Short-time large-scale restructuring of the solar photosphere

Abstract

SOLAR granulation consists of small-scale brightness variations on the Sun's surface, caused by horizontal inhomogeneities in the temperature and density of the photosphere¹. Individual granules are typically 1,000 km across and have lifetimes of about 5 minutes, but the two-dimensional pattern has generally been considered stationary, apart from small deviations over the solar surface and variations during the solar cycle². Here I show that the nature of the granulation pattern changes on a timescale of 5–10 minutes (ref. 3). The number of granules increases coherently by a factor of 1.2–1.6 over an area of (4–6) x 10⁸ km², accompanied by a change in the total granular area of a factor of 1.4 and a change in the mean area by a factor of 2, in antiphase with the number of granules. When the number of granules is increasing, formation of new granules by fragmentation exceeds their disappearance by merging by a factor of 3.6, whereas when the number of granules is decreasing merging occurs twice as fast as fragmentation. The mechanism for these changes is unclear.