The Geotail plasma wave instrument has found the auroral myriametric radiation (AMR). Its frequency range is about 1--30 kHz similar to the trapped continuum radiation, and its occurrence shows a good correlation with auroral kilometric radiation (AKR). This suggests the source location of AMR is similar to that of AKR. Ray tracing is performed for L-O mode waves radiated just above the local plasma frequency in the auroral plasma cavity. The waves are guided in the cavity, propagate far from the Earth, and are observed as AMR. In the source region these guided waves are observed by the DE 1 satellite and reported as the trapped L-O mode waves within the cavity. A limitation on initial conditions of wave normal angles for the ray tracing derived from a comparison with these observations suggests that its generation mechanism is similar to that of the nonthermal continuum. It is, however, generated in the auroral plasma cavity and it is not mode-converted from the upper hybrid mode waves. The ray tracing results are consistent with AMR observations by Geotail. ¿ 1998 American Geophysical Union