Solar granulation from photosphere to low chromosphere observed in Ba?II 4554???line

摘要

Aims. The purpose of this paper is to characterize thestatistical properties of solar granulation in the photosphere and lowchromosphere up to 650km. Methods. We use velocity and intensity variations obtained at different atmospheric heights from observations in Ba II4554?. The observations were done during good seeing conditionsat the VTT at the Observatorio del Teide on Tenerife. The line coreforms rather high in the atmosphere and allows granulation propertiesto be studied at heights that have been not accessed before in similarstudies. In addition, we analyze the synthetic profiles of the BaII 4554? line by the same method computed taking NLTE effects into account in the 3D hydrodynamical model atmosphere. Results. We suggest a 16-column model of solar granulationdepending on the direction of motion and on the intensity contrastmeasured in the continuum and in the uppermost layer. We calculate theheights of intensity contrast sign reversal and velocity sign reversal.We show that both parameters depend strongly on the granulationvelocity and intensity at the bottom photosphere. The larger the twoparameters, the higher the reversal takes place in the atmosphere. Onaverage, this happens at about 200-300km. We suggest that thisnumber also depends on the line depth of the spectral line used inobservations. Despite the intensity andvelocity reversal, about40% of the column structure of granulation is preserved up to heightsaround 650km. Key words: Sun: photosphere - Sun: chromosphere - Sun: granulation - techniques: spectroscopic - radiative transfer