  We analyse the spatial distribution and vertical stratification of the
physical parameters of the solar atmosphere when an X-class flare occurs. We
made use of observations acquired by the Interferometric Bidimensional
Spectropolarimeter instrument when observing the full Stokes parameters for the
Fe I 6173 A and Ca II 8542 A transitions. We analysed the observed spectra
using the newly developed DeSIRe code to infer the atmospheric parameters at
photospheric and chromospheric layers over the entire observed field of view.
Our findings reveal that the chromosphere is characterised by temperature
enhancements and strong upflows in the flare ribbon area, which indicates that
the flaring event is producing hot material that is moving outwards from the
Sun. We did not detect any trace of temperature enhancements or strong
velocities (of any sign) at photospheric layers, signalling that the impact of
the flaring event mainly happens at the middle and upper layers. The
information about the magnetic field vector revealed relatively smooth
stratifications with height for both magnetic field strength and inclination.
Still, when examining the spatial distribution of the magnetic field
inclination, we observed the presence of large-scale mixed polarities in the
regions where the flare ribbon is located. These results suggest that the
interaction between those mixed polarities could be the flare's triggering
mechanism.
