Author name code: alsina-ballester ADS astronomy entries on 2022-09-14 author:Alsina Ballester, Ernest ------------------------------------------------------------------------ Title: The polarization signals of the solar K I D lines and their magnetic sensitivity Authors: Alsina Ballester, Ernest Bibcode: 2022arXiv220811728A Altcode: This work aims to identify the relevant physical processes in shaping the intensity and polarization patterns of the solar K I D lines through spectral syntheses, placing particular emphasis on the D2 line. The theoretical Stokes profiles were obtained by numerically solving the radiative transfer problem for polarized radiation considering one-dimensional semi-empirical models of the solar atmosphere. The calculations account for scattering polarization, partial frequency redistribution (PRD) effects, hyperfine structure (HFS), J- and F-state interference, multiple isotopes, and magnetic fields of arbitrary strength and orientation. The intensity and circular polarization profiles of both D lines can be suitably modeled while neglecting both J-state interference and HFS. The magnetograph formula can be applied to both lines, without including HFS, to estimate weak longitudinal magnetic fields in the lower chromosphere. By contrast, modeling their scattering polarization signals requires the inclusion of HFS. The D2 scattering polarization amplitude is strongly depolarized by HFS, but it remains measurable. An appreciable error is incurred in the scattering polarization profile if PRD effects are not taken into account. Collisions during scattering processes also have an appreciable depolarizing effect. Finally, the D2 scattering polarization signal is especially sensitive to magnetic fields with strengths around 10 G and it strongly depends on their orientation. Despite this, its center-to-limb variation relative to the amplitude at the limb is largely insensitive to the field strength and orientation. These findings highlight the value of the K I D2 line polarization for diagnostics of the solar magnetism, and show that the linear and circular polarization signals of this line are primarily sensitive to magnetic fields in the lower chromosphere and upper photosphere, respectively. Title: The transfer of polarized radiation in resonance lines with partial frequency redistribution, J-state interference, and arbitrary magnetic fields. A radiative transfer code and useful approximations Authors: Alsina Ballester, E.; Belluzzi, L.; Trujillo Bueno, J. Bibcode: 2022A&A...664A..76A Altcode: 2022arXiv220412523A
Aims: We present the theoretical framework and numerical methods we have implemented to solve the problem of the generation and transfer of polarized radiation in spectral lines without assuming local thermodynamical equilibrium, while accounting for scattering polarization, partial frequency redistribution (due to both the Doppler effect and elastic collisions), J-state interference, and hyperfine structure. The resulting radiative transfer code allows one to model the impact of magnetic fields of an arbitrary strength and orientation through the Hanle, incomplete Paschen-Back, and magneto-optical effects. We also evaluate the suitability of a series of approximations for modeling the scattering polarization in the wings of strong resonance lines at a much lower computational cost, which is particularly valuable for the numerically intensive case of three-dimensional radiative transfer.
Methods: We examine the suitability of the considered approximations by using our radiative transfer code to model the Stokes profiles of the Mg II h & k lines and of the H I Lyman-α line in magnetized one-dimensional models of the solar atmosphere.
Results: Neglecting Doppler redistribution in the scattering processes that are unperturbed by elastic collisions (i.e., treating them as coherent in the observer's frame) produces a negligible error in the scattering polarization wings of the Mg II resonance lines and a minor one in the Lyman-α wings, although it is unsuitable to model the cores of these lines. For both lines, the scattering processes that are perturbed by elastic collisions only give a significant contribution to the intensity component of the emissivity. Neglecting collisional as well as Doppler redistribution (so that all scattering processes are coherent) represents a rough but suitable approximation for the wings of the Mg II resonance lines, but a very poor one for the Lyman-α wings. The magnetic sensitivity in the scattering polarization wings of the considered lines can be modeled by accounting for the magnetic field in only the ηI and ρV coefficients of the Stokes-vector transfer equation (i.e., using the zero-field expression for the emissivity). Title: The polarization angle in the wings of Ca I 4227: A new observable for diagnosing unresolved photospheric magnetic fields Authors: Capozzi, Emilia; Alsina Ballester, Ernest; Belluzzi, Luca; Trujillo Bueno, Javier Bibcode: 2022A&A...657A..44C Altcode: 2021arXiv211108967C Context. When observed in quiet regions close to the solar limb, many strong resonance lines show conspicuous linear polarization signals, produced by scattering processes (i.e., scattering polarization), with extended wing lobes. Recent studies indicate that, contrary to what was previously believed, the wing lobes are sensitive to the presence of relatively weak longitudinal magnetic fields through magneto-optical (MO) effects.
