Author name code: watanabe-hiroko ADS astronomy entries on 2022-09-14 =author:"Watanabe, Hiroko" ------------------------------------------------------------------------ Title: Observations of umbral dots and their physical models Authors: Watanabe, Hiroko Bibcode: 2014PASJ...66S...1W Altcode: 2014arXiv1407.4581W; 2014PASJ..tmp..111W The Hinode satellite opens a new era in sunspot research, because of its high spatial resolution and temporal stability. Fine-scale structures in sunspots, called umbral dots (UDs), have become one of the hottest topics in terms of close observations of magnetoconvection. In this paper, a brief review of the observed properties of UDs is given based on recent literature. UDs born in the periphery of the umbra exhibit inward migration, and their speeds are positively correlated with the magnetic field inclination. Longer-lasting UDs tend to be larger and brighter, while the lifetimes of UDs show no relation to their background magnetic field strength. UDs tend to disappear, or stop their proper motion by colliding with a locally strong field region. The spatial distribution of UDs is not uniform over an umbra, but is rather located at the boundaries of cellular patterns. From our two-dimensional correlation analysis, we measured the characteristic width of the cell boundaries (≈ 0{^''.}5) and the size of the cells (≈ 6″). We then performed a simplified analysis to obtain statistics of how the UD distribution is random or clustered using Hinode blue continuum images. We have found a hint that the UDs become less dense and more clustered for later-phase sunspots. These results may be related to the evolutional change of the subsurface structure of a sunspot. Based on these observational results, we discuss their physical models by means of numerical simulations of magnetoconvection. Title: Formation and Decay of Rudimentary Penumbra around a Pore Authors: Watanabe, Hiroko; Kitai, Reizaburo; Otsuji, Kenichi Bibcode: 2014ApJ...796...77W Altcode: We analyze the evolution of a pore in the active region NOAA 10940 using the data obtained by the Hinode satellite on 2007 February 3. The pore we analyzed showed the formation of a rudimentary penumbra structure, succeeded by an abrupt disappearance after about 5 hr. The pore had an approximate radius of 3.5 Mm and a total magnetic flux of 3.0 × 1019 Mx, which is a little smaller than the necessary magnetic flux for penumbral formation supposed by Rucklidge et al. (1-1.5 × 1020 Mx). Our observation describes a rare phenomenon which was in the unstable phase between a pore and a sunspot. The area of the dark umbra gradually decreased when the rudimentary penumbral filaments formed the penumbral structure, meaning that the penumbra develops at the expense of the umbral magnetic flux. This statement was confirmed by a rough estimation of the magnetic flux variation observed by the Hinode Fe I magnetogram. Five hours after the formation phase, the decay phase began. In this decaying phase, multiple opposite polarity patches are found to appear in the exterior of the pore (a different location from the penumbra formation site). We interpret these opposite polarities as signatures of the horizontal magnetic field, which preferably appears in the course of the unstable reconfiguration of the magnetic field structure. During the course of the disappearance of the penumbra, the horizontal penumbral field seems to become vertical because of the dark umbral area that recovered by about 10%. Title: Morphological study of penumbral formation Authors: Kitai, Reizaburo; Watanabe, Hiroko; Otsuji, Ken'ichi Bibcode: 2014PASJ...66S..11K Altcode: 2014PASJ..tmp...96K; 2014arXiv1407.4573K Penumbrae are known to be areas of mainly horizontal magnetic field surrounding umbrae of relatively large and mature sunspots. In this paper, we observationally studied the formation of penumbrae in NOAA 10978, where several penumbral formations were observed in G-band images of the Solar Optical Telescope on board Hinode. Thanks to the continuous observation by Hinode, we could morphologically follow the evolution of sunspots and found that there are several paths to the penumbral formation: (1) active accumulation of magnetic flux, (2) rapid emergence of magnetic field, and (3) appearance of twisted or rotating magnetic tubes. In all of these cases, magnetic fields are expected to sustain high inclination at the edges of flux tube concentration longer than the characteristic growth