EFFECTS OF AN INHOMOGENEOUS TEMPERATURE DISTRIBUTION AT THE CMB ON POLARITY REVERSALS OF THE EARTHS MAGNETIC-FIELD

Time evolution of the magnetic field is examined numerically for some models of thermally driven MHD dynamo in a spherical shell. Special at tention is paid to whether the polarity of the dipole magnetic field, in the models, reverses its sign during time evolution. Here we presen t the results for two typical models. In one model, the temperature is held constant at both boundaries of a spherical shell, whereas in the other, the distribution of temperature is represented by the degree 2 and order 2 constituent of spherical harmonics. The former shows an o scillatory variation and hence the polarity is reversed rather periodi cally The latter results in a rather stationary state and the magnetic field tends to stay at one polarity state. These numerical results im ply that the thermal interaction between the core and the mantle can c ontrol the frequency of reversal.