[MOVIE] Evolution of internetwork magnetic elements in the quiet Sun
Evolution of internetwork magnetic elements
This magnetogram sequence shows the evolution of the quiet Sun at the center of the solar disk as observed by the Hinode satellite on 2010 January 20. Longitudinal magnetograms are maps of the magnetic field on the solar surface, obtained by observing the circular polarization of selected spectral lines. In this case, the Na I D1 line at 5896 Å was recorded by the Narrowband Filter Imager onboard Hinode. It samples the mid-upper photosphere. In magnetograms like the ones displayed here, white patches indicate magnetic fields pointing away from the Sun, while black patches represent magnetic fields pointing towards the Sun interior (positive and negative polarities, respectively).
The movie shows the evolution of supergranular cells at the disk center, the strong magnetic fields located at the boundaries of the cells (the so-called magnetic network), and the weaker magnetic fields occurring in the cell interiors (the so-called quiet Sun internetwork). The movie covers 19.5 hours of continuous observations and is unprecedented in terms of duration, cadence, and magnetic field sensitivity. Each frame in the movie corresponds to 60 seconds of solar time.
One can observe tiny magnetic elements of both polarities popping up all over the supergranular cell interiors. These internetwork elements migrate radially outwards to the cell boundaries. On their way to the network, they often interact with other elements. When they encounter elements of the same polarity, they merge with them. If the interaction involves opposite polarity fields, the elements cancel out, disappearing totally or partially. They may also fade in situ, without obvious interactions with other elements. Internetwork elements that reach the cell boundaries merge or cancel with network elements. It has been estimated that the weak internetwork elements, despite their short lifetimes, are able to supply the entire magnetic flux of the network in a matter of 10-20 hours. Therefore, they are essential ingredients to understand the magnetism of the solar surface.
The accompanying image shows one of the magnetograms saturated at 20 G, to reveal the weakest magnetic signals.