| Mar 28 (Fri) 13:30-15:00 | David E McKenzie (Department of Physics, Montana State University) |
| Recent Work on Turbulence and Reconnection: Exceptions to the Rules | |
| In studying the coronae of active stars like the Sun, there are some general conditions that we accept as firm rules. As an example: Most solar physicists accept that "some" magnetic reconnection happens in solar flares, but there's a persistent notion that reconnection cannot be sustained for long times, despite plentiful evidence of hours-long reconnection episodes. It is a matter of faith also that turbulence doesn't matter (and rarely exists on large scales) in the solar corona, because the magnetic field completely dominates over all other forces. Starting with beautiful and eye-catching movies of solar eruptions, I will argue that the exceptions to these rules are sometimes more important than the rules themselves. | |
| January 27 (Mon) 15:00-16:00 | Lindsay Glesener (Postdoc at UC Berkeley/JSPS short-term postdoc at NAOJ) |
| Searching for solar flare acceleration regions with current and future instrumentation | |
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This seminar will discuss two independent methods of investigating particle acceleration sites in solar flares. Standard theories place magnetic reconnection and particle acceleration in the corona, where densities are low. Locations and energetics of accelerated electron populations can be studied by means of bremsstrahlung hard X-rays (HXRs), while spectroscopic extreme ultraviolet (EUV) data provide information about inflows and outflows around the reconnection site, temperature and density diagnostics, and turbulent plasma. By combining HXR and EUV spectroscopic images, accelerated electrons can be studied in the context of hot plasma flows. This seminar will highlight coronal features of the 2013 May 15 X-class flare, using HXR data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and EUV data from the EUV Imaging Spectrometer (EIS). Energetic electron populations and plasma flows at and above the looptop will be discussed. For future investigations of faint HXR sources in the corona, instruments with greater sensitivity and dynamic range are required. The Focusing Optics X-ray Solar Imager (FOXSI) rocket payload demonstrates the advances in both these qualities by use of direct focusing optics, as opposed to the indirect imaging technique utilized by RHESSI and prior HXR missions. FOXSI is a NASA sounding rocket payload built by a collaboration of UC Berkeley, NASA/Marshall, and ISAS, and it combines grazing-incidence HXR optics with solid-state strip detectors to increase HXR sensitivity and imaging dynamic range. FOXSI flew for the first time on 2012 November 2, successfully demonstrating the capabilities of this technology to produce focused images of solar HXR sources. The motivation, instrument, flight, and results will be presented here. | |
| December 17 (Tue) | Patrick Antolin (NAOJ) |
| Fine strand-like structure in the corona from MHD transverse oscillations | |
| High resolution observations in coronal lines with Hi-C, or in chromospheric lines from coronal rain events, indicate that the magnetic field may tends to organize itself in the corona in fine strand-like structures of a few hundred kilometers. Numerical models, however, have so far failed to explain such organization. In this work we present through 3D MHD simulations, a model that easily leads to the generation of strand-like structure in loops. This model is based on the observational finding that the corona is permeated with small-scale transverse MHD waves. Here we show that even very small amplitudes of these waves very easily lead to Kelvin-Helmholtz instabilities, producing fine scale structure in loops. Through forward modelling we show that the roll-ups (eddies) generated from the instability are locally enhanced density regions leading to current sheets, which appear as strand-like structure from the line-of-sight effects. | |
| November 1 (Fri) 15:00-16:00 | Dr. Pui Chiu (Peter) Yuen (MSSL/UCL) |
| Solar Orbiter Extreme-Ultraviolet Imager and Solar Wind Analyser Instruments Telemetry/Telecommand database | |
| Solar Orbiter (SO) Extreme-Ultraviolet Imager (EUI) instrument consists of two High Resolution Imagers (HRI) and one Full-Sun Imager (FSI) which include Lyman-Alpha, dual bands 17.4nm and 30.4nm. These telescopes are 47.4mm and 30mm in diameters. The instrument has its own Data Processing Unit (DPU). For the Solar Wind Analyser (SWA) instrument, it has 3 sensors which are the Electron Analyser System (EAS), Proton-Alpha Sensor (PAS) and Heavy Ion Sensor (HIS). Similar to EUI, it has a DPU to administrate the input and output data. Two Telemetry (TM)/Telecommand (TC) databases for the EUI and SWA are developed using Satellite Control and Operation System 2000 (SCOS-2000). The mandatory, houskeeping and science TM/TC databases are defined for the SO mission that will be discussed and demonstrated in details. | |
| October 18 (Fri) 15:00-16:00 | Kazumasa Iwai (NAOJ) |
