Letter to the Editor

Regular structures of the solar photosphere

(Persistence of the granular field and trenching in the brightness relief)

¹ Institute of Nuclear Physics, Lomonosov Moscow State University, 117234 Moscow, Russia
² Kiepenheuer-Institut für Sonnenphysik, Schöneckstrasse 6, 79104 Freiburg, Germany e-mail: pnb@kis.uni-freiburg.de

Corresponding author: A. V. Getling, A.Getling@ru.net

Received: 29 October 2001
Accepted: 10 December 2001

Abstract

The simple procedure of time averaging, when applied to the photospheric brightness field, 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 field 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 sufficiently 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–Bénard convection. In addition, the brightness values at a local averaged-field 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 findings support the suggestion that granules are associated with overheated blobs carried by the convective circulation.