MIDDLE ATMOSPHERE TIDES AND COUPLING BETWEEN ATMOSPHERIC REGIONS

Atmospheric tides are discussed from the perspective of how these waves serve to dynamically couple different regions of the atmosphere from the ground to about 150 km. Emphasis is placed on theoretical and modeling efforts which address new mechanisms, with a view towards providing some direction to future theory, modeling, experimental, and data analysis activities. A major area of recent and projected future research concerns the interactions between tides, gravity waves, and the mean zonal flow. Tidal wind oscillations between 70 and 100 km modulate the transmissivity of gravity waves to the thermosphere, as well as the deposition of momentum within this height regime due to gravity waves propagating upwards from tropospheric sources. These modulated momentum fluxes in turn feed back to modify the tidal winds as. well as the mean zonal flow; in addition, the tidal winds deposit net momentum and heat at the base of the thermosphere as they themselves undergo dissipation. Other promising areas of research include tide/tide and tide-planetary wave interactions, and the responses to transient tidal forcing. In addition, the mutual interactions between tidal dynamics and neutral and ionized constituent densities between 100 and 175 km can now be addressed by newly-developed thermosphere-ionosphere general circulation models which include self-consistent interactions between the neutral and ionized species. Future spectral modeling of middle atmosphere tides would also benefit from new calculations of mean monthy thermotidal heating profiles that take into account new empirical prescriptions of seasonal-latitudinal and longitudinal variations of H2O and O3 densities derived from measurements by satellite sensors.