Designing a New Coronal Magnetic Energy Diagnostic

Since there are no direct magnetic measurements, spectropolarimetry has been used as an indirect measurement of magnetic field strength, structure, and interactions, allowing modeling to recreate observations and reconstruct the magnetic field. In the sun's corona, excess in magnetic energy (free energy) over a minimum potential field drives events such as Coronal Mass Ejections (CMEs). However, polarimetric measurements of the corona are particularly challenging because the corona is not as bright as the surface of the sun. Only recently have coronal polarimetric observations been possible using instruments such as NCAR's Coronal Multi Channel Polarimeter (CoMP). By using a model (magnetic field and plasma environment) of the solar corona that has been energized relative to a potential field model, we created synthetic observables resembling those of CoMP. We also created synthetic observables from a potential field magnetic model using two distinct plasma density models. A diagnostic of non-potentiality (free energy) was created by direct subtraction of the synthetic observables generated by the potential models from the ones generated by the energized model. Also, we calculated a single-valued Non-Potentiality Index (NPI) as a sum of squared differences between the energized and potential synthetic observables. We found that the NPI calculated from the circular polarization observable showed a strong correlation with free energy, while, although the NPI linear polarization observable showed correlation to free energy, it was more sensitive to changes in the density models. Our work thus demonstrates the capabilities of polarization measurements for diagnosing non-potentiality in the corona.