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Published online by Cambridge University Press: 12 April 2016
The 20 year old conclusion that more than 90% of the magnetic flux recorded by magnetographs in quiet and active regions is in strong-field, kG form has recently been supported by direct observations of Zeeman splitting in the infrared (near 1.6 μm). The magnetic and thermodynamic properties of the kG fluxtubes have been explored in considerable detail over the past decade, in particular through Fourier transform spectrometer observations combined with Stokes inversion procedures. The weak fields have proven to be much more elusive, and it was not until last year that the first definite identifications of intrinsically weak (less than kG) fields in the low photosphere could be made, using the Stokes V profiles of an infrared line pair.