On the Short-Range Longitudinal Variation of Pre-Reversal Enhancement of Vertical Plasma Drift and Associated Implications

Abstract

Pre-reversal enhancement of vertical plasma drift (PRE) is a unique feature of the equatorial ionosphere and plays an important role in defining the state and stability of the evening ionosphere. In this paper, we investigate short-range longitudinal variations of PRE and its consequence on the longitudinal configuration of the equatorial bottomside F layer and the equatorial plasma bubble (EPB) phenomenon. We use simultaneous observations made using three longitudinally separated ionosondes located close to the magnetic equator and spread over a longitude zone of 24° in the Asian sector to study longitudinal variations in the vertical plasma drift, V_z and the height of the F layer base. The peak V_z as well as the temporal pattern of V_z show large longitudinal variations and the maximum difference in the peak V_z between two stations is found to be in the range of 29–49 m s⁻¹, which is remarkable. The large longitudinal difference in V_z is attributed to localized polarization process, which acts additively to the large-scale PRE process. The longitudinal variation in V_z could result in both positive and negative tilt of the F layer base, which is shown to have a considerable role on the growth of the Rayleigh-Taylor instability for the formation of EPB. The plausible origins of longitudinal variation in PRE and its consequences are discussed.