Equatorial electrojet irregularities investigations using a [formula omitted] back-scatter radar and a digisonde at São Luı́s: some initial results

Abstract

A new 50 MHz coherent back-scatter radar has recently become operational at the Equatorial Space Observatory of INPE at São Luı́s (2.33°S, 44.2°W, dip: −0.5°), in Brazil, located close to the center of the equatorial electrojet. Preliminary results from a 12-day campaign in December 1999 involving this radar and a nearby digisonde are presented in this paper. The range–time–intensity (RTI) maps of electrojet irregularities show short-period ( ∼5 min or larger) fluctuations and significant day-to-day variability. A notable characteristic is the midday descent in the altitude of the RTI pattern observed on some days when the dominant Doppler spectra are of type-2. This feature is similar to the diurnal variation of the base height of the q-type sporadic-E-layer ( h′ E s− q ) simultaneously observed by the digisonde. Quasi-periodic fluctuations in the RTI and type-1 and type-2 spectral intensities seem to indicate electric field modulation from winds associated with typical gravity wave periods. Large surges in the westward irregularity drift velocity, presenting a higher velocity tail to the Doppler spectral distribution, is observed at sunset concurrent with the evening F-layer vertical uplift as observed by the digisonde. Some implications of these results on the E- and F-region electrodynamics are discussed.