Abstract
Abstract. We analyzed pre-midnight equatorial F region observations made by the 30 MHz coherent backscatter radar of São Luis, Brazil between August 2010 and February 2012. These measurements were processed, and used to create monthly maps of the echo occurrence as a function of local time and height. The maps show the inter-annual variability associated with equatorial spread F (ESF) occurrence in the Brazilian longitude sector. We also constructed monthly curves of the evening vertical drifts, for the Brazilian sector, using measurements by the ion velocity meter (IVM) onboard the C/NOFS satellite. The IVM evening drifts show a good overall agreement with the Scherliess and Fejer (1999) empirical model. Measured and model drifts show the development of the pre-reversal enhancement (PRE) of the vertical plasma drifts during ESF season. Using joint radar and satellite measurements, we found that evening (18:00–18:30 LT) mean non-negative drifts provide a necessary but not sufficient condition for the occurrence of topside ESF echoes. Evening downward (negative) drifts preceded the absence of topside ESF irregularities.
Highlights
Equatorial spread F (ESF) is the general name given to signatures of a broad spectrum of field-aligned electron density irregularities, which are commonly observed in the lowlatitude F region ionosphere after sunset hours (e.g. Fejer and Kelley, 1980).First, large scale-size ionospheric perturbations develop as a result of a primary plasma instability.secondary plasma instabilities drive the generation of smaller scale irregularities on the walls the primary, large-scale electron density perturbations (e.g. Saito et al, 1998; Hysell et al, 2009)
In particular, on combining observations of drifts made by satellite sensors over the Brazilian longitude sector (∼ 45◦ W) and the relation of these drifts to equatorial spread F (ESF) measured by a ground-based radar
We have analyzed observations of equatorial spread F (ESF) events and evening plasma drifts made in the Brazilian longitude sector (∼ 45◦ W)
Summary
Equatorial spread F (ESF) is the general name given to signatures of a broad spectrum of field-aligned electron density irregularities, which are commonly observed in the lowlatitude F region ionosphere after sunset hours (e.g. Fejer and Kelley, 1980). Large scale-size (tens of km) ionospheric perturbations develop as a result of a primary plasma instability. The occurrence of the large-scale size ESF irregularities are often attributed to the so-called Generalized RayleighTaylor (GRT) plasma instability. Theoretical and numerical analysis of the GRT instability indicate that the linear growth rate maximizes in the equatorial bottomside F region around sunset hours, which is in good agreement with ESF observations In particular, on combining observations of drifts made by satellite sensors over the Brazilian longitude sector (∼ 45◦ W) and the relation of these drifts to ESF measured by a ground-based radar Such a study is timely given the upcoming satellite missions (ICON and COSMIC-2) equipped with sensors capable of measuring ionospheric plasma drifts.
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