| Measurements of Chromospheric and Coronal Magnetic Fields using the Radio Observation: method and its application | |
| The magnetic field of the solar atmosphere is an important clue to understanding and forecasting many solar phenomena such as flares and coronal mass ejections. In magnetized plasma, ordinary and extraordinary modes of the radio free-free emission have different optical depths. Hence, the radio circular polarization observation enables us to derive the longitudinal component of the magnetic field. In this study, we have derived coronal and chromospheric magnetic fields from circular polarization observations by Nobeyama Radioheliograph (NoRH). NoRH observes the full solar disk every 1 second at 17 GHz (intensity and circular polarization) and 34 GHz (intensity). We observed several active regions at the disc center and limb, and derived magnetic fields. We found that the derived magnetic fields contain both the coronal and chromospheric components. At the center of the active region, the chromospheric and coronal components cannot be separated, and the derived magnetic field is emission-measure weighted. On the other hand, we can assume that there is almost no chromospheric circularly polarized component and derive the pure coronal magnetic field strength from the limb observation. | |
| October 2 (Wed) 15:00-16:00 | Bruce W. Lites (NCAR) |
| THE SOLAR CYCLE DEPENDENCE OF THE WEAKEST INTERNETWORK FLUX | |
| In a prior analysis using 45 data sets measured with the Hinode/SOT Spectro-Polarimeter (SP) during 2007, Lites (2011, ApJ 737, p. 52) examined the weakest components of the internetwork flux and their possible association with the stronger, larger scale flux of the quiet Sun. No association of the weakest mixed-polarity flux to the stronger, larger-scale flux patterns. Also, the weakest flux remained very nearly equally balanced between positive and negative flux, even in quiet Sun regions that had significant overall flux imbalance. The observed behavior of these data taken near the minimum of the solar cycle suggests that this weak flux arises from a local, small-scale dynamo process. A local, small-scale dynamo should be independent from the large-scale dynamo of the solar cycle. In the present study, we examine the SP 諛ｼ\F2\FCirradiance data諛ｼ\F2\FD taken in identical fashion every month since late 2008. In all, 990 separate SP maps were processed. Each month these data span the full range of solar latitude from pole-to-pole. We look for solar-cycle signatures of the weakest components of the magnetic flux as a function of both time and solar latitude. As expected for a local small-scale dynamo process, the preliminary examination of the data shows no visible patterns that would suggest an association of the weakest flux with solar activity. On the other hand, the weak transverse (horizontal) flux appears to increase in the activity belt as the solar cycle rises, suggesting possibly the solar cycle flux produces a canopy of magnetic field. | |
| August 19 (Mon) 15:30-16:30 | Gu Liyi) (U. Tokyo, PD) |
| Towards a Deeper Understanding of the Hot Plasmas In Galaxy Clusters: Indications of A Magnetosphere Model and Observations of Galaxy-Plasma Interactions | |
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Hot plasmas in galaxy clusters (ICM) can be regarded as a ideal plasma confined stably mostly by the gravity of dark matter. It has a temperature of 2-15 keV, a number density of 1e3-4 m^-3 in the center,and magnetized to a few uG. ICM is most mysterious plasma ever observed, when the most puzzling questions are, i.e., how is the ICM thermally stabilized against radiative cooling, and how is it polluted with heavy elements up to large radius. Based on several observational results, we proposed that the ICM in the cluster center is two-phased, when a corona-like magnetic structure confines the cool phase ICM and separates it from the hot phase one. The magnetic loops are heated via magnetic reconnections and/or dissipation of MHD turbulence and waves, which are generated by interactions between moving member galaxies and the hot plasmas. The member galaxies gradually lose dynamical energy to the ICM and infall to the center, while the heavy elements synthesized in the galaxies were stripped out and left in the cluster outskirt. The new ASTRO-H telescope might provide unique opportunity to detect for the first time the MHD dynamics in the ICM. We are looking forward active contributions from plasma physicians to the fascinating subject. | |
| August 6 (Tue) 15:00-16:00 | Robert Cameron (Max Planck Institute for Solar System Research) |
| What determines the strength of solar cycles? | |
| The link between the smallest resolvable scales using Hinode and the evolution of the Sun's global magnetic field will be discussed. The non-linear mechanisms which limit the strength of the solar dynamo, as well as the processes which introduce randomness into the cycle strengths will be discussed using various types of observations. | |
