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Aims. We investigate the oscillatory properties of the quiet solar chromosphere in relation to the underlying photosphere, with particular regard to the effects of the magnetic topology. Methods. For the first time we perform a Fourier analysis on a sequence of line-of-sight velocities measured simultaneously in a photospheric (Fe I 709.0 nm) and a chromospheric line (Ca II 854.2 nm). The velocities were obtained from full spectroscopic data acquired at high spatial resolution with the Interferometric BIdimensional Spectrometer (IBIS). The field of view encompasses a full supergranular cell, allowing us to discriminate between areas with different magnetic characteristics. Results. We show that waves with frequencies above the acoustic cut-off propagate from the photosphere to upper layers only in restricted areas of the quiet Sun. A large fraction of the quiet chromosphere is in fact occupied by "magnetic shadows", surrounding network regions, that we identify as originating from fibril-like structures observed in the core intensity of the Ca II line. We show that a large fraction of the chromospheric acoustic power at frequencies below the acoustic cut-off, residing in the proximity of the magnetic network elements, directly propagates from the underlying photosphere. This supports recent results arguing that network magnetic elements can channel low-frequency photospheric oscillations into the chromosphere, thus providing a way to input mechanical energy in the upper layers.

Context. The chromosphere remains a poorly understood part of the solar atmosphere, as current modeling and observing capabilities are still ill-suited to investigate in depth its fully 3-dimensional nature. In particular, chromospheric observations that can preserve high spatial and temporal resolution while providing spectral information over extended fields of view are still very scarce. Aims. In this paper, we seek to establish the suitability of imaging spectroscopy performed in the Ca II 854.2 nm line as a means to investigate the solar chromosphere at high resolution. Methods. We utilize monochromatic images obtained with the Interferometric BIdimensional Spectrometer (IBIS) at multiple wavelengths within the Ca II 854.2 nm line and over several quiet areas. We analyze both the morphological properties derived from narrow-band monochromatic images and the average spectral properties of distinct solar features such as network points, internetwork areas and fibrils. Results. The spectral properties derived over quiet-Sun targets are in full agreement with earlier results obtained with fixed-slit spectrographic observations, highlighting the reliability of the spectral information obtained with IBIS. Furthermore, the very narrowband IBIS imaging reveals with much clarity the dual nature of the Ca II 854.2 nm line: its outer wings gradually sample the solar photosphere, while the core is a purely chromospheric indicator. The latter displays a wealth of fine structures including bright points, akin to the Ca II H 2V and K 2V grains, as well as fibrils originating from even the smallest magnetic elements. The fibrils occupy a large fraction of the observed field of view even in the quiet regions, and clearly outline atmospheric volumes with different dynamical properties, strongly dependent on the local magnetic topology. This highlights the fact that 1-D models stratified along the vertical direction can provide only a very limited representation of the actual chromospheric physics. Conclusions. Imaging spectroscopy in the Ca II 854.2 nm line currently represents one of the best observational tools to investigate the highly structured and highly dynamical chromospheric environment. A high performance instrument such as IBIS is crucial in order to achieve the necessary spectral purity and stability, spatial resolution, and temporal cadence.

Stably stratified fluids, such as stellar and planetary atmospheres, can support and propagate gravity waves. On Earth these waves, which can transport energy and momentum over large distances and can trigger convection, contribute to the formation of our weather and global climate. Gravity waves also play a pivotal role in planetary sciences (e.g. Young et al. 1997) and modern stellar physics (Charbonnel & Talon 2007). They have also been proposed as an agent for the heating of stellar atmospheres and coronae (Mihalas & Toomre 1981), the exact mechanism behind which is one of the outstanding puzzles in solar

Context. Adaptive optics systems are used on several advanced solar telescopes to enhance the spatial resolution of the recorded data. In all cases, the correction remains only partial, requiring post-facto image reconstruction techniques such as speckle interferometry to achieve consistent, near-diffraction limited resolution. Aims. This study investigates the reconstruction properties of the Kiepenheuer-Institut Speckle Interferometry Package (KISIP) code, with focus on its phase reconstruction capabilities and photometric accuracy. In addition, we analyze its suitability for real-time reconstruction. Methods. We evaluate the KISIP program with respect to its scalability and the convergence of the implemented algorithms with dependence on several parameters, such as atmospheric conditions. To test the photometric accuracy of the final reconstruction, comparisons are made between simultaneous observations of the Sun using the ground-based Dunn Solar Telescope and the space-based Hinode/SOT telescope. Results. The analysis shows that near real-time image reconstruction with high photometric accuracy of ground-based solar observations is possible, even for observations in which an adaptive optics system was utilized to obtain the speckle data.