Expansion of solar magnetic flux tubes large and small

In the solar photosphere the magnetic field of magnetic elements and sunspo ts is known to expand with height. In the case of sunspots this expansion i s known to be very rapid, with the field forming an almost horizontal canop y. In this contribution we present new results on the superpenumbral canopy of sunspots based on fits to Stokes I and V profiles of infrared spectral lines. The new models take pressure balance across the boundary of the cano py field into account, which leads to significantly lower canopy base heigh ts than previously determined from similar data. Due to the lower canopy base height, the density above the canopy base is l arger so that estimates of the mass transported by the Evershed effect in t he canopy need to be revised upwards: approximately 15-50% of the mass flow ing through the penumbra travels beyond the sunspot boundary above the cano py base. A comparison with small flux tubes leads to the surprising result that alth ough the two types of features have magnetic fluxes that differ by 5-6 orde rs of magnitude, their relative rate of expansion with height is very simil ar, suggesting that at least in this respect sunspots can be described by t he thin-tube approximation. The remaining small differences between the relative expansion of the two t ypes of flux tubes is qualitatively compatible with the presence of magneti c flux that returns into the solar interior at the spot boundary, as has be en proposed by Westendorp Plaza et al. (1997).