ner_tags: B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O B-Software O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O B-Observatory O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O
tokens: Earth-Sun distance by changing the pixel scale accordingly. After the telemetric problems which occurred in January 2008, the images of the synoptic program were binned by a factor of two. Fortunately, this is not a problem in this work, since the images taken before this date were binned by a factor of two for analysis. So the size of all the analyzed images is 2048 × 1024 pixels. The program ended in February 2016, when both cameras broke down. All images were calibrated with the standard solar reduction software distributed under SSWIDL, which corrects for bad pixels, readout errors, dark current and flat field. A 1024 × 512 pixel subfield of a calibrated image is shown in Fig. 1 . In each image, the left and the right square subfields are analyzed separately; this helps us, by comparing the results in each of them, to disentangle solar variations from instrumental effects, which is crucial for our investigation (see the next section and Muller et al. 2011 ). Fig. 1. A 1024 × 512 (114′′ × 57′′) subfield of a 2048 × 1024 (228′′ × 114′′) blue continuum HINODE/SOT image from the synoptic program. 3. Granulation images analysis As mentioned in Sect. 2 , a significant number of images from the synoptic program appear to be blurred to a varying degree. In order to get a reliable variation, the sharpest images must be selected, and only these ones used for further analysis. About 25% of the images have been actually removed because of blurring. The method of selection is described in detail in Muller et al. (2011) and only a summary is presented here. In a first step, the images containing dark columns, sunspots pores, abnormal granulation 1 were removed visually; the images which clearly appear out of focus were also removed visually. In the second step the granulation contrast and scale of the selected images were derived from the power spectrum ( Muller et al. 2007 , 2011 ), separately in the left and right half fields of view of size 114′′ × 114′′. The root mean square of the intensity fluctuations, Irms, which, for simplicity, we refer to as contrast, is the square root of the integral, above the noise level, of the power spectrum in the granulation range, between 0′′̣3 (in order to remove the high frequency noise) and 4′′ (in order to remove non-granular larger scale fluctuations, like the 5-min oscillations and the mesogranulation). The scale is defined as the inverse of the mean wavenumber of the power spectrum in the granulation range, converted in arcseconds. The contrast and the scale derived in this way are about 12% and about 1′′̣6 (1160 km) respectively. When the contrast of the left field-of-view (FOV) of the selected images is plotted versus the contrast of the right FOV, they appear correlated: when the contrast is large (small) in one FOV it is also large (small) in the other FOV (see Fig. 5 in Muller et al. 2011 , which shows the correlation for the images selected in January 2007). But as the granulation evolves independently