Aims: We theoretically investigate the sensitivity of the scattering polarization wings of the Ca I 4227 Å line to the MO effects, and we explore its diagnostic potential for inferring information on the longitudinal component of the photospheric magnetic field.
Methods: We calculate the intensity and polarization profiles of the Ca I 4227 Å line by numerically solving the problem of the generation and transfer of polarized radiation under non-local thermodynamic equilibrium conditions in one-dimensional semi-empirical models of the solar atmosphere, taking into account the joint action of the Hanle, Zeeman, and MO effects. We consider volume-filling magnetic fields as well as magnetic fields occupying a fraction of the resolution element.
Results: In contrast to the circular polarization signals produced by the Zeeman effect, we find that the linear polarization angle in the scattering polarization wings of Ca I 4227 presents a clear sensitivity, through MO effects, not only to the flux of the photospheric magnetic field, but also to the fraction of the resolution element that the magnetic field occupies.
Conclusions: We identify the linear polarization angle in the wings of strong resonance lines as a valuable observable for diagnosing unresolved magnetic fields. Used in combination with observables that encode information on the magnetic flux and other properties of the observed atmospheric region (e.g., temperature and density), it can provide constraints on the filling factor of the magnetic field. Title: Demonstration of Chromospheric Magnetic Mapping with CLASP2.1 Authors: McKenzie, David; Ishikawa, Ryohko; Trujillo Bueno, Javier; Auchere, F.; Kobayashi, Ken; Winebarger, Amy; Kano, Ryouhei; Song, Donguk; Okamoto, Joten; Rachmeler, Laurel; De Pontieu, Bart; Vigil, Genevieve; Belluzzi, Luca; Alsina Ballester, Ernest; del Pino Aleman, Tanausu; Bethge, Christian; Sakao, Taro; Stepan, Jiri Bibcode: 2021AGUFMSH52A..06M Altcode: Probing the magnetic nature of the Suns atmosphere requires measurement of the Stokes I, Q, U and V profiles of relevant spectral lines (of which Q, U and V encode the magnetic field information). Many of the magnetically sensitive lines formed in the chromosphere and transition region are in the ultraviolet spectrum, necessitating observations above the absorbing terrestrial atmosphere. The Chromospheric Layer Spectro-Polarimeter (CLASP2) sounding rocket was flown successfully in April 2019, as a follow-on to the successful flight in September 2015 of the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP). Both projects were funded by NASAs Heliophysics Technology and Instrument Development for Science (H-TIDeS) program to develop and test a technique for observing the Sun in ultraviolet light, and for quantifying the polarization of that light. By demonstrating successful measurement and interpretation of the polarization in hydrogen Lyman-alpha and the Mg II h and k spectral lines, the CLASP and CLASP2 missions are vital first steps towards routine quantitative characterization of the local thermal and magnetic conditions in the solar chromosphere. In October of 2021, we re-flew the CLASP2 payload with a modified observing program to further demonstrate the maturity of the UV spectropolarimetry techniques, and readiness for development into a satellite observatory. During the reflight, called CLASP2.1, the spectrograph slit was scanned across an active region plage to acquire a two-dimensional map of Stokes V/I, to demonstrate the ability of UV spectropolarimetry to yield chromospheric magnetic fields over a large area. This presentation will display preliminary results from the flight of CLASP2.1. Title: A novel fourth-order WENO interpolation technique. A possible new tool designed for radiative transfer Authors: Janett, Gioele; Steiner, Oskar; Alsina Ballester, Ernest; Belluzzi, Luca; Mishra, Siddhartha Bibcode: 2021arXiv211011885J Altcode: Context. Several numerical problems require the interpolation of discrete data that present various types of discontinuities. The radiative transfer is a typical example of such a problem. This calls for high-order well-behaved techniques to interpolate both smooth and discontinuous data. Aims. The final aim is to propose new techniques suitable for applications in the context of numerical radiative transfer. Methods. We have proposed and tested two different techniques. Essentially non-oscillatory (ENO) techniques generate several candidate interpolations based on different substencils. The smoothest candidate interpolation is determined from a measure