Solar Seminar 2015 (Log)


Place: Hiinode meeting room (#1754) at Building A, 7-F
Regular Time: 15:00-16:30 on Wednesday
Organizer: Lee Kyoung-Sun


Upcoming seminar schedule

Sakao - Oct 28
Toriumi - Nov 11
Ohyama - Nov 25


October 21 (Wed) Dr. Mark Cheung (LMSAL) PDF
Probing the Thermal Structure of the Solar Corona using SDO/AIA
We present a validated method to perform differential emission measure (DEM) inversions on extreme ultraviolet imaging observations of the solar corona taken by the Atmospheric Imaging Assembly onboard NASA's Solar Dynamics Observatory. We begin with a description of the method and proceed to discuss test cases used for validation. We then present applications of the method to a number of science cases, including the (1) thermal structure of active regions and emerging flux regions, (2) magnetic reconnection outflows and (3) chromospheric evaporation in solar flares.

October 14 (Wed) Dr. Yusuke Iida (ISAS Hinode team)
Investigation of Magnetic field transport on the solar surface by use of the MHD simulation
The magnetic field transport by convection on the solar surface is one of key processes for the surface flux transport model. In the previous seminar, I reported that the super-diffusion scaling of the magnetic elements motion is changed to sub-diffusive scaling in time scale longer than 2x10^4 s and speculated that this is because the network structure traps the magnetic field (Submitted to Space Weather and Space Climate). However, it is not clear if this kind of magneto-convection system can be formed and maintained even in the pure theoretical discussion. Hence I started to collaborate with Dr. Hotta and investigate if this situation is achieved by use of the 3-D MHD numerical simulation. In the presentation, I will show the primitive results of the transport of the magnetic field in the numerical simulation and the problems we are facing.

October 1 (Thu) Dr. Jie Zhang (George Mason University) PDF
Observations and Understanding of Solar Eruptions
Solar eruptions, in the forms of solar flares and coronal mass ejections (CMEs), are the most energetic phenomena in the solar system. Solar eruptions are the known cause of severe space weather that may affect satellite operation, communication, navigation and other advanced modern technological systems. In this talk, I will introduce existing physical mechanisms of solar eruptions, with a focus on two contrasting paradigms: the non-ideal MHD process of magnetic reconnection versus the ideal process of magnetic flux rope instability. To examine the validity of these two paradigms, I will present the state-of-the-art observations of solar eruptions from Solar Dynamic Observatory (SDO) spacecraft and other data sources. In particular, I will examine the possible observational evidences of magnetic flux ropes (MFRs) before and during eruptions, which are the key test of physical mechanisms. Morphological, dynamic and thermal properties of CMEs will be discussed. It is suggested that the pre-existence of an MFR play the essential role for producing solar eruptions.

September 30 (Wed) Dr. David H. Brooks (ISAS Hinode team/ George Mason University)
The Origin of the Slow Solar Wind
The source regions of the slow solar wind are still under debate. Recently, high temperature outflows at the edges of active regions were detected by Hinode, and it has been proposed that they could be a slow solar wind source. In this talk, I will discuss some of the recent evidence for, and problems with, this scenario from EIS observations.

September 2 (Wed) Dr. Toshifumi Shimizu (ISAS/JAXA) PDF
Magnetic twists and energy releases in solar flares
Solar flares abruptly release free energy stored as a non-potential magnetic field in the corona. The nature of magnetic twists would be one of important parameters for understanding how the stored energy is released with occurrence of flares. In this talk, I will present our recent analysis on X5.4 flare on 7 March 2012 and discuss the role of magnetic twists formed in the corona.

