Neutral Atmosphere - Ionosphere Coupling at Equatorial Latitudes: Evidence from SpreadFEx and Guidance for Future Measurements

The Spread F Experiment (SpreadFEx) was performed in Brazil during two moon-down periods from September to November 2005. We employed extensive ground-based observations of gravity waves (GWs), plasma structures, electron densities, and mean atmospheric and ionospheric conditions using airglow, digisonde, VHF and meteor radar, balloon, and GPS instrumentation at multiple sites in Brazil, as well as satellite measurements of deep convection and plasma bubble structures. The intent of SpreadFEx was to assess the potential contributions of GWs to plasma instabilities and plasma bubbles extending to higher altitudes. Our measurements, analyses, and theory revealed significant GW activity arising from deep convection, apparent neutral density (and related wind and temperature) perturbations accompanying GWs having large spatial scales extending well into the thermosphere and ionosphere, plasma perturbations at the bottomside F layer suggestive of these GW influences, and anticipated tidal influences on GW propagation and plasma instability growth. While the SpreadFEx campaign helped to better quantify the role of neutral dynamics in plasma processes, it did not adequately address the role of neutral winds in the F layer. Hence, our future measurement efforts are anticipated to concentrate on definition of F-layer neutral winds, their tidal composition and longitudinal variability, and their correlations with plasma bubble statistics in support of the C/NOFS science mission.