Abstract : The objectives of this grant are to delineate and to better understand oscillations in ionospheric structure which occur at planetary-wave periods (i.e., 2-10 days). Effort has concentrated on analyses of about 30 years' of archived ionosonde data from a global array of stations, and some satellite-based measurements of total electron content. The study has produced statistics concerning amplitude variability, season dependence and longitudinal structure pertaining to the quasi two days oscillation. The P.I. has also formulated some theories concerning the physical origin of the quasi two days ionospheric oscillation.