August 26 (Wed) Takayoshi Oba (D3, Sokendai in ISAS) PDF
Height velocity structure of photospheric convection in granules and intergranular lanes with Hinode/SOT
The solar photosphere is the visible surface of the Sun, where numerous numbers of bright granules, called granulation, surrounded by narrow dark intergranular lanes, are observed anywhere. These granular patterns are a manifestation of convective motions. A height structure of velocity field is important to know for the convective instability, however, it remains unclear observationally. We tackle this problem by using bisector analysis, derivation of the Doppler velocity at each intensity level in a photospheric absorption line. The issue in the analysis was that the 5-minute oscillations were included in the velocity structure; The 5-minute oscillations may give velocity signals in the same order of magnitude with that of convection. We removed the 5-minute oscillations signals from the data by using the k-ω diagram and investigated the height structure of the pure convective motions.  The spectral data for the bisector analysis was acquired with the spectro-polarimeter (SP) of the Hinode / Solar Optical Telescope (SOT). The data set is a 2-second cadence time series of the sit-and-stare Stokes IQUV measurements for 45 minutes, with the simultaneous series of BFI blue continuum images. The SP slit was placed at the fixed position in the quiet region at the disk center.  To investigate the mechanisms of convection, we focused on the dependence of the vertical velocity amplitude on height. The average amplitude decreases from 0.65 km/s to 0.40 km/s with height in granules where the upward mass motions may be observed in general. On the other hand, it increases from 0.30 km/s to 0.50 km/s with depth in intergranular lanes, where the downward motions are dominantly observed. Theoretically, if the photosphere is in convective stable condition, the amplitude of the velocity decreases with depth. Hence our results cannot be explained with the convective stable condition and we need the extra force to break the convective stable condition in the intergranular region. We suggest that radiative cooling is very effective in the downflow region and the energy loss through it may result in accelerating downward motions.

July 15 (Wed) Yumi Bamba (D3, Nagoya University / Hinode group in ISAS/JAXA)
Two-step Triggering Process of the X1.0 Three-ribbon Flare in the Great Active Region NOAA 12192
In this study, we clarify the triggering process of the X1.0 flare produced in the great active region (AR) NOAA 12192 on 2014 October 24. The AR 12192 had very complicated magnetic structure, which was classified to #-type sunspot and produced six X-class flares during disk passage. The AR showed complicated shape of the PIL, and the X1.0 flare produced three flare-ribbons in contract to the standard two-ribbon flare. We analyzed magnetograms and filtergrams of each layer in the solar atmosphere obtained by Hinode/SOT and SDO/HMI, AIA. We investigated the correlation between the magnetic structures and the strong emissions in the chromosphere, and the non-potentiality of the photospheric magnetic field. Moreover, we compared the observed features and the coronal magnetic fields extrapolated by the NLFFF method (Inoue+2014) in order to clarify the trigger process of the flare. As a result, we identified the "flare trigger field" of the X1.0 flare, and found that the triggering process was two-step from the preceding C9.7 to the X1.0 flares. The flare trigger process satisfied one of the two types of flare trigger process proposed by Kusano+2012 using the numerical simulation. Moreover, we found that the flare trigger field locates slight off of the PIL although the numerical simulation of Kusano+2012 puts the flare trigger field just above the PIL.Therefore, our results give a specific suggestion that the theoretical flare trigger model is applicable even though the small flare trigger field is located off the PIL as long as the topological conditions proposed by Kusano+2012 are satisfied.

July 8 (Wed) Dr. Takuma Matsumoto (Project researcher in Hinode group in ISAS/JAXA) PDF
Competition between shock and turbulent heating in the coronal loop system
We have performed 2.5-dimensional magnetohydrodynamic (MHD) simulations with high spatial resolution in order to distinguish between competing models in the coronal heating problem. We focused on a single coronal loop that was powered by Alfven waves excited in the photosphere. As a natural consequence of the transportation and dissipation of Alfven waves, a coronal structure was reproduced in our simulations. The coronal structure was maintained as the spatial resolution was changed from 50 km to 6 km. The heating mechanisms changed gradually across a magnetic canopy at the height of 4 Mm. Below the magnetic canopy, a compressible heating mechanism due to the formation of shocks was dominant. Above the magnetic canopy, a development of MHD turbulence provided an incompressible heating to balance the cooling by radiation and thermal conduction.

July 1 (Wed) Yusuke Kawabata (M2, The University of Tokyo) PDF
Homologous flares occurred at the quadrupolar field
Solar flares are understood as abrupt release of magnetic energy by magnetic reconnection. We sometimes observe a series of flares which occur in the similar locations of the same active region and and show similar shapes of flare brightening in UV and EUV. Such flares are called `Homologous flares'. In this talk, I will report our analysis of homologous flares occurred at the quadrupolar field. In the first ten days of February 2014, more than 10 M class flares occurred on AR 11967. Using EUV images from the Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO), we identified some of the flares are homologous and show X-shaped brightening. We recognized the location of flare ribbons from Solar Optical Telescope (SOT) on board Hinode. By superposing the flare ribbons image on the magnetogram data observed by SOT, we found that four magnetic region contribute to the flares. In order to know the connectivity of each region, we apply a nonlinear force-free field modeling and found that the coronal magnetic field shows quadrupolar configuration with a null point. I want to discuss the temporal change of the coronal magnetic structure which makes flares homologous.

