Solar coronal loops are the building blocks of the solar corona. These bright and dynamic structures are shaped by the magnetic field that expands into the solar atmosphere. They can be observed in X-ray and extreme ultraviolet (EUV), revealing the high plasma temperature (1 MK - 10 MK) of the corona. However, it is still a matter of debate how the magnetic energy is dissipated to heat the coronal plasma. In order to properly differentiate between heating mechanisms, the location and frequency of the energy deposition, in particular, must be properly constrained.
For this colloquium, I will explain how coronal heating models can be tested via the study of the cooling of the plasma in active regions. In particular, I will show how the extracted cooling properties can help constraining the spatio-temporal properties of the heating in the solar atmosphere. I will put particular emphasis on the thermal non-equilibrium model, which predict evaporation and condensation cycles of the plasma when the heating is highly-stratified and quasi constant. Recent observations have demonstrated that understanding the characteristics of thermal non-equilibrium is an important step to constrain the circulation of mass and energy in the solar atmosphere.
