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[SIT21-29] Dependence of the dipole component dominancy on the Rayleigh number and inner core size in geodynamo simulations
Keywords:Geodynamo, Inner core size, Rayleigh number, Dipole component dominancy
In ri/ro = 0.25 and 0.35 cases, fdip is approximately 0.8 at Ra/Racrit ≒ 2.0 and gradually decreases to approximately 0.45 with increase of Ra/Racrit up to around 6.0, where Racrit is the critical Rayleigh number. By referring to the obtained fitting curve, we find that the magnetic energy for the dipole component is more than 5 times larger than the extrapolated value for l = 1 at Ra/Racrit ≒ 2.0 and decreases with increase of Ra/Racrit in both aspect ratios. The dependency of the dipole component dominancy on the Rayleigh number is similar in both aspect ratio cases. However, in the ri/ro = 0.15 case, fdip is approximately 0.4 at Ra/Racrit ≒ 8.0 and decreases to approximately 0.1 with increase of Ra/Racrit up to around 15.6. At Ra/Racrit = 8.1 and 9.0, the amplitude of the dipole component is comparable to extrapolated value from the fitting curves. At Ra/Racrit > 10.1, the magnetic energy for l = 1 component is smaller than that for the l = 2 component. Consequently, the magnetic field obtained in the simulation results is non-dipolar. To summarize above, we categorize the present dynamo simulations as shown in Figure 1. Here we define strong/weak dipolar dynamo by a condition that the magnetic energy is larger/smaller than the kinetic energy. The axial dipolar component becomes small in all three ratio cases for larger Rayleigh numbers. Non-dipolar components become larger for the smaller inner core. In other words, for ri/ro < 0.35, it is likely that the dipolar magnetic field is dominant for larger inner core.