for the local smoothness, thereby enabling the essential non-oscillatory property. Weighted ENO (WENO) techniques use a convex combination of all candidate substencils to obtain high-order accuracy in smooth regions while keeping the essentially non-oscillatory property. In particular, we have outlined and tested a novel well-performing fourth-order WENO interpolation technique for both uniform and nonuniform grids. Results. Numerical tests prove that the fourth-order WENO interpolation guarantees fourth-order accuracy in smooth regions of the interpolated functions. In the presence of discontinuities, the fourth-order WENO interpolation enables the non-oscillatory property, avoiding oscillations. Unlike Bézier and monotonic high-order Hermite interpolations, it does not degenerate to a linear interpolation near smooth extrema of the interpolated function. Conclusions. The novel fourth-order WENO interpolation guarantees high accuracy in smooth regions, while effectively handling discontinuities. This interpolation technique might be particularly suitable for several problems, including a number of radiative transfer applications such as multidimensional problems, multigrid methods, and formal solutions. Title: Solving the Paradox of the Solar Sodium D1 Line Polarization Authors: Alsina Ballester, Ernest; Belluzzi, Luca; Trujillo Bueno, Javier Bibcode: 2021PhRvL.127h1101A Altcode: 2021arXiv210808334A Twenty-five years ago, enigmatic linear polarization signals were discovered in the core of the sodium D1 line. The only explanation that could be found implied that the solar chromosphere is practically unmagnetized, in contradiction with other evidences. This opened a paradox that has challenged physicists for many years. Here we present its solution, demonstrating that these polarization signals can be properly explained in the presence of magnetic fields in the gauss range. This result opens a novel diagnostic window for exploring the elusive magnetism of the solar chromosphere. Title: Mapping of Solar Magnetic Fields from the Photosphere to the Top of the Chromosphere with CLASP2 Authors: McKenzie, D.; Ishikawa, R.; Trujillo Bueno, J.; Auchere, F.; del Pino Aleman, T.; Okamoto, T.; Kano, R.; Song, D.; Yoshida, M.; Rachmeler, L.; Kobayashi, K.; Narukage, N.; Kubo, M.; Ishikawa, S.; Hara, H.; Suematsu, Y.; Sakao, T.; Bethge, C.; De Pontieu, B.; Vigil, G.; Winebarger, A.; Alsina Ballester, E.; Belluzzi, L.; Stepan, J.; Asensio Ramos, A.; Carlsson, M.; Leenaarts, J. Bibcode: 2021AAS...23810603M Altcode: Coronal heating, chromospheric heating, and the heating & acceleration of the solar wind, are well-known problems in solar physics. Additionally, knowledge of the magnetic energy that powers solar flares and coronal mass ejections, important drivers of space weather, is handicapped by imperfect determination of the magnetic field in the sun's atmosphere. Extrapolation of photospheric magnetic measurements into the corona is fraught with difficulties and uncertainties, partly due to the vastly different plasma beta between the photosphere and the corona. Better results in understanding the coronal magnetic field should be derived from measurements of the magnetic field in the chromosphere. To that end, we are pursuing quantitative determination of the magnetic field in the chromosphere, where plasma beta transitions from greater than unity to less than unity, via ultraviolet spectropolarimetry. The CLASP2 mission, flown on a sounding rocket in April 2019, succeeded in measuring all four Stokes polarization parameters in UV spectral lines formed by singly ionized Magnesium and neutral Manganese. Because these ions produce spectral lines under different conditions, CLASP2 thus was able to quantify the magnetic field properties at multiple heights in the chromosphere simultaneously, as shown in the recent paper by Ishikawa et al. In this presentation we will report the findings of CLASP2, demonstrating the variation of magnetic fields along a track on the solar surface and as a function of height in the chromosphere; and we will illustrate what is next for the CLASP missions and the demonstration of UV spectropolarimetry in the solar chromosphere. Title: Magnetic Imaging of the Outer Solar Atmosphere (MImOSA): Unlocking the driver of the dynamics in the upper solar atmosphere Authors: Peter, H.; Alsina Ballester, E.; Andretta, V.; Auchere, F.; Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.; Chitta, L. P.; Dalmasse, K.; del Pino Aleman, T.; Feller, A.; Froment, C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski, D.; Solanki, S. K.; Stepan, J.; Teriaca, L.; Trujillo