  We investigate the diagnostic potential of the spectral lines at 850 nm for
understanding the magnetism of the lower atmosphere. For that purpose, we use a
newly developed 3D simulation of a chromospheric jet to check the sensitivity
of the spectral lines to this phenomenon as well as our ability to infer the
atmospheric information through spectropolarimetric inversions of noisy
synthetic data. We start comparing the benefits of inverting the entire
spectrum at 850 nm versus only the Ca II 8542 A spectral line. We found a
better match of the input atmosphere for the former case, mainly at lower
heights. However, the results at higher layers were not accurate. After several
tests, we determined that we need to weight more the chromospheric lines than
the photospheric ones in the computation of the goodness of the fit. The new
inversion configuration allows us to obtain better fits and consequently more
accurate physical parameters. Therefore, to extract the most from multi-line
inversions, a proper set of weights needs to be estimated. Besides that, we
conclude again that the lines at 850 nm, or a similar arrangement with Ca II
8542 A plus Zeeman sensitive photospheric lines, poses the best observing
configuration for examining the thermal and magnetic properties of the lower
solar atmosphere.
