The structure of the magnetic field in the outer galaxy from rotation measure observations through the disk

High-resolution 21 cm polarization data from the Canadian Galactic Plane Survey are yielding radio sources with well-defined rotation measures (RMs) at a solid angle density of roughly 1 source deg(-2), approximately 10 times greater than previous RM surveys in the plane of the Galaxy. The predominance of negative RMs in the second quadrant suggests, in contradiction to previous work, that there is no global magnetic field reversal between the solar circle and the Perseus arm. In addition, these data reveal details in the magnetoionic medium not previously observed and suggest that the random component of the magnetic field may be preferentially aligned to the uniform component, in contrast to the common assumption of an isotropic distribution.