SH41B-1618
GEMSIS-Sun: Modeling of Particle Acceleration and Transport in Solar Flares
GEMSIS (Geospace Environment Modeling System for Integrated Studies) is one of projects in Solar- Terrestrial Environment Laboratory, Nagoya University. Its final goal is to build a geospace-environment model based on various (satellite and ground-based) observational facts in order to understand the dynamic energy-transport-processes taking place in geospace. In the first three years (2007.4 - 2010.3), we set a few individual scientific targets as fundamental elements/information for the final model. One of them is to know how particles are accelerated, transported, and lose their energies in solar flares. It is evident from many observations such as X-rays, gamma-rays, and microwaves that a large amount of high-energy particles are produced in solar flares. However, the dynamics of these particles is not completely understood so far. The GEMSIS-Sun group approaches this research topic through integrated studies, i.e., an empirical modeling of particle dynamics and analyses of various data observed with Hinode, RHESSI, Nobeyama Radioheliograph, and so on. It is widely believed that a solar flare is a consequence of magnetic reconnection. Based on the magnetic reconnection model, we are developing a numerical model for particle acceleration and transport in the flare region. Since the temporal and spatial scales of particles are much shorter than the flare scale (roughly by ten to the six for ions), the full-particle approach is yet unrealistic for the empirical understanding. We therefore employ the guiding-center kinetic equation of particles so that we can perform the calculation in the coronal actual parameter range. By the direct comparison between observations and the calculation, we will empirically discuss the acceleration and transport mechanisms of particles in solar flares.
SH41B-1619
Observational Study of Particle Acceleration in the 2006 December 13 Flare
We study the particle acceleration in a flare on 2006 December 13, by using the Hinode, RHESSI, Nobeyama Radio Polarimeters (NoRP) and Nobeyama Radioheliograph (NoRH) observations. For technical reasons, both RHESSI and NoRH have a problem in imaging in this flare. Since we have succeeded in solving the problem, it is now possible to discuss the particle acceleration mechanism from an image analysis. This flare shows very long-lasting (1 hour) non-thermal emissions, consisting of many spikes. We focus on the second major spike at 02:29 UT, because the RHESSI image is available only in this period. The RHESSI 35-100 keV HXR image shows double sources located at the footpoints of the western soft X-ray (SXR) loop seen by the Hinode/XRT. The non-linear force-free (NLFF) modeling based on a magnetogram data by Inoue et al. shows the NLFF to potential magnetic transition of the loop, which would induce the electric field and then accelerate particles. Overlaying the HXR image on the photospheric three-dimensional magnetic field map taken by the Hinode Spectro-Polarimeter, we find that the HXR sources are located at the region where the horizontal magnetic fields invert. The NoRH 34 GHz microwave images show the loop structure connecting the HXR sources. The microwave peaks do not located at the top of the loop but between the loop top and the footpoints. The NoRP microwave spectrum shows the soft-hard-soft pattern in the period, same as the HXR spectrum (Ning 2008). From these observational results we suggest that the electrons were accelerated parallel to the magnetic field line near the magnetic separatrix.
SH41B-1620
White Light Flare Observations from the Solar Optical Telescope onboard Hinode
In association with solar flares, we sometimes observe emission of white light continuum, which is referred to as a gwhite light flareh. White light flares are very infrequent, and the processes causing them are still unclear. Since close correlations of white light and hard X-ray emission were reported in many events (e.g. Hudson et al., 2006), the mechanism seems to involve emission of white light by nonthermal electron beams. The Solar Optical Telescope (SOT) is capable making observations in white light. We used SOT G-band observations to search for white-light flare counterparts to flares of GOES X-ray class C and higher. Among 155 solar flares over the first two years of the Hinode mission, we found eight white-light flare events. The white-light events tended to occur in larger events, however two occurred in C-class flares. The white light emission was located inside the flare ribbon emission, where the ribbons were observed in SOT Ca II H images. The amount of white-light emission is correlated with the emission in GOES soft X-rays and RHESSI hard X-rays. The location of the white light emission is located at almost the same place as the hard X-ray emission. However, just a weak correlation was seen between white light emission and magnetic field strength observed by the SOT Spectro Polarimeter. We consider these observations in terms of hard X-ray production and particle acceleration scenarios.
