On the origin of quiet-Sun magnetic fields revealed with Hinode

Ishikawa Ryohko, ryoko.ishikawa@nao.ac.jp, National Astronomical Observatory of Japan, Japan
Tsuneta Saku, National Astronomical Observatory of Japan

Abstract
In the quiet regions of the Sun, strong kG vertical fields are concentrated around the boundaries of supergranulation, and are referred to as network fields. The region inside the network is referred to as the internetwork region and contains weak magnetic fields smaller in size, consisting of mixed-polarity magnetic fields. The origin of the quiet-Sun magnetic fields has not been well understood. Nevertheless, the properties and the origin of these magnetic fields would be a consequence of interaction with the convective motions with various temporal and spatial scales. Magnetic fields in the internetwork quiet region were considered to be vertical with respect to the solar surface. Hinode spectropolarimetric observations have changed this paradigm; it is revealed that quiet-Sun is overflowing with a granular-scale inclined (horizontal) magnetic fields. The properties have been extensively investigated with Hinode . However, vertical and horizontal magnetic fields in the internetwork region are considered to be separate entities and have thus far not been investigated together. Therefore, we broaden our scope to clarify the origin and properties of quiet-Sun magnetic fields, both vertical and horizontal, in a unified way. We find the clear positional association between the newly investigated horizontal magnetic fields and vertical fields known for decades to exist. Furthermore, we study the relationship between these small-scale magnetic fields and various convective motions such as the granule, mesogranule and supergranules. With our combined knowledge of these properties, we conjecture that magnetic fields in the internetwork regions are provided by the emergence of small-scale horizontal fields with bipolar footpoints, and the vertical magnetic fields of the footpoints are intensified to kG fields owing to convective collapse. Resultant strong vertical fields are advected by the supergranular flow, and eventually form network fields.