Evolution of bright points in the quiet Sun

The appearance (dissolution) of high-contrast G-band BPs is found to be related to the local increase (decrease) of the magnetic filling factor, without appreciable changes in the field strength. The cancellation of opposite-polarity BPs can be the signature of either magnetic reconnection or the emergence/submergence of magnetic loops.

Emergence of small-scale magnetic loops through the quiet solar photosphere

A significant fraction of the magnetic flux present in internetwork regions appears in the form of Ω-shaped loops. The emergence rate is 0.02 loops per hour and arcsec-2, which brings 1.1 × 1012 Mx s-1 arcsec-2 of new flux to the solar surface. Initially, the loops are observed as small patches of linear polarization above a granular cell. Shortly afterward, two footpoints of opposite polarity become visible in circular polarization within or at the edges of the granule and start moving toward the adjacent intergranular space. The orientation of the footpoints does not seem to obey Hale's polarity rules. The loops are continuously buffeted by convective motions, but they always retain a high degree of coherence. Interestingly, 23% of the loops that emerge in the photosphere reach the chromosphere (16 cases out of 69). They are first detected in Fe I 630 nm magnetograms and 5 minutes later in Mg I b 517.3 nm magnetograms. After about 8 minutes, some of them are also observed in Ca II H line-core images, where the footpoints produce small brightness enhancements.

Supersonic, horizontal flows in the solar granulation

Using data from the spectropolarimeter aboard the Hinode satellite, direct evidence of fast horizontal plasma motions in quiet-Sun granules is presented. Their visibility increases toward the limb due to more favorable viewing conditions. At the resolution of Hinode, the horizontal flows give rise to asymmetric intensity profiles with very inclined blue wings and even line satellites located blueward of the main absorption feature. Doppler shifts of up to 9 km s-1 are observed at the edges of bright granules, demonstrating that the flows reach supersonic speeds.

Chromospheric brightenings during the emergence of small-scale magnetic structures

We report on Hinode observations of chromospheric Ca II H brightenings associated with a repeated, small-scale flux emergence event. We describe this process and investigate the evolution of the magnetic flux, G-band brightness, and Ca II H intensity in the emerging region. Our results suggest that energy is released in the chromosphere as a consequence of interactions between the emerging flux and the preexisting magnetic field, in agreement with recent 3D numerical simulations.

The magnetic landscape of the Sun’s polar regions

We present observations of the magnetic landscape of the polar region of the Sun that are unprecedented in terms of spatial resolution, field of view, and polarimetric precision. They were carried out with the Solar Optical Telescope aboard Hinode. Using a Milne-Eddington inversion, we find many vertically oriented magnetic flux tubes with field strengths as strong as 1 kG scattered in latitude between 70° and 90°. They all have the same polarity, consistent with the global polarity of the polar region. The field vectors are observed to diverge from the centers of the flux elements, consistent with a view of magnetic fields that are expanding and fanning out with height. The polar region is also found to have ubiquitous horizontal fields.

Convective instability as the origin of the formation of kG flux tubes

Evidence of convective instability based on observations with the Solar Optical Telescope (SOT) aboard Hinode is provided. The cooling of an equipartition field strength flux tube precedes a transient downflow reaching 6 km s-1 and the intensification of the field strength to 2 kG. These observations agree very well with the theoretical predictions.

Magnetic field emergence in quiet Sun granules

We describe a new form of small-scale magnetic flux emergence in the quiet Sun. This process seems to take vertical magnetic fields from subsurface layers to the photosphere, where they appear above granular convection cells. The circular polarization maps derived from the observed Fe I 630 nm lines show clear magnetic signals emerging at the center of granular cells. We do not find any evidence for linear polarization signals associated with these events. The magnetic flux patches grow with time, occupying a significant fraction of the granular area. The signals then fade until they disappear completely. The typical lifetime of these events is of the order of 20 min. No significant changes in the chromosphere are seen to occur in response to the emergence, as revealed by co-spatial Ca II H filtergrams. The Stokes I and V profiles measured in the emerging flux concentrations show strong asymmetries and Doppler shifts.

Inclined magnetic fields over the quiet Sun

A significant fraction of the quiet Sun scanned area with Hinode, including granules, turns out to be covered by magnetic fields. We derive field strength and inclination probability density functions from a Milne-Eddington inversion of the observed Stokes profiles. They show that the internetwork consists of very inclined, hG fields. As expected, network areas exhibit a predominance of kG field concentrations. The high spatial resolution of Hinode's spectropolarimetric measurements brings to an agreement the results obtained from the analysis of visible and near-infrared lines.