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Context. Waves in the magnetized solar atmosphere are one of the favourite means of transferring and depositing energy into the solar corona. The study of waves brings information not just on the dynamics of the magnetized plasma, but also on the possible ways in which the corona is heated. Aims. The identification and analysis of the phase singularities or dislocations provide us with a complementary approach to the magnetoacoustic and Aflvén waves propagating in the solar atmosphere. They allow us to identify individual wave modes, shedding light on the probability of excitation or the nature of the triggering mechanism. Methods. We use a time series of Doppler shifts measured in two spectral lines, filtered around the three-minute period region. The data show a propagating magnetoacoustic slow mode with several dislocations and, in particular, a vortex line. We study under what conditions the different wave modes propagating in the umbra can generate the observed dislocations. Results. The observed dislocations can be fully interpreted as a sequence of sausage and kink modes excited sequentially on average during 15 min. Kink and sausage modes appear to be excited independently and sequentially. The transition from one to the other lasts less than three minutes. During the transition we observe and model the appearance of superoscillations inducing large phase gradients and phase mixing. Conclusions. The analysis of the observed wave dislocations leads us to the identification of the propagating wave modes in umbrae. The identification in the data of superoscillatory regions during the transition from one mode to the other may be an important indicator of the location of wave dissipation. [ABSTRACT FROM AUTHOR]

Macroscopic velocity fields in stellar atmospheres significantly affect the shapes of the emergent Stokes profiles. The inextricable coupling between the angle and frequency variables becomes more complex in a moving medium when compared to a static medium. In this paper we consider both complete frequency redistribution (CRD) and partial frequency redistribution (PRD) in the line scattering of a two-level atom in the presence of an external weak magnetic field. For simplicity we consider empirical velocity laws to represent motion of the atmospheric layers. We present emergent Stokes profiles computed with CRD, angle-averaged PRD, and angle-dependent PRD. We show that angle-dependent PRD effects are important both in non-magnetic and magnetized scattering when vertical velocity gradients are present in the atmosphere. The results are presented for simple atmospheric models. They are expected to be of relevance to polarized line formation in slowly expanding chromospheric layers. [ABSTRACT FROM PUBLISHER]

Scattering line polarization and the Hanle effect are among the most important mechanisms for diagnostics of the solar and stellar atmospheres. The fact that real stellar atmospheres are horizontally inhomogeneous makes the spectral synthesis and interpretation very challenging because the effect of thermodynamic fluctuations on spectral line polarization is entangled with the action of magnetic fields. This applies to the spatially resolved as well as to the averaged spectra. The necessary step towards the interpretation of such spectra is to study the line formation in sufficiently realistic 3D MHD models and compare the synthetic spectra with observations. This paper gives an overview of recent progress in the field of 3D NLTE synthesis of polarized spectral lines resulting from investigations with the radiative transfer code PORTA. [ABSTRACT FROM PUBLISHER]

It is well-known that partial frequency redistribution (PRD) is the basic physical mechanism to correctly describe radiative transfer in spectral lines. In the case of polarized line scattering, the PRD becomes particularly important to describe the line-wing polarization, instead of the well-known mechanism of complete redistribution (CRD). Historically, the two-level atom PRD scattering matrices for polarized line scattering were first derived in the 1970's, and later generalized to the case of arbitrary fields in 1997. The latter formulation of the PRD matrices have subsequently been used in the solution of the line transfer equation to successfully model the non-magnetic (resonance scattering) and the magnetic (Hanle scattering) polarization observations. In recent years, using the Kramers-Heisenberg approach, we formulated PRD matrices for various physical mechanisms like quantum interference involving fine- and hyperfine-structure states in a two-term atom. The effect of collisions is included in an approximate way. We have used these PRD matrices to model the observed linear polarization in several interesting lines of the Second Solar Spectrum. In this paper I present a few results which highlight the importance of PRD in the interpretation of the polarized Stokes profiles. [ABSTRACT FROM PUBLISHER]

The synoptic observations of the magnetic field of the Sun have continued at the National Solar Observatory (NSO) since 1970s. The daily full-disk maps of the longitudinal magnetic field are regularly combined to form Carrington maps of the photospheric magnetic flux per solar rotation. These maps continue to be used by the international research community for a variety of studies related to solar magnetism as well as for space weather studies. The current NSO synoptic facility is the Synoptic Optical Long-term Investigation of the Sun (SOLIS), which regularly provides photospheric vector and chromospheric longitudinal full-disk magnetograms, among other data products. In the near future, an upgrade of SOLIS to produce chromospheric vector magnetograms is planned. We present the design of a new polarization modulator package for full Stokes polarimetry of the chromospheric Ca II 854.2 nm spectral line. [ABSTRACT FROM PUBLISHER]

Is it physically feasible to perform the chromospheric diagnosis using spatial maps of scattering polarization at the solar disk center? To investigate it we synthesized polarization maps (in 8542 Å) resulting from MHD solar models and NLTE radiative transfer calculations that consider Hanle effect and vertical macroscopic motions. After explaining the physical context of forward scattering and presenting our results, we arrive at the definition of Hanle polarity inversion lines. We show how such features can give support for a clearer chromospheric diagnosis in which the magnetic and dynamic effects in the scattering polarization could be disentangled. [ABSTRACT FROM PUBLISHER]

