The primary objectives of the project are, 1) to develop a computer program, based on the mathematical framework known as Vector Tomography, that can extract the 3-dimensional magnetic field structure the solar corona directly from observations of the polarization of the spectral lines originating from the corona, 2) to apply this program to the coronal polarization data that are been collected on a regular basis, and 3) to provide a new dataset that reveals the 3D thermal and magnetic field structure of the solar corona to allow for scientists in the solar and space physics community to study how the energetic eruptions of the sun occur.

The magnetic field of the solar corona is the dominant field in the outer layer of the solar atmosphere. It shapes the appearance of the corona, and directing the flow of the particles within. It’s evolution, sometime happens abruptly, is believed to be responsible for explosive eruptions. However, the exact physical processes of how these eruptions, in the form of solar flares, filament eruptions, and coronal mass ejections (CMEs), happen is still not clear. Observations that provide detailed information about the 3D structure of the magnetic fields, how they evolve in time during eruptions, and how they drive the dynamics of the coronal gas will allow scientists to understand the physics of the solar eruptions and eventually be able to predict when an eruption might occur. However, despite of its importance and decades of effort, direct measurement of the 3D coronal magnetic fields remains a challenging observational problem. Observationally, measurements of the polarization of the spectral lines emitted by the million-degree gases of the solar corona are the most direct method of remote sensing of the corona magnetic fields. However, due to the low density of the corona, the polarization signals we detect are in fact the sum of the polarization signals from many different source regions along our observation sight line with different magnetic fields. Therefore, direct translation of the observed polarization signals into magnetic fields is in general not possible.

Tomography is a technique that uses multiple observations of a 3D object from several different view angles to disentangle the scrambled information in the data to reconstruct the 3D structure of the object. It is a well-developed technique that has found application in many fields. For examples, Computed Tomographic imaging now are routinely used for non-invasive diagnostics of the internal organs of the human body.  While the observations of the Sun is mostly done from a single sight line from the earth, the rotation of the Sun present us with the opportunity to observe the structures of the Sun from different viewing angles, and allows us to apply Tomographic Inversion technique to recover the 3D structure of the coronal magnetic fields.

Dr. Haosheng Lin, the project principle investigator (PI), and Dr. Maxim Kramar, project co-investigator has completed the development of the vector tomographic inversion program that utilizes information about the orientation of the linear polarization of coronal emission lines, and density and temperature of the coronal gas, to recover the 3D structure of the coronal magnetic fields. The vector tomographic inversion program was thoroughly tested with simulated observations derived from numerical model of the corona. We then applied the program to real CEL polarization data obtained by Dr. Steve Tomczyk of the High Altitude Observatory, and coronal temperature and density data derived from space coronal observations in the extreme ultra violet wavelength regime to provide the first direct ‘Observation’ of the 3D magnetic field structure of the solar corona.

The tomographic inversion program developed in this project ...

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