Plasma bubbles detection in the African Equatorial Ionosphere

Abstract

Equatorial plasma bubbles (EPBs) are ionospheric plasma density field-aligned depletions that grow from irregularities caused by the generalized Rayleigh-Taylor instability mechanism in the post-sunset equatorial sector. The interest of studying EPBs is explained because plasma density depletions generate rapid changes in both amplitude and phase of the radio signals that go through the bubble producing ionospheric scintillations that degrade communications and navigation signals. We describe herein a methodology implemented to detect EPBs using slant total electron content (sTEC) by means of subtracting their trend against Universal Time from the original data. This procedure allows us to estimate EPBs size by measuring the amplitude variation in the resulting graphs. As a case of study, we present the results obtained by applying this method to the available calibrated data of sTEC from EGNOS Test Bed (BRAZ, DOUA, LOME, and NDJA) and IGS (ASC1, MALI, and NKLG) stations with the aim of detecting plasma bubbles in the African equatorial region during 2004. In order to characterize their seasonal dependence in each station, we analyse the temporal evolution of the number of detected bubbles per month in each station, and the monthly sTEC depletion size averages. In addition, we are able to locate each bubble both geographically and temporally by estimating the coordinates of its associated pierce point, as first approximation, and retrieving the local time of their occurrence.