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The total and polarized radio continuum emission of IC 342 was observed infour wavelength bands with the Effelsberg and VLA telescopes. The frequencydependence of the radial scalelength of synchrotron emission indicatesenergy-dependent propagation of the cosmic-ray electrons, probably via thestreaming instability. The equipartition strength of the total magnetic fieldis typically 15 muG, that of the ordered field 5 muG. Faraday rotation of thepolarization angles reveals an underlying regular field of only about 0.5 muGstrength with a large-scale axisymmetric spiral pattern, signature of amean-field dynamo, and an about 10x stronger field that fluctuates on scales ofa few 100 pc. The magnetic field around the bar in the central region of IC 342resembles that of large barred galaxies; its regular spiral field is directedoutwards, opposite to that in the disk. The polarized emission in the disk isconcentrated in: (1) a narrow arm of about 300 pc width, displaced inwards withrespect to the eastern arm by about 200 pc, indicating magnetic fieldscompressed by a density wave; (2) a broad arm of 300-500 pc width around thenorthern arm with systematic variations in polarized emission, polarizationangles, and Faraday rotation measures on a scale of about 2 kpc, indicative ofa helically twisted flux tube generated by the Parker instability; (3) arudimentary "magnetic arm" in an interarm region in the north-west; (4) severalbroad spiral arms in the outer galaxy, related to spiral arms in the totalneutral gas; (5) short features in the outer south-western galaxy, probablydistorted by tidal interaction. - The generation and development of "magneticarms" by a mean-field dynamo probably need a spiral pattern that is stable overa few galactic rotation periods. The dynamo in IC 342 is slow and weak,probably disturbed by the bar, tidal interaction, or a transient spiralpattern.

Magnetic fields in the nearby spiral galaxy IC 342: A multi-frequency radio polarization study