOT), which has a 50 cm diameter clear aperture and provides a continuous series of diffraction-limited visible light images from space. The telescope was developed through international collaboration between Japan and US. In order to achieve the diffraction-limited performance, thermal and structural modeling of the telescope was extensively used in its development phase to predict how the optical performance changes dependent on the thermal condition in orbit. Not only the modeling, we devoted many efforts to verify the optical performance in ground tests before the launch. The verification in the ground tests helped us to find many issues, such as temperature dependent focus shifts, which were not identified only through the thermal-structural modeling. Another critical issue was micro-vibrations induced by internal disturbances of mechanical gyroscopes and momentum wheels for attitude control of the spacecraft. Because the structural modeling was not accurate enough to predict how much the image quality was degraded by the micro-vibrations, we measured their transmission in a spacecraft-level test.

We present an optical and thermal design of one of major instrumental payload planned for SOLAR-C mission/Plan-B (high resolution spectroscopic option): the telescope assembly of Solar Ultra-violet Visible and near IR observing Telescope (SUVIT). To accommodate a launcher's nosecone size, a wide observing wavelength coverage from UV (down to 280 nm) through near IR (up to 1100 nm), and an 0.1 arcsec resolution in the field of 200 arcsec diameter, a short telescope design was made for a 1.5 m aperture solar Gregorian telescope with the compact design of three-mirror collimator unit.

Two mission concepts (plan A: out-of-ecliptic mission and plan B: high resolution spectroscopic mission) have been studied for the next Japanese-led solar mission Solar-C, which will follow the scientific success of the Hinode mission. The both mission concepts are concluded as equally important and attractive for the promotion of space solar physics. In the meantime we also had to make efforts for prioritizing the two options, in order to proceed to next stage of requesting the launch of Solar-C mission at the earliest opportunity. This paper briefly describes the two mission concepts and the current status on our efforts for prioritizing the two options. More details are also described for the plan B option as the first-priority Solar-C mission. The latest report from the Solar-C mission concept studies was documented as "Interim Report on the Solar-C Mission Concept."

It is presented the conceptual design of a focal plane instrument for the Solar UV-Vis-IR Telescope (SUVIT) aboard the next Japanese solar mission SOLAR-C. A primary purpose of the telescope is to achieve precise as well as high resolution spectroscopic and polarimetric measurements of the solar chromosphere with a big aperture of 1.5 m, which is expected to make a significant progress in understanding basic MHD processes in the solar atmosphere. The focal plane instrument consists of two packages: A filtergraph package is to get not only monochromatic images but also Dopplergrams and magnetograms using a tunable narrow-band filter and interference filters. A spectrograph package is to perform accurate spectro-polarimetric observations for measuring chromospheric magnetic fields, and is employing a Littrow-type spectrograph. The most challenging aspect in the instrument design is wide wavelength coverage from 280 nm to 1.1 mu m to observe multiple chromospheric lines, which is to be realized with a lens unit including fluoride glasses. A high-speed camera for correlation tracking of granular motion is also implemented in one of the packages for an image stabilization system, which is essential to achieve high spatial resolution and high polarimetric accuracy.

The solar chromosphere is an important boundary, through which all of the plasma, magnetic fields and energy in the corona and solar wind are supplied. Since the Zeeman splitting is typically smaller than the Doppler line broadening in the chromosphere and transition region, it is not effective to explore weak magnetic fields. However, this is not the case for the Hanle effect, when we have an instrument with high polarization sensitivity (similar to 0.1%). "Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP)" is the sounding rocket experiment to detect linear polarization produced by the Hanle effect in Lyman-alpha line (121.567 nm) and to make the first direct measurement of magnetic fields in the upper chromosphere and lower transition region. To achieve the high sensitivity of similar to 0.1% within a rocket flight (5 minutes) in Lyman-alpha line, which is easily absorbed by materials, we design the optical system mainly with reflections. The CLASP consists of a classical Cassegrain telescope, a polarimeter and a spectrometer. The polarimeter consists of a rotating 1/2-wave plate and two reflecting polarization analyzers. One of the analyzer also works as a polarization beam splitter to give us two orthogonal linear polarizations simultaneously. The CLASP is planned to be launched in 2014 summer.

LEMUR is a VUV imaging spectrograph with 0.28 '' resolution. Incident solar radiation is imaged onto the spectrograph slit by a single mirror telescope consisting of a 30-cm steerable f/12 off-axis paraboloid mirror. The spectrograph slit is imaged and dispersed by a highly corrected grating that focuses the solar spectrum over the detectors. The mirror is coated with a suitable multilayer with B4C top-coating providing a reflectance peak around 18.5 nm besides the usual B4C range above 500 angstrom. The grating is formed by two halves, one optimized for performances around 185 angstrom and the other above 500 angstrom. Three intensified CCD cameras will record spectra above 50 nm while a large format CCD array with an aluminum filter will be used around 185 angstrom.