SH41B-1621
Launching Process of Coronal Mass Ejections
Coronal mass ejections (CMEs) are one the most spectacular explosive phenomena, in which large amount of mass and magnetic flux are ejected to the interplanetary space, as a result of a disruption of coronal magnetic field. It is very important for space weather science to understand the whole process of CMEs because of their close relation with geoeffective events. However, the physics of how and when CMEs are launched have not yet been understood. Although disruptions of coronal field (eruptions) are often observed as flares, in many cases, they are not accompanied by CMEs. The fact implies that occurrences of eruptions are not sufficient condition for CMEs and they are affected by some kinds of factor, for example, the interactions between magnetic field structure in an eruption and the ambient global scale magnetic field, such as confinement and reconnection. In order to examine the condition whether the eruption of coronal field can be launched as a CME, we performed a three-dimensional MHD simulation of a twisted flux rope ejected from a small and strong magnetic field active region surrounded by a global coronal magnetic field. We carried out the simulations for various configurations aiming to systematically reveal the condition for the capability of CME formation. As a result, we found, for example, that a flux rope cannot be ejected as a CME due to magnetic tension force of anchored field under weak surrounding field, while it can be ejected under moderately strong surrounding field. In the case with strong surrounding field, the significant amount of the magnetic flux inside of the ejecting flux rope reconnects with the ambient field and then the footpoint of the flux rope appears to move outward into weak field region. As the results, inward magnetic tension force of the large scale magnetic field become weak, while outward one becomes strong due to relaxation of the complex structure just after reconnection. The ejected flux rope shows tilting rotation in the direction perpendicular to the ejection line in the case where the CME is successfully formed. The tilting motion, which results from a relaxation of complex field structure, is much important for the determination of the field structure inside a propagating CME as well as for forecasting the orientation of magnetic field at the orbit of the Earth.
SH41B-1622
Is the polar region different from the quiet region of the Sun?
We present the magnetic landscape of the polar region of the Sun as observed with Hinode (Tsuneta et al 2008). We found many vertically-oriented magnetic flux tubes with field strength as strong as 1 kG that are scattered in the whole polar region. They all have the same polarity. Probability distribution function, that is number of pixels as a function of the magnetic field strength, for the unsigned vertical field strength is exactly the same as that for the quiet Sun. Uni-polarity of the polar region differentiates it from the quiet Sun, which has mixed polarity. Difference and similarity between the quiet sun and the polar regions are summarized (Ito and Tsuneta, 2008), and its implication for the solar wind acceleration will be discussed.
SH41B-1623
Nature of Small-Scale Jets On the Solar Chromosphere Revealed with Hinode
The Solar Optical Telescope aboard Hinode has revealed the nature of small-scale jets of the solar chromosphere. Jet-like structures are ubiquitous there not only in the quiet Sun but also in active region and even in sunspot penumbra. They are likely to play an important role in maintaining the energy balance of the local atomsphere and the mass balance of the corona. High time and spatial resolution observations for the first time have revealed that the small-scale jets consist of highly dynamic multi-threads of as thin as a few tenths of arcsecond and shows prominent lateral movement or oscillation with rotation on its axis during its life. The fine structure and lateral motion indicate that the small-scale can be ejected by magnetic reconnection at footpoints. Since the most small-scale jets emanate from seemingly uni-polar magnetic region and the relevant magnetic reconnection should take place in unresolved spatial scale contrary to the larger-scale jets in which bipole magnetic structures are found at their footpoints. We discuss multi-scale structures of the chromospheric jets.
SH41B-1624
Plasma Outflows in the Corona as Observed With Hinode XRT
We present imaging observations of plasma outflows in the solar corona made with X-Ray Telescope (XRT) aboard Hinode satellite. The XRT employs a back-illuminated CCD as the focal-plane imaging device which enables us, together with an optimized set of analysis filters, to investigate, for the first time, dynamic behavior of relatively cool (1-2 MK, say) plasmas in the corona. The XRT revealed a clear pattern of continuous outflow of plasmas from the edge of an active region NOAA AR 10942 right adjacent to a coronal hole. Plasmas of temperature ~1 MK flowed out with a sub-sonic velocity of typically ~140 km/s along magnetic field lines that are most likely open towards the interplanetary space. These outflowing plasmas may constitute a fraction of the (slow) solar wind. In addition to this discovery, the XRT has so far identified rich patterns of continuous outflows including those from coronal hole boundaries and along fan-like field lines rooted inside coronal holes. XRT observations of such plasma outflows in the corona are presented and their possible implications to the solar wind discussed.