time of downward magnetic pumping. Title: Temporal Evolution of Velocity and Magnetic Field in and around Umbral Dots Authors: Watanabe, Hiroko; Bellot Rubio, Luis R.; de la Cruz Rodríguez, Jaime; Rouppe van der Voort, Luc Bibcode: 2012ApJ...757...49W Altcode: 2012arXiv1207.6006W We study the temporal evolution of umbral dots (UDs) using measurements from the CRISP imaging spectropolarimeter at the Swedish 1 m Solar Telescope. Scans of the magnetically sensitive 630 nm iron lines were performed under stable atmospheric conditions for 71 minutes with a cadence of 63 s. These observations allow us to investigate the magnetic field and velocity in and around UDs at a resolution approaching 0farcs13. From the analysis of 339 UDs, we draw the following conclusions: (1) UDs show clear hints of upflows, as predicted by magnetohydrodynamic simulations. By contrast, we could not find systematic downflow signals. Only in very deep layers, we detect localized downflows around UDs, but they do not persist in time. (2) We confirm that UDs exhibit weaker and more inclined fields than their surroundings, as reported previously. However, UDs that have strong fields above 2000 G or are in the decay phase show enhanced and more vertical fields. (3) There are enhanced fields at the migration front of UDs detached from penumbral grains, as if their motion were impeded by the ambient field. (4) Long-lived UDs travel longer distances with slower proper motions. Our results appear to confirm some aspects of recent numerical simulations of magnetoconvection in the umbra (e.g., the existence of upflows in UDs), but not others (e.g., the systematic weakening of the magnetic field at the position of UDs). Title: Overview of Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) Authors: Narukage, Noriyuki; Tsuneta, Saku; Bando, Takamasa; Kano, Ryouhei; Kubo, Masahito; Ishikawa, Ryoko; Hara, Hirohisa; Suematsu, Yoshinori; Katsukawa, Yukio; Watanabe, Hiroko; Ichimoto, Kiyoshi; Sakao, Taro; Shimizu, Toshifumi; Kobayashi, Ken; Robinson, Brian; Kim, Tony; Winebarger, Amy; West, Edward; Cirtain, Jonathan; De Pontieu, Bart; Casini, Roberto; Trujillo Bueno, Javier; Stepan, Jiri; Manso Sainz, Rafael; Belluzzi, Luca; Asensio Ramos, Andres; Carlsson, Mats Bibcode: 2011SPIE.8148E..0HN Altcode: 2011SPIE.8148E..16N 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 (~ 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 ~ 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. Title: Ellerman Bombs at High Resolution. I. Morphological Evidence for Photospheric Reconnection Authors: Watanabe, Hiroko; Vissers, Gregal; Kitai, Reizaburo; Rouppe van der Voort, Luc; Rutten, Robert J. Bibcode: 2011ApJ...736...71W Altcode: 2011arXiv1105.4008W High-resolution imaging-spectroscopy movies of solar active region NOAA 10998 obtained with the Crisp Imaging Spectropolarimeter at the Swedish 1-m Solar Telescope show very bright, rapidly flickering, flame-like features that appear intermittently in the wings of the Balmer Hα line in a region with moat flows and likely some flux emergence. They show up at regular Hα blue-wing bright points that outline the magnetic network, but flare upward with much larger brightness and distinct "jet" morphology seen from aside in the limbward view of these movies. We classify these features as Ellerman bombs and present a morphological study of their appearance at the unprecedented spatial, temporal, and spectral resolution of these observations. The bombs appear along the magnetic network with footpoint extents up to 900 km. They show apparent travel away from the spot along the pre-existing network at speeds of about 1 km s-1. The bombs flare repetitively with much rapid variation at timescales of seconds only, in the form of upward jet-shaped brightness features. These reach heights of 600-1200 km and tend to show blueshifts; some show bi-directional Doppler signature and some seem accompanied with an Hα surge. They are not seen in the core of Hα due to shielding by overlying chromospheric fibrils. The network where they originate has normal properties. The morphology of these jets strongly supports deep-seated photospheric reconnection of emergent or moat-driven magnetic flux with pre-existing strong vertical network fields as the mechanism underlying the Ellerman bomb phenomenon. Title: Observations of Plasma Blob Ejection from a Quiescent Prominence by Hinode Solar Optical Telescope Authors: Hillier, Andrew; Isobe, Hiroaki; Watanabe, Hiroko