Dynamics of small-scale convective motions

Previous studies have discovered a population of small granules with diameters less than 800 km showing differing physical properties. High resolution simulations and observations of the solar granulation, in combination with automated segmentation and tracking algorithms, allow us to study the evolution of the structural and physical properties of these granules and surrounding vortex motions with high temporal and spatial accuracy. We focus on the dynamics of granules (lifetime, fragmentation, size, position, intensity, vertical velocity) over time and the influence of strong vortex motions. Of special interest are the dynamics of small granules compared to regular-sized granules. We developed a temporal tracking algorithm based on our developed segmentation algorithm for solar granulation. This was applied to radiation hydrodynamics simulations and high resolution observations of the quiet Sun by SUNRISE/IMaX. The dynamics of small granules differ in regard to their diameter, intensity and depth evolution compared to regular granules. The tracked granules in the simulation and observations reveal similar dynamics (lifetime, evolution of size, vertical velocity and intensity). The fragmentation analysis shows that the majority of granules in simulations do not fragment, while the opposite was found in observations. Strong vortex motions were detected at the location of small granules. Regions of strong vertical vorticity show high intensities and downflow velocities, and live up to several minutes. The analysis of granules separated according to their diameter in different groups reveals strongly differing behaviors. The largest discrepancies can be found within the groups of small, medium-sized and large granules and have to be analyzed independently. The predominant location of vortex motions on and close to small granules indicates a strong influence on the dynamics of granules

Numerical Simulation of Coronal Waves interacting with Coronal Holes: I. Basic Features

We developed a new numerical code that is able to perform 2.5D simulations of a magnetohydrodynamic (MHD) wave propagation in the corona, and its interaction with a low density region, such as a coronal hole (CH). We show that the impact of the wave on the CH leads to different effects, such as reflection and transmission of the incoming wave, stationary features at the CH boundary, or formation of a density depletion. We present a comprehensive analysis of the morphology and kinematics of primary and secondary waves, that is, we describe in detail the temporal evolution of density, magnetic field, plasma flow velocity, phase speed and position of the wave amplitude. Effects like reflection, refraction and transmission of the wave strongly support the theory that large scale disturbances in the corona are fast MHD waves and build the major distinction to the competing pseudo-wave theory. The formation of stationary bright fronts was one of the main reasons for the development of pseudo-waves. Here we show that stationary bright fronts can be produced by the interactions of an MHD wave with a CH. We find secondary waves that are traversing through the CH and we show that one part of these traversing waves leaves the CH again, while another part is being reflected at the CH boundary inside the CH. We observe a density depletion that is moving in the opposite direction of the primary wave propagation. We show that the primary wave pushes the CH boundary to the right, caused by the wave front exerting dynamic pressure on the CH

Fractal Dimension Analysis of Solar Granulation- Boxcounting dimension

The fractal dimension of high resolution Hinode solar granulation observations and numerical simulations is studied and the results are compared. These observations are not influenced by atmospheric seeing conditions and therefore allow a more realistic estimate of the fractal dimension than in previous works. Though arriving at similar results for observations and simulation data, non integer fractal dimension $<2$, some differences in the numerical values occur, and these are discussed

Solar Ca II K plage regions as proxies for magnetic fields of solar like stars

Solar plage regions can be observed directly, whereas plage regions as well as star-spots on solar like stars, can only be detected via their contribution to spectral irradiances of these stars. Such a spectral irradiance can be modelled by fractions belonging to the quiet star, the plage regions, and the star-spots. The idea is, to measure these fractions as well as the intensity enhancement due to plage regions on our Sun and then use this information to be able to model solar like stars. We verify the close connection between the size of the plage regions and the luminosity of the Sun, given by a correlation coefficient of 0.822. The size of the plage regions varies from 0%, when the Sun is very quiet, up to 2.7% for a more active Sun (a complete solar cycle is not yet analysed and hence our study does not contain an activity maximum). The used data sets are full-disc images taken by the RISE/PSPT instrument during the period from 2005 to 2012, at the MLSO

Detection of small convective patterns in observations and simulations

Recent results from high resolution solar granulation observations indicate the existence of a population of small granular cells on scales below 600 km in diameter, located in the intergranular lanes. We studied a set of Hinode SOT images and high resolution radiation hydrodynamics simulations in order to analyze small granular cells and to study their physical properties. An automated image segmentation algorithm specifically adapted to high resolution simulations for the identification of granules was developed. The algorithm was also used to analyze and compare physical quantities provided by the simulation and the observations. We found that small granules make a distinct contribution to the total area of granules. Both in observations and simulations, small granular cells exhibit on average lower intensities and vertical velocities

Two-Fluid 2.5D MHD-Code for Simulations in the Solar Atmosphere

We investigate magnetic reconnection due to the evolution of magnetic flux tubes in the solar chromosphere. We developed a new numerical two-fluid magnetohydrodynamic (MHD) code which will perform a 2.5D simulation of the dynamics from the upper convection zone up to the transition region. Our code is based on the Total Variation Diminishing Lax-Friedrichs scheme and makes use of an alternating-direction implicit method, in order to accommodate the two spatial dimensions. Since we apply a two-fluid model for our simulations, the effects of ion-neutral collisions, ionization/recombination, thermal/resistive diffusivity and collisional/resistive heating are included in the code. As initial conditions for the code we use analytically constructed vertically open magnetic flux tubes within a realistic stratified atmosphere. Initial MHD tests have already shown good agreement with known results of numerical MHD test problems like e.g. the Orszag-Tang vortex test