Ca II H imaging observations by the Hinode Solar Optical Telescope (SOT) have revealed that the chromosphere is extremely dynamic and that ejections and jets are well observed in moat region around sunspots. X-ray and EUV observations show frequent occurrence of microflaring activities around sunspots; small emerging flux or moving magnetic features approaching opposite pre-existing magnetic flux can be identified on the footpoints for half of microflares studied, while no encounters of opposite polarities are observed at footpoints for the others even with SOT high spatial magnetorams (Kano at al. 2010). Another observations tell the involvement of twisted magnetic fields in the microflares accompanied by no polarity encounters at the footpoints. Some type of sunspot light bridges shows recurrent occurrence of chromospheric ejections, and photospheric vector magnetic field data suggests that twsited magnetic flux tubes lying along light bridge play vital roles in producing such ejections (Shimizu et al. 2009). This presentation reviewed observational findings from these studies. We will need to understand the 3D configuration of magnetic fields for better understanding of activity triggers in the solar atmosphere.

Using Hinode SP and C-band observations, we examined the relationship between magnetic field structure and penumbral length as well as Evershed flow speed. The latter two are positively correlated with magnetic inclination angle or horizontal field strength within 1.5 kilogauss, which is in agreement with recent magnetoconvective simulations of Evershed effect. This work thus provides direct observational evidence supporting the magnetoconvection nature of penumbral structure and Evershed flow in the presence of strong and inclined magnetic field.

We studied 16 sunspots with different sizes and shapes using the observations with the Hinode Solar Optical Telescope. The ratio of C-band and Call H images reveal rich structures both within the umbra and penumbra of most spots. The striking features are the compact blob at the foot point of the umbra side of the penumbral fibrils with disk center-limb side asymmetry. In this paper, we present properties of these features using the spectropolarimetry and images in G-band, Call and blue filters. We discuss the results using the contemporary models of the sunspots.

Microflares, which are small energetic events in the solar corona, are an example of dynamical phenomena suitable for understanding energy release processes in the solar corona. We identified 55 microflares around a well-developed sunspot surrounded by a moat with high-cadence X-ray images from the Hinode X-ray Telescope, and searched for their photospheric counterparts in line-of-sight magnetograms taken with the Hinode Solar Optical Telescope. We found opposite magnetic polarities encountering each other around the footpoints of 28 microflares, while we could not find such encounters around the footpoints of the other 27 microflares. Emerging magnetic fluxes in the moat were the dominant origin causing the encounters of opposite polarities (21 of 28 events). Unipolar moving magnetic features (MMFs) with negative polarities the same as the sunspot definitely caused the encounters of opposite polarities for five microflares. The decrease of magnetic flux, i.e., magnetic flux cancellation, was confirmed at the encountering site in typical examples of microflares. Microflares were not isotropically distributed around the spot the microflares with emerging magnetic fluxes (EMFs) were observed in the direction where magnetic islands with the same polarity as the spot were located at the outer boundary of the moat, while the microflares with negative MMFs were observed in the direction where magnetic islands with polarity opposite to the spot were located at the outer boundary of the moat. We also found that EMFs in the moat had a unique orientation in which those with the same polarity as the spot is closer to the spot than the other one that had the opposite polarity to the spot. These observational results lead to two magnetic configurations including magnetic reconnection for triggering energy release at least in half of the microflares around the spot, and suggest that the global magnetic structures around the spot strongly affect what kinds of polarity encounters are formed in the sunspot moat. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

