Periodic Reporting for period 4 - POLMAG (Polarized Radiation Diagnostics for Exploring the Magnetism of the Outer Solar Atmosphere )
Okres sprawozdawczy: 2022-07-01 do 2023-12-31
The solar atmosphere (photosphere, chromosphere, transition region and corona) is permeated by magnetic fields, with strengths going from only a few gauss to thousands of gauss. The magnetic field controls the solar activity, the clearest manifestation of which is the 11 year sunspot cycle, as well as the ejection of particles and magnetized plasma from the outer solar atmosphere (upper chromosphere, transition region and corona). The explosive events caused by the magnetic activity in the outer solar atmosphere drive the near-Earth space weather, which impacts our life on Earth.
We need to “measure” the magnetic field in the outer solar atmosphere for understanding how the upper chromosphere and the million-degree corona are sustained, how the solar wind and the acceleration of particles is driven, and how the eruptive phenomena that produce the near-Earth space weather are activated. However, our empirical knowledge on solar magnetic fields is basically restricted to the Sun’s visible surface (the photosphere). In practice, we have remained blind to the main driver of solar activity, namely the magnetic field in the outer solar atmosphere.
The information about the magnetic field that permeates the solar atmosphere is encoded in the polarization of the spectral line radiation emitted by the atoms and molecules of the solar atmospheric plasma. POLMAG has achieved a breakthrough in the development and application of polarized radiation diagnostic methods for exploring the magnetic fields of the solar chromosphere, transition region, and corona via the interpretation of the light polarization produced by optically polarized atoms and the Hanle and Zeeman effects in ultraviolet, visible, and near-infrared spectral lines.
To that end, we combined expertise on atomic physics, the quantum theory of radiation, high-precision spectropolarimetry and plasma diagnostic techniques, advanced methods in numerical radiative transfer, and the confrontation of spectropolarimetric observations with spectral synthesis in increasingly realistic three-dimensional models of the solar atmosphere.
Remarkably, our theoretical investigations on the polarization of the solar UV spectrum motivated two suborbital space experiments, which we carried out in 2019 and 2021 in collaboration with NASA and Japan. These CLASP2 and CLASP2.1 missions provided unprecedented spectropolarimetric data of quiet and active regions of the solar atmosphere in the near-UV spectral region of the Mg II h & k lines, and the interpretation of the data via the application of our plasma diagnostic techniques has allowed us to map solar magnetic fields from the photosphere to the base of the solar corona.
We need to “measure” the magnetic field in the outer solar atmosphere for understanding how the upper chromosphere and the million-degree corona are sustained, how the solar wind and the acceleration of particles is driven, and how the eruptive phenomena that produce the near-Earth space weather are activated. However, our empirical knowledge on solar magnetic fields is basically restricted to the Sun’s visible surface (the photosphere). In practice, we have remained blind to the main driver of solar activity, namely the magnetic field in the outer solar atmosphere.
The information about the magnetic field that permeates the solar atmosphere is encoded in the polarization of the spectral line radiation emitted by the atoms and molecules of the solar atmospheric plasma. POLMAG has achieved a breakthrough in the development and application of polarized radiation diagnostic methods for exploring the magnetic fields of the solar chromosphere, transition region, and corona via the interpretation of the light polarization produced by optically polarized atoms and the Hanle and Zeeman effects in ultraviolet, visible, and near-infrared spectral lines.
To that end, we combined expertise on atomic physics, the quantum theory of radiation, high-precision spectropolarimetry and plasma diagnostic techniques, advanced methods in numerical radiative transfer, and the confrontation of spectropolarimetric observations with spectral synthesis in increasingly realistic three-dimensional models of the solar atmosphere.
Remarkably, our theoretical investigations on the polarization of the solar UV spectrum motivated two suborbital space experiments, which we carried out in 2019 and 2021 in collaboration with NASA and Japan. These CLASP2 and CLASP2.1 missions provided unprecedented spectropolarimetric data of quiet and active regions of the solar atmosphere in the near-UV spectral region of the Mg II h & k lines, and the interpretation of the data via the application of our plasma diagnostic techniques has allowed us to map solar magnetic fields from the photosphere to the base of the solar corona.
The main final results achieved are:
- A novel technique to explore the elusive magnetism of the quiet Sun photosphere, and theoretical predictions.
- The impact of time dependence on the scattering polarization of the Sr I 460.7 nm line.
- New plasma diagnostic tool for exploring the magnetism of the lower solar chromosphere.
- CLASP1: constraints on the geometrical complexity and magnetization of the chromosphere-corona transition region.
- CLASP2 and CLASP2.1: a novel suborbital space experiment for exploring the magnetism of the upper solar chromosphere.
- The scattering polarization wings of the hydrogen Lyman-alpha line are sensitive to chromospheric magnetic fields.
- Development of improved numerical methods for the angular integration in 3D radiative transfer problems.
- Investigation of the Hanle and Zeeman effects in the resonance and subordinate ultraviolet lines of Mg II.
- New spectro-polarimetric observations with their analysis and interpretation.
- The public version of 3D radiative transfer code PORTA.
- An accurate 3D formal solution method of the Stokes-vector transfer equation for PORTA.
- Confronting forward scattering observations of the Ca II 854.2 nm line with 3D radiative transfer simulations.
- Novel method for mapping the azimuth of the magnetic field vector directly from forward-scattering observations in the Ca II 854.2 nm line.
- The effects of 3D radiative transfer on the polarization of chromospheric lines.
