Faraday rotation of linearly polarized radio waves from the Crab Nebula by the solar corona

Position angles of linearly polarized radio waves from the Crab Nebula (Tau A) were measured at wavelength lambda = 7.2 cm, in the middle of June 1971, at which time the source was occulted by the outer solar corona. The observed variation in the rotation measure suggests that there exist local structures in the magnetic field and electron density of the corona. The local structures have two typical scale lengths of the order of 0.1 and 1 R/sub sub solar /, respectively, at a distance of 5 to 10 R/sub sub solar / from the Sun. The field strength and electron density in the local structures are larger than the averaged values by a factor of 15 for the structures of scale length 0.1 R/ sup sub solar / and 4 for those of scale length 1 R/ sub solar /. Observed values of the electron density and scale length of the local structures are the same, in order of magnitude, as those for coronal streamers. The direction of the magnetic field reverses in the large scale local structure, which is identified with a radial extension of a helment streamer. (auth)