Hinode/Solar Optical Telescope (SOT) observations reveal two new dynamic modes in quiescent solar prominences: large-scale (20-50 Mm) "arches" or "bubbles" that "inflate" from below into prominences, and smaller-scale (2-6 Mm) dark turbulent upflows. These novel dynamics are related in that they are always dark in visible-light spectral bands, they rise through the bright prominence emission with approximately constant speeds, and the small-scale upflows are sometimes observed to emanate from the top of the larger bubbles. Here we present detailed kinematic measurements of the small-scale turbulent upflows seen in several prominences in the SOT database. The dark upflows typically initiate vertically from 5 to 10 Mm wide dark cavities between the bottom of the prominence and the top of the chromospheric spicule layer. Small perturbations on the order of 1 Mm or less in size grow on the upper boundaries of cavities to generate plumes up to 4-6 Mm across at their largest widths. All plumes develop highly turbulent profiles, including occasional Kelvin-Helmholtz vortex "roll-up" of the leading edge. The flows typically rise 10-15 Mm before decelerating to equilibrium. We measure the flowfield characteristics with a manual tracing method and with the Nonlinear Affine Velocity Estimator (NAVE) "optical flow" code to derive velocity, acceleration, lifetime, and height data for several representative plumes. Maximum initial speeds are in the range of 20-30 km s(-1), which is supersonic for a similar to 10,000 K plasma. The plumes decelerate in the final few Mm of their trajectories resulting in mean ascent speeds of 13-17 km s(-1). Typical lifetimes range from 300 to 1000 s (similar to 5-15 minutes). The area growth rate of the plumes (observed as two-dimensional objects in the plane of the sky) is initially linear and ranges from 20,000 to 30,000 km(2) s(-1) reaching maximum projected areas from 2 to 15 Mm(2). Maximum contrast of the dark flows relative to the bright prominence plasma in SOT images is negative and ranges from -10% for smaller flows to -50% for larger flows. Passive scalar "cork movies" derived from NAVE measurements show that prominence plasma is entrained by the upflows, helping to counter the ubiquitous downflow streams in the prominence. Plume formation shows no clear temporal periodicity. However, it is common to find "active cavities" beneath prominences that can spawn many upflows in succession before going dormant. The mean flow recurrence time in these active locations is roughly 300-500 s (5-8 minutes). Locations remain active on timescales of tens of minutes up to several hours. Using a column density ratio measurement and reasonable assumptions on plume and prominence geometries, we estimate that the mass density in the dark cavities is at most 20% of the visible prominence density, implying that a single large plume could supply up to 1% of the mass of a typical quiescent prominence. We hypothesize that the plumes are generated from a Rayleigh-Taylor instability taking place on the boundary between the buoyant cavities and the overlying prominence. Characteristics, such as plume size and frequency, may be modulated by the strength and direction of the cavity magnetic field relative to the prominence magnetic field. We conclude that buoyant plumes are a source of quiescent prominence mass as well as a mechanism by which prominence plasma is advected upward, countering constant gravitational drainage.

We report on G-band emission observed by the Solar Optical Telescope on board the Hinode satellite in association with the X1.5-class flare on 2006 December 14. The G-band enhancements originate from the footpoints of flaring coronal magnetic loops, coinciding with nonthermal hard X-ray bremsstrahlung sources observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager. At the available 2 minute cadence, the G-band and hard X-ray intensities are furthermore well correlated in time. Assuming that the G-band enhancements are continuum emission from a blackbody, we derived the total radiative losses of the white-light flare (white-light power). If the G-band enhancements additionally have a contribution from lines, the derived values are overestimates. We compare the white-light power with the power in hard X-ray producing electrons using the thick-target assumption. Independent of the cutoff energy of the accelerated electron spectrum, the white-light power and the power of accelerated electrons are roughly proportional. Using the observed upper limit of similar to 30 keV for the cutoff energy, the hard X-ray producing electrons provide at least a factor of 2 more power than needed to produce the white-light emission. For electrons above 40 keV, the powers roughly match for all four of the time intervals available during the impulsive phase. Hence, the flare-accelerated electrons contain enough energy to produce the white-light flare emissions. The observed correlation in time, space, and power strongly suggests that electron acceleration and white-light production in solar flares are closely related. However, the results also call attention to the inconsistency in apparent source heights of the hard X-ray (chromosphere) and white-light (upper photosphere) sources.

The formation and evolution process and magnetic configuration of solar prominences remain unclear. In order to study the formation process of prominences, we examine continuous observations of a prominence in NOAA AR 10953 with the Solar Optical Telescope on the Hinode satellite. As reported in our previous Letter, we find a signature suggesting that a helical flux rope emerges from below the photosphere under a pre-existing prominence. Here we investigate more detailed properties and photospheric indications of the emerging helical flux rope, and discuss their relationship to the formation of the prominence. Our main conclusions are: (1) a dark region with absence of strong vertical magnetic fields broadens and then narrows in Ca II H-line filtergrams. This phenomenon is consistent with the emergence of the helical flux rope as photospheric counterparts. The size of the flux rope is roughly 30,000 km long and 10,000 km wide. The width is larger than that of the prominence. (2) No shear motion or converging flows are detected, but we find diverging flows such as mesogranules along the polarity inversion line. The presence of mesogranules may be related to the emergence of the helical flux rope. (3) The emerging helical flux rope reconnects with magnetic fields of the pre-existing prominence to stabilize the prominence for the next several days. We thus conjecture that prominence coronal magnetic fields emerge in the form of helical flux ropes that contribute to the formation and maintenance of the prominence.

