PLANETARY-WAVES IN THE THERMOSPHERE-IONOSPHERE SYSTEM

In the limit of an isothermal atmosphere without dissipation, the equa tions governing atmospheric motions admit solutions corresponding to ' 'free'' (unforced) oscillations for discrete zonal wavenumbers and per iods. Global oscillations belonging to the rotational subclass are ref erred to as free Rossby waves or Rossby normal modes. Despite the exis tence of mean winds, nonisothermality, and dissipation, atmospheric ma nifestations of these waves apparently exist. To date the study of suc h oscillations has been confined mainly to the troposphere and stratos phere (0-50 km), which includes the source region for the disturbances . However, there is increasing evidence that the effects of free Rossb y waves extend into the mesosphere/lower thermosphere (ca. 80-150 km) and ionosphere (ca. 90-400 km). The present work draws upon recent num erical modeling results and data analyses as a framework for discussin g the penetration of planetary wave effects into the upper regions of the atmosphere, especially the ionospheric dynamo region (ca. 100-170 km) and the electrodynamic interactions which ensue there. Attention i s primarily focused on the westward propagating normal modes of wavenu mber s = 1 (periods of 5, 10 and 16 days), and the so-called ''2-day w ave'' which is normally associated with the mixed Rossby-gravity mode with s = 3.