On the fine structure of the quiet solar \Ca II K atmosphere

We investigate the morphological, dynamical, and evolutionary properties of the internetwork and network fine structure of the quiet sun at disk centre. The analysis is based on a $\sim$6 h time sequence of narrow-band filtergrams centred on the inner-wing \Ca II K$_{\rm 2v}$ reversal at 393.3 nm. The results for the internetwork are related to predictions derived from numerical simulations of the quiet sun. The average evolutionary time scale of the internetwork in our observations is 52 sec. Internetwork grains show a tendency to appear on a mesh-like pattern with a mean cell size of $\sim$4-5 arcsec. Based on this size and the spatial organisation of the mesh we speculate that this pattern is related to the existence of photospheric downdrafts as predicted by convection simulations. The image segmentation shows that typical sizes of both network and internetwork grains are in the order of 1.6 arcs.Comment: 8 pages, 9 figure

Lower solar atmosphere and magnetism at ultra-high spatial resolution

We present the scientific case for a future space-based telescope aimed at very high spatial and temporal resolution imaging of the solar photosphere and chromosphere. Previous missions (e.g., HINODE, SUNRISE) have demonstrated the power of observing the solar photosphere and chromosphere at high spatial resolution without contamination from Earth's atmosphere. We argue here that increased spatial resolution (from currently 70 km to 25 km in the future) and high temporal cadence of the observations will vastly improve our understanding of the physical processes controlling solar magnetism and its characteristic scales. This is particularly important as the Sun's magnetic field drives solar activity and can significantly influence the Sun-Earth system. At the same time a better knowledge of solar magnetism can greatly improve our understanding of other astrophysical objects

NLTE Spectral Synthesis Based on 3D MHD Convection Simulations - Understanding the Role of the Magnetic Field in Intensity Variations

While the magnetic field is considered to be the main driver for Solar Spectral Irradiance (SSI) variations, the detailed physical mechanisms that explain this relation are not yet fully understood. In this paper we analyze the effect of small scale magnetic field on the intensity in Ca II 393.4 nm and various continuum wavelengths calculated with the NLTE radiative tranfer code SolMod3D. The code calculates NLTE level populations and line spectra based on 3D MHD simulations carried out with CO5BOLD. This enables us to study in great detail the effect of the varying small scale magnetic field on intensity variations. The results are important for a better understanding of the role of small-scale magnetic field in irradiance variations