Photospheric Magnetic Field at Small Scales

Abstract

Polarimetric measurements with high spatial resolution and in the near infrared spectral range show a continuous distribution of field strength from the weakest measurable to the thermal equipartition value. The shape of the distribution depends on the location at the solar surface, which is incompatible with the proposition of a universal probability density function for the magnetic field strength. This local dependence indicates that separate physical processes for intensifying the flux density act at the solar surface on distinct spatial and temporal scales. The true challenge, thus, consists in discovering the diverse physical processes that cause magnetic structuring. Three amplification mechanisms are reviewed and confronted with probability density functions derived from observations: The convective collapse, magnetoconvective flux intensification, and magnetic intensification by thermal relaxation. Magnetohydrodynamic simulations of the convective collapse predict a continuous distribution of weak field strengths with an additional distinct component of thermal equipartition energy not unlike that measured in the network. Simulations of the fast dynamo are more compatible with the distribution measured in the inter network.