Properties of Granules in Upflows and Downflows

Normal-mode observations of seven quiet regions, obtained by the Hinode spacecraft, are used to analyze the physical properties of granules with mean upward and downward Doppler velocity. We identify 75 146 granules from the observations with a granuledetection method. Then the granules are divided into two subsets: one with negative mean Doppler velocity (granule-upflows), and the other with positive mean Doppler velocity (granule-downflows). Next, the statistical properties and distributions of these two subsets of granules are measured and discussed. We also study the relation between the Doppler velocity of granules and other properties. Several conclusions are drawn from the statistical analysis: i) The majority (73.5%) of granules have negative mean Doppler velocity (blueshift). ii) The continuum-intensity distribution of granule-upflows reaches a peak at 1.05, while that of granules-downflows reaches a peak at 0.99. iii) Granule-upflows are greater than granule-downflows if transverse, absolute longitudinal and unsigned flux density are smaller than 100 G, while granule-upflows are less than granule-downflows if the flux densities are greater than 100 G. iv) Granuledownflows are – on average – slightly smaller and fainter than granule-upflows. Also, the flux densities of granule-downflows are slightly higher. v) The mean Doppler velocity within intergranular lanes is the most highly correlated with that within granules among the eight properties of granules.