  The Sun is the most constrained and well-studied of all stars. As a
consequence, the physical ingredients entering solar models are used as a
reference to study all other stars observed in the Universe. However, our
understanding of the solar structure is still imperfect, as illustrated by the
current debate on the heavy element abundances in the Sun. We wish to provide
additional information on the solar structure by carrying out structural
inversions of a new physical quantity, a proxy of the entropy of the solar
plasma which properties are very sensitive to the temperature gradient below
the convective zone. We use new structural kernels to carry out direct
inversions of an entropy proxy of the solar plasma and compare the solar
structure to various standard solar models built using various opacity tables
and chemical abundances. We also link our results to classical tests commonly
found in the literature. Our analysis allows us to probe more efficiently the
uncertain regions of the solar models, just below the convective zone, paving
the way for new in-depth analyses of the Sun taking into account additional
physical uncertainties of solar models beyond the specific question of chemical
abundances.
