Comments on Solar Convection

Abstract

AbstractThis contribution discusses observational aspects of the evolution of individual structures of solar convection.It has been shown, that mesogranulation is a convective phenomenon that fits well into the gap between granulation and supergranulation. Apparently this observation justifies the view that the three members of the granulation family represent sections of a broad continuum of convective motions spanning the range of sizes from a yet unknown fraction of 1 Mm to about 50 Mm. Nevertheless, power spectra of velocity and brightness fluctuations exhibit three maxima, separated by intervals with significantly less power near 3 Mm and 7.5 Mm. Do these gaps give reasons for reconsidering the old idea, that each of the three characteristic scales has its own source layer at a certain depth in the convection zone?Power spectra of the granular energy distribution near the observational limit of spatial resolution suggest a continuous transfer of kinetic energy to smaller eddies by turbulent decay of the larger scale elements. Morphological studies of granular evolution and a comparison of the observed spectral line bisectors with theoretical predictions seem to disprove this idea. These observations imply either that the turbulent cascade, if it exists, is buried in the spatially unresolved part of the power distribution, or that radiative losses ultimately limit the life time of individual granules on all scales.