Bueno, J. Bibcode: 2021arXiv210101566P Altcode: The magnetic activity of the Sun directly impacts the Earth and human life. Likewise, other stars will have an impact on the habitability of planets orbiting these host stars. The lack of information on the magnetic field in the higher atmospheric layers hampers our progress in understanding solar magnetic activity. Overcoming this limitation would allow us to address four paramount long-standing questions: (1) How does the magnetic field couple the different layers of the atmosphere, and how does it transport energy? (2) How does the magnetic field structure, drive and interact with the plasma in the chromosphere and upper atmosphere? (3) How does the magnetic field destabilise the outer solar atmosphere and thus affect the interplanetary environment? (4) How do magnetic processes accelerate particles to high energies? New ground-breaking observations are needed to address these science questions. We suggest a suite of three instruments that far exceed current capabilities in terms of spatial resolution, light-gathering power, and polarimetric performance: (a) A large-aperture UV-to-IR telescope of the 1-3 m class aimed mainly to measure the magnetic field in the chromosphere by combining high spatial resolution and high sensitivity. (b) An extreme-UV-to-IR coronagraph that is designed to measure the large-scale magnetic field in the corona with an aperture of about 40 cm. (c) An extreme-UV imaging polarimeter based on a 30 cm telescope that combines high throughput in the extreme UV with polarimetry to connect the magnetic measurements of the other two instruments. This mission to measure the magnetic field will unlock the driver of the dynamics in the outer solar atmosphere and thereby greatly advance our understanding of the Sun and the heliosphere. Title: Fast and accurate approximation of the angle-averaged redistribution function for polarized radiation Authors: Paganini, A.; Hashemi, B.; Alsina Ballester, E.; Belluzzi, L. Bibcode: 2021A&A...645A...4P Altcode: 2020arXiv201003508P Context. Modeling spectral line profiles taking frequency redistribution effects into account is a notoriously challenging problem from the computational point of view, especially when polarization phenomena (atomic polarization and polarized radiation) are taken into account. Frequency redistribution effects are conveniently described through the redistribution function formalism, and the angle-averaged approximation is often introduced to simplify the problem. Even in this case, the evaluation of the emission coefficient for polarized radiation remains computationally costly, especially when magnetic fields are present or complex atomic models are considered.
Aims: We aim to develop an efficient algorithm to numerically evaluate the angle-averaged redistribution function for polarized radiation.
Methods: The proposed approach is based on a low-rank approximation via trivariate polynomials whose univariate components are represented in the Chebyshev basis.
Results: The resulting algorithm is significantly faster than standard quadrature-based schemes for any target accuracy in the range [10-6, 10-2]. Title: Magnetic Sensitivity in the Wing Scattering Polarization Signals of the Hydrogen Lyman-α Line of the Solar Disk Radiation Authors: Alsina Ballester, E.; Belluzzi, L.; Trujillo Bueno, J. Bibcode: 2019ApJ...880...85A Altcode: 2019arXiv190110994A The linear polarization produced by scattering processes in the hydrogen Lyα line of the solar disk radiation is a key observable for probing the chromosphere-corona transition region (TR) and the underlying chromospheric plasma. While the line-center signal encodes information on the magnetic field and the three-dimensional structure of the TR, the sizable scattering polarization signals that the joint action of partial frequency redistribution and J-state interference produce in the Lyα wings have generally been thought to be sensitive only to the thermal structure of the solar atmosphere. Here we show that the wings of the Q/I and U/I scattering polarization profiles of this line are actually sensitive to the presence of chromospheric magnetic fields, with strengths similar to those that produce the Hanle effect in the line core (i.e., between 5 and 100 G, approximately). In spite of the fact that the Zeeman splitting induced by such weak fields is very small compared to the total width of the line, the magneto-optical effects that couple the transfer equations for Stokes Q and U are actually able to produce sizable changes in the Q/I and U/I wings. We find that magnetic fields with longitudinal components larger than 100 G produce an almost complete depolarization of the wings of the Lyα Q/I profiles within a ±5 Å spectral range around the line center, while stronger fields are required for the U/I wing signals to be depolarized to a similar extent. The theoretical results presented here further expand the diagnostic content of the unprecedented spectropolarimetric observations provided by the Chromospheric Lyman-Alpha Spectro-Polarimeter. Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter Authors: McKenzie, D. E.; Ishikawa, R.; Trujillo Bueno, J.; Auchére, F.; Rachmeler, L. A.; Kubo, M.; Kobayashi, K.; Winebarger, A. R.; Bethge, C. W.; Narukage, N.; Kano, R.; Ishikawa, S.; de Pontieu, B.; Carlsson, M.; Yoshida, M.; Belluzzi, L.; Štěpán, J.; del Pino Alemán, T.; Alsina Ballester, E.; Asensio Ramos, A. Bibcode: 2019ASPC..526..361M Altcode: The hydrogen Lyman-α line at 121.6 nm and the Mg k line at 279.5 nm are especially relevant for deciphering the magnetic structure of the chromosphere since their line-center signals are formed in the chromosphere and transition region, with unique sensitivities to magnetic fields. We propose the Chromospheric LAyer Spectro-Polarimeter (CLASP2), to build upon the success of the first CLASP flight, which measured the linear polarization in H I Lyman-α. The existing CLASP instrument will be refitted to measure all four Stokes parameters in the 280 nm range, including variations due to the anisotropic radiation pumping, the Hanle effect, and the Zeeman effect. Title: The Transfer of Resonance Line Polarization with PRD in the General Hanle-Zeeman Regime Authors: Alsina Ballester, E.; Belluzzi, L.; Trujillo Bueno, J. Bibcode: 2019ASPC..526..119A Altcode: We present numerical radiative transfer calculations of the four Stokes parameters of the radiation emerging from one-dimensional model atmospheres. In this investigation we account for the impact of partial frequency redistribution (PRD) in scattering and the joint action of the Hanle and Zeeman effects. Strong resonance lines of interest for chromospheric magnetic field diagnostics have been considered, namely the Ca I line at 4227 Å and the Mg II k line at 2795 Å. The Stokes profiles of these lines have been obtained by considering two-level atomic models, both in the absence and in the presence of magnetic fields. We draw attention to the fact that the magneto-optical terms of the transfer equations for Stokes Q and U are responsible for an interesting and previously unnoticed magnetic sensitivity of their scattering polarization profiles beyond the Doppler core. This important discovery contributes to paint a more detailed picture of the influence of relatively weak magnetic fields on the observable linear polarization signals of strong chromospheric lines, highlighting the importance of a PRD treatment for such lines. Title: A novel fourth-order WENO interpolation technique. A possible new tool designed for radiative transfer Authors: Janett, Gioele; Steiner, Oskar; Alsina Ballester, Ernest; Belluzzi, Luca; Mishra, Siddhartha Bibcode: 2019A&A...624A.104J Altcode: Context. Several numerical problems require the interpolation of discrete data that present at the same time (i) complex smooth structures and (ii) various types of discontinuities. The radiative transfer in solar and stellar atmospheres is a typical example of such a problem. This calls for high-order well-behaved techniques that are able to interpolate both smooth and discontinuous data.
Aims: This article expands on different nonlinear interpolation techniques capable of guaranteeing high-order accuracy and handling discontinuities in an accurate and non-oscillatory fashion. The final aim is to propose new techniques which could be suitable for applications in the context of numerical radiative transfer.
Methods: We have proposed and tested two different techniques. Essentially non-oscillatory (ENO) techniques generate several candidate interpolations based on different substencils. The smoothest candidate interpolation is determined from a measure for the local smoothness, thereby enabling the essentially non-oscillatory property. Weighted ENO (WENO) techniques use a convex combination of all candidate substencils to obtain high-order accuracy in smooth regions while keeping the essentially non-oscillatory property. In particular, we have outlined and tested a novel well-performing fourth-order WENO interpolation technique for both uniform and nonuniform grids.
