Takuma Matsumoto

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.

NONLINEAR PROPAGATION OF ALFVÉN WAVES DRIVEN BY OBSERVED PHOTOSPHERIC MOTIONS: APPLICATION TO THE CORONAL HEATING AND SPICULE FORMATION

We have performed MHD simulations of Alfven wave propagation along an open flux tube in the solar atmosphere. In our numerical model, Alfven waves are generated by the photospheric granular motion. As the wave generator, we used a derived temporal spectrum of the photospheric granular motion from G-band movies of Hinode/Solar Optical Telescope. It is shown that the total energy flux at the corona becomes larger and the transition regions height becomes higher in the case when we use the observed spectrum rather than the white/pink noise spectrum as the wave generator. This difference can be explained by the Alfven wave resonance between the photosphere and the transition region. After performing Fourier analysis on our numerical results, we have found that the region between the photosphere and the transition region becomes an Alfven wave resonant cavity. We have confirmed that there are at least three resonant frequencies, 1, 3, and 5 mHz, in our numerical model. Alfven wave resonance is one of the most effective mechanisms to explain the dynamics of the spicules and the sufficient energy flux to heat the corona.

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.

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.

Magnetohydrodynamic Shocks in and above Post-flare Loops: Two-dimensional Simulation and a Simplified Model

Solar flares are an explosive phenomenon, where super-sonic flows and shocks are expected in and above the post-flare loops. To understand the dynamics of post-flare loops, a two-dimensional magnetohydrodynamic (2D MHD) simulation of a solar flare has been carried out. We found new shock structures in and above the post-flare loops, which were not resolved in the previous work by Yokoyama and Shibata 2001. To study the dynamics of flows along the reconnected magnetic field, kinematics and energetics of the plasma are investigated along selected field lines. It is found that shocks are crucial to determine the thermal and flow structures in the post-flare loops. On the basis of the 2D MHD simulation, we have developed a new post-flare loop model which we call the pseudo-2D MHD model. The model is based on the 1D MHD equations, where all the variables depend on one space dimension and all the three components of the magnetic and velocity fields are considered. Our pseudo-2D model includes many features of the multi-dimensional MHD processes related to magnetic reconnection (particularly MHD shocks), which the previous 1D hydrodynamic models are not able to include. We compare the shock formation and energetics of a specific field line in the 2D calculation with those in our pseudo-2D MHD model, and we found that they give similar results. This model will allow us to study the evolution of the post-flare loops in a wide parameter space without expensive computational cost and without neglecting important physics associated with magnetic reconnection.

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

Competition between shock and turbulent heating in coronal loop system

2.5-dimensional magnetohydrodynamic (MHD) simulations are performed with high spatial resolution in order to distinguish between competing models of the coronal heating problem. A single coronal loop powered by Alfven waves excited in the photosphere is the target of the present study. The coronal structure is reproduced in our simulations as a natural consequence of the transportation and dissipation of Alfven waves. Further, the coronal structure is maintained as the spatial resolution is changed from 25 to 3 km, although the temperature at the loop top increases with the spatial resolution. The heating mechanisms change gradually across the magnetic canopy at a height of 4 Mm. Below the magnetic canopy, both the shock and the MHD turbulence are dominant heating processes. Above the magnetic canopy, the shock heating rate reduces to less than 10 % of the total heating rate while the MHD turbulence provides significant energy to balance the radiative cooling and thermal conduction loss or gain. The importance of compressibility shown in the present study would significantly impact on the prospects of successful MHD turbulence theory in the solar chromosphere.

Importance of MHD Waves Observed with Hinode

Robust and high spatial resolution observations made by Hinode enable us to understand waves in the solar atmosphere. It also enables us to estimate the energy supplied by waves and to discover the dissipation processes of waves. Moreover, by specifying the wave modes and estimating plasma density using spectroscopy, precise measurements of the coronal magnetic field can be obtained, which are now available. However, if we interpret all periodic events as waves, we will miss out on some important features, such as mass flows. In this document, I will explain energy transfer and magnetic field estimation using waves and quasiperiodic upflows that have observational features similar to those of waves.