Longitudinal and day-to-day variations of equatorial spread F occurrence from observations over south America

Abstract

In this work we studied the longitudinal and day-to-day variability of equatorial spread F occurrence over South America. Digisonde from the equatorial stations of São Luís and Jicamarca, and Total Electron Content (TEC) data from several GPS receivers were used to analyse the ionospheric conditions conductive to ionospheric plasma irregularity generation during the solar minimum months of September 2009 to January 2010. To support this analysis an Automatic-Bubble- Detection-Algorithm was used to detect abrupt decreases that plasma bubbles introduce in the TEC values. The bubble occurrence pattern over SA observed in this work maximizes on September-October (equinox) in the west and November-January (December solstice) in the east-longitudes. However, on a day-to-day basis bubble signatures are also detected all over SA during this period. Besides being observed during days with pronounced prereversal enhancement (PRE), as expected, the TEC depletions were also observed during days without PRE, during equinox at Jicamarca and December solstice at São Luís. This unexpected occurrence of TEC depletions (TECds) suggests that seeding mechanisms, like periodic structures are present and modify the onset conditions of bubble-events. In this report are shown evidences of wave-like structures previous to bubble development.