June 24 (Wed) Kyoung-Sun Lee (ISAS, project researcher in Hinode group) PDF
Topics in the IRIS workshop 4 and a study on the evaporation flow in a bright kernel of an X1.6 flare observed by IRIS, Hinode, and RHESSI
In this seminar, I will introduce some topics discussed in the IRIS workshop 4 in last May. And I will present an observational study of the evaporation flow in an X1.6 flare. The flare occurred at the AR 12192 on 2014 October 22 around 14:10 UT and was observed by IRIS, Hinode, and RHESSI simultaneously. Using those multiple observations, we found a bright kernel that showed an intensity enhancement in multi-wavelengths. Taking advantage of the spectroscopic observation of the IRIS and EIS, we measured Doppler velocities in the bright kernel through the chromosphere and corona. When the flare occurs, emissions from hotter coronal lines, Fe XV -Fe XXIV (2-16 MK), show upflows (30-200 km s-1) while choromospheric temperature lines of He II and Si IV (~0.1 MK) found to be downflows (30-60 km s-1). The upflows indicate the chromospheric evaporated flows and the downflows may be caused by the compression due to the explosive evaporation. Those upflows and downflows last more than an hour after the flare onset. In addition, white light and Hard X-ray emission were also detected at this kernel from SOT continuum and RHESSI. I will discuss the temperature dependence and temporal evolution of the intensity and Doppler velocity in different spectral lines using the combination of the EIS and IRIS observations and their relationship with the white light and Hard X-ray emission.

June 17 (Wed) Ryuichi Kanoh (M2, The University of Tokyo) PDF
Study on the connectivity between the photospheric magnetic fields and counterparts in the upper atmosphere with Hinode and IRIS
Understanding the mechanisms that heats solar corona and accelerates the solar wind is an important remaining task for solar physicists. Generally, magnetic fields are thought to play a key role in these problems. Therefore, connectivity between the photospheric magnetic fields and their counterparts in the upper atmosphere is one of essential information. Moreover, typical time scale of activities in the upper atmosphere is quite short (about a few minutes). In this talk, for the above reasons, we present an unique set of the high-cadence observations coordinated between Hinode Solar Optical Telescope (SOT)'s spectro-polarimeter and Interface Region Imaging Spectrograph (IRIS). My talk contains mainly two topics. One is about sunspot light bridge's activities, and the other one is about MHD waves. I will report our results so far, and talk about my future plans of these studies.

June 10 (Wed) Dr. Kirill Kuzanyan (Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN) Moscow, Russia)
Measuring helicity of solar magnetic fields and its implication to the solar dynamo
Monitoring of magnetic field vector at solar surface in active regions has been systematically started in 1980s with the use of ground-based vector magnetographs. For now several observatories in the USA, Japan and China have long-term data covering more than two solar cycles. Recently more advanced data on solar vector magnetic field become available due to space missions Hinode and SDO. Our measurements can be used to compute proxies of magnetic helicity in the Sun. This poses an additional constrains on dynamo models which are behind the solar magnetic cyclicity. I outline the key effects of magnetic helicity measurements over the solar cycle and development of simple self-consistent dynamo models.

June 3 (Wed) Dr. Shinosuke Ishikawa (New project researcher in ISAS Hinode team)
Instrument development for next generation solar observations
In next generation solar observations, high sensitivity instruments are desired. To detect hard X-rays (HXRs) from faint sources including sources in the quiet Sun, we have performed a sounding rocket experiment FOXSI (Focusing Optics Solar X-ray Imager). I have developed a fine-pitch HXR detector with cadmium telluride (CdTe) semiconductor as the FOXSI focal plane detector for the imaging and spectroscopy. The FOXSI flight is successfully performed and images from the Sun are obtained with the detector position resolution of 65 um, finest as a CdTe diode detector ever. In the other wavelengths, high sensitivity UV spectropolarimetry is desired for magnetic field observation of upper chromoshpere and above using the Hanle effect. We develop a high precision spectropolarimator for a sounding rocket experiment CLASP (Chromospheric Lyman-Alpha SpectroPolarimeter), and I have developed and evaluated a high precision waveplate rotator for CLASP. In a rotation uniformity test experiment, it is measured that the error caused by the rotation uniformity is ~0.01%, and confirmed it has a sufficient precision for CLASP. In this talk, I will summarize my work for these instruments and future plan for the developments.

