<P> In kinematic dynamo theory the velocity field is prescribed, instead of being a dynamic variable . This method cannot provide the time variable behavior of a fully nonlinear chaotic dynamo but is useful in studying how magnetic field strength varies with the flow structure and speed . </P> <P> Using Maxwell's equations simultaneously with the curl of Ohm's law, one can derive what is basically the linear eigenvalue equation for magnetic fields (B) which can be done when assuming that the magnetic field is independent from the velocity field . One arrives at a critical magnetic Reynolds number above which the flow strength is sufficient to amplify the imposed magnetic field, and below which it decays . </P> <P> The most functional feature of kinematic dynamo theory is that it can be used to test whether a velocity field is or is not capable of dynamo action . By applying a certain velocity field to a small magnetic field, it can be determined through observation whether the magnetic field tends to grow or not in reaction to the applied flow . If the magnetic field does grow, then the system is either capable of dynamo action or is a dynamo, but if the magnetic field does not grow, then it is simply referred to as non-dynamo . </P> <P> The membrane paradigm is a way of looking at black holes that allows for the material near their surfaces to be expressed in the language of dynamo theory . </P>

Earth's magnetic field is generated by the dynamo effect in the