Figure 1.

Cartoon representation of coronal magnetic field expansion, inspired by similar figures from Gabriel [8], Peter [11], Cranmer & van Ballegooijen [12] and Tian et al. [13]. (a) On supergranular scales the field is concentrated most strongly in the bright chromospheric network. Flux tubes expand laterally with increasing height to form a funnel/canopy structure. (b) On smaller scales, the field is concentrated into intergranular flux tubes that are jostled by convection and experience MHD turbulence. Granulation image adapted from Abramenko et al. [14], and turbulent flux-tube cross sections adapted from Asgari-Targhi et al. [15]. (Online version in colour.)