‘Turbulence’ and the Photospheric Granulation

Abstract

EARLY high-resolution photographs of the solar photosphere showed a well-defined pattern of bright granules with diameters lying mostly in the range 1–2 sec. of arc. The similarity of this structure to laboratory convection patterns led to the view that the granules represent convective cells of the Bénard type. However, although some modern observers^1–3 apparently confirmed the existence of a granular structure with the same narrow distribution of sizes, others reached contrary conclusions. In particular, on the basis of photometric measurements of photographs obtained at Mt. Wilson, some workers^4–6 have concluded that the solar surface actually presents the appearance of random brightness fluctuations. These brightness fluctuations have been identified with so-called ‘turbulent eddies’. In fact, the view is now widely held that the photosphere is in a state of aerodynamic turbulence. (This conclusion has been opposed by Plaskett⁷.) This interpretation, however, does not accord with results derived from sequences of high-quality photographs of the granulation obtained recently by Leighton⁸ in the United States and by us⁹ in Australia. These cinematographic observations strongly support the convective interpretation and argue against the existence of turbulence.