We present high-resolution magnetic field measurements of a sunspot light bridge (LB) that produced chromospheric plasma ejections intermittently and recurrently for more than 1 day. The observations were carried out with the Hinode Solar Optical Telescope on 2007 April 29 and 30. The spectro-polarimeter reveals obliquely oriented magnetic fields with vertical electric current density higher than 100 mA m(-2) along the LB. The observations suggest that current-carrying highly twisted magnetic flux tubes are trapped below a cusp-shaped magnetic structure along the LB. The presence of trapped current-carrying flux tubes is essential for causing long-lasting chromospheric plasma ejections at the interface with pre-existing vertically oriented umbral fields. A bidirectional jet was clearly detected, suggesting magnetic reconnections occurring at very low altitudes, slightly above the height where the vector magnetic fields are measured. Moreover, we found another strong vertical electric current on the interface between the current-carrying flux tube and pre-existing umbral field, which might be a direct detection of the currents flowing in the current sheet formed at the magnetic reconnection sites.

Aims. We study the vector magnetic field of a filament observed over a compact active region neutral line.Methods. Spectropolarimetric data acquired with TIP-II (VTT, Tenerife, Spain) of the 10â ‰ 830 Å spectral region provide full Stokes vectors that were analyzed using three different methods: magnetograph analysis, Milne-Eddington inversions, and PCA-based atomic polarization inversions.Results. The inferred magnetic field strengths in the filament are around 600-700 G by all these three methods. Longitudinal fields are found in the range of 100-200 G whereas the transverse components become dominant, with fields as high as 500-600 G. We find strong transverse fields near the neutral line also at photospheric levels.Conclusions. Our analysis indicates that strong (higher than 500 G, but below kG) transverse magnetic fields are present in active region filaments. This corresponds to the highest field strengths reliably measured in these structures. The profiles of the helium 10 830 Å lines observed in this active region filament are dominated by the Zeeman effect. © 2009 ESO.

The Solar Optical Telescope on-board Hinode is providing a new view of the fine scale dynamics in sunspots with its high spatial resolution and unprecedented image stability. We present three features related to the Ever-shed flow each of which raises a new puzzle in sunspot dynamics; i.e., twisting appearance of penumbral filaments, the source and sink of individual Evershed flow channels, and the net circular polarization in penumbrae with its spatial relation to the Evershed flow channels.

The Hinode Spectro-Polarimeter has revealed the presence Of surprisingly strong horizontal magnetic fields nearly everywhere in the quiet solar atmosphere. These horizontal fields, along with measures of the vertical fields, may be the signature of the "hidden turbulent flux" of the quiet Sun. The measured horizontal fields average at least to 55 Gauss: nearly 5 times that of the measured longitudinal apparent flux density. The nature of these fields are reviewed, and discussed in the light of recent magneto-convection numerical simulations of the quiet Sun.

In spite of the large number of magnetohydrodynamic (MHD) simulations of emerging flux tubes in the solar atmosphere, radiation properties of the phenomenon remain poorly understood. This is because heating at the footpoints of the emerging magnetic field lines is significant and the effects associated with heat conduction and evaporation have largely been neglected. In this study, we have performed three-dimensional (3-D) multi-wavelength radiation transfer calculations on a MHD model of an emerging flux tube in order to examine the MHD model and also to identify a possible heating mechanism for explaining the properties of observed X-ray coronal loops. It is found that the current dissipation model is difficult for reproducing the structure of X-ray loops observed by Hinode XRT and Yohkoh SXT. This suggests that alternative models of the heating process should be incorporated into our MHD models. We left unresolved issues of the heating process as future work.

We present observations of the magnetic landscape of the polar region of the Sun that are unprecedented in terms of spatial resolution, field of view, and polarimetric precision. They were carried out with the Solar Optical Telescope aboard Hinode. Using a Milne-Eddington inversion, we find many vertically oriented magnetic flux tubes with field strengths as strong as 1 kG scattered in latitude between 70 degrees and 90 degrees. They all have the same polarity, consistent with the global polarity of the polar region. The field vectors are observed to diverge from the centers of the flux elements, consistent with a view of magnetic fields that are expanding and fanning out with height. The polar region is also found to have ubiquitous horizontal fields. The polar regions are the source of the fast solar wind, which is channeled along unipolar coronal magnetic fields whose photospheric source is evidently rooted in the strong-field, vertical patches of flux. We conjecture that vertical flux tubes with large expansion around the photospheric-coronal boundary serve as efficient chimneys for Alfven waves that accelerate the solar wind.

We estimate the temporal change of magnetic flux normal to the solar surface in a decaying active region by using a time series of the spatial distribution of vector magnetic fields in the photosphere. The vector magnetic fields are derived from full spectropolarimetric measurements with the Solar Optical Telescope aboard Hinode. We compare a magnetic flux loss rate to a flux transport rate in a decaying sunspot and its surrounding moat region. The amount of magnetic flux that decreases in the sunspot and moat region is very similar to magnetic flux transported to the outer boundary of the moat region. The flux loss rates [(dF/dt)(loss)] of magnetic elements with positive and negative polarities balance each other around the outer boundary of the moat region. These results suggest that most of the magnetic flux in the sunspot is transported to the outer boundary of the moat region as moving magnetic features, and then removed from the photosphere by flux cancellation around the outer boundary of the moat region.