- POLMAG-Corona code for modeling the polarization of spectral line radiation scattered by the solar corona.
- The H I and He II Lyman-alpha lines: a Hanle-effect line ratio technique.
- HanleRT-TIC, a non-LTE spectral synthesis and inversion code for the solar chromosphere.
- Development of the new generation of non-LTE Stokes inversion techniques
- Modeling the scattering polarization observed by CLASP in the wings of Lyman-alpha and Mg II h & k taking into account magneto-optical effects
- Unprecedented mapping of the magnetic field in the upper chromosphere.
- CLASP2/2.1 space missions demonstrated the diagnostic capability of UV spectropolarimetry
- Publication in Physical Review Letters of our resolution of a long-standing paradox in solar physics.
- Unprecedented spectropolarimetric observations in the H-alpha line.
We have provided the theoretical background and plasma diagnostic techniques needed for investigating the magnetism of the solar upper atmosphere via the physical interpretation of spectropolarimetric observations with the new generation of ground-based and space solar telescopes. Our CLASP2 and CLASP2.1 space experiments have paved the way for developing a solar space telescope to investigate the upper chromosphere via ultraviolet spectropolarimetry. For more information, see the POLMAG webpage.
- A novel technique to explore the elusive magnetism of the quiet Sun photosphere, and theoretical predictions.
- The impact of time dependence on the scattering polarization of the Sr I 460.7 nm line.
- New plasma diagnostic tool for exploring the magnetism of the lower solar chromosphere.
- CLASP1: constraints on the geometrical complexity and magnetization of the chromosphere-corona transition region.
- CLASP2 and CLASP2.1: a novel suborbital space experiment for exploring the magnetism of the upper solar chromosphere.
- The scattering polarization wings of the hydrogen Lyman-alpha line are sensitive to chromospheric magnetic fields.
- Development of improved numerical methods for the angular integration in 3D radiative transfer problems.
- Investigation of the Hanle and Zeeman effects in the resonance and subordinate ultraviolet lines of Mg II.
- New spectro-polarimetric observations with their analysis and interpretation.
- The public version of 3D radiative transfer code PORTA.
- An accurate 3D formal solution method of the Stokes-vector transfer equation for PORTA.
- Confronting forward scattering observations of the Ca II 854.2 nm line with 3D radiative transfer simulations.
- Novel method for mapping the azimuth of the magnetic field vector directly from forward-scattering observations in the Ca II 854.2 nm line.
- The effects of 3D radiative transfer on the polarization of chromospheric lines.
- POLMAG-Corona code for modeling the polarization of spectral line radiation scattered by the solar corona.
- The H I and He II Lyman-alpha lines: a Hanle-effect line ratio technique.
- HanleRT-TIC, a non-LTE spectral synthesis and inversion code for the solar chromosphere.
- Development of the new generation of non-LTE Stokes inversion techniques
- Modeling the scattering polarization observed by CLASP in the wings of Lyman-alpha and Mg II h & k taking into account magneto-optical effects
- Unprecedented mapping of the magnetic field in the upper chromosphere.
- CLASP2/2.1 space missions demonstrated the diagnostic capability of UV spectropolarimetry
- Publication in Physical Review Letters of our resolution of a long-standing paradox in solar physics.
- Unprecedented spectropolarimetric observations in the H-alpha line.
We have provided the theoretical background and plasma diagnostic techniques needed for investigating the magnetism of the solar upper atmosphere via the physical interpretation of spectropolarimetric observations with the new generation of ground-based and space solar telescopes. Our CLASP2 and CLASP2.1 space experiments have paved the way for developing a solar space telescope to investigate the upper chromosphere via ultraviolet spectropolarimetry. For more information, see the POLMAG webpage.
The results summarized above are a few selected highlights of the research we have carried out in the POLMAG research group. In our opinion, all this progress is beyond the state of the art and represents solid advances and breakthroughs.
We have completed the development of the various advanced polarized radiation plasma diagnostic techniques mentioned above, and we have made them publicly available. We have also obtained new spectropolarimetric observations using ground-based solar telescopes and advanced instruments; their analysis and physical interpretation has led to new insights on the magnetism of the solar atmosphere. Likewise, we have fully exploited the unprecedented data we have obtained with our CLASP2 and CLASP2.1 space experiments, improving our empirical understanding of the upper solar atmosphere (see the review by Trujillo Bueno & del Pino Alemán 2022).
In 2024 and 2025 we expect to continue publishing important papers. In addition, over the last few years we have been invited to deliver several review lectures at international conferences, including also an outreach lecture to students of the MIT (USA). All our papers and plasma diagnostic techniques are freely available via ArXiv, publications in open source journals and through the POLMAG website.
We have completed the development of the various advanced polarized radiation plasma diagnostic techniques mentioned above, and we have made them publicly available. We have also obtained new spectropolarimetric observations using ground-based solar telescopes and advanced instruments; their analysis and physical interpretation has led to new insights on the magnetism of the solar atmosphere. Likewise, we have fully exploited the unprecedented data we have obtained with our CLASP2 and CLASP2.1 space experiments, improving our empirical understanding of the upper solar atmosphere (see the review by Trujillo Bueno & del Pino Alemán 2022).
In 2024 and 2025 we expect to continue publishing important papers. In addition, over the last few years we have been invited to deliver several review lectures at international conferences, including also an outreach lecture to students of the MIT (USA). All our papers and plasma diagnostic techniques are freely available via ArXiv, publications in open source journals and through the POLMAG website.