A nonlinear model for the short-scale auroral density cavity (SSADC) is presented. Specifically, it is shown that the SSADC is associated with nonlinear short wavelength (in comparison with the collisionless electron skin depth) dispersive convective cells (DCCs) whose frequencies are much smaller than the ion gyrofrequency. In a stationary frame, the relevant equations governing the dynamics of the nonlinear DCCs are put in the form of an energy integral with an effective potential. The latter is analyzed to demonstrate the existence of density cavities (or holes). Larger amplitude cavities are necessarily quasi-stationary. The present theoretical model is capable of describing the salient features of SSADCs that are seen in data from the Freja satellite. ¿ 2000 American Geophysical Union