We investigate waves observed by the Cluster wideband instrument (WBD) during an orbital conjunction with the Polar spacecraft. During this perigee pass, Polar was at the upper extent of the auroral kilometric radiation (AKR) source region in the Southern Hemisphere nightside auroral region. Cluster was located at higher altitude above this region and observed AKR with clear signatures of ordered fine structure striations (rain). Using electron particle data observed by HYDRA on board Polar, we have modeled the electron distribution function within the AKR source region. This distribution function is unstable to a number of low-frequency wave modes and supports EMIC waves propagating along the magnetic field line. These waves appear to be feasible to stimulate the growth of AKR, producing the ordered fine structure observed by WBD on board Cluster, but further analysis will be important, especially plasma simulations.