Parallelization of the SIR code

A high-resolution 3-dimensional model of the photospheric magnetic field is essential for the investigation of small-scale solar magnetic phenomena. The SIR code is an advanced Stokes-inversion code that deduces physical quantities, e.g. magnetic field vector, temperature, and LOS velocity, from spectropolarimetric data. We extended this code by the capability of directly using large data sets and inverting the pixels in parallel. Due to this parallelization it is now feasible to apply the code directly on extensive data sets. Besides, we included the possibility to use different initial model atmospheres for the inversion, which enhances the quality of the results

New insights into the temporal evolution of MBPs

Magnetic bright points (MBPs) are among the most fascinating and interesting manifestations of small-scale solar magnetic fields. In the present work the temporal evolution of MBPs is followed in data sets taken by the Hinode satellite. The analysed data and obtained results confirm a recently presented study done with Sunrise/IMaX data, namely that MBPs are features undergoing fast evolution with magnetic fields starting around the equipartition field strength, then showing strong downflows (between 2 to 4 km/s) causing the magnetic field to amplify into the kG range (700 to 1500 G) before dissolving again. Furthermore the initial field inclinations depend on the initial magnetic field strengths and show an evolution with more vertical angles at some point during the evolution

Analysis and segmentation of the solar convection

Die Beobachtung der Sonne und ihrer Oberfl\ue4chenph\ue4nomene erfolgt rund um die Uhr von Teleskopen. Um die gro fen Datenmengen verarbeiten zu k\uf6nnen, ist der Einsatz von automatischen Bildverarbeitungsprogrammen unumg\ue4nglich. Diese Arbeit besch\ue4ftigt sich mit der Implementierung eines Bildsegmentierungsprogrammes zur Analyse der Sonnengranulation. Als Granulation bezeichnet man die durch Konvektion entstehenden zellf\uf6rmigen Strukturen der Photosph\ue4reDer MLT Algorithmus besch\ue4ftigt sich mit dem Problem der Segmentierung der Granulation mit Hilfe der Berechnung verschiedener Intensit\ue4tslevels. In jedem Level werden Pixel hinzugef\ufcgt und nicht zusammengeh\uf6rende Strukturen voneinander getrennt. Das Ergebnis der Segmentierung h\ue4ngt stark von der Qualit\ue4t der Bilder ab. In dieser Arbeit werden hochaufl\uf6sende Bilder vom japanischen Weltraumteleskop ?Hinode? verwendet.Um die Implementierung des MLT Algorithmus hinsichtlich seiner Laufzeiteffizienz zu verbessern, wurde er in der Programmiersprache C++ implementiert. Die Segmentierungsresultate wurden mit den IDL Ergebnissen verglichen. Beide Implementierungen produzieren \ufcbereinstimmende Ergebnisse, verifiziert durch eine zwei dimensionaler Kreuz-Korrelationen mit dem Ergebnis von ?=0.96. Die Laufzeit des Algorithmus konnte mittels C++ bei der Berechnung eines 512 x 512 Pixel Bildes um den Faktor 20 gesteigert werdenZus\ue4tzlich zur Auswertung von Beobachtungsdaten, existieren numerische Modelle zur Analyse thermodynamischer Gr\uf6 fen. Das ANTARES Model ist ein 3D Code zur Beschreibung des hydrodynamischen Strahlungstransports, um die Konvektion im Bereich der Sonnenoberfl\ue4che zu modellieren. Zur genauen Bestimmung der Struktur der Photosph\ue4re werden Korrelationen der thermodynamischen Gr\uf6 fen berechnet und mit Berechnungen am selben Modeldatensatz geringerer r\ue4umlicher Aufl\uf6sung verglichen. Diese Korrelationen zeigen keine signifikanten Abweichungen von jenen basierend auf Datens\ue4tzen h\uf6herer Aufl\uf6sung.In solar astrophysics data in form of images enable the observation of surface phenomena in order to investigate underlying processes. Telescopes produce huge amounts of data, which can only be appropriately analyzed via the application of automated image processing. This thesis deals with the implementation of an image segmentation algorithm for the analysis of the solar granulation. The granulation is a distinct feature of the solar photosphere generated by convection. The examined multiple level tracking (MLT) algorithm successfully deals with the problem of solar granulation segmentation by the application of multiple threshold levels. At each level existing structures are extended whereas those adjacent to each other are separated and the results are labeled for further calculations.The segmentation results strongly depend on the quality of the images. The high resolution images of the photosphere, this research work is based on, are provided by the Japanese Hinode Solar Optical Telescope (SOT). In order to improve the implementation of the MLT algorithm, concerning runtime performance, an existing IDL version was re-implemented in C++. A comparison showed that the implementations produce very similar results with an average two dimensional cross correlation of ? = 0.96. The major improvement lies in the enhanced runtime performance. Applied to a Hinode 512 x 512 pixel input image, using three threshold levels, an average speedup by a factor of around 20 could be achieved.In addition to the analysis of observational data the numeric ANTARES model, a 3D radiation hydrodynamics code modeling solar surface convection, was examined in order to determine the structure of the photosphere. Results have been obtained by calculating and comparing correlation height-functions using a model data set. As a verification, results were compared to calculations from former research. These correlations showed no significant deviation and support observational results.Abweichender Titel laut cbersetzung der Verfasserin/des VerfassersGraz, Univ., Masterarb., 201