Kenichi Otsuji

Chromospheric Anemone Jets as Evidence of Ubiquitous Reconnection

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.

Giant Chromospheric Anemone Jet Observed with Hinode and Comparison with Magnetohydrodynamic Simulations: Evidence of Propagating Alfvén Waves and Magnetic Reconnection

Hinode discovered a beautiful giant jet with both cool and hot components at the solar limb on 2007 February 9. Simultaneous observations by the Hinode SOT, XRT, and TRACE 195 A satellites revealed that hot (~5 × 106 K) and cool (~104 K) jets were located side by side and that the hot jet preceded the associated cool jet (~1-2 minutes). A current-sheet-like structure was seen in optical (Ca II H), EUV (195 A), and soft X-ray emissions, suggesting that magnetic reconnection is occurring in the transition region or upper chromosphere. Alfven waves were also observed with Hinode SOT. These propagated along the jet at velocities of ~200 km s−1 with amplitudes (transverse velocity) of ~5-15 km s−1 and a period of ~200 s. We performed two-dimensional MHD simulation of the jets on the basis of the emerging flux-reconnection model, by extending Yokoyama and Shibatas model. We extended the model with a more realistic initial condition (~106 K corona) and compared our model with multiwavelength observations. The improvement of the coronal temperature and density in the simulation model allowed for the first time the reproduction of the structure and evolution of both the cool and hot jets quantitatively, supporting the magnetic reconnection model. The generation and the propagation of Alfven waves are also reproduced self-consistently in the simulation model.

Small-Scale Magnetic-Flux Emergence Observed with Hinode Solar Optical Telescope

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 6302 A, G band, and Ca II H. In Stokes I images of Fe 6302 A, 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 Ca II H images. StokesV images of Fe 6302 A showed pairs of opposite polarities at footpoints of each filament. These magnetic concentrations were identified to correspond to bright points in G band/Ca II 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 4.2 km s 1 during the initial phase of evolution, and decrease to about 1 km s 1 10 minutes later. (2) Ca II H filaments appear almost simultaneously with the formation of dark lanes in Stokes I in an observational cadence of 2 minutes. (3) The lifetime of the dark lanes in the Stokes I and G band is 8 minutes, while that of Ca filament is 12 minutes. An interesting phenomena was observed, that an emerging flux tube expanded laterally in the photosphere with a speed of 3.8 km s . A discussion on the horizontal expansion of the flux tube is given with refernce to previous simulation studies.

Observations of Chromospheric Anemone Jets with Hinode Ca II Broadband Filtergraph and Hida Ca II Spectroheliograph

We report on the first simultaneous observations of chromospheric “anemone” jets in solar active regions with the Hinode Solar Optical Telescope (SOT) Ca II H broadband filtergraph and the Ca II K spetroheliograph on the Domeless Solar Telescope (DST) at Hida Observatory. During the period of coordinated observations, nine chromospheric anemone jets were simultaneously observed with the two instruments. These observations revealed three important features: (1) the jets are generated in the lower chromosphere; i.e., these cannot be seen in Ca II K3 ;( 2) the length and lifetime of the jets are 0.4–5 Mm and 40–320 s, respectively; (3) the apparent velocity of the jets observed with the SOT is 3–24 km s � 1 , while the Ca II K3 component at the jets shows a blueshift (in 5 events) in the range of 2–6 km s � 1 . The chromospheric anemone jets are associated with mixed polarity regions, which are either small emerging flux regions or moving magnetic features. It is found that the Ca II K line often shows red or blue asymmetry in the K2/K1 component; the footpoint of the jets associated with emerging flux regions often shows a redshift (2–16 km s � 1 ), while the one with moving magnetic features shows a blueshift (� 5k m s � 1 ). A detailed analysis of the magnetic evolution of the jet-forming regions revealed that the reconnection rate (or canceling rate) of the total magnetic flux at the footpoint of the jets is on the order of 10 16 Mx s � 1 , and the resulting magnetic energy release rate is (1.1–10) � 10 24 erg s � 1 , with a total energy release of (1–13) � 10 26 erg for the duration of the magnetic cancellation, � 130 s. These are comparable to the estimated total energy, � 10 26 erg, in a single chromospheric anemone jet. In addition to the DST Ca II K spectroheliogram and the SOT Ca II H broadband filtergram, we also used for analysis an SOT magnetogram as well as a Hida H˛ filtergram. We present a physical model of the jet based on the observation, and discuss the relation between chromospheric anemone jets and Ellerman bombs.

