The nature of the solar wind-magnetosphere-ionosphere (SW-M-I) coupling has been a subject of intense study and scientific interest. We report results from a numerical simulation of the SW-M-I system which shed light on the physics and behavior of the controlling processes. The current-voltage relationship is characteristic of a magnetohydrodynamic dynamo with a load operating near short circuit conditions. We discuss the operation of the dynamo, its location with respect to the magnetosphrere, and important implications of the results for both the earth and other planets with intrinsic magnetic fields. ¿ American Geophysical Union 1987