Bibcode: 2011PASJ...63L..19H Altcode: 2011arXiv1103.3750H We report findings from 0''.2 resolution observations of the 2007 October 03 quiescent prominence observed with the Solar Optical Telescope on the Hinode satellite. The observations show clear ejections from the top of the quiescent prominence of plasma blobs. The ejections, originating from the top of prominence threads, are impulsively accelerated to approximately Alfvén velocities and then undergo ballistic motion. The ejections have a characteristic size between ∼ 1000-2000 km. These characteristics are similar to downwardly propagating knots (typical size ∼ 700 km) that have been observed in prominence threads, we suggest that the plasma blob ejections could be the upward moving counterpart to the downwardly propagating knots. We discuss the tearing instability as a possible mechanism to explain the ejections. Title: Temporal Evolution of a Rapidly-Moving Umbral Dot Authors: Watanabe, Hiroko; Tritschler, Alexandra; Kitai, Reizaburo; Ichimoto, Kiyoshi Bibcode: 2010SoPh..266....5W Altcode: 2010SoPh..tmp..147W We performed two-dimensional spectroscopic observations of the preceding sunspot of NOAA 10905 located off disk center (S8 E36, μ≈0.81) by using the Interferometric BI-dimensional Spectrometer (IBIS) operated at the Dunn Solar Telescope (DST) of the National Solar Observatory, New Mexico. The magnetically insensitive Fe I line at 709.04 nm was scanned in wavelength repetitively at an interval of 37 s to calculate sequences of maps of the line-wing and line-core intensity, and the line-of-sight Doppler velocity at different line depths (3% to 80%). Visual inspection of movies based on speckle reconstructions computed from simultaneous broadband data and the local continuum intensity at 709.04 nm revealed an umbral dot (UD) intruding rapidly from the umbral boundary to the center of the umbra. The apparent motion of this object was particularly fast (1.3 km s−1) when compared to typical UDs. The lifetime and size of the UD was 8.7 min and 240 km, respectively. The rapid UD was visible even in the line-core intensity map of Fe I 709.04 nm and was accompanied by a persistent blueshift of about 0.06 km s−1. Title: Internal Fine Structure of Ellerman Bombs Authors: Hashimoto, Yuki; Kitai, Reizaburo; Ichimoto, Kiyoshi; Ueno, Satoru; Nagata, Shin'ichi; Ishii, Takako T.; Hagino, Masaoki; Komori, Hiroyuki; Nishida, Keisuke; Matsumoto, Takuma; Otsuji, Kenichi; Nakamura, Tahei; Kawate, Tomoko; Watanabe, Hiroko; Shibata, Kazunari Bibcode: 2010PASJ...62..879H Altcode: We conducted coordinated observations of Ellerman bombs (EBs) between Hinode Satellite and Hida Observatory (HOP12). CaII 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 CaII 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 CaII 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 CaII 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. Title: Spicule Dynamics over a Plage Region Authors: Anan, Tetsu; Kitai, Reizaburo; Kawate, Tomoko; Matsumoto, Takuma; Ichimoto, Kiyoshi; Shibata, Kazunari; Hillier, Andrew; Otsuji, Kenichi; Watanabe, Hiroko; Ueno, Satoru; Nagata, Shin'ichi; Ishii, Takako T.; Komori, Hiroyuki; Nishida, Keisuke; Nakamura, Tahei; Isobe, Hiroaki; Hagino, Masaoki Bibcode: 2010PASJ...62..871A Altcode: 2010arXiv1002.2288A 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). Title: Characteristic Dependence of Umbral Dots on thier Magnetic Structure Authors: Watanabe, Hiroko; Kitai, Reizaburo; Ichimoto, Kiyoshi Bibcode: 2010cosp...38.2933W Altcode: 2010cosp.meet.2933W Umbral dots (UDs) were observed in a stable sunspot in NOAA 10944 by the Hinode Solar Optical Telescope on 2007 March 1. The observation program consisted of blue continuum images and spectropolarimetric profiles of Fe I 630 nm line. An automatic detection algorithm for UDs was applied to the 2 hr continuous blue continuum images, and using the obtained data, the lifetime, size, and proper motion of UDs were calculated. The magnetic structure of the sunspot was derived through the inversion of the spectropolarimetric profiles. We calculated the correlations between UD's parameters (size, lifetime, occurrence rate, proper motion) and magnetic fields (field strength, inclination, azimuth), and obtained the following results. (1) Both the lifetime and size of UDs are almost constant regardless of the magnetic field strength at their emergence site. (2) The speed of UDs increases as the field inclination