SH52A-01 INVITED
The Multiscale Physics of Magnetic Reconnection
The release of magnetic energy in a large-scale system requires the formation of narrow boundary layers where the frozen-in condition is violated and the magnetic field reconnects. The structure of these boundary layers has been explored with in situ satellite observations in the Earth's magnetosphere, laboratory experiments and computer simulations. In the collisionless environment of the Earth's magnetosphere there is now substantial evidence for the distinct electron and ion inertial scale structure of the dissipation region that has been predicted by theory. In the case of the solar corona it has been proposed that the onset of fast reconnection occurs as the width of Sweet-Parker current layer falls below the ion inertial scale and there is some indirect observational support for this hypothesis. A critical question is whether the release of energy in flares occurs at a single, large-scale x-line or in a turbulent environment with many interacting islands. The efficient production of energetic electrons and ions in impulsive flares seems to favor the turbulent model as do some observations of structure formation during flare energy release. Understanding the mechanisms for island formation and the ultimate size spectrum of magnetic islands in a turbulent reconnection model remain key issues.
SH52A-02
Role of Loss of Equilibrium and Magnetic Reconnection in Coronal Eruptions: Resistive and Hall MHD simulations
It has long been suggested that eruptive phenomena such as coronal mass ejections, prominence eruptions, and large flares might be caused by a loss of equilibrium in a coronal flux rope (Van Tend and Kuperus, 1978). Forbes et al. (1994) developed an analytical two-dimensional model in which eruptions occur due to a catastrophic loss of equilibrium and relaxation to a lower-energy state containing a thin current sheet. Magnetic reconnection then intervenes dynamically, leading to the release of magnetic energy and expulsion of a plasmoid. We have carried out high-Lundquist-number simulations to test the loss-of equilibrium mechanism, and demonstrated that it does indeed occur in the quasi-ideal limit. We have studied the subsequent dynamical evolution of the system in resistive and Hall MHD models for single as well as multiple arcades. The typical parallel electric fields are super-Dreicer, which makes it necessary to include collisionless effects via a generalized Ohm's law. It is shown that the nature of the local dissipation mechanism has a significant effect on the global geometry and dynamics of the magnetic configuration. The presence of Hall currents is shown to alter the length of the current sheet and the jets emerging from the reconnection site, directed towards the chromosphere. Furthermore, Hall MHD effects break certain symmetries of resistive MHD dynamics, and we explore their observational consequences.
SH52A-03
The Thermal Structures of Solar Corona Revealed with Hinode/XRT
The solar corona has a wide temperature range from less than 1MK (1,000,000K) to more than 10MK. The X-ray telescope (XRT) on board the Hinode satellite has 9 X-ray analysis filters with different temperature responses making it possible to detect both cool and hot coronal plasmas. Using the data observed with this telescope, we successfully derived the coronal temperature and emission measure around the whole sun, i.e., for not only active regions but also quiet regions and coronal holes. We also found that coronal structures are nicely classified using the temperature and emission measure. And the coronal structures were found to depend on the length of structure and the heating flux. Furthermore, we calculated the coronal potential magnetic field using the photospheric magnetic field. To compare the heating flux estimated with coronal temperature and the calculated coronal magnetic field might be the great clue to solving the big coronal heating question: why does the hot 1MK corona stably exist above the cool 6,000K solar surface? In this talk, we will show some results of our latest studies about the coronal thermal structures.
SH52A-04
Formation of Solar Magnetic Flux Tubes and Convective Instability
The observational evidence for the formation of solar magnetic flux tubes induced by convective instability was obtained by Hinode Solar Optical Telescope (SOT). Based on the seeing free observation with SOT, we found 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. Convective instability in the flux tubes is discussed by comparing the observations with numerical models.