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 1.0 MK and an emission measure in the range of 10(25.5)-10(26.0) cm(-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 100 Mm, and constant temperatures above 100 Mm. 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.

Continuous observations of sunspot penumbrae with the Solar Optical Telescope aboard Hinode clearly show that the outer boundary of the penumbra fluctuates around its averaged position. The penumbral outer boundary moves inward when granules appear in the outer penumbra. We discover that such granules appear one after another while moving magnetic features (MMFs) are separating from the penumbral "spines'' (penumbral features that have fields that are stronger and more vertical than those of their surroundings). These granules that appear in the outer penumbra often merge with bright features inside the penumbra that move with the spines as they elongate toward the moat region. This suggests that convective motions around the penumbral outer boundary are related to the disintegration of magnetic flux in the sunspot. We also find that dark penumbral filaments frequently elongate into the moat region in the vicinity of MMFs that detach from penumbral spines. Such elongating dark penumbral filaments correspond to nearly horizontal fields extending from the penumbra. Pairs of MMFs with positive and negative polarities are sometimes observed along the elongating dark penumbral filaments. This strongly supports the notion that such elongating dark penumbral filaments have magnetic fields with a "sea serpent''- like structure. Evershed flows, which are associated with the penumbral horizontal fields, may be related to the detachment of the MMFs from the penumbral spines, as well as to the formation of the MMFs along the dark penumbral filaments that elongate into the moat region.

The Solar Optical Telescope (SOT) aboard the Solar-B satellite (Hinode) is designed to perform high-precision photometric and polarimetric observations of the Sun in visible light spectra (388-668 nm) with a spatial resolution of 0.2-0.3 arcsec. The SOT consists of two optically separable components: the Optical Telescope Assembly (OTA), consisting of a 50-cm aperture Gregorian with a collimating lens unit and an active tip-tilt mirror, and an accompanying Focal Plane Package (FPP), housing two filtergraphs and a spectro-polarimeter. The optomechanical and optothermal performance of the OTA is crucial to attain unprecedented high-quality solar observations. We describe in detail the instrument design and expected stable diffraction-limited on-orbit performance of the OTA, the largest state-of-the-art solar telescope yet flown in space.

The Solar Optical Telescope (SOT) onboard Hinode aims to obtain vector magnetic fields on the Sun through precise spectropolarimetry of solar spectral lines with a spatial resolution of 0.2-0.3 arcsec. A photometric accuracy of 10(-3) is achieved and, after the polarization calibration, any artificial polarization from crosstalk among Stokes parameters is required to be suppressed below the level of the statistical noise over the SOT's field of view. This goal was achieved by the highly optimized design of the SOT as a polarimeter, extensive analyses and testing of optical elements, and an end-to-end calibration test of the entire system. In this paper we review both the approach adopted to realize the high-precision polarimeter of the SOT and its final polarization characteristics.

The Solar Optical Telescope (SOT) aboard the Hinode satellite (formerly called Solar-B) consists of the Optical Telescope Assembly (OTA) and the Focal Plane Package (FPP). The OTA is a 50-cm diffraction-limited Gregorian telescope, and the FPP includes the narrowband filtergraph (NFI) and the broadband filtergraph (BFI), plus the Stokes Spectro-Polarimeter (SP). The SOT provides unprecedented high-resolution photometric and vector magnetic images of the photosphere and chromosphere with a very stable point spread function and is equipped with an image-stabilization system with performance better than 0.01 arcsec rms. Together with the other two instruments on Hinode (the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer (EIS)), the SOT is poised to address many fundamental questions about solar magnetohydrodynamics. This paper provides an overview; the details of the instrument are presented in a series of companion papers.

High-resolution Ca II H broad-band filter images of NOAA 10933 on 2007 January 5 were obtained by the Solar Optical Telescope aboard the Hinode satellite. Many small-scale (similar to 1 '') bright points were observed outside the sunspot and inside the emerging flux region. We identified some of these bright points with Ellerman bombs (EBs) by using Ha images taken by the Domeless Solar Telescope at Hida observatory. The sub-arcsec structures of two EBs seen in Ca it H were studied in detail. Our observation showed the following two aspects: (1) The Ca II H bright points identified with EBs were associated with the bipolar magnetic field structures, as reported by previous studies. (2) The structure of the Ca II H bright points turned out to consist of the following two parts: a central elongated bright core (0.'' 7 x 0.'' 5) located along the magnetic neutral line and a diffuse halo (1.'' 2 x1.'' 8).

