A method is developed to determine the physical parameters of the spatially unresolved photospheric network. The apparent magnetic fluxes are recorded simultaneously in the two FeI lines 5250 and 5247 A, which belong to the same multiplet and have practically the same oscillator strength and excitation potential of the lower level, but differ in the effective Land6 factor. By analysing magnetograph recordings in this pair of lines together with simultaneous recordings in the two FeI lines 5250 and 5233 ~, it is possible to separate the effects on the line profiles due to Zeeman splitting and temperature enhancement in the network.From an analysis of the observations the following properties of the photospheric network are obtained: Field strengths of about 2000 G are present in the network in quiet regions. The characteristic size of the magnetic-field structures in the network appears to be in the range 100-300 kin. The 5250/~ line is weakened by roughly 50 ~ in the network. If the line had been non-magnetic, the weakening would have been about 20 ~. The rest of the weakening is caused by the strong Zeeman splitting. The downward velocity at the supergranular cell boundaries is estimated to be of the order of 0.5 km s -1.

The magnetic flux that is generated by dynamo processes inside the Sun emerges in the form of bipolar magnetic regions. The properties of these directly observable signatures of the dynamo can be extracted from full-disk solar magnetograms. The most homogeneous, high-quality synoptic data set of solar magnetograms has been obtained with the MDI instrument on the SOHO spacecraft during 1995-2011. We have developed an IDL program which has, when applied to the 73,838 magnetograms of the MDI data set, automatically identified 160,079 bipolar magnetic regions that span a range of scale sizes across nearly four orders of magnitude. The properties of each region have been extracted and statistically analysed, in particular with respect to the polarity orientations of the bipolar regions, including their tilt angle distributions and their violations of Hale's polarity law. The latitude variation of the average tilt angles (with respect to the E-W direction), which is known as Joy's law, is found to closely follow the relation 32.1 • × sin(latitude). There is no indication of a dependence on region size that one may expect if the tilts were produced by the Coriolis force during the buoyant rise of flux loops from the tachocline region. A few percent of all regions have orientations that violate Hale's polarity law. We show explicit examples, from different phases of the solar cycle, where well defined medium-size bipolar regions with opposite polarity orientations occur side by side in the same latitude zone in the same magnetogram. Such oppositely oriented large bipolar regions cannot be part of the same toroidal flux system, but different flux systems must coexist at any given time in the same latitude zones. These examples are incompatible with the paradigm of coherent, subsurface toroidal flux ropes as the source of sunspots, and instead show that fluctuations must play a major role at all scales for the turbulent dynamo. To confirm the profound role of fluctuations at large scales we show explicit examples where large bipolar regions differ fromthe average Joy's law orientation by an amount between 90 • and 100 • . We see no observational support for a separation of scales or a division between a global and a local dynamo, since also the smallest scales in our sample retain a nonrandom component that significantly contributes to the accumulated emergence of a north-south dipole moment that will lead to the replacement of the old global poloidal field with a new one that has the opposite orientation.

The theory of the Hanle effect is used to interpret the linear polarization measured in a number of spectral lines on the solar disk near the heliographic north and south poles, in search for a turbulent magnetic field in the solar atmosphere. The Hanle depolarization is separated from a number of other effects, including collisional depolarization and scattering geometry. Although the main aim of the paper is to elucidate the physics of the Hanle effect as applied to the Sun, our results indicate the existence of hidden or turbulent magnetic flux near the temperature minimum of the solar atmosphere, with a field strength between 10 and 100 G. This field is hidden in the sense that it is not seen in measurements of the longitudinal Zeeman effect (solar magnetograms). It carries more total magnetic flux than the kG network fields.

Abstract.To clarify the physical nature of the enigmatic scattering polarization in the Na i D1 and D2 line cores we have explored their behavior with full Stokes vector polarimetry in regions with varying degree of magnetic activity near the solar limb. These observations represent the first time that ZIMPOL II, the second generation of our CCD based imaging polarimeter systems, has been used for a scientific program. With ZIMPOL II the four Stokes images can be demodulated and recorded with a single CCD sensor such that the resulting images of the fractional polarization Q/I, U/I, and V /I are entirely free from spurious features due to seeing or flat-field effects. The polarization in the cores of the lines, in particular in D2, exhibits dramatic and unexpected spatial variations in both Q/I and U/I, including polarization self-reversals of the D2 Q/I core peak. As the fluctuations in the Q, U , and V parameters appear to be relatively uncorrelated, we have parametrized the profiles and made scatter plots of the extracted parameters. Comparison with synthetic scatter plots based on different theoretical models suggests that the polarization signals in the cores of the D2 and D1 lines have different physical origins: While the D1 core is likely to be governed by ground-state atomic polarization, the D2 core is dominated by the alignment of the excited state and by effects of partial frequency redistribution.