REVERSING THE AXISYMMETRICAL (M = 0) MAGNETIC-FIELDS IN THE MILKY-WAY

Observations show that the large-scale magnetic field of the Milky Way can be matched to the Azimuthal (m = O), radial (n = 0 1, 2), and vertical (p = O) modes of the turbulent dynamo theory. In particular, the Milky Way has an axisymmetric component of its large-scale magnetic field (dynamo's azimuthal mode m = O). As viewed from the top of the Galaxy (at b = + 90-degrees), the magnetic field lines are going clockwise near the Sun (r = 8 kpc), near the Perseus arm (r = 10 kpc), and near the Scutum arm (r = 5.5 kpc), but they are going counterclockwise near the Sagittarius arm (r = 6.5 kpc). Here an application is made of the turbulent dynamo theory to explain the radial dependence of the azimuthal magnetic field. The observed radial potential of the Milky Way allows the dynamo theory to predict two magnetic field reversals within the solar circle but no field reversal beyond the solar circle up to 15 kpc (dynamo's radial mode n = O, 1, 2). In particular, this matching of theory with observations of the Scutum arm allows a firm prediction of a clockwise direction of the magnetic field in the "Perseus + I" (r = 12 kpc). The theory and the observations are in agreement that the directions of the magnetic field lines above and below the Galactic plane are the same (dynamo's z-mode p = O).