Measurements of magnetic fields and the analysis of stokes profiles

Recent advances in polarimetry allowing the recording of polarized line profiles with high spectral resolution and signal-to-noise ratio over large portions of the solar spectrum offer rich new diagnostic possibilities. Thus we can now in a systematic way build models of the height variation of the magnetic field, temperature, density, and mass motions in the spatially unresolved subarcsecond magnetic structures. The analysis of the Stokes spectra also allows us to build a foundation for proper diagnostics of vector magnetic fields, a goal that cannot be achieved before the intrinsic properties of the spatially unresolved magnetic fields have been determined. Another new diagnostic tool is the Hanle effect. A recent exploratory survey of coherence effects through the recording of the linear polarization with high spectral resolution throughout the whole visible solar spectrum aims at establishing a foundation for the exploitation of the Hanle effect on the solar disk.This review describes these developments, most of which have taken place in the 1980s, and summarizes the results obtained so far.