SH52A-05
Fine scale structures of sunspots and their role on global sunspot energetics
The sunspot has highly structured atmosphere of strongly magnetized plasma; In visible light, the umbra contains a number of small bright patches called as umbral dots in its dark background, the penumbra consists of numerous bright and dark filaments with a width of 0.2--0.3 arcsec. The origin of these features has been a topic under debate for long time in the sunspot physics.The 'brightness' of sunspots is another topic under debate on sunspot physics, i.e., how the energy for maintaining the brightness of umbrae (10- 20% of normal photosphere) and penumbrae (70-80% of normal photosphere) are carried to the solar surface. The Solar Optical Telescope (SOT) aboard Hinode revealed the close relationship between the fine scale filamentary structures and the plasma motions (Evershed flow) in sunspot penumbra; The Evershed flow is confined in narrow channels with nearly horizontal magnetic fields embedded in deep layer of penumbral atmosphere. It is a dynamic phenomenon with the flow velocity close to the sound speed in the photosphere, and individual flow channels are associated with tiny upflow (source) at the inner end and down flow (sink) at the outer end. The penumbral bright grains are well correlated with the upflowing gas, thus the Evershed effect can be interpreted as a consequence of the thermal convection under the strong inclined magnetic field of sunspot penumbra. We will present the new picture of the sunspot penumbra, and discuss the role of the fine structures on the global sunspot energetics.
SH52A-06
Data-driven Multiscale Simulation Study of Solar Eruption Based on Hinode Vector Magnetogram
Solar eruptions, which arise as flares and coronal mass ejection (CME), are the most energetic phenomena in our solar system, and can often influence even the geo-space environment. However, the initiation mechanism and the physical condition for the onset of them are not yet well understood. The objective of this study is to clarify how the multiscale interaction between small scale magnetic reconnection and the large scale evolution of the solar coronal magnetic field interact with each other for the initiation of solar eruptions. In order to obtain that, we have developed a realistic magnetohydrodynamics (MHD) simulation, which is driven by a high resolution vector magnetogram observed by Solar Optical Telescope (SOT) onboard Hinode. The simulation is performed by incorporating the advanced magnetofrictional model for the nonlinear force-free extrapolation and the three different MHD models for active region, global corona, and the interplanetary space, respectively. Using the model, we have successfully performed the first-ever data- driven simulation of the eruptive event caused by the X-class solar flare, which occurred in the active region NOAA 10930 on Dec. 13, 2006. The simulation result indicates that magnetic reconnection triggered in a strongly sheared region causes a large scale eruption, in which a plasmoid with helical magnetic flux is ejected at super-Alfvenic speed. The direction and speed of plasmoid ejection are well consistent with the observation by EUV imaging spectrometer (EIS) onboard Hinode. The evolution of field line topology is also consistent with the SOT observation of flare ribbons. The propagation of CME, which is formed as a result of the plasmoid ejection, is calculated by handing over the output data of the active region model to the coronal model. The results indicate that the tether cutting scenario is well consistent with the observation, and also suggest us that the data-driven simulation might be usable for some kind of now-casting simulation of solar eruption, which could assess what type of solar eruption is able to arise from particular active regions.
SH52A-07 INVITED
The SOLAR-C mission
Solar-physics community in Japan has so far developed 3 solar missions, i.e., Hinotori, Yohkoh, and Hinode, over past 25 years. Japan has started the conceptual studies for realizing the forth mission (SOLAR-C) in the coming decade. Two mission concepts are now under study. Plan A is to perform magnetic, helioseismic, and X-ray observations of the solar polar regions from out of the ecliptic to investigate properties of the polar region, magnetic and flow structures inside the Sun down to the bottom of the convection zone. Plan B is to perform high throughput, high cadence spectroscopic/polarimetric and EUV/X-ray observations with high spatial resolution, focusing on chromosphere and transition region as interface layer from the photosphere to corona, to investigate magnetism of the Sun and its roles in heating and dynamics of solar atmosphere. JAXA SOLAR-C working group, organized in ISAS of JAXA with participation of japanese researchers, refines both plans, compare science, technology, and other constraints, and will prioritize the two plans. We recognize that success of Hinode and Yohkoh is due to strong international collaborations. The working group hopes strong international support for realizing the SOLAR-C mission and invites US and European participation to the SOLAR-C program, following our remarkable history of collaboration. International SOLAR-C science definition meeting will be held this November at ISAS with participants from US and European countries. This presentation will report on the mission concept and current study status, including discussions in the international Solar-C science definition meeting.