Assessing SOLIS 854.2 A Diagnostics of the Chromospheric Magnetic Field

Here we report the result of a study in which we attempted to quantify the heights at which chromospheric magnetic field measurement constraints may be applied to the nonlinear force free field (NLFFF) extrapolations. To make this assessment, we produced NLFFF magnetic data cubes from vector magnetic field maps obtained by the HMI instrument onboard the Solar Dynamics Observatory (SDO), which we compared with ready-to-use line of sight (LOS) chromospheric magnetic field maps from the National Solar Observatory’s SOLIS instrument, produced by the weak-field approximation method from Ca 8542 spectral line measurements. We modeled five active regions as they progressed across the solar disk, analyzing the correlation between the SOLIS measurements and the LOS magnetic field at various heights in the NLFFF data cubes. We examined the dependence of these heights on latitude, longitude, distance from the solar center, resolution of the model, and different solar features. Although our investigation did not produce precise heights for use in future modeling efforts, we discovered a systematic mismatch between the SOLIS weak-field approximation and the NLFFF extrapolations, which suggests that accurate heights could be identified after a revaluation of the SOLIS data calibration.