The introduction to this review summarizes chromosphere observation in two figures. The first part showcases the historical emphasis on the eclipse chromosphere in the development of NLTE line formation theory and criticizes 1D modeling. The second part advertises recent breakthroughs after many decades of standstill. The third part discusses what may or should come next.

I review some recent advances in methods to diagnose polarized radiation with which we may hope to explore the magnetism of the solar chromosphere and corona. These methods are based on the remarkable signatures that the radiatively induced quantum coherences produce in the emergent spectral line polarization and on the joint action of the Hanle and Zeeman effects. Some applications to spicules...

A generalization of a recently developed MHD model of a proposed heating mechanism for the middle chromosphere is presented. The generalization consists of including the ideal gas equation of state, allowing the temperature to vary with position, and allowing the hydrogen flow velocity to vary with height in a specified manner. These generalizations allow for a self consistent calculation of a ...

Before the onset of a flare is observed in hard X-rays there is often a prolonged pre-flare or pre-heating phase with no detectable hard X-ray emission but pronounced soft X-ray emission suggesting that energy is being released and deposited into the corona and chromosphere already at this stage. This work analyses the temporal evolution of coronal source heating and the chromospheric response ...

Context. Interferometers provide accurate diameter measurements of stars by analyzing both the continuum and the lines formed in photospheres and chromospheres. Tests of the geometrical extent of the chromospheres are therefore possible by comparing the estimated radius in the continuum of the photosphere and the estimated radii in chromospheric lines. Aims. We aim to constrain the geometrical ...

The chromosphere in internetwork regions of the quiet Sun was regarded as a static and homogeneous layer for a long time. Thanks to advances in observations and numerical modelling, the wave nature of these atmospheric regions received increasing attention during the last decade. Recent three-dimensional radiation magnetohydrodynamic simulations with CO5BOLD feature the chromosphere of internet...

We use synchronous movies from the Dutch Open Telescope sampling the G band, Ca iiH, and Hα with five-wavelength profile sampling to study the response of the chromosphere to acoustic events in the underlying photosphere. We first compare the visibility of the chromosphere in Ca iiH and Hα, demonstrate that studying the chromosphere requires Hα data, and summarize recent developments in underst...

We summarizerecent results from self-consistent non-LTE radiation hydrodynamicssimulations of the propagation of acoustic waves through the non-magnetic solar chromosphere. References to more detailed write-ups of the work are given. The simulations closely match the observed behaviour of Ca II H 2 V bright grains. Observations of CO-lines, that are problematicto explain in semi-empiricalone-co...

We have studied the chromosphere of active binary systems using the information provided by several optical spectroscopic features that could be used as chromospheric activity indicators. The simultaneous observations of diierent lines, that are formed at diierent heights in the chromosphere (from the region of temperature minimum to the higher chromosphere), are of special interest for stellar...

We present an algorithm to reconstruct chromosphere concentration images directly rather than following the traditional two-step process of reconstructing wavelength-dependent absorption coefficient images and then calculating chromosphere concentration images. This procedure imposes prior spectral information into the image reconstruction that results in a dramatic improvement in the image con...