The Hinode Solar Optical Telescope (SOT) is the first space-borne visible-light telescope that enables us to observe magnetic-field dynamics in the solar lower atmosphere with 0.2-0.3 arcsec spatial resolution under extremely stable (seeing-free) conditions. To achieve precise measurements of the polarization with diffraction-limited images, stable pointing of the telescope (< 0.09 arcsec, 3 sigma) is required for solar images exposed on the focal plane CCD detectors. SOT has an image stabilization system that uses image displacements calculated from correlation tracking of solar granules to control a piezo-driven tip-tilt mirror. The system minimizes the motions of images for frequencies lower than 14 Hz while the satellite and telescope structural design damps microvibration in higher frequency ranges. It has been confirmed from the data taken on orbit that the remaining jitter is less than 0.03 arcsec (3 sigma) on the Sun. This excellent performance makes a major contribution to successful precise polarimetric measurements with 0.2-0.3 arcsec resolution.

Context. Net circular polarization (NCP) of spectral lines in sunspots has been most successfully explained by the presense of discontinuities in the magnetic field inclination and flow velocity along the line-of-sight in the geometry of the embedded flux tube model of penumbrae (Delta gamma-effect). Aims. The fine scale structure of NCP in a sunspot is examined with special attention paid to spatial relations of the Evershed flow to confirm the validity of the present interpretation of the NCP of sunspots. Methods. High resolution spectro-polarimetric data of a positive-polarity sunspot obtained by the Solar Optical Telescope aboard Hinode are analysed. Results. A positive NCP is associated with the Evershed flow channels in both limb-side and disk center-side penumbrae and with up-flows in the penumbra at disk center. The negative NCP in the disk center-side penumbra is generated in inter-Evershed flow channels. Conclusions. The first result is apparently inconsistent with the current explanation of NCP with the Delta gamma-effect but rather suggests a positive correlation between the magnetic field strength and the flow velocity as the cause of the NCP. The second result serves as strong evidence for the presence of gas flows in inter-Evershed flow channels.

Aims. We report the discovery of isolated, small-scale emerging magnetic fields in a plage region with the Solar Optical Telescope aboard Hinode. Methods. Spectro-polarimetric observations were carried out with a cadence of 34 s for the plage region located near disc center. The vector magnetic fields are inferred by Milne-Eddington inversion. Results. The observations reveal widespread occurrence of transient, spatially isolated horizontal magnetic fields. The lateral extent of the horizontal magnetic fields is comparable to the size of photospheric granules. These horizontal magnetic fields seem to be tossed about by upflows and downflows of the granular convection. We also report an event that appears to be driven by the magnetic buoyancy instability. We refer to buoyancy-driven emergence as type 1 and convection-driven emergence as type 2. Although both events have magnetic field strengths of about 600 G, the filling factor of type 1 is a factor of two larger than that of type 2. Conclusions. Our finding suggests that the granular convection in the plage regions is characterized by a high rate of occurrence of granular-sized transient horizontal fields.

Convective instability has been a mechanism used to explain the formation of solar photospheric flux tubes with kG field strength. However, the turbulence of the Earth's atmosphere has prevented ground-based observers from examining the hypothesis with precise polarimetric measurement on the subarcsecond scale flux tubes. Here we discuss observational evidence of this scenario based on observations with the Solar Optical Telescope ( SOT) aboard Hinode. The cooling of an equipartition field strength flux tube precedes a transient downflow reaching 6 km s(-1) and the intensification of the field strength to 2 kG. These observations agree very well with the theoretical predictions.

We report findings from multihour 0.2(n) resolution movies of solar quiescent prominences (QPs) observed with the Solar Optical Telescope ( SOT) on the Hinode satellite. The observations verify previous findings of filamentary downflows and vortices in QPs. SOT observations also verify large-scale transverse oscillations in QPs, with periods of 20-40 minutes and amplitudes of 2-5 Mm. The upward propagation speed of several waves is found to be similar to 10 km s(-1), comparable to the sound speed of a 10,000 K plasma, implying that the waves are magnetoacoustic in origin. Most significantly, Hinode SOT observations reveal that dark, episodic upflows are common in QPs. The upflows are 170-700 km in width, exhibit turbulent flow, and rise with approximately constant speeds of similar to 20 km s(-1) from the base of the prominence to heights of similar to 10-20 Mm. The upflows are visible in both the Ca II H-line and Ha bandpasses of SOT. The new flows are seen in about half of the QPs observed by SOT to date. The dark upflows resemble buoyant starting plumes in both their velocity profile and flow structure. We discuss thermal and magnetic mechanisms as possible causes of the plumes.

