At the end of last year, the time had come: construction of the new KIS building officially began on December 12, 2020. Until the end of the year, however, only the construction site was set up. In the meantime, however, the work is "visibly" progressing. The excavation pit has already been dug. You can now follow the progress of the construction work via a webcam (link: portal1658.webcam-profi.de ).

The picture of the month shows the status of the work as of March 15, 2021.

Stokes inversion codes allow us to infer the physical properties of the solar atmosphere (temperature, magnetic field, etc.) from observations of the polarization signals in spectral lines. Until now, all inversion codes available provide those physical parameters as a function of the vertical optical depth (τ_c). Converting from τ_c to the more useful z-coordinate depends upon physical parameters such as density and pressure, that are obtained under the assumption of hydrostatic equilibrium. Pressure and density thus obtained are highly inaccurate in and around sunspots and active regions because the magnetic field breaks the assumption of hydrostatic equilibrium. Our newly developed inversion code is the first one that determines the gas pressure and density by considering the effects of the magnetic field (magnetic pressure and tension) thus providing a much more accurate conversion to z. Because of this our code can be used to determine electric currents in the solar atmosphere and...

Sometimes, it can get pretty mathematical in solar physics too. Opposite formula describes the dynamical evolution of a vortical or swirling motion, of which there exists various types in the solar atmosphere. A vortex or swirl can be intuitively described as the rotation of fluid parcels around a common axis. Despite this simple concept, a rigorous mathematical definition is still an open issue in fluid mechanics. An effective physical quantity for characterising swirls is the swirling strength for which we have now derived the corresponding dynamical equation.

In a recent Letter to The Astrophysical Journal (Fischer et al., 2020) we report on cases of granular lanes showing magnetic activity.

GREGOR, the largest solar telescope in Europe, which is operated by a German consortium and located on Teide Observatory, Spain, has obtained unprecedented images of the fine-structure of the Sun. Following a major redesign of GREGOR’s optics, carried out by a team of scientists and engineers from the Leibniz Institute for Solar Physics (KIS), the Sun can be observed at a higher resolution than before from Europe.

The first images from ESA/NASA's new Sun-observing spacecraft Solar Orbiter were released to the public on 16 July 2020. It carries 10 scientific instruments, including the Photospheric-Helioseismic Imager (PHI) for which KIS has built an Image Stabilization System (ISS).

Numerical simulations provide great insight into the various wave phenomena that occur in the solar atmosphere. However, a proper comparison with the observations of the real Sun require us to understand how these phenomena affect spectral lines. Synthetic observables derived from numerical simulation are becoming necessary as they help us to properly interpret observational data.

The stability of sunspots is one of the long-standing unsolved puzzles in the field of solar magnetism and the solar cycle. The thermal and magnetic structure of the sunspot beneath the solar surface is not accessible through observations, thus processes in these regions that contribute to the decay of sunspots can only be studied through theoretical and numerical studies.

For the past year, all departments of KIS worked together to carry out the biggest change of GREGOR since its inauguration. By replacing the relay optics and rearranging the AO and the majority of the instruments in the optics lab, we were able to significantly improve GREGOR's image quality and prepare the telescope for future instrumentation upgrades.

Magnetic flux cancelation refers to the interaction of opposite polarity magnetic elements leading to magnetic flux removal from the solar surface. If the interacting elements are previously unconnected, their cancelation is treated as an observational signature of magnetic reconnection.

Using high-resolution data obtained with the GREGOR telescope on Tenerife, we witnessed such a magnetic field reconnection event. The Integral Field Unit (IFU, built by Instituto de Astrofísica de Canarias, IAC) of the GREGOR Infrared Spectrograph (GRIS) recorded the Stokes profiles in the photospheric Si i 10827Å spectral line targeting the quiet-Sun at disk center.