Dynamo Process and the Magnetic Field of the Earth and Planets

Three-dimensional, fully nonlinear dynamo models were first presented in 1995 by two groups in Japan and USA. Since then, about ten groups have reported similar simulation results, and some important properties of the dynamos became known from these studies. Also in recent years, new observational results accumulated for the magnetic fields of planets (including satellites), and indicate very diverse dynamo and induction effects in these bodies. In this review, we first go through the method employed for the geodynamo simulations, and show how the magnetic field is generated and maintained by the convection system in the rotating spheres and spherical shells through a process similar to α-effect studied by kinematic models. We then review the observation of the planetary magnetic fields in the solar system, and investigate the conditions required for maintaining the dynamo process. Using these results, we examine the magnetic fields of the individual planets and consider how these fields are produced; by dynamo, induction, or remanent field.