The magnetic field is the main driver of the spectacular activity of the solar atmosphere, which covers the photosphere, chromosphere, transition region, and corona. This is true also for many other stars, although it is in the Suns atmosphere where we can observe the consequences of the interaction between an astrophysical plasma and its magnetic field in incomparable detail. In the Sun, this interaction controls the heating of the coronal plasma to millions of degrees, the explosive energy release in flares and coronal mass ejections, and the particle acceleration events. Even though the Sun is one of the best observed astrophysical objects, we do not fully understand how fundamental processes like magnetic reconnection, hydro-magnetic instabilities, and plasma waves produce the energization and the dynamical activity of the solar upper atmosphere, including the eruptive phenomena molding the near-Earth space weather. To further advance our understanding of these phenomena, we need to improve our empirical knowledge of their main driver, namely the magnetic field

While the variation of the intensity of the electromagnetic radiation with wavelength, that is, the intensity spectrum, encodes information about the thermodynamic and dynamic properties of the emitting plasma such as temperature, macroscopic velocity, density, etc., the magnetic field information is encoded in the polarization of the spectral line radiation.

This project aims to empirically push the limits of our understanding on the magnetic field and the plasma dynamics in the solar atmosphere. Despite the significant focus on the solar atmosphere, this project also pretends to study the magnetic field in other solar-like stars. In particular, in this project we aim at significantly contribute to clarify the following presently unresolved problems:

a. What is the structure, connectivity and cycle modulation of the magnetic field throughout the solar atmosphere from the photosphere to the corona?

b. How is the magnetism in other solar-like stars?

c. What are the most adequate spectral lines for the diagnostics of the magnetic field in the different regions of the solar atmosphere?

To this end, we will combine cutting-edge spectro-polarimetric observations, data analysis, theoretical modeling, and inference methods, including the application of both existing spectral synthesis and inversion codes and new plasma diagnostic techniques to be developed during this project.