March 31, 2017, 1:00 pm - 2:00 pm

March 31, 1:00 pm - 2:00 pm

A Brief History of Faraday Rotation Observations of Coronal Mass Ejections

Jason E Kooi (U.S. Naval Research Laboratory)

Coronal mass ejections (CMEs) are large-scale eruptions of plasma from the Sun and play an important role in space weather. Faraday rotation (FR) is the rotation of the plane of polarization that results when a linearly polarized signal passes through a magnetized plasma and is proportional to the path integral through the plasma of the electron density and the line-of-sight component of the magnetic field. The sources of these radio signals can be either natural (pulsars and extragalactic sources such as radio galaxies) or artificial (spacecraft). For decades, FR has been used to provide unique insights into the plasma structure of the Sun's corona at distances of 2 - 20 solar radii. Similarly, FR observations of radio sources occulted by CMEs have provided information on the plasma structure of a CME shortly after launch. I present a brief history of FR observations of CMEs, from the initial discovery of FR "transients" using Pioneer 6 to modern observations of CME FR using pulsars and radio galaxies. In particular, I report on recent white-light and radio observations made of three CMEs in August 2012. These sensitive Very Large Array full-polarization observations were made using a "constellation" of extragalactic radio sources through the solar corona at heliocentric distances that ranged from 6 - 15 solar radii. Two sources were occulted by a single CME and a third source was occulted by two CMEs. A constant-density force-free flux rope embedded in the background corona was used to model the effects of the CMEs and infer their plasma densities and axial magnetic field strengths.