May 27 (Wed) Dr. Sam Krucker (UC Berkeley & FHNW Switzerland) & Dr. Lindsay Glesener (UC Berkeley) PPT
Co-spatial White Light and Hard X-ray Flare Footpoints seen above the Solar Limb
This talk will report on analysis of three solar flares that occur within one degree of limb passage, with the goal to investigate the source height of chromospheric footpoints in white light (WL) and hard X-rays (HXR). We find the WL and HXR (>30 keV) centroids to be largely co-spatial and from similar heights for all events, with altitudes around 800 km above the photosphere or 300-450 km above the limb height. To be compatible with the standard thick target model, these rather low altitudes require very low ambient densities within the flare footpoints, in particular if the HXR-producing electrons are only weakly beamed. That the WL and HXR emissions are co-spatial suggests that the observed WL emission mechanism is directly linked to the energy deposition by flare accelerated electrons with energies above ~30 keV. If the WL emission is from low-temperature (~10 000 K) plasma as currently thought, the energy deposition by HXR-producing electrons above ~30 keV seems only to heat chromospheric plasma to such low temperatures. This implies that flare-accelerated electrons above ~30 keV are not responsible for chromospheric evaporation, but that >30keV electrons lose their energy through radiation in the optical range.

May 27 (Wed) Dr. Lindsay Glesener (UC Berkeley) PDF
Summary of FOXI results and future plans

May 13 (Wed) Dr. Carlos Quintero Noda (New Postdoctoral researcher in ISAS Hinode group) PDF
Spatial deconvolution of spectropolarimetric data: application to quiet Sun magnetic elements
Observations of the Sun from the Earth are always limited by the presence of the atmosphere, which strongly disturbs the images. A solution to this problem is to place the telescopes in space satellites, which produce observations without any (or limited) atmospheric aberrations. However, even though the images from space are not affected by atmospheric seeing, the optical properties of the instruments still limit the observations. In the case of diffraction limited observations, the PSF establishes the maximum allowed spatial resolution, defined as the distance between two nearby structures that can be properly distinguished. In addition, the shape of the PSF induce a dispersion of the light from different parts of the image, leading to what is commonly termed as stray light or dispersed light. This effect produces that light observed in a spatial location at the focal plane is a combination of the light emitted in the object at relatively distant spatial locations. We aim to correct the effect that the spatial PSF produces using a deconvolution method, and we decided to applied the code to Hinode/SP quiet Sun observations. I will explain in this talk the validity of the deconvolution process with noisy data and how we analyze the physical properties of quiet Sun magnetic elements after the deconvolution process.

April 30 (Thu) Masanori Yamada (Ibaraki University / ISAS Hinode group) PDF
Fluctuating the Speckle is detected by 'Hinode' XRT according to solar activity
Solar energetic particles (SEPs) and Plasma in the Earth's magnetosphere generate signals which are not came from the observation target. On the captured image, these signals are similar to trajectories and small scars. In this study, these "false" signals are referred to as the Speckles. Speckles become indication of how many SEPs flew on the satellite orbit. It gives important information on which to explore the surrounding space environment. For the above reason, in this study we analyzed Hinode / X-Ray Telescope (XRT) images and detected speckles. The data were captured by the flare-time-patrol mode, which temporal resolution is higher than normal observation mode and these are irreversibly compressed. From analysis result, speckle has been found to increase in the high latitude zone in orbit. Moreover, this increase has caused a change in the same manner as proton flux observed by GOES satellites. I will talk about my results in detail.

April 23 (Thu) Takuya Takahashi (Kyoto University) PDF
Prominence Activation by Coronal Fast Mode Shock
Our universe is full of explosive phenomena such as supernovae, flares and jets. These explosions lead to the formation of shock waves, which sometimes interact with dense materials which is referred to as 'clouds'. We find some example of such shock-cloud interaction on our Sun. Associated with a large solar flare occurred on Mar 7, 2012, a wave-like coronal disturbance (known as EUV waves) was observed. The EUV wave 'hit' a polar prominence leading to its oscillation. We found that the prominence strongly brightened when EUV wave 'pushed' it. Based on observational features, we interpreted the EUV wave as fast mode MHD shock propagated in the corona. We could successfully explained prominence acceleration and compression as a process of shock cloud interaction which is a potential tool to diagnose physical quantities of coronal shock and prominence itself.


Past Seminars

2014

2013