TY  - JOUR
A1  - Teriaca, Luca
A1  - Andretta, Vincenzo
A1  - Auchere, Frederic
A1  - Brown, Charles M.
A1  - Buchlin, Eric
A1  - Cauzzi, Gianna
A1  - Culhane, J. Len
A1  - Curdt, Werner
A1  - Davila, Joseph M.
A1  - Del Zanna, Giulio
A1  - Doschek, George A.
A1  - Fineschi, Silvano
A1  - Fludra, Andrzej
A1  - Gallagher, Peter T.
A1  - Green, Lucie
A1  - Harra, Louise K.
A1  - Imada, Shinsuke
A1  - Innes, Davina
A1  - Kliem, Bernhard
A1  - Korendyke, Clarence
A1  - Mariska, John T.
A1  - Martinez-Pillet, Valentin
A1  - Parenti, Susanna
A1  - Patsourakos, Spiros
A1  - Peter, Hardi
A1  - Poletto, Luca
A1  - Rutten, Robert J.
A1  - Schuehle, Udo
A1  - Siemer, Martin
A1  - Shimizu, Toshifumi
A1  - Socas-Navarro, Hector
A1  - Solanki, Sami K.
A1  - Spadaro, Daniele
A1  - Trujillo-Bueno, Javier
A1  - Tsuneta, Saku
A1  - Dominguez, Santiago Vargas
A1  - Vial, Jean-Claude
A1  - Walsh, Robert
A1  - Warren, Harry P.
A1  - Wiegelmann, Thomas
A1  - Winter, Berend
A1  - Young, Peter
T1  - LEMUR large european module for solar ultraviolet research
JF  - Experimental astronomy : an international journal on astronomical instrumentation and data analysis
N2  - The solar outer atmosphere is an extremely dynamic environment characterized by the continuous interplay between the plasma and the magnetic field that generates and permeates it. Such interactions play a fundamental role in hugely diverse astrophysical systems, but occur at scales that cannot be studied outside the solar system. Understanding this complex system requires concerted, simultaneous solar observations from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at high spatial resolution (between 0.1'' and 0.3''), at high temporal resolution (on the order of 10 s, i.e., the time scale of chromospheric dynamics), with a wide temperature coverage (0.01 MK to 20 MK, from the chromosphere to the flaring corona), and the capability of measuring magnetic fields through spectropolarimetry at visible and near-infrared wavelengths. Simultaneous spectroscopic measurements sampling the entire temperature range are particularly important. These requirements are fulfilled by the Japanese Solar-C mission (Plan B), composed of a spacecraft in a geosynchronous orbit with a payload providing a significant improvement of imaging and spectropolarimetric capabilities in the UV, visible, and near-infrared with respect to what is available today and foreseen in the near future. The Large European Module for solar Ultraviolet Research (LEMUR), described in this paper, is a large VUV telescope feeding a scientific payload of high-resolution imaging spectrographs and cameras. LEMUR consists of two major components: a VUV solar telescope with a 30 cm diameter mirror and a focal length of 3.6 m, and a focal-plane package composed of VUV spectrometers covering six carefully chosen wavelength ranges between 170 and 1270 . The LEMUR slit covers 280'' on the Sun with 0.14'' per pixel sampling. In addition, LEMUR is capable of measuring mass flows velocities (line shifts) down to 2 km s (-aEuro parts per thousand 1) or better. LEMUR has been proposed to ESA as the European contribution to the Solar C mission.
KW  - Sun: atmosphere
KW  - Space vehicles: instruments
KW  - Techniques: spectroscopy
KW  - ESA cosmic vision
Y1  - 2012
U6  - https://doi.org/10.1007/s10686-011-9274-x
SN  - 0922-6435
VL  - 34
IS  - 2
SP  - 273
EP  - 309
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Liu, Rui
A1  - Kliem, Bernhard
A1  - Titov, Viacheslav S.
