ON THE TAILWARD EXPANSION OF CURRENT DISRUPTION DURING SUBSTORMS

Three possible models of the tailward expansion of current disruption during substorms are proposed. Two of the three are related to the tailward propagation of hydromagnetic waves; one is the rarefaction wave, and the other is an Alfven wave reflected at the ionosphere. The last model is based on the tailward expansion of a magnetic field configuration unstable to an instability which triggers current disruption. Each of the models is discussed, and is evaluated by comparing the expansion velocity expected from the model with that observed.