Develop flexible atmospheric-node handling for many-line inversions

Develop an inversion framework that permits different numbers of optical-depth nodes for temperature, magnetic-field strength, line-of-sight velocity, and other atmospheric parameters, and determine whether this improves the representation of highly resolved solar many-line spectra.

Background

The many-line inversions use a common three-node atmospheric model for several parameters. The authors found that seven nodes produced a reasonable temperature stratification, but the available spectral lines did not constrain an equivalent number of nodes for the magnetic field and Doppler velocity.

The SPINOR code used in the study does not allow different atmospheric parameters to have different node counts. This forces a compromise that may contribute to systematic line-fit residuals and remaining areas with implausible atmospheric values.

References

In our experiments, we found that seven nodes provided a well-constrained and reasonable temperature stratification. Unfortunately, due to the sensitivity and formation height of the observed lines, we were unable to constrain more nodes in the magnetic field and the Doppler velocity. However, as it currently stands, SPINOR does not permit a different number of nodes for different atmospheric parameters, making the compromise of three height nodes necessary.

— Towards solar many-line inversions  (2610.01251 - Hölken, 1 Oct 2026) in Chapter 5, Section “Fit quality”