Lower hybrid solitary structures (LHSS) are observed to be composed of wave modes rotating in the right-handed sense about the geomagnetic field. The data analyzed were measured at altitudes near 800 km in the auroral ionosphere by the plasma wave interferometer aboard the AMICIST rocket. Clear evidence of these modes is obtained by an estimation of the local frequency-wavenumber spectrum derived from wavelet analysis of the electric field. This evidence demonstrates that the phase velocity direction reverses as the payload traverses the structure, implying that the structure is composed of rotating electric fields. These observations are consistent with the result of three-dimensional numerical simulations investigating lower hybrid wave behavior in the presence of a density cavity. This suggests that the observed characteristics of LHSS may be explained by the excitation of localized lower hybrid eigenmodes and the scattering of background VLH hiss from plasma density depletions.¿ 1997 American Geophysical Union