A High-resolution, Inversion-based Synoptic Study of Solar Granulation

Abstract

The convectively driven, weakly magnetized regions of the solar photosphere dominate the Sun’s surface at any given time, but the temporal variations of these quiet regions of the photosphere throughout the solar cycle are still not well known. To look for cycle-dependent changes in the convective properties of the quiet Sun photosphere, we use high spatial and spectral resolution spectropolarimetric observations obtained by the Hinode Solar Optical Telescope and apply the Spectropolarimetric Inversions Based on Response Functions code to infer physical conditions in the lower solar photosphere. Using a homogeneous set of 49 data sets, all taken at the disk center, we analyze the temperature stratification and the line-of-sight velocities of the granules and intergranules over a period of 15 years. We use a k-means clustering technique applied to the spectral profiles to segment the granules and intergranules based on both intensity and velocity. We also examine the profile bisectors of these different structures and compare them to past analyses. Our results show fairly constant properties over this period with no clear dependence on the solar cycle. We do, however, find a slight increase in the photospheric temperature gradient during the declining phase of the solar cycle. Our findings could have significant implications for understanding the coupling between the quiet Sun atmosphere and the global solar dynamo.