A1  - Chen, Jun
A1  - Wang, Yuming
A1  - Wang, Haimin
A1  - Liu, Chang
A1  - Xu, Yan
A1  - Wiegelmann, Thomas
T1  - STRUCTURE, STABILITY, AND EVOLUTION OF MAGNETIC FLUX ROPES FROM THE PERSPECTIVE OF MAGNETIC TWIST
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We investigate the evolution of NOAA Active Region (AR) 11817 during 2013 August 10–12, when it developed a complex field configuration and produced four confined, followed by two eruptive, flares. These C-and-above flares are all associated with a magnetic flux rope (MFR) located along the major polarity inversion line, where shearing and converging photospheric flows are present. Aided by the nonlinear force-free field modeling, we identify the MFR through mapping magnetic connectivities and computing the twist number ${{ \mathcal T }}_{w}$ for each individual field line. The MFR is moderately twisted ($| {{ \mathcal T }}_{w}| \lt 2$) and has a well-defined boundary of high squashing factor Q. We found that the field line with the extremum $| {{ \mathcal T }}_{w}| $ is a reliable proxy of the rope axis, and that the MFR's peak $| {{ \mathcal T }}_{w}| $ temporarily increases within half an hour before each flare while it decreases after the flare peak for both confined and eruptive flares. This pre-flare increase in $| {{ \mathcal T }}_{w}| $ has little effect on the AR's free magnetic energy or any other parameters derived for the whole region, due to its moderate amount and the MFR's relatively small volume, while its decrease after flares is clearly associated with the stepwise decrease in the whole region's free magnetic energy due to the flare. We suggest that ${{ \mathcal T }}_{w}$ may serve as a useful parameter in forewarning the onset of eruption, and therefore, the consequent space weather effects. The helical kink instability is identified as the prime candidate onset mechanism for the considered flares.
KW  - coronal mass ejections (CMEs)
KW  - Sun: corona
KW  - Sun: filaments, pominences
KW  - Sun: flares
KW  - Sun: magnetic fields
Y1  - 2016
U6  - https://doi.org/10.3847/0004-637X/818/2/148
SN  - 0004-637X
SN  - 1538-4357
VL  - 818
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Fuhrmann, Marcel
A1  - Seehafer, Norbert
A1  - Valori, Gherardo
A1  - Wiegelmann, Thomas
T1  - A comparison of preprocessing methods for solar force-free magnetic field extrapolation
Y1  - 2011
UR  - http://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/full_html/ 2011/02/aa15453-10/aa15453-10.html
SN  - 0004-6361
ER  - 
TY  - JOUR
A1  - DeRosa, Marc L.
A1  - Schrijver, Carolus J.
A1  - Barnes, Graham
A1  - Leka, K. D.
A1  - Lites, Bruce W.
A1  - Aschwanden, Markus J.
A1  - Amari, Tahar
A1  - Canou, Aurélien
A1  - McTiernan, James M.
A1  - Régnier, Stéphane
A1  - Thalmann, Julia K.
A1  - Valori, Gherardo
A1  - Wheatland, Michael S.
A1  - Wiegelmann, Thomas
A1  - Cheung, Mark C. M.
A1  - Conlon, Paul A.
A1  - Fuhrmann, Marcel
A1  - Inhester, Bernd
A1  - Tadesse, Tilaye
T1  - A critical assessment of nonlinear force-free field modeling of the solar corona for active region 10953
N2  - Nonlinear force-free field (NLFFF) models are thought to be viable tools for investigating the structure, dynamics, and evolution of the coronae of solar active regions. In a series of NLFFF modeling studies, we have found that NLFFF models are successful in application to analytic test cases, and relatively successful when applied to numerically constructed Sun-like test cases, but they are less successful in application to real solar data. Different NLFFF models have been found to have markedly different field line configurations and to provide widely varying estimates of the magnetic free energy in the coronal volume, when applied to solar data. NLFFF models require consistent, force-free vector magnetic boundary data. However, vector magnetogram observations sampling the photosphere, which is dynamic and contains significant Lorentz and buoyancy forces, do not satisfy this requirement, thus creating several major problems for force-free coronal modeling efforts. In this paper, we discuss NLFFF modeling of NOAA Active Region 10953 using Hinode/SOT-SP, Hinode/XRT, STEREO/SECCHI-EUVI, and SOHO/MDI observations, and in the process illustrate three such issues we judge to be critical to the success of NLFFF modeling: (1) vector magnetic field data covering larger areas are needed so that more electric currents associated with the full active regions of interest are measured, (2) the modeling algorithms need a way to accommodate the various uncertainties in the boundary data, and (3) a more realistic physical model is needed to approximate the photosphere-to-corona interface in order to better transform the forced photospheric magnetograms into adequate approximations of nearly force-free fields at the base of the corona. We make recommendations for future modeling efforts to overcome these as yet unsolved problems.
Y1  - 2009
UR  - http://iopscience.iop.org/0004-637X/
U6  - https://doi.org/10.1088/0004-637x/696/2/1780
SN  - 0004-637X
ER  -