Discovery of ubiquitous small-scale fields

Tsuneta Saku, saku.tsuneta@nao.ac.jp, National Astronomical Observatory of Japan, Japan

Abstract
The remarkable properties of the ubiquitous small-scale fields have been revealed with Hinode in the past 5 years after its launch. Their magnetic vectors are predominantly horizontal with respect to the solar surface as opposed to the known vertical fields. They have a form of isolated flux tubes, and their size is always smaller than that of the granular convection pattern. They appear transiently with life time ranging from 1 to 10 min. They are indeed ubiquitous, since they are seen everywhere in the quiet Sun, a plage region, and the polar region. There is no difference in the histograms of the horizontal magnetic field strengths in those different parts of the Sun. Time-wise, their magnetic flux in the north polar region is stable between 2008-2011, while the vertical magnetic fields associated with the kG-magnetic patches have considerable change associated with the solar cycle evolution. Their intrinsic magnetic field strengths are essentially smaller than the equi-partition field strength (500-700G) corresponding to the granular convection. Magnetic flux carried by the ubiquitous small-scale fields is orders of magnitude larger than those of sunspots and active regions averaged over the sunspot cycle. All these observations consistently and coherently point to a local dynamo process: a process of amplification of seed magnetic fields with the surface turbulent convection. Role of granular, meso-granular and super-granular convections in the dynamo process is not yet understood. Whether there is a relationship between such a local process with a global dynamo process is yet known as well. The origin of the vertical magnetic vector fields in the quiet Sun has been a matter of debate over the years in solar physics. There are accumulating pieces of evidence in the quiet sun and in the polar region that such vertical magnetic fields originate from the emergence of these ubiquitous horizontal magnetic fields followed by a process called convective collapse. If indeed the ubiquitous small-scale flux tubes reach chromospheres and corona, it carries enough energy to heat the chromospheres and corona, providing a new concept on the heating of the upper atmosphere of the stars. Finally, These observations imply that if turbulence exists anywhere in the cosmos, it will have magnetic fields as strong as their equi-partition field strength. This may bridge the very weak magnetic fields in re-ionization era and the current strong magnetic fields of galaxies and clusters of galaxies.