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

Author(s)

Rodrigues, F. S. ^[1] ; Hysell, D. L. ^[1] ; de Paula, E. R. ^[2]

Affiliation

^[1] Cornell Univ, Ithaca, NY 14853 - USA

^[2] INPE, Sao Jose Dos Campos, SP - Brazil

• Document type: Journal article
• Source: Annales Geophysicae; v. 26, n. 11, p. 3355-3364, 2008.
• Web of Science Citations: 22

Abstract

The 30 MHz coherent backscatter radar located at the equatorial observatory in Sao Luis, Brazil (2.59 degrees S, 44.21 degrees W, -2.35 degrees 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 F 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 (similar to 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 F. 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 F forecasting. (AU)