INFRARED LINES AS PROBES OF SOLAR MAGNETIC FEATURES - XIII - THE RELATIVE FLUX IN WEAK AND STRONG QUIET-SUN MAGNETIC-FIELDS

An estimate of the fraction of magnetic flux in intrinsically weak-fie ld form, i.e. fields with less than 1 kG intrinsic strength, in the qu iet Sun is presented. We find that on average approximately 2/3 of the flux is in weak-field form, although our data allow a range of values between 25% and 85%. These estimates have been derived with the help of radiative transfer model calculations from low-noise scans through the quiet Sun at fixed wavelengths within a Zeeman sensitive spectral line at 1.56 mu m. They represent the first rapidly modulated polarime tric observations of solar 1.56 mu m radiation. These scans show that the polarimetric signature near the core of the line exhibits a very d ifferent spatial structure than in the outer line wings. Since the out er part of the line profile is only sensitive to intrinsically strong magnetic fields, while the central part reacts also to intrinsically w eak fields, this implies that intrinsically weak fields are distribute d differently on the surface than strong fields are (weak-field featur es lie closer together). The spatial distribution suggests that the st rong fields we are observing are network elements, whereas the weak fi elds are intranetwork features. Further results, such as the average d istance between weak and strong field features, flux distribution, spa tial power spectra and the Stokes asymmetry of intrinsically weak fiel ds are also presented. In particular, we find that the flux per magnet ic feature is distributed lognormally, in agreement with a similar fin ding for sunspot umbral areas by Bogdan et al. (1988).