Linear theory analysis and particle-in-cell simulations show that a spatial transverse gradient in the ion drift parallel to the magnetic field, ${\mathrm{dV}}_{\mathrm{di}}/dx\le {\Omega }_i$, where ${\Omega }_i$ is the ion cyclotron frequency, can generate a broadband multimode spectrum extending from $\omega \ll {\Omega }_i$ to $\omega \gg {\Omega }_i$. Nonlinearly, these waves lead to multiscale spatially coherent structures, substantial cross-field transport, ion energization, and phase-space diffusion. Large spikes are formed in the parallel electric field time series. These signatures are similar to the Fast Auroral Snapshot satellite observations in the upward current region.

• Received 28 June 2000

DOI:https://doi.org/10.1103/PhysRevLett.85.4285