Radio Measurements of Coronal Magnetic Fields

The measurement of magnetic field strengths in the solar corona using radio observations is reviewed. This is a well established technique that exploits the fact that the electron gyrofrequency for typical coronal magnetic field strengths (100–2000 Gauss) lies in the radio frequency range. Opacity from the resulting gyroresonance emission from hot plasma above active regions allows the direct measurement of the field strength, while some information on the direction of the magnetic field can be obtained from polarization measurements. In addition to the gyroresonance technique which works for strong fields above active regions, other measurements, such as the polarization of bremsstrahlung, also can provide information on weaker quiet–Sun fields. This paper is intended as a text version of the presentation, and in particular citations are not intended to be complete.