Coherent backscatter radar imaging in Brazil: Large-scale waves in the bottomside F-region at the onset of equatorial spread F

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Abstract

<p><strong>Abstract.</strong> The 30 MHz coherent backscatter radar located at the equatorial observatory in São Luís, Brazil (2.59&amp;deg; S, 44.21&amp;deg; W, &amp;minus;2.35&amp;deg; dip lat) has been upgraded to perform coherent backscatter radar imaging. The wide field-of-view of this radar makes it well suited for radar imaging studies of ionospheric irregularities. Radar imaging observations were made in support to the spread <I>F</I> Experiment (SpreadFEx) campaign. This paper describes the system and imaging technique and presents results from a bottom-type layer that preceded fully-developed radar plumes on 25 October 2005. The radar imaging technique was able to resolve decakilometric structures within the bottom-type layer. These structures indicate the presence of large-scale waves (~35 km) in the bottomside F-region with phases that are alternately stable and unstable to wind-driven gradient drift instabilities. The observations suggest that these waves can also cause the initial perturbation necessary to initiate the Generalized Rayleigh-Taylor instability leading to spread <I>F</I>. The electrodynamic conditions and the scale length of the bottom-type layer structures suggest that the waves were generated by the collisional shear instability. These results indicate that monitoring bottom-type layers may provide helpful diagnostics for spread <I>F</I> forecasting.</p>

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Rodrigues, F. S., Hysell, D. L., & De Paula, E. R. (2008). Coherent backscatter radar imaging in Brazil: Large-scale waves in the bottomside F-region at the onset of equatorial spread F. Annales Geophysicae, 26(11), 3355–3364. https://doi.org/10.5194/angeo-26-3355-2008

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