Overview and Summary of the Spread F Experiment (SpreadFex)

We provide here an overview of, and a summary of results arising from, an extensive experimental campaign (the Spread F Experiment, or SpreadFEx) performed from September to November 2005, with primary measurements in Brazil. The motivation was to define the potential role of neutral atmosphere dynamics, specifically gravity wave motions propagating upward from the lower atmosphere, in seeding Rayleigh-Taylor instability (RTI) and plasma bubbles extending to higher altitudes. Campaign measurements focused on the Brazilian sector and included ground-based optical, radar, digisonde, and GPS measurements at a number of fixed and temporary sites. Related data on convection and plasma bubble structures were also collected by GOES 12, and the GUVI instrument aboard the TIMED satellite

The spread-F Experiment (SpreadFEx): Program overview and first results

We performed an extensive experimental campaign (the spread F Experiment, or SpreadFEx) from September to November 2005 to attempt to define the role of neutral atmosphere dynamics, specifically wave motions propagating upward from the lower atmosphere, in seeding equatorial spread F and plasma bubbles extending to higher altitudes. Campaign measurements focused on the Brazilian sector and included ground-based optical, radar, digisonde, and GPS measurements at a number of fixed and temporary sites. Related data on convection and plasma bubble structures were also collected by GOES 12 and the GUVI instrument aboard the TIMED satellite. Initial results of our analyses of SpreadFEx and related data indicate 1) extensive gravity wave (GW) activity apparently linked to deep convection predominantly to the west of our measurement sites, 2) the presence of small-scale GWactivity confined to lower altitudes, 3) larger-scaleGWactivity apparently penetrating to much higher altitudes suggested by electron density and TEC fluctuations in the E and F regions, 4) substantial GW amplitudes implied by digisonde electron densities, and 5) apparent direct links of these perturbations in the lower F region to spread F and plasma bubbles extending to much higher altitudes. Related efforts with correlative data are defining 6) the occurrence and locations of deep convection, 7) the spatial and temporal evolutions of plasma bubbles, the 8) 2D (height-resolved) structures of plasma bubbles, and 9) the expected propagation of GWs and tides from the lower atmosphere into the thermosphere and ionosphere

Convection: the likely source of the medium-scale gravity waves observed in the OH airglow layer near Brasilia, Brazil, during the SpreadFEx campaign

Six medium-scale gravity waves (GWs) with horizontal wavelengths of λH=60–160 km were detected on four nights by Taylor et al. (2009) in the OH airglow layer near Brasilia, at 15° S, 47° W, during the Spread F Experiment (SpreadFEx) in Brazil in 2005. We reverse and forward ray trace these GWs to the tropopause and into the thermosphere using a ray trace model which includes thermospheric dissipation. We identify the convective plumes, convective clusters, and convective regions which may have generated these GWs. We find that deep convection is the highly likely source of four of these GWs. We pinpoint the specific deep convective plumes which likely excited two of these GWs on the nights of 30 September and 1 October. On these nights, the source location/time uncertainties were small and deep convection was sporadic near the modeled source locations. We locate the regions containing deep convective plumes and clusters which likely excited the other two GWs. The last 2 GWs were probably also excited from deep convection; however, they must have been ducted ~500–700 km if so. Two of the GWs were likely downwards-propagating initially (after which they reflected upwards from the Earth\u27s surface), while one of the GWs was likely upwards-propagating initially from the convective plume/cluster. We also estimate the amplitudes and vertical scales of these waves at the tropopause, and compare their scales with those from a simple, linear convection model. Finally, we calculate each GW\u27s dissipation altitude, location, and amplitude. We find that the dissipation altitude depends sensitively on the winds at and above the OH layer. We also find that several of these GWs may have penetrated to high enough altitudes to potentially seed equatorial spread F (ESF) if located somewhat farther from the magnetic equator

Mesosphere-ionosphere coupling processes observed in the F-layer bottom-side oscillation

During the Spread FEx campaign, under the NASA Living with a star (ILWS) program which was carried out in the South American Magnetic Equatorial region from September to November 2005, we observed formation of the bottom-type spread F and simultaneous occurrence of mesospheric gravity wave events. The events were monitored by the ionosonde, coherent radar and airglow OI 630.0 nm and OH imager. It is found that the bottom-type scattering layer has a wave form generated most probably by local gravity waves. Reverse ray-tracing of the observed gravity waves indicate their possible sources in the troposphere or thermosphere. Forward ray-tracing indicates their penetration into the ionosphere. The present work summarizes the observational evidence and results of the data analysis and discusses the mesosphere–ionosphere coupling processes