angle at their emergence site gets larger. (3) The direction of movement of UDs is nearly parallel to the direction of the horizontal component of magnetic field in the region with strongly inclined field, while UDs in the region with weakly inclined field show virtually no proper motion. Our results describe the basic properties of magnetoconvection in sunspots. Title: Parameters of the Magnetic Flux inside Coronal Holes Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl; Watanabe, Hiroko Bibcode: 2009SoPh..260...43A Altcode: 2009arXiv0908.2460A The parameters of the magnetic flux distribution inside low-latitude coronal holes (CHs) were analyzed. A statistical study of 44 CHs based on Solar and Heliospheric Observatory (SOHO)/MDI full disk magnetograms and SOHO/EIT 284 Å images showed that the density of the net magnetic flux, Bnet, does not correlate with the associated solar wind speeds, Vx. Both the area and net flux of CHs correlate with the solar wind speed and the corresponding spatial Pearson correlation coefficients are 0.75 and 0.71, respectively. A possible explanation for the low correlation between Bnet and Vx is proposed. The observed non-correlation might be rooted in the structural complexity of the magnetic field. As a measure of the complexity of the magnetic field, the filling factor, f(r), was calculated as a function of spatial scales. In CHs, f(r) was found to be nearly constant at scales above 2 Mm, which indicates a monofractal structural organization and smooth temporal evolution. The magnitude of the filling factor is 0.04 from the Hinode SOT/SP data and 0.07 from the MDI/HR data. The Hinode data show that at scales smaller than 2 Mm, the filling factor decreases rapidly, which means a multifractal structure and highly intermittent, burst-like energy release regime. The absence of the necessary complexity in CH magnetic fields at scales above 2 Mm seems to be the most plausible reason why the net magnetic flux density does not seem to be related to the solar wind speed: the energy release dynamics, needed for solar wind acceleration, appears to occur at small scales below 1 Mm. Title: Magnetic Structure of Umbral Dots Observed with the Hinode Solar Optical Telescope Authors: Watanabe, Hiroko; Kitai, Reizaburo; Ichimoto, Kiyoshi; Katsukawa, Yukio Bibcode: 2009PASJ...61..193W Altcode: 2008arXiv0811.1074W A high-resolution, seeing-free spectroscopic observation of a decaying sunspot was made with the Solar Optical Telescope aboard the Hinode satellite. The target was NOAA 10944, located in the west side of the solar surface from 2007 March 2 to March 4. The umbra included many umbral dots (UDs) with a size of ∼300 km in continuum light. We report on the magnetic structures and Doppler velocity fields around UDs, based on the Milne-Eddington inversions of the two iron absorption lines at 6302Å. Histograms of the magnetic field strength (B), inclination angle (i), and Doppler velocity (v) of UDs showed a center-to-limb variation; observed at the disk center, the UDs had (i) slightly smaller field strength (ΔB = -17Gauss) and (ii) relative blue shifts (Δv = 28m s-1) compared to their surroundings. When the sunspot got close to the limb, UDs and their surroundings showed almost no difference in the magnetic and Doppler values. This center-to-limb variation can be understood by the formation height difference in a cusp-shaped magnetized atmosphere around UDs, due to the weakly magnetized hot gas intrusion. In addition, some UDs showed the oscillatory light curves with multiple peaks separated around 10min, which may indicate the presence of the oscillatory convection. We discuss our results within the frameworks of two theoretical models: the monolithic model (Schüssler & Vögler 2006, ApJ, 641, L73) and the field-free intrusion model (Spruit & Scharmer 2006, A&A, 447, 343). Title: Cooperative Observation of Ellerman Bombs between the Solar Optical Telescope aboard Hinode and Hida/Domeless Solar Telescope Authors: Matsumoto, Takuma; Kitai, Reizaburo; Shibata, Kazunari; Nagata, Shin'ichi; Otsuji, Kenichi; Nakamura, Tahei; Watanabe, Hiroko; Tsuneta, Saku; Suematsu, Yoshinori; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Katsukawa, Yukio; Tarbell, Theodore D.; Lites, Bruce W.; Shine, Richard A.; Title, Alan M. Bibcode: 2008PASJ...60..577M Altcode: High-resolution CaIIH broad-band filter images of NOAA10933 on 2007 January 5 were obtained by the Solar Optical Telescope aboard the Hinode