We present an exceptional data set acquired with the Vacuum Tower Telescope (Tenerife, Spain) covering the pre-flare, flare, and post-flare stages of an M3.2 flare. The full Stokes spectropolarimetric observations were recorded with the Tenerife Infrared Polarimeter in the He i 1083.0 nm spectral region. The object under study was active region NOAA 11748 on 2013 May 17. During the flare the chomospheric He i 1083.0 nm intensity goes strongly into emission. However, the nearby photospheric Si i 1082.7 nm spectral line profile only gets shallower and stays in absorption. Linear polarization (Stokes Q and U) is detected in all lines of the He i triplet during the flare. Moreover, the circular polarization (Stokes V) is dominant during the flare, being the blue component of the He i triplet much stronger than the red component, and both are stronger than the Si i Stokes V profile. The Si i inversions reveal enormous changes of the photospheric magnetic field during the flare. Before the flare magnetic field concentrations of up to ~1500 G are inferred. During the flare the magnetic field strength globally decreases and in some cases it is even absent. After the flare the magnetic field recovers its strength and initial configuration. [ABSTRACT FROM PUBLISHER]

Context. Paper I presents the magnetic structure, inferred for the photosphere and the chromosphere, of a filament that developed in active region (AR) NOAA 10781, observed on 2005 July 3 and July 5. Aims. In this paper we complement those results with the velocities retrieved from Doppler shifts measured at the chromosphere and the photosphere in the AR filament area. Methods. The velocities and magnetic field parameters were inferred from full Stokes inversions of the photospheric Si ɪ 10 827 Å line and the chromospheric He ɪ 10 830 Å triplet. Various inversion methods with different numbers of atmospheric components and different weighting schemes of the Stokes profiles were used. The velocities were calibrated on an absolute scale. Results. A ubiquitous chromospheric downflow is found in the faculae surrounding the filament, with an average velocity of 1.6 km s-1. The filament region, however, displays upflows in the photosphere on both days, when the linear polarization (which samples the transverse component of the fields) is given more weight in the inversions. The upflow speeds of the transverse fields in the filament region average -0.15 km s-1. In the chromosphere, the situation is different for the two days of observation. On July 3, the chromospheric portion of the filament is moving upward as a whole with a mean speed of -0.24 km s-1. However, on July 5 only the section above an orphan penumbra shows localized upflow patches, while the rest of the filament is dominated by the same downflows observed elsewhere in the facular region. Photospheric supersonic downflows that last for tens of minutes are detected below the filament, close to the PIL. Conclusions. The observed velocity pattern in this AR filament strongly suggests a scenario where the transverse fields are mostly dominated by upflows. The filament flux rope is seen to be emerging at all places and both heights, with a few exceptions in the chromosphere. This happens within a surrounding facular region that displays a generalized downflow in the chromosphere and localized downflows of supersonic character at the photosphere. No large scale downflow of transverse field lines is observed at the photosphere. [ABSTRACT FROM AUTHOR]

Aims. A thorough multiwavelength, multiheight study of the vector magnetic field in a compact active region filament (NOAA 10781) on 2005 July 3 and 5 is presented. We suggest an evolutionary scenario for this filament. Methods. Two different inversion codes were used to analyze the full Stokes vectors acquired with the Tenerife Infrared Polarimeter (TIP-II) in a spectral range that comprises the chromospheric He i 10 830 Å multiplet and the photospheric Si i 10 827 Å line. In addition, we used SOHO/MDI magnetograms, as well as BBSO and TRACE images, to study the evolution of the filament and its active region (AR). High-resolution images of the Dutch Open Telescope were also used. Results. An active region filament (formed before our observing run) was detected in the chromospheric helium absorption images on July 3. The chromospheric vector magnetic field in this portion of the filament was strongly sheared (parallel to the filament axis), whereas the photospheric field lines underneath had an inverse polarity configuration. From July 3 to July 5, an opening and closing of the polarities on either side of the polarity inversion line (PIL) was recorded, resembling the recently discovered process of the sliding door effect seen by Hinode. This is confirmed with both TIP-II and SOHO/MDI data. During this time, a newly created region that contained pores and orphan penumbrae at the PIL was observed. On July 5, a normal polarity configuration was inferred from the chromospheric spectra, while strongly sheared field lines aligned with the PIL were found in the photosphere. In this same data set, the spine of the filament is also observed in a different portion of the field of view and is clearly mapped by the silicon line core. Conclusions. The inferred vector magnetic fields of the filament suggest a flux rope topology. Furthermore, the observations indicate that the filament is divided in two parts, one which lies in the chromosphere and another one that stays trapped in the photosphere. Therefore, only the top of the helical structure is seen by the helium lines. The pores and orphan penumbrae at the PIL appear to be the photospheric counterpart of the extremely low-lying filament. We suggest that orphan penumbrae are formed in very narrow PILs of compact ARs and are the photospheric manifestation of flux ropes in the photosphere. [ABSTRACT FROM AUTHOR]

The introductory lecture that has been delivered at this Symposium is a condensed version of an extended course held by the author at the XII Canary Island Winter School from November 13 to November 21, 2000. The full series of lectures can be found in Landi Degl'Innocenti (2002). The original reference is organized in 20 Sections that are here itemized: 1. Introduction, 2. Description of polarized radiation, 3. Polarization and optical devices: Jones calculus and Muller matrices, 4. The Fresnel equations, 5. Dichroism and anomalous dispersion, 6. Polarization in everyday life, 7. Polarization due to radiating charges, 8. The linear antenna, 9. Thomson scattering, 10. Rayleigh scattering, 11. A digression on Mie scattering, 12. Bremsstrahlung radiation, 13. Cyclotron radiation, 14. Synchrotron radiation, 15. Polarization in spectral lines, 16. Density matrix and atomic polarization, 17. Radiative transfer and statistical equilibrium equations, 18. The amplification condition in polarized radiative transfer, and 19. Coupling radiative transfer and statistical equilibrium equations.The introductory lecture delivered at the Symposium has covered the subjects itemized above with the exclusion of Sections 10, 11, 14, 18, and 19. [ABSTRACT FROM PUBLISHER]