SH41B-1625
Cooperative observation of solar atmospheric heating by Hida observatory and Hinode
At Hida observatory of Kyoto University, we continue to study solar activities and fine structures with Domeless Solar Telescope (DST) and Solar Magnetic Activity Research Telescope (SMART). In this work, we will report some recent cooperative observational results with Hinode on the following topics: (1) Plage heating and waves Analysis of a long time series of CaII K spectrograms at a plage area showed us a clear co-existence of 3- and 5-min oscillation in Doppler velocity. We simulated the response of the VAL model atmosphere to the input of 3-min/5-min acoustic disturbances, in 1-D geometry and found that plage chromosphere is heated unsteadily by acoustic shock waves as was proposed by Carlsson and Stein (1997). (2) Disk spicules in and around plage regions We clearly identified numerous ejecting features in a plage area. Their morphological shapes of thin tapered cylinder and their dynamics strongly suggest that they are spicules in plage area. Plage spicules were observed to move under constant deceleration, which are driven by acoustic shock waves predicted by Shibata and Suematsu (1980) and Hansteen et al. (2007). Our results will be discussed from the view point of Type I, II classification of limb spicules ( de Pontieu et al. 2007). (3) Umbral dots We have confirmed that umbral dots are manifestation of magneto-convection in strong magnetic filed from the analysis of Hinode/SOT/BFI&SP. We will discuss the plausibility of monolithic umbral model from the oscillatory brightening of umbral dots. (4) X-ray brightenings in the supergranular network XRT showed us numerous bright points in solar quiet regions. Possible relation between these XBPs and supergranular network pattern in quiet chromosphere was studied. XBPs were found to be located in the network not in the cell center. Many of network bright XBPs were consisted of magnetically bipolar loops. (5) Ellerman bombs By studying the fine structure of Ellerman bomb, we have found core-halo structure and loop like fine-structures in the chromosphere. Discussions on the origin of bombs will be given from the viewpoint of magnetic reconnection theory.
SH41B-1626
Wavelet and Coherence Analysis of Ground Level Proton Events
The intensity time me profiles of Relativistic Solar Protons (RSP) in the period 1942 to 2006 were analyzed by means of the Morlet Spectral technique: the periodicities of their time series were determined. Furthermore, RSP time series together with those of several solar activity indexes were analyzed by means of the Wavelet Coherence spectral method. In spite of the short time interval, several periodicities of RSP have been determined in this work,: the short]term (ST) periodicities, in the order of days, all them harmonic of the 11 years solar activity cycle. We have also determined ultra]short term (UST) periodicities, in the order of minutes to hours. We have shown by means of Coherence analysis that most of the established (ST) periodicities, also appear in subphotospheric and coronal layers. This synchronization seems to indicate that RSP phenomena is not a local one, but involve global regions of the sun atmosphere.
SH41B-1627
High-Resolution Helioseismology from Hinode
The Solar Optical Telescope (SOT) on the Hinode space mission
provides unique multi-wavelength high-resolution data for local
helioseismic diagnostics of the sub-photospheric structure
and dynamics of the Sun. The helioseismology data from
Hinode have allowed us for the first time to observe
oscillations of very high angular degree and high frequencies.
The Hinde data provide a potential for substantial improvement
of the spatial resolution of time-distance helioseismology
in near-surface layers of the Sun, compared to the previous
SOHO/MDI data. The Hinode data have also provided important
insight in the nature of sunspot oscillations. Simultaneous
observations of solar oscillations in two different spectral
interval have allowed us to investigate the mode physics and
the correlated component of stochastic excitation.
In addition, a new type of flare-excited MHD oscillations
was detected from Hinode observations of the solar flare
of December 13, 2006.
http://hinode.nao.ac.jp/