Regular structures of the solar photosphere

Abstract

The simple procedure of time averaging, when applied to the photospheric brightness eld, reveals quasi-regular structures of the photospheric and subphotospheric flows. We use an 8-h sub-set of the series of photospheric images obtained on 5 June 1993 with the Swedish Vacuum Solar Telescope, La Palma. First, the averaged images are far from completely smeared and contain a multitude of bright, granular-sized blotches even if the averaging period is as long as 8 h. This suggests that granules prefer to originate at certain sites, where they emerge repeatedly, and the granular eld demonstrates a sort of persistence for many hours. Second, the resulting patterns display relatively regular structures, which can be revealed only if the averaging period is suciently long (the optimum seems to lie between 2 and 3 h). The averaged brightness relief is \trenched: it comprises systems of concentric rings and arcs as well as straight or slightly wavy lines and systems of parallel strips. The trenching patterns resemble the so-called target patterns observed in experiments on Rayleigh{B enard convection. In addition, the brightness values at a local averaged-eld maximum and at a nearby minimum exhibit a distinct tendency to vary in antiphase. Thus, a previously unknown type of self-organization is manifest in the solar atmosphere, and our ndings support the suggestion that granules are associated with overheated blobs carried by the convective circulation.