Coronal mass ejections (CMEs) are large eruptions of magnetized plasma from the Sun that play an important role in space weather. The key to understanding the fundamental physics of a CME is measurement of the plasma properties of a CME within heliocentric distances of < 20 solar radii. In particular, determining the strength and orientation of the CME’s magnetic field is critical to space weather forecasting. There is widespread recognition in the astronomy and space physics communities that Faraday rotation (FR), a radioastronomical propagation measurement, is an extremely valuable diagnostic for studying CMEs. Faraday rotation measurements can be used to directly probe the magnetic field structures of CMEs, as well as the ambient solar wind.
In this program, we employ a multi-disciplinary approach of: targeted full-polarization radio observations of CMEs to detect FR along with total intensity observations of angular broadening; white-light observations to obtain the plasma density along the line of sight where FR was observed; and utilize the derived magnetic field and electron density values as boundary conditions for physical models of the plasma and magnetic field structure of CMEs.
Radio observations probing the solar wind and CME plasma structure are typically performed using single-dish telescopes like the Robert C. Byrd Green Bank Telescope (GBT) or interferometers like the Karl G. Jansky Very Large Array (VLA). Complementing VLA observations, we simultaneously record total intensity data at 340 MHz with the VLA Low-band Ionosphere and Transient Experiment (VLITE) that can be used to measure angular broadening of background sources due to density irregularities through the CMEs and probe the density structure. Many CMEs and solar flares are also associated with low frequency radio bursts, which can be studied with the network of Deployable Low-band Ionosphere and Transient Experiment (DLITE) arrays developed by the U.S. Naval Research Laboratory (NRL).
We also use well-developed methods to independently determine the total electron density from observations of Thomson-scattered white light detected by NRL-designed imagers on current NASA missions SOHO and STEREO. This program will also begin developing entirely new methods to enhance FR observations using white-light imagers onboard Parker Solar Probe, Solar Orbiter, and the upcoming NASA small explorer mission Polarimeter to Unify the Corona and Heliosphere (PUNCH).
Recent publications related to this opportunity include:
- J. E. Kooi et al.: “Modern Faraday Rotation Studies to Probe the Solar Wind,” Frontiers in Astronomy and Space Sciences, 9, 841866 (2022)
- J. F. Helmboldt et al.: “The Deployable Low-band Ionosphere and Transient Experiment,” Radio Science, 56, e07298 (2021)
- J. E. Kooi et al.: “VLA Measurements of Faraday Rotation through a Coronal Mass Ejection Using Multiple Lines of Sight,” Solar Physics, 296, 11 (2021)
solar corona; solar wind; coronal mass ejection; coronal plasma density; coronal magnetic fields; radio astronomy; radio polarimetry; radio interferometry;