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

Abstract

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 GW activity confined to lower altitudes, 3) larger-scale GW activity 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.

Coherent backscatter radar imaging in Brazil: large-scale waves in the bottomside F-region at the onset of equatorial spread <I>F</I>

“…However, a reduced number of observations could be used for the generation of in-beam radar images due to a technical problem with one of the receiver channels. Primary attention has been given to observations made during the period of 24-27 October 2005, when good sky conditions for airglow measurements were found and preliminary results from a number of different observation instruments indicated the occurence of spread F (Fritts et al, 2008). This paper focuses on the night of 25 October 2005 when a strong bottom-type layer was detected and radar images could be generated.…”

Simultaneous observation of ionospheric plasma bubbles and mesospheric gravity waves during the SpreadFEx Campaign

“…However, very little work has reported direct evidence on the bubble seeding by specific dynamical event in the lower atmosphere (Fritts et al, 2008a;Abdu et al, 2009). The purpose of the present work is, therefore, to investigate direct evidence of the plasma bubble formation and mesospheric gravity wave activities.…”

First observation of an undular mesospheric bore in a Doppler duct

“…The main objective of the campaign was the observation and modeling of gravity waves potentially capable of seeding plasma instabilities in the equatorial ionosphere (Fritts et al, 2009). During the campaign, several kinds of mesospheric front events were observed at São João do Cariri (7.4 • S, 36.5 propagation conditions.…”