This paper deals with the description of a mechanism that could cause the generation of large-amplitude temporal oscillations in the structure of the electron acceleration region of an auroral arc. The fluctuations are triggered by the fact that a self-consistent steady state can disrupt as the mobile plasma electrons rearrange themselves into a more 'stable' configuration on a time scale characterized by the electron transit time across the acceleration region. During this rearrangement the ions remain essentially frozen. A cyclic behavior results, since the ions eventually respond, thus driving the system back toward its original steady state. The period of these oscillations is approximately the ion transit time. We obtain a description of those characteristics of the steady state necessary for the generation of fluctuations. As a specific example, we consider the recent one-dimensional auroral double layer model of Kan and Lee showing that it exhibits a negative dynamic resistance. This property is necessary for the production of periodic (~10 Hz) modulations in the precipitating electron flux. This result suggest explanations for two kinds of events observed to be correlated with auroral arcs. These are the quasi-periodic flickering aurora and the existence of low-frequency modulations in the envelope of electrostatic hydrogen cyclotron waves.