Dipolar and non-dipolar dynamos in a thin shell geometry with implications for the magnetic field of Mercury

Dynamo action possibly working in the fluid core of Mercury is examined using numerical models in a thin spherical shell. Dipolar (DP) dynamos are obtained in the regime of columnar flows outside the tangent cylinder (TC), whereas non-dipolar (NDP) dynamos dominated by the multipole components are found in the regime of flows both inside and outside the TC. It turns out that columnar-like convective motions not only outside but also inside the TC are responsible for the NDP dynamo. The electrically conducting inner core enhances the strength of large-scale magnetic field, but predominance of the NDP components remains due to the thin shell geometry. These results suggest that Mercury may have more complicated magnetic field than has been considered.