Standard 1D solar atmosphere as initial condition for MHD simulations and switch-on effects

Many applications in Solar physics need a 1D atmospheric model as initial condition or as reference for inversions of observational data. The VAL atmospheric models are based on observations and are widely used since decades. Complementary to that, the FAL models implement radiative hydrodynamics and showed the shortcomings of the VAL models since almost equally long time. In this work, we present a new 1D layered atmosphere that spans not only from the photosphere to the transition region, but from the solar interior up to far in the corona. We also discuss typical mistakes that are done when switching on simulations based on such an initial condition and show how the initial condition can be equilibrated so that a simulation can start smoothly. The 1D atmosphere we present here served well as initial condition for HD and MHD simulations and should also be considered as reference data for solving inverse problems.Comment: 10 pages, 3 figures, published versio

Application of the electromotive force as a shock front indicator in the inner heliosphere

The electromotive force (EMF) describes how the evolution and generation of a large-scale magnetic field is influenced by small-scale turbulence. Recent studies of in-situ measurements have shown a significant peak in the EMF while a coronal mass ejection (CME) shock front passes by the spacecraft. The goal of this study is to use the EMF as an indicator for the arrival of CME shock fronts. With Helios spacecraft measurements we carry out a statistical study on the EMF during CMEs in the inner heliosphere. We develop an automated shock front detection algorithm using the EMF as the main detection criterion and compare the results to an existing CME database. The properties of the EMF during the recorded events are discussed as a function of the heliocentric distance. Our algorithm reproduces most of the the events from Kilpua et al. (2015) and finds many additional CME-like events which proves the EMF as a good shock front indicator. The largest peaks in the EMF are found from 0 to 50 minutes after the initial shock. We find a power law of -1.54 and -2.18 for two different formulations of the EMF with the heliocentric distance.Comment: 6 pages, 5 figures, publishe

Coronal loops above an Active Region - observation versus model

We conducted a high-resolution numerical simulation of the solar corona above a stable active region. The aim is to test the field-line braiding mechanism for a sufficient coronal energy input. We also check the applicability of scaling laws for coronal loop properties like the temperature and density. Our 3D-MHD model is driven from below by Hinode observations of the photosphere, in particular a high-cadence time series of line-of-sight magnetograms and horizontal velocities derived from the magnetograms. This driving applies stress to the magnetic field and thereby delivers magnetic energy into the corona, where currents are induced that heat the coronal plasma by Ohmic dissipation. We compute synthetic coronal emission that we directly compare to coronal observations of the same active region taken by Hinode. In the model, coronal loops form at the same places as they are found in coronal observations. Even the shapes of the synthetic loops in 3D space match those found from a stereoscopic reconstruction based on STEREO spacecraft data. Some loops turn out to be slightly over-dense in the model, as expected from observations. This shows that the spatial and temporal distribution of the Ohmic heating produces the structure and dynamics of a coronal loops system close to what is found in observations.Comment: 7 pages, 7 figures, special issu

Pressure profiles of distant galaxy clusters in the Planck catalog

Successive releases of Planck data have demonstrated the strength of the Sunyaev--Zeldovich (SZ) effect in detecting hot baryons out to the galaxy cluster peripheries. To infer the hot gas pressure structure from nearby galaxy clusters to more distant objects, we developed a parametric method that models the spectral energy distribution and spatial anisotropies of both the Galactic thermal dust and the Cosmic Microwave Background, that are mixed-up with the cluster SZ and dust signals. Taking advantage of the best angular resolution of the High Frequency Instrument channels (5 arcmin) and using X-ray priors in the innermost cluster regions that are not resolved with Planck, this modelling allowed us to analyze a sample of 61 nearby members of the Planck catalog of SZ sources ($0 < z < 0.5$, $\tilde{z} = 0.15$) using the full mission data, as well as to examine a distant sample of 23 clusters ($0.5 < z < 1$, $\tilde{z} = 0.56$) that have been recently followed-up with XMM-Newton and Chandra observations. We find that (i) the average shape of the mass-scaled pressure profiles agrees with results obtained by the Planck collaboration in the nearby cluster sample, and that (ii) no sign of evolution is discernible between averaged pressure profiles of the low- and high-redshift cluster samples. In line with theoretical predictions for these halo masses and redshift ranges, the dispersion of individual profiles relative to a self-similar shape stays well below 10 % inside $r_{500}$ but increases in the cluster outskirts.Comment: 12 pages, 10 figure

A multiscale regularized restoration algorithm for XMM-Newton data

We introduce a new multiscale restoration algorithm for images with few photons counts and its use for denoising XMM data. We use a thresholding of the wavelet space so as to remove the noise contribution at each scale while preserving the multiscale information of the signal. Contrary to other algorithms the signal restoration process is the same whatever the signal to noise ratio is. Thresholds according to a Poisson noise process are indeed computed analytically at each scale thanks to the use of the unnormalized Haar wavelet transform. Promising preliminary results are obtained on X-ray data for Abell 2163 with the computation of a temperature map.Comment: To appear in the Proceedings of `Galaxy Clusters and the High Redshift Universe Observed in X-rays', XXIth Moriond Astrophysics Meeting (March 2001), Eds. Doris Neumann et a