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 attention is paid to whether the polarity of the dipole magnetic field, in the models, reverses its sign during time evolution. Here we present 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 oscillatory variation and hence the polarity is reversed rather periodically The latter results in a rather stationary state and the magnetic field tends to stay at one polarity state. These numerical results imply that the thermal interaction between the core and the mantle can control the frequency of reversal.