衛星に搭載された太陽センサーは出来るだけ精度良く太陽方向を測定し,その信号は衛星の姿勢安定化に使用される.「ひので」(Solar-B)衛星に搭載された望遠鏡は今までにない高い角分解能で太陽を観測する装置であり,衛星には極めて高い姿勢安定化が要求された.このために,我々は,ランダム誤差1 秒角(3σ),±0.5 度視野にわたりバイアス誤差2 秒角(p-p)という高い位置決定精度で太陽方向を測定することができる超高精度太陽センサー「UFSS」を開発した.性能検証モデル品を用いて高精度計測を可能とする手法を確立し,フライトモデル製作に向けた性能検証を行い,フライト品設計に反映させた.また確立した計測手法を用いてフライト品の性能検証を行った.

Continuous observations were obtained of NOAA AR 10953 with the Solar Optical Telescope (SOT) on board the Hinode satellite from 2007 April 28 to May 9. A prominence was located over the polarity inversion line (PIL) to the southeast of the main sunspot. These observations provided us with a time series of vector magnetic fields on the photosphere under the prominence. We found four features: (1) The abutting opposite-polarity regions on the two sides along the PIL first grew laterally in size and then narrowed. (2) These abutting regions contained vertically weak but horizontally strong magnetic fields. (3) The orientations of the horizontal magnetic fields along the PIL on the photosphere gradually changed with time from a normal-polarity configuration to an inverse-polarity one. (4) The horizontal magnetic field region was blueshifted. These indicate that helical flux rope was emerging from below the photosphere into the corona along the PIL under the preexisting prominence. We suggest that this supply of a helical magnetic flux to the corona is associated with evolution and maintenance of active region prominences.

High time cadence unprecedented images at the limb with Ca II H line filtergraph from the Solar Optical Telescope (SOT) aboard Hinode have revealed that a spicule consists of highly dynamic multi-threads (typically twin) as thin as a few tenths of an aresecond, and shows prominent lateral movement or oscillation with rotation on its axis during its life. This multithread structure and lateral motion indicate that the spicules can be driven by magnetic reconnection at unresolved spatial scales at their footpoints.

On-orbit performance of the Solar Optical Telescope (SOT) aboard Hinode is described with some attention to its unpredicted aspects. In general, SOT reveals an excellent performance and has been providing outstanding data. Some unexpected features exist, however, in behaviours of the focus position, throughput and structural stability. Most of them are recovered by the daily operation i.e., frequent focus adjustment, careful heater setting and corrections in data analysis. The tunable filter contains air bubbles which degrade the data quality significantly. Schemes for tuning the filter without disturbing the bubbles have been developed and tested, and some useful procedures to obtain Dopplergrams and magnetograms are now available. October and March, when the orbit of satellite becomes nearly perpendicular to the direction towards the Sun, provide a favourable condition for continuous runs of the narrow-band filter imager.

Observations of very quiet Sun using the Solar Optical Telescope/Spectro-Polarimeter (SOT/SP) aboard the Hinode spacecraft reveal that the quiet internetwork regions are pervaded by horizontal magnetic flux. The spatial average horizontal apparent flux density derived from wavelength-integrated measures of Zeeman-induced linear polarization is B-app(T) = 55 Mx cm(-2), as compared to the corresponding average vertical apparent flux density of vertical bar B-app(L)vertical bar = 11 Mx cm(-2). Distributions of apparent flux density are presented. Magnetic fields are organized on mesogranular scales, with both horizontal and vertical fields showing "voids'' of reduced flux density of a few granules spatial extent. The vertical fields are concentrated in the intergranular lanes, whereas the stronger horizontal fields are somewhat separated spatially from the vertical fields and occur most commonly at the edges of the bright granules. High-S/N observations from disk center to the limb help to constrain possible causes of the apparent imbalance between vertical bar B-app(L)vertical bar and B-app(T), with unresolved structures of linear dimension on the surface smaller by at least a factor of 2 relative to the SOT/SP angular resolution being one likely cause of this discrepancy. Other scenarios for explaining this imbalance are discussed. The horizontal fields are likely the source of the '' seething'' fields of the quiet Sun discovered by Harvey et al. The horizontal fields may also contribute to the '' hidden'' turbulent flux suggested by studies involving Hanle effect depolarization of scattered radiation.

This article summarizes results of studies presented in two papers already published: Lites et al. (2007a); Lites et al. (2007b). Please see these for further details.

We review briefly the observational understanding of emergence of flux in both the quiet Sun and active regions in the light of first results from the joint Japan/US/UK Hinode mission. That spacecraft is now providing us with our first continuous, high resolution measurements of the photospheric vector magnetic field, along with high resolution observations of the thermal and dynamic properties of the chromosphere and corona. This review is intended to present a few very early results and to highlight the potential for discovery offered by this extraordinary new mission. The discovery of ubiquitous horizontal magnetic flux in the quiet internetwork regions is presented.