Umbral Fine Structures in Sunspots Observed with Hinode Solar Optical Telescope

High resolution imaging observation of a sunspot umbra was done with Hinode Solar Optical Telescope (SOT). Filtergrams in wavelengths of blue and green continuum 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. 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 space observation, we could first follow the temporal behavior of these events. The derived properties of internal structure of the umbra are discussed in viewpoint of magnetoconvection in a strong magnetic field.

Statistical Study on the Nature of Solar-Flux Emergence

We studied 101 flux emergence events ranging from small ephemeral regions to large emerging flux regions that were observed with the Hinode Solar Optical Telescope filtergram. We investigated how the total magnetic flux of the emergence event controls the nature of emergence. To determine the modes of emergences, horizontal velocity fields of the global motion of the magnetic patches in the flux emerging sites were measured by local correlation tracking. Between two main polarities of the large emerging flux regions with more than around 2 � 10 19 Mx, there were converging flows of anti-polarity magnetic patches. On the other hand, small ephemeral regions showed no converging flow, but a simple diverging pattern. When we looked into the detailed features in the emerging sites, irrespective of the total flux and the spatial size, all of the emergence events were observed to consist of single or multiple elementary emergence unit(s). The typical size of unitary emergence is 4 Mm, and consistent with simulation results. From a statistical study of the flux emergence events, the maximum spatial distance between two main polarities, the magnetic flux growth rate and the mean separation speed were found to follow the power-law functions of the total magnetic flux with indices of 0.27, 0.57, and � 0.16, respectively. From a discussion on the observed power-law relations, we obtained a physical view of solar flux emergence, in which the emerging magnetic fields float and evolve while balancing to the surrounding turbulent atmosphere.

Spicule Dynamics over a Plage Region

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).

Ca II K Spectral Study of an Emerging Flux Region using the Domeless Solar Telescope in Hida Observatory

A cooperative observation with Hida Observatory and the Hinode satellite was performed on an emerging flux region. Successive Ca II K spectro-heliograms of the emerging flux region were taken by the Domeless Solar Telescope of Hida Observatory. Hinode observed the emerging flux region with Ca II Ha nd FeI Stokes IQUV filtergrams. In this study, detailed dynamics and the temporal evolution of the magnetic flux emergence was studied observationally. The event was first detected in the photospheric magnetic field signals; 3 minutes later, a horizontal expansion of the dark area was detected. Then, 7 minutes later than the horizontal expansion, the emerging loops were detected with a maximal rise speed of 2.1 km s � 1 at chromospheric heights. The observed dynamics of the emerging magnetic flux from the photosphere to the upper chromosphere was very consistent with the results of

A statistical analysis of current helicity and twist in solar active regions over the phases of the solar cycle using the spectro-polarimeter data of Hinode

Current helicity and twist of solar magnetic fields are important quantities to characterize the dynamo mechanism working in the convection zone of the Sun. We have carried out a statistical study on the current helicity of solar active regions observed with the Spectro-Polarimeter (SP) of Hinode Solar Optical Telescope (SOT). We used SOT-SP data of 558 vector magnetograms of a total of 80 active regions obtained from 2006 to 2012. We have applied spatial smoothing and division of data points into weak and strong field ranges to compare the contributions from different scales and field strengths. We found that the current helicity follows the so-called hemispheric sign rule when the weak magnetic fields (absolute field strength

Formation and decay of rudimentary penumbra around a pore

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