| May 22 (Wed) | Jun Lin (Yunnan Astron. Obs.) |
| CME/Flare Reconnecting Current Sheets: Observations and Theories | |
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Eruptive solar flares involve the formation of long current sheets (CSs) connecting coronal mass ejections (CMEs) to the associated flares. The formation of such CSs was predicted by the catastrophe model of solar eruptions and has also been found in numerical experiments of CMEs. In addition, observations showed plasma flows continuously moving along CSs toward and away from the Sun. In those flows, many plasma blobs were identified. Associated with these results, observations also indicated that the CME/flare CS could be as thick as ~10^5 km. This constitutes a serious challenge to our long-existing understanding and knowledge on the reconnecting CS. This review will go through the development of theories on the CS and the consequent observations, present possible mechanisms for large scale CS, and discuss the coupling of various scales of processes through which magnetic reconnection takes place in the thick CS at a reasonably fast rate required for the rapid energy release during the major flare. The results of the most recent observations and numerical experiments will also be displayed. | |
| May 14 (Tue) | Tettsuya Magar (K(Kyung Hee U.) |
| Modeling of Magnetic Structures on the Sun: Force-free ranges and eruption mechanism of these structures | |
| Once they are formed on the Sun, magnetic structures are basically not bounded by external objects, so these structures tend to expand outward. On the other hand, since the plasma beta is low in the solar corona, the magnetic field evolves toward the state where the magnetic field is balanced itself in the corona, which is called the force-free state. Our particular interest is to investigate the range of the solar atmosphere within which the force-free state is achieved. For this purpose we perform three-dimensional MHD simulations to obtain several magnetic structures with different configurations via flux emergence, and we apply a virial energy analysis for these structures to derive their force-free ranges. On the basis of this analysis, we discuss a mechanism for solar eruptions (e.g. CMEs) characterized by the curvature and scale height of emerging magnetic field. This mechanism relates to the transfer of magnetic field from the quasi-static (force-free) range to the expansion range; both ranges coexist in the same system. This is different from the standard picture of the loss-of-equilibrium (instability) where the eruption arises in the system that maintains force-free equilibrium as a whole and follows the quasi-static evolution along a sequence of equilibria with temporally changing photospheric boundary conditions. | |
| April 30 (Tue) | Lee Kyoung-Sun (ISAS) |
| Study of small-scale reconnection features using spectroscopy and stereoscopy | |
| Solar coronal bright points (BPs) and jets are considered as the small-scale magnetic reconnection features, such as microflares or nanoflares. These magnetic reconnection features could transport energy from the chromosphere to the corona or supply mass to the solar wind. Therefore, investigation of BPs and jets is important to know their mechanism as well as the heating process of the corona and acceleration of the solar wind. Recently, the new satellite observations for the first time allow us to investigate their spectroscopic properties and 3-D structures in stereoscopic view with higher resolutions. First, I will present observational studies of the BPs and jets using spectroscopy and stereoscopy that I did during PhD course, briefly. Then, I will introduce my research plan for determination of the heights (chromosphere or corona) of bright points or reconnection sites associated with the BPs using spectroscopic and stereoscopic methods. The condition for the magnetic reconnection in solar atmosphere is different between chromosphere and corona. I will investigate the reconnection heights of the BPs and compare their plasma properties depending on the reconnection height, statistically. | |
| April 25 (Wed) | Shinsuke Takasao (Kyoto U.) |
| A Unified Scenario of Solar Chromospheric Jets | |
| Hinode shows us that the solar chromosphere is full of jets, collimated plasma flows. There is a strong possibility that they are proxies of the energy transport processes from the photosphere to the corona. To understand energy transport processes, which are related to the coronal heating problem, it is necessary to understand the basic physics of chromospheric jets. With this in mind, I will introduce how chromospheric jets are related to the energy transportation by waves/shocks. This point may be related to the physics in the ionosphere. Then I will discuss acceleration mechanisms of chromospheric jets, particularly chromospheric jets associated with magnetic reconnection between an emerging flux and an ambient magnetic field. Finally, I will show a schematic picture of a unified scenario of such kind of chromospheric jets. | |