satellite. Many small-scale (∼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 Hα images taken by the Domeless Solar Telescope at Hida observatory. The sub-arcsec structures of two EBs seen in CaIIH were studied in detail. Our observation showed the following two aspects: (1) The CaIIH bright points identified with EBs were associated with the bipolar magnetic field structures, as reported by previous studies. (2)The structure of the CaIIH bright points turned out to consist of the following two parts: a central elongated bright core (0.7" × 0.5") located along the magnetic neutral line and a diffuse halo (1.2"×1.8"). Title: Chromospheric Anemone Jets as Evidence of Ubiquitous Reconnection Authors: Shibata, Kazunari; Nakamura, Tahei; Matsumoto, Takuma; Otsuji, Kenichi; Okamoto, Takenori J.; Nishizuka, Naoto; Kawate, Tomoko; Watanabe, Hiroko; Nagata, Shin'ichi; UeNo, Satoru; Kitai, Reizaburo; Nozawa, Satoshi; Tsuneta, Saku; Suematsu, Yoshinori; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Katsukawa, Yukio; Tarbell, Theodore D.; Berger, Thomas E.; Lites, Bruce W.; Shine, Richard A.; Title, Alan M. Bibcode: 2007Sci...318.1591S Altcode: 2008arXiv0810.3974S 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. Title: Small-Scale Magnetic-Flux Emergence Observed with Hinode Solar Optical Telescope Authors: Otsuji, Kenichi; Shibata, Kazunari; Kitai, Reizaburo; Ueno, Satoru; Nagata, Shin'ichi; Matsumoto, Takuma; Nakamura, Tahei; Watanabe, Hiroko; Tsuneta, Saku; Suematsu, Yoshinori; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Katsukawa, Yukio; Tarbell, Theodore D.; Lites, Bruce; Shine, Richard A.; Title Alan M. Bibcode: 2007PASJ...59S.649O Altcode: 2007arXiv0709.3207O We observed small-scale magnetic-flux emergence in a sunspot moat region by the Solar Optical Telescope (SOT) aboard the Hinode satellite. We analyzed filtergram images observed at wavelengths of Fe 6302Å, G band, and CaII H. In Stokes I images of Fe 6302Å, emerging magnetic flux was recognized as dark lanes. In the G band, they showed to be their shapes almost the same as in Stokes I images. These magnetic fluxes appeared as dark filaments in CaII H images. Stokes V images of Fe 6302Å showed pairs of opposite polarities at footpoints of each filament. These magnetic concentrations were identified to correspond to bright points in G band/CaII H images. From an analysis of time-sliced diagrams, we derived the following properties of emerging flux, which are consistent with those of previous studies: (1) Two footpoints separate each other at a speed of 4.2kms-1 during the initial phase of evolution, and decrease to about 1kms-1 10minutes later. (2) CaII H filaments appear almost simultaneously with the formation of dark lanes in Stokes I in an observational cadence of 2minutes. (3) The lifetime of the dark lanes in the Stokes I and G band is 8minutes, while that of Ca filament is 12minutes. An interesting phenomena was observed, that an emerging flux tube expanded laterally in the photosphere with a speed of 3.8kms-1. A discussion on the horizontal expansion of the flux tube is given with refernce to previous simulation studies. Title: Umbral Fine Structures in Sunspots Observed with Hinode Solar Optical Telescope Authors: Kitai, Reizaburo; Watanabe, Hiroko; Nakamura, Tahei; Otsuji, Ken-ichi; Matsumoto, Takuma; UeNo, Satoru; Nagata, Shin'ichi; Shibata, Kazunari; Muller, Richard; Ichimoto, Kiyoshi; Tsuneta, Saku; Suematsu, Yoshinori; Katsukawa, Yukio; Shimizu, Toshifumi; Tarbell, Theodore D.; Shine, Richard A.; Title, Alan M.; Lites, Bruce Bibcode: 2007PASJ...59S.585K Altcode: 2007arXiv0711.3266K A high resolution imaging observation of a sunspot umbra was made with the Hinode Solar Optical Telescope. Filtergrams at wavelengths of the blue and green continua were taken during three consecutive days. The umbra consisted of a dark core region, several diffuse components, and numerous umbral dots. We derived basic properties of umbral dots (UDs), especially their temperatures, lifetimes, proper motions, spatial distribution, and morphological evolution. The brightness of UDs is confirmed to depend on the brightness of their surrounding background. Several UDs show fission and fusion. Thanks to the stable condition of the space observation, we could for the first time follow the temporal behavior of these events. The derived properties of the internal structure of the umbra are discussed from the viewpoint of magnetoconvection in a strong magnetic field.