Equatorial electrojet 3-M irregularity dynamics during magnetic disturbances over Brazil: results from the new VHF radar at São Luı́s

Abstract

Data collected during the first two observational campaigns, conducted in August 1998 and December 1999, using the new coherent back-scatter radar, developed at INPE, that became operational at the magnetic equatorial site at São Luı́s, (2.33S,44.2W), Brazil, are analyzed in this paper. The spatial and temporal distribution of 3-m irregularity power in the form of range–time–intensity maps and spectral distribution in the form of spectrograms are analyzed for ‘quiet’ conditions and during geomagnetic storm disturbances. The analysis has brought out some new findings, besides confirming some of the already known storm response features of the EEJ and its plasma instabilities. Among the highlights of the results are: the electrical coupling between the equatorial and auroral electrojets is important even on a ‘quiet’ day, and gets very strong during magnetic storm disturbances; disturbance prompt penetration electric field, and the delayed electric field from disturbance dynamo, control the 3-m plasma wave development and inhibition in different degrees during the storm main phase and recovery phase; the amplitudes of the disturbance are larger during the morning hours than in the afternoon, in agreement with theoretical models; the height dependence of the relative dominance of the type-1 and type-2 waves generated by disturbance electric field is different from that of quiet conditions, the relative power of the type-2 getting enhanced at higher levels in the former case. A few other results are also discussed in this paper.