The Structure and Magnetic Field of the Solar Corona

Abstract

Observations of the radio star Taurus-A when it passed close to the Sun in June 1958 have shown that the scattering of radio waves in the solar corona is highly anisotropic and this is interpreted in terms of irregularities aligned in the general magnetic field of the Sun. The direction of the field can thus be investigated, and has been found to be approximately radial between 10 and 30 solar radii. The scattering irregularities can be regarded as an extension of the fine structure seen on eclipse photographs. The anisotropic scattering also provides a possible explanation of the observed variations of integrated intensity from the radio star at closest approach. It is suggested that the corona at maximum phase is expanding and that the observed radial field is the result of localized fields from the surface being carried out in the corona by the expanding gas The typical polar field at sunspot minimum could then be caused by a consistent N–S asymmetry in the localized fields during the preceding maximum phase. When the extreme minimum corona of the 1954 eclipse is treated as a magneto-hydrostatically stable configuration, the surface field strength at the poles can be calculated. The result, 1.5 gauss, agrees well with the photospheric measurements by Babcock.