Found 37 talks archived in The Sun

The quiet Sun (the 99%, or more, of the solar surface not covered by sunspots or active regions) is receiving increased attention in recent years; its role on the global magnetism and its complexity are being increasingly recognised. A picture of a rather stochastic quiet Sun magnetism is emerging. From these recent works, the quiet Sun magnetism is presented as a myriad of magnetic field vectors having an isotropical distribution with a cascade of scales down to the mean free path of the photon. But this chaotic representation also shows clear signs of intermittency: at a low frequency rate (0.022 events h^-1 arcsec^-2) the magnetic field appear in the quiet Sun forming well-organised loop structures at granular scales. More interesting, these loops rise to higher layers and their energy input into the chromosphere can be important for the heating of this layer. In the talk, I will present a pedagogic view of the quiet Sun magnetism. I will focus on the ascent of the smallest ever observed magnetic flux emergence through the solar atmosphere. More specifically, I will show how to infer from high resolution, spectro-polarimetric observations (taken with the SOT instrument onboard Hinode) the magnetic topology of the fields, how they rise through the photosphere to the chromosphere, and the implications of this phenomena for chromospheric (and coronal) heating.

The magnetic landscape of the polar region (Tsuneta et al, 2008) is characterized by vertical kilogauss patches with super-equipartition field strength, a coherence in polarity, lifetimes of 5-15 hr, and ubiquitous weaker transient horizontal fields (Lites et al 2008, Ishikawa & Tsuneta, 2008, 2009). Polar region in 2007 have abundant vertical fields much stronger than the quiet Sun. Unipolar appearance and disappearance of the kG vertical patches must be closely related to properties of the horizontal flow field in the polar region. Difference and similarity between the quiet sun and the polar region are summarized, and its implication for solar dynamo will be discussed. All the open field lines forming the polar coronal hole essentially originate from such magnetic patches, and the fast solar wind would emanate from these vertical flux tubes seen in the photosphere. We conjecture that vertical flux tubes with large expansion around the photospheric-coronal boundary serve as efficient chimneys for Alfven waves that accelerate the solar wind. Indeed, we discovered propagating Alfven waves (kink mode) with magneto-acoustic waves (sausage mode) in the solar photosphere with period of 4-13 minutes with Hinode spectro-polarimeter (Fujimura and Tsuneta, 2009). We found that these fluctuations are superposition of ascending and descending Alfven waves with almost equal intensities from the analysis of the phase relationship between transverse magnetic and velocity fluctuations. Aflven waves along flux tubes in the quiet sun appear to be efficiently reflected back probably at photosphere-corona boundary. It would be very interesting to measure possible change in the reflectivity of Alfven waves depending on the magnetic environment.

We have discovered small whirlpools in the Sun, with a size similar to the terrestrial hurricanes (<0.5 Mm). The theory of solar convection predicts them, but they had remained elusive so far. The vortex flows are created at the downdrafts where the plasma returns to the solar interior after cooling down, and we detect them because some magnetic bright points (BPs) follow a logarithmic spiral in their way to be engulfed by a downdraft. Our disk center observations show 0.009 vortexes per Mm², with a lifetime of the order of 5 min, and with no preferred sense of rotation. They are not evenly spread out over the surface, but they seem to trace the supergranulation and the mesogranulation. These observed properties are strongly biased by our type of measurement, unable to detect vortexes except when they are engulfing magnetic BPs.