A Novel Approach to Study the Vertical Distribution of Multi-Scale Equatorial Ionospheric Irregularities Using High-Rate e-POP GAP-O Measurements

It is well known that Equatorial Plasma Bubbles (EPBs) are responsible for scintillations in signals from Global Navigation Satellite Systems (GNSS) in the low latitude region. However, there is still insufficient knowledge of the vertical evolution of multi-scale equatorial irregularities that disturb radio communications. To fully understand this phenomenon, it is crucial to obtain a clear picture of the physical mechanisms that control EPBs and predict the occurrence of scintillations. The GPS Attitude, Positioning, and Profiling Experiment occultation receiver (GAP-O) on board the Enhanced Polar Outflow Probe (e-POP) is a dual-frequency receiver, mounted on the anti-ram side of the spacecraft, and normally pointing in the horizontal direction. It is primarily used for radio occultation measurements and can operate at sampling rates of 20, 50, and 100 Hz. E-POP flies in an elliptical orbit with a perigee of 320 km and an apogee of 1500 km. This, together with its high-rate measurements, make GAP-O capable of determining the altitudes at which scintillation-causing irregularities occur. In this study, while flying in low-latitude region and during post-sunset hours, we re-oriented e-POP for short periods to make the GAP-O receiver point in the zenith direction. In this novel experiment, we computed different ionospheric indices including phase scintillation index, σ_φ, and rate of change of total electron content (ROTI) using 50 and 100 Hz measurements, allowing us to examine vertical dependence of signal scintillation on ionospheric irregularities with different scale sizes in the equatorial region.