THE DISK-DYNAMO MODEL FOR NATURAL DYNAMOS

We analyze the kinematic and the dynamic self-excited disk dynamo mode ls for natural dynamos. In the kinematic model (given disk angular vel ocity), the magnetic field can either increase or decrease exponential ly with time, or it can be constant if the angular velocity has a spec ific value that is a function of the geometry and of the resistance of the circuit. With the dynamic disk dynamo (given mechanical power inp ut), there are both transient and steady-state solutions, and the stea dy-state magnetic flux density is proportional to the square root of t he power input. The polarity of the induced magnetic held in either dy namo is the same as the seed field, and erratic polarity reversals can be expected if the power input is erratic.