Progressing Towards Faraday Rotation Tomography of the Solar Wind

Abstract

Understanding the coronal plasma, in particular the plasma density and magnetic field strength and structure, is critical to understanding the foundational physics of the solar wind, which requires continuous, consistent measurements over heliocentric distances < 10 R ⊙ . Detection of Faraday rotation (FR) is the best radio remote-sensing method for continuously probing the plasma structure, including the magnetic field, of the solar wind and coronal mass ejections (CMEs). As we develop the technology and methodology to evolve from measuring FR along ≈ 10 to 10s to 100s of lines of sight (LOS), we can begin to move beyond the previous era in which sporadic FR measurements only sampled a very localized region of the corona and imagine a future in which continuous FR measurements sample the entire corona. With 10s (spacecraft), 100s (pulsars and radio galaxies), or 1000s (Galactic synchrotron background) of LOS, we would be able to generate full, 2-D FR sky maps of the corona. An FR sky map time series could be combined using tomographic methods to generate a 3-D representation of the coronal magnetic field. Spacecraft could be used to quickly generate high time-cadence, low spatial-resolution FR tomographic scans suitable for studying fast, transient structures such as CMEs, critical to developing early warning space weather forecasting systems. Natural radio sources could then be used to slowly generate high-resolution FR tomographic scans suitable for studying slowly-evolving coronal structures such as streamers, stream interaction regions, or co-rotating interaction regions.