It has been frequently observed in longitudinal magnetograms that magnetic elements disappear when a magnetic polarity element approaches and collides with another polarity element. We examine 12 collision events observed with the Advanced Stokes Polarimeter. We find formation of new magnetic connection between the colliding opposite polarity elements both in the photosphere and in the corona. In some cases, the opposite polarity elements to be collided appear at different times and at widely separated positions. Magnetic fields horizontal to the solar surface are spontaneously formed on the polarity inversion line (PIL) between such colliding elements, and transient bright X-ray loops connecting the opposite polarity elements appear. We suggest that formation of the coronal loops and the photospheric horizontal fields are due to magnetic reconnection between the colliding field lines, possibly at multiple locations with different heights. We also find that a global change in the direction of the photospheric horizontal fields between the colliding elements occurs in association with formation and disappearance of Ha dark filaments. Initial horizontal fields perpendicular to the PIL become parallel to the PIL, when dark filaments are observed along the PIL. They return to being perpendicular to the PIL at around the time of the disappearance of the dark filament. © 2007. The American Astronomical Society. All rights reserved.

Alfven waves have been invoked as a possible mechanism for the heating of the Sun's outer atmosphere, or corona, to millions of degrees and for the acceleration of the solar wind to hundreds of kilometers per second. However, Alfven waves of sufficient strength have not been unambiguously observed in the solar atmosphere. We used images of high temporal and spatial resolution obtained with the Solar Optical Telescope onboard the Japanese Hinode satellite to reveal that the chromosphere, the region sandwiched between the solar surface and the corona, is permeated by Alfven waves with strong amplitudes on the order of 10 to 25 kilometers per second and periods of 100 to 500 seconds. Estimates of the energy flux carried by these waves and comparisons with advanced radiative magnetohydrodynamic simulations indicate that such Alfven waves are energetic enough to accelerate the solar wind and possibly to heat the quiet corona.

The penumbra of a sunspot is composed of numerous thin, radially extended, bright and dark filaments carrying outward gas flows (the Evershed flow). Using high-resolution images obtained by the Solar Optical Telescope aboard the solar physics satellite Hinode, we discovered a number of penumbral bright filaments revealing twisting motions about their axes. These twisting motions are observed only in penumbrae located in the direction perpendicular to the symmetry line connecting the sunspot center and the solar disk center, and the direction of the twist (that is, lateral motions of intensity fluctuation across filaments) is always from limb side to disk-center side. Thus, the twisting feature is not an actual twist or turn of filaments but a manifestation of dynamics of penumbral filaments with three-dimensional radiative transfer effects.

Solar prominences are cool 10(4) kelvin plasma clouds supported in the surrounding 106 kelvin coronal plasma by as-yet-undetermined mechanisms. Observations from Hinode show fine-scale threadlike structures oscillating in the plane of the sky with periods of several minutes. We suggest that these represent Alfven waves propagating on coronal magnetic field lines and that these may play a role in heating the corona.

We observed fine-scale jetlike features, referred to as penumbral microjets, in chromospheres of sunspot penumbrae. The microjets were identified in image sequences of a sunspot taken through a Ca II H-line filter on the Solar Optical Telescope on board the Japanese solar physics satellite Hinode. The microjets' small width of 400 kilometers and short duration of less than 1 minute make them difficult to identify in existing observations. The microjets are possibly caused by magnetic reconnection in the complex magnetic configuration in penumbrae and have the potential to heat the corona above a sunspot.

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 similar 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.

The heating of the solar chromosphere and corona is a long- standing puzzle in solar physics. Hinode observations show the ubiquitous presence of chromospheric anemone jets outside sunspots in active regions. They are typically 3 to 7 arc seconds = 2000 to 5000 kilometers long and 0.2 to 0.4 arc second = 150 to 300 kilometers wide, and their velocity is 10 to 20 kilometers per second. These small jets have an inverted Y- shape, similar to the shape of x- ray anemone jets in the corona. These features imply that magnetic reconnection similar to that in the corona is occurring at a much smaller spatial scale throughout the chromosphere and suggest that the heating of the solar chromosphere and corona may be related to small- scale ubiquitous reconnection.

We analyze Fe I 630 nm observations of the quiet Sun at disk center taken with the spectropolarimeter of the Solar Optical Telescope aboard the Hinode satellite. A significant fraction of the scanned area, including granules, turns out to be covered by magnetic fields. We derive field strength and inclination probability density functions from a Milne-Eddington inversion of the observed Stokes profiles. They show that the internetwork consists of very inclined, hG fields. As expected, network areas exhibit a predominance of kG field concentrations. The high spatial resolution of Hinode's spectropolarimetric measurements brings to an agreement the results obtained from the analysis of visible and near-infrared lines.