Numerical Simulation of Current Sheet Formation in a Quasi-Separatrix Layer using Adaptive Mesh Refinement

The formation of a thin current sheet in a magnetic quasi-separatrix layer (QSL) is investigated by means of numerical simulation using a simplified ideal, low-$\beta$, MHD model. The initial configuration and driving boundary conditions are relevant to phenomena observed in the solar corona and were studied earlier by Aulanier et al., A&A 444, 961 (2005). In extension to that work, we use the technique of adaptive mesh refinement (AMR) to significantly enhance the local spatial resolution of the current sheet during its formation, which enables us to follow the evolution into a later stage. Our simulations are in good agreement with the results of Aulanier et al. up to the calculated time in that work. In a later phase, we observe a basically unarrested collapse of the sheet to length scales that are more than one order of magnitude smaller than those reported earlier. The current density attains correspondingly larger maximum values within the sheet. During this thinning process, which is finally limited by lack of resolution even in the AMR studies, the current sheet moves upward, following a global expansion of the magnetic structure during the quasi-static evolution. The sheet is locally one-dimensional and the plasma flow in its vicinity, when transformed into a co-moving frame, qualitatively resembles a stagnation point flow. In conclusion, our simulations support the idea that extremely high current densities are generated in the vicinities of QSLs as a response to external perturbations, with no sign of saturation.Comment: 6 Figure

Current sheet formation and magnetic reconnection in solar magnetic fields

Diese Arbeit beschreibt magnetische Rekonnexion an dünnen Stromschichten in Konfigurationen ohne verschwindendes Magnetfeld. Dabei wird eine Methode entwickelt, die die Bestimmung der Rekonnexionsrate ohne die Einbeziehung eines parallelen elektrischen Feldes ermöglicht. Zusätzlich werden grundsätzliche geometrische Unterschiede zwischen Rekonnexion in zwei und drei Dimensionen beschrieben. Neben dem analytischen Teil beschreibt die Arbeit auch hochauflösende numerische Simulationen einer Konfiguration, die starke Gradienten in der Konnektivität der magnetischen Feldlinien aufweist. Im Gegensatz zu früheren, schlechter aufgelösten Simulationen werden die starken Gradienten in dieser Arbeit als bevorzugte Orte identifiziert, an denen sich starke Stromschichten bilden.This work describes magnetic reconnection at thin current sheets in configurations non-vanishing magnetic field. Therefor a method is developed, which allows a measurement of the reconnection rate without employing the parallel electric field. Furthermore the general geometrical differences between reconnection in two and three dimensions are described. In addition to the analytic part, this work describes high resolution numerical simulations of a configuration, which possesses strong gradients in the connectivity of magnetic field lines. As opposed to earlier simulations with lower resolution these simulations identify the strong gradients as favorable places for the formation of intense current sheets

The new Buddy-Checkpointing Feature of SIONlib for Task-Local Parallel I/O Support

In this talk we will present the new buddy-checkpointing feature of SIONlib, which is designed to support checkpointing of simulation data on node-local storage for application that uses a task-local I/O pattern. With this new feature, SIONlib is able to store data in a virtual shared file container on local storage of the compute nodes, whereas local data is automatically and transparently mirrored to local storage of a set of buddy nodes. The buddy-checkpointing feature of SIONlib has been developed within the EU-project DEEP-ER to support task-local I/O on hierarchical I/O infrastructures. Additionally, SIONlib can work together with the multi-level checkpoint library SCR to support buddy-checkpointing for SIONlib file container

JUBE – A Flexible, Application- and Platform-Independent Environment for Benchmarking

Automating benchmarks is important for reproducibility and hence comparability, which is the major intent when performing benchmarks. Furthermore managing different combinations of parameters is error-prone and often results in a significant amount of work especially if the parameter space gets large. In order to alleviate these problems, we developed JUBE, which supports performing and analysing benchmarks in a systematic way.JUBE is an open source software tool, written in Python, providing command line accessible options to execute generic configuration files which describe the structure and behaviour of a specific benchmark. It allows adapting custom workflows to new architectures easily.Because of the generic layout JUBE can also be used for testing or production scenarios whenever a structured workflow generation and evaluation is needed

HPC-Tools JUBE, LLview and SIONlib at JSC: Recent developments

In this talk we will present the recent developments of the benchmarking environment JUBE, the batch system monitoring tool LLview, and the parallel I/O library SIONlib. In detail, we will present how the benchmarking environment JUBE is integrated into a performance evaluation work ow, which is applied in the EU-project EoCoE. For LLview we will show the recently implemented job-based monitoring of I/O metrics. For SIONlib we will focus on the work we did in the EU-project DEEP-ER to support the efficient use of node-local storage in parallel task-local I/O