Evening time multi-instrumental verification of ionospheric irregularity in East Africa, Ethiopia

Abstract

This study verifies ionospheric irregularity and its associated scintillation using five independent observations during June solstice and September equinox, 2014 over the understudied and data scarce East African longitude sector. Simultaneous measurements of ionospheric irregularity through Communication and Navigation Outage Forcasting System (C/NOFS), Scintillation Networks and Decision Aid (SCINDA) GPS receivers, Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), GNSS GPS, VHF dedicated beacon receivers as well as ionosonde were carried out in the region. C/NOFS has detected prereversal enhancement (PRE, the most accepted trigger of equatorial spread F (ESF)) at ~19:00 LT during September equinox and at ~20:00 LT for June solstice. The PRE detection during June is further confirmed by the ionosonde derived uplift movement of hmF2 over the region. Rate of change of TEC index (ROTI) is also found to be capable of capturing the evening time ionospheric irregularities in a way consistent to the dedicated scintillation measuring instruments regardless of the spatial difference between the two GNSS GPS sites in East Africa. Overall, throughout the in situ and ground-based ionospheric irregularity measurements, extreme scintillation starts to occur at around 19:00 LT and continued until midnight. Besides, the power spectral density (PSD) was computed using the Fast Fourier Transform (FFT) algorithm for S4 data measured while receiving L-band and VHF signals as well as while measuring C/NOFS ion density. Upon the captured strength of ionospheric irregularity, the noisy portion of frequency on PSD is wider in VHF and C/NOFS driven irregularity index than the corresponding L-band irregularity observation. Most importantly the calculated slope (m) and the strength of irregularity (β) using the power spectral law has enabled us to produce a model which better fits the observed spectrum. It was also found that the PSD theoretical modeling better matches for L-band than VHF and Ni spectral observation.