In the coming four years the governance structure for the European Solar Telescope (EST) needs to be defined. For this various governance models for multi-national collaborations need to be studied. In this presentation I will define the important steps to arrive at the EST governance structure. These steps follow general principles to define organizational models. Furthermore, the requirements already defined by the EU in form of practical guidelines for defining the legal framework for a consortium operating such an infrastructure and the European Charter for Access to Research Infrastructures will be reviewed.

We analyze a conned multiple-ribbon M2.1 flare that originated from a fan-spine coronal magnetic field coguration, within active region NOAA 12268. The observed ribbons form in two steps. First, two primary ribbons form at the main flare site, followed by the formation of secondary ribbons at remote locations. We observe a number of plasma flows at extreme-ultraviolet temperatures during the early phase of the flare (as early as 15 min before the onset) propagating towards the formation site of the secondary ribbons. The secondary ribbon formation is co-temporal with the arrival of the pre-flare generated plasma flows. The primary ribbons are co-spatial with RHESSI hard X-ray sources, whereas no enhanced X-ray emission is detected at the secondary ribbons sites. The (E)UV emission, associated with the secondary ribbons, peaks 1 min after the last RHESSI hard X-ray enhancement. A nonlinear force-free model of the coronal magnetic field reveals that the secondary flare ribbons are not directly connected to the primary ribbons, but to regions nearby. Detailed analysis suggests that the secondary brightenings flare produced due to dissipation of kinetic energy of the plasma flows (heating due to compression), and not due to non-thermal particles accelerated by magnetic reconnection, as is the case for the primary ribbons.

B. Lemmerer, A. Hanslmeier, T. Zaqarashvili, J. Koza, M. Temmer, A. Veronig, H. Grimm-Strele, H. Muthsam, F. Calvo, O. Steiner

Simulations of the solar convection including radiation transport allow us to examine and track photospheric shock waves in detail unparalleled by direct observation. It is still not clear which processes trigger shocks and how significant a role they play for the energy transport to the upper layers of the atmosphere. Apart from traditional techniques of shock wave detection that rely on a search for the concentration of contour lines of pressure, density, and temperature and for the localization of Mach number isosurfaces, we employ recent post-processing methods specifically aimed at the analysis of computational fluid dynamics (CFD) data that allow us to more accurately locate and segment shock fronts as they propagate through the photospheric plasma. We present an application of different detection algorithms on radiation hydrodynamics (RHD) and radiation magnetohydrodynamics (RMHD) simulation data of the photosphere that are based on an edge detection technique as well as a method to locate shock surface normals based on the local pressure gradient. We will compare the emergence of shock patterns in these two qualitatively different simulations and discuss the correlation of the shock structures with the underlying flow field.

Zurab Vashalomidze, Teimuraz Zaqarashvili, Jan Rybak, Arnold Hanslmeier

We present results of spectral inversion of the Halpha and Ca II 8542 A lines observed by the imaging spectropolarimeter CRISP at the Swedish 1-m Solar Telescope in chromospheric jet identified in the quiet-Sun atmosphere. The inversion aims to reveal increased turbulence in these jets as a possible consequence of Kelvin-Helmholtz instabilities expected for strongly-sheared plasma flows at jet interfaces. To verify the results physical parameters of the chromospheric jets are inferred by different variants of cloud model inversion technique. The cloud model parameters of the chromospheric jets are supplemented by their lifetimes, widths, maximum lengths, apparent longitudinal velocities, transversal displacements, and transversal velocities to compare them with parameters of Rapid blueshifted events.

From numerical simulations of highest spatial resolution and high resolution observations, we may guess the science questions to be tackled with future large solar telescopes. Selected examples are discussed, trying to determine the instrument requirements for answering questions regarding polarimetric accuracy or spatial and temporal resolution. Besides such foreseeable science questions, however, it is worthwhile to recall that the best discoveries come unexpectedly and to wonder about what instrument capabilities may be most likely conducive to the unexpected.

Reza Rezaei, IAC

We present high-resolution full-Stokes measurements of sunspots, using the highly-sensitive full-split (g=3) infrared line Fe I 1564.85 nm, and compare them with simultaneous continuum intensity measurements. We extend the classical work of Kopp & Rabin (1992, Solar Phys. 141, 253) from the intensity to the full Stokes vector. The data were obtained with the GREGOR Infrared Spectrograph (GRIS) on May 11, 2015, using the adaptive optics system. The observations include three large sunspots of active region 12339, with spatial resolution better than 0.5" in the spectral scans. The continuum intensity is corrected for instrumental scattered light and the brightness temperature is calculated. Magnetic field strength and inclination are derived directly from the line split and ratio of Stokes components. The continuum intensity relation to the field strength and inclination are studied separately in the umbra, light bridges, and penumbra. The results agree with previous studies but the higher spatial resolution leads to a larger scatter of values in the continuum intensity (temperature) and magnetic-field relations.