A search for the footpoints of solar magnetic fields

Abstract

High-resolution measurements of magnetic fields have been made in quiet and active regions in order to determine whether the photospheric fine-structures (‘crinkles’), recently photographed by Dunn (1972), coincide with the footpoints of strong, compact fields. Magnetic fields ranging up to 1400 G have been measured in small structures that lie at the centers of spicule bushes or within a plage. However, the diameters of the flux tubes, at the height where Fei 6302.5 forms, are typically 1″–2″, compared with crinkle dimensions of 0.25″ × 1″. This discrepancy cannot be explained by a sharp height variation of the flux tube cross-section. By comparing our results with Dunn's photographs, we conclude that although crinkles appear to lie at or near the strongest field intensities, photospheric magnetic flux is not confined solely within the area of the crinkles, but may extend over a larger area defined by the ‘abnormal’ granulation (Dunn et al., 1973; Dunn and Zirker, 1973).