Results: Numerical tests prove that the fourth-order WENO interpolation guarantees fourth-order accuracy in smooth regions of the interpolated functions. In the presence of discontinuities, the fourth-order WENO interpolation enables the non-oscillatory property, avoiding oscillations. Unlike Bézier and monotonic high-order Hermite interpolations, it does not degenerate to a linear interpolation near smooth extrema of the interpolated function. Conclusion. The novel fourth-order WENO interpolation guarantees high accuracy in smooth regions, while effectively handling discontinuities. This interpolation technique might be particularly suitable for several problems, including a number of radiative transfer applications such as multidimensional problems, multigrid methods, and formal solutions. Title: Current State of UV Spectro-Polarimetry and its Future Direction Authors: Ishikawa, Ryohko; Sakao, Taro; Katsukawa, Yukio; Hara, Hirohisa; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Kubo, Masahito; Auchere, Frederic; De Pontieu, Bart; Winebarger, Amy; Kobayashi, . Ken; Kano, Ryouhei; Narukage, Noriyuki; Trujillo Bueno, Javier; Song, Dong-uk; Manso Sainz, Rafael; Asensio Ramos, Andres; Leenaarts, Jorritt; Carlsson, Mats; Bando, Takamasa; Ishikawa, Shin-nosuke; Tsuneta, Saku; Belluzzi, Luca; Suematsu, Yoshinori; Giono, Gabriel; Yoshida, Masaki; Goto, Motoshi; Del Pino Aleman, Tanausu; Stepan, Jiri; Okamoto, Joten; Tsuzuki, Toshihiro; Uraguchi, Fumihiro; Champey, Patrick; Alsina Ballester, Ernest; Casini, Roberto; McKenzie, David; Rachmeler, Laurel; Bethge, Christian Bibcode: 2018cosp...42E1564I Altcode: To obtain quantitative information on the magnetic field in low beta regions (i.e., upper chromosphere and above) has been increasingly important to understand the energetic phenomena of the outer solar atmosphere such as flare, coronal heating, and the solar wind acceleration. In the UV range, there are abundant spectral lines that originate in the upper chromosphere and transition region. However, the Zeeman effect in these spectral lines does not give rise to easily measurable polarization signals because of the weak magnetic field strength and the larger Doppler broadening compared with the Zeeman effect. Instead, the Hanle effect in UV lines is expected to be a suitable diagnostic tool of the magnetic field in the upper atmospheric layers. To investigate the validity of UV spectro-polarimetry and the Hanle effect, the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP), which is a NASA sounding- rocket experiment, was launched at White Sands in US on September 3, 2015. During its 5 minutes ballistic flight, it successfully performed spectro-polarimetric observations of the hydrogen Lyman-alpha line (121.57 nm) with an unprecedentedly high polarization sensitivity of 0.1% in this wavelength range. CLASP observed the linear polarization produced by scattering process in VUV lines for the first time and detected the polarization signals which indicate the operation of the Hanle effect. Following the success of CLASP, we are confident that UV spectro-polarimetry is the way to proceed, and we are planning the second flight of CLASP (CLASP2: Chromospheric LAyer SpectroPolarimeter 2). For this second flight we will carry out spectro-polarimetry in the Mg II h and k lines around 280 nm, with minimum modifications of the CLASP1 instrument. The linear polarization in the Mg II k line is induced by scattering processes and the Hanle effect, being sensitive to magnetic field strengths of 5 to 50 G. In addition, the circular polarizations in the Mg II h and k lines induced by the Zeeman effect can be measurable in at least plage and active regions. The combination of the Hanle and Zeeman effects could help us to more reliably infer the magnetic fields of the upper solar chromosphere. CLASP2 was selected for flight and is being developed for launch in the spring of 2019.Based on these sounding rocket experiments (CLASP1 and 2), we aim at establishing the strategy and refining the instrument concept for future space missions to explore the enigmatic atmospheric layers via UV spectro-polarimetry. Title: Magneto-optical Effects in the Scattering Polarization Wings of the Ca I 4227 Å Resonance Line Authors: Alsina Ballester, E.; Belluzzi, L.; Trujillo Bueno, J. Bibcode: 2018ApJ...854..150A Altcode: 2017arXiv171100372A; 2017arXiv171100372B The linear polarization pattern produced by scattering processes in the Ca I 4227 Å resonance line is a valuable observable for probing the solar atmosphere. Via the Hanle effect, the very significant Q/I and U/I line-center signals are sensitive to the presence of magnetic fields in the lower chromosphere with strengths between 5 and 125 G, approximately. On the other hand, partial frequency redistribution (PRD) produces sizable signals in the wings of the Q/I profile, which have always been thought to be insensitive to the presence of magnetic fields. Interestingly, novel observations of this line revealed a surprising behavior: fully unexpected signals in the wings of the U/I profile and spatial variability in the wings of both Q/I and U/I. We show that the magneto-optical (MO) terms of the Stokes-vector transfer equation produce sizable signals in the wings of U/I and a clear sensitivity of the Q/I and U/I wings to the presence of photospheric magnetic fields with strengths similar to those that produce the Hanle effect in the line core. This radiative transfer investigation on the joint action of scattering processes and the Hanle and Zeeman effects in the Ca I 4227 Å line should facilitate the development of more reliable techniques for exploring the magnetism of stellar atmospheres. To this end, we can now exploit the circular polarization produced by the Zeeman effect, the magnetic sensitivity caused by the above-mentioned MO effects in the Q/I and U/I wings, and the Hanle effect in the line core. Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter Authors: Rachmeler, Laurel A.; McKenzie, D. E.; Ishikawa, R.; Trujillo-Bueno, J.; Auchere, F.; Kobayashi, K.; Winebarger, A.; Bethge, C.; Kano, R.; Kubo, M.; Song, D.; Narukage, N.; Ishikawa, S.; De Pontieu, B.; Carlsson, M.; Yoshida, M.; Belluzzi, L.; Stepan, J.; del Pino Alemán, T.; Alsina Ballester, E.; Asensio Ramos, A. Bibcode: 2017shin.confE..79R Altcode: We present the instrument, science case, and timeline of the CLASP2 sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha Spectro-Polarimeter) sounding rocket flight in 2015 resulted in the first-ever linear polarization measurements of solar hydrogen Lyman-alpha line, which is sensitive to the Hanle effect and can be used to constrain the magnetic field and geometric complexity of the upper chromosphere. Ly-alpha is one of several upper chromospheric lines that contain magnetic information. In the spring of 2019, we will re-fly the modified CLASP telescope to measure the full Stokes profile of Mg II h & k near 280 nm. This set of lines is sensitive to the upper chromospheric magnetic field via both the Hanle and the Zeeman effects. Title: The Transfer of Resonance Line Polarization with Partial Frequency Redistribution in the General Hanle-Zeeman Regime Authors: Alsina Ballester, E.; Belluzzi, L.; Trujillo Bueno, J. Bibcode: 2017ApJ...836....6A Altcode: 2016arXiv160905723B; 2016arXiv160905723A; 2017ApJ...836....6B The spectral line polarization encodes a wealth of information about the thermal and magnetic properties of the solar atmosphere. Modeling the Stokes profiles of strong resonance lines is, however, a complex problem both from a theoretical and computational point of view, especially when partial frequency redistribution (PRD) effects need to be taken into account. In this work, we consider a two-level atom in the presence of magnetic fields of arbitrary intensity (Hanle-Zeeman regime) and orientation, both deterministic and micro-structured. Working within the framework of a rigorous PRD theoretical approach, we have developed a numerical code that solves the full non-LTE radiative transfer problem for polarized radiation, in one-dimensional models of the solar atmosphere, accounting for the combined action of the Hanle and Zeeman effects, as well as for PRD phenomena. After briefly discussing the relevant equations, we describe the iterative method of solution of the problem and the numerical tools that we have developed and implemented. We finally present some illustrative applications to two resonance lines that form at different heights in the solar atmosphere, and provide a detailed physical interpretation of the calculated Stokes profiles. We find that magneto-optical effects have a strong impact on the linear polarization signals that PRD effects produce in the wings of strong resonance lines. We also show that the weak-field approximation has to be used with caution when PRD effects are considered. Title: The Magnetic Sensitivity of the Mg II k Line to the Joint Action of Hanle, Zeeman, and Magneto-optical Effects Authors: Alsina Ballester, E.; Belluzzi, L.; Trujillo Bueno, J. Bibcode: 2016ApJ...831L..15A Altcode: 2016arXiv161000649A We highlight the main results of a radiative transfer investigation on the magnetic sensitivity of the solar Mg II k resonance line at 2795.5 Å, accounting for the joint action of the Hanle and Zeeman effects as well as partial frequency redistribution phenomena. We confirm that at the line center, the linear polarization signals produced by scattering processes are measurable, and that they are sensitive, via the Hanle effect, to magnetic fields with strengths between 5 and 50 G, approximately. We also show that the Zeeman effect produces conspicuous circular polarization signals, especially for longitudinal fields stronger than 50 G, which can be used to estimate the magnetization of the solar chromosphere via the familiar magnetograph formula. The most novel result is that magneto-optical effects produce, in the wings of the line, a decrease of the Q/I scattering polarization pattern and the appearance of U/I signals (I.e., a rotation of the plane of linear polarization). This sensitivity of the Q/I and U/I wing signals to both weak (∼5 G) and stronger magnetic fields expands the scientific interest of the Mg II k line for probing the chromosphere in quiet and active regions of the Sun.