This project investigates tidal coupling between the neutral lower atmosphere and the ionosphere at equatorial and near-polar latitudes. The recent discovery that tropospheric tides have a strong effect on the structure of the equatorial ionosphere at altitudes extending up through the F-region motivates this work, and was the basis for the targeted approach to addressing the effects of tidal coupling on the ionosphere that will be undertaken. Analysis of recent ultraviolet (UV) nightglow observations from the TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) and IMAGE (Imager for Magnetosphere-to-Aurora Global Exploration) satellites demonstrated that there is a correlation between zonal structures seen in the nighttime ionosphere with the atmospheric tides. The coupling mechanism was interaction of tides in the neutral atmosphere with the E-region dynamo, which couples the zonal structure via plasma uplift through F-region altitudes. This project will use a combination of experimental data and simulations to investigate the global nature of tidal effects on the ionosphere, from their apparent origins through the thermosphere. The Constellation Observing System for Meteorology, Ionosphere and Climate and Taiwan's Formosa Satellite Mission #3 (COSMIC/FORMOSAT-3) mission provides over 1500 GPS (Global Positioning System's) radio occultation profiles of electron density from 100 to 450 km altitude every day, as well as profiles of temperature, pressure, and refractivity from near the surface to 60 km altitude with substantial geographic and temporal resolution. The profiles have tight accuracies such that the tidal structures that affect the ionosphere should be clearly evident at ionospheric altitudes; in addition, tidal features consistent with tropospheric forcing may also be detectable in the stratosphere and troposphere. The GPS radio occultation profiles, of electron density, temperature, pressure, and refractivity, are a good resource for comparison with ionospheric and tidal studies using incoherent scatter radar (ISR) measurements of electron density, ion drift velocities and temperatures, and derived neutral winds. ISR measurements from Poker Flat, Millstone Hill, and Jicamarca will be used to allow examination of tidal effects at equatorial, mid, and high northern latitudes with high temporal and local spatial coverage. The observations of tidal structure with altitude, latitude, and season will be compared with simulations from the TIME-GCM/GSWM (Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model/Global Scale Wave Model).
