Equatorial Plasma Bubbles Observed at Dawn and After Sunrise Over South America During the 2015 St. Patrick's Day Storm

This paper presents an analysis of Equatorial Plasma Bubble (EPB) events that occurred during pre- and post-sunrise hours in the South America sector on 18 March 2015, when the St. Patrick's Day geomagnetic storm was in the recovery phase. The data from a set of multi-diagnostic instruments, including Global Navigation Satellite Systems (GNSS) receivers, L-band GNSS ionospheric scintillation monitors, ionosondes, and a Fabry-Perot interferometer, are analyzed. Strong L-band amplitude scintillation was observed with spread-F and total electron content (TEC) fluctuations at times when the electron density and tTEC were minimum with respect to their diurnal variations. The EPBs remained observed for about 3:30 hr after sunrise on the east coast of the South American continent. The daytime ionospheric irregularities show a longitudinal dependency between the west and east coasts, separated by about 3,600 km. Our analysis of the observations suggests that a Disturbance Dynamo Electric Field effect caused by storm-time wind perturbations might have triggered the Rayleigh-Taylor instability near local dawn on the east and west coasts of the South American continent. The effects of ambient ionosphere-thermosphere conditions on the evolution of irregularities are assessed to understand the longitudinal differences. The assessment includes the effect of the E region that appears in the morning hours and the effects of geomagnetic declination and tilting the solar-terminator.