Variability in Zonal Drift Velocity of Equatorial Plasma Bubbles: A Review

Abstract

The Equatorial Plasma Bubble is a phenomenon occurring in the F-layer of Earth's ionosphere that can disrupt communication and navigation systems. One key aspect of Equatorial Plasma Bubble under active investigation is its zonal drift velocity, which offers an in-depth understanding of plasma behaviour and the natural dynamics of the F-region ionosphere. Previous studies have examined the variations of zonal drift velocity using various tools, including all-sky imagers and radar equipment. This paper aims to review the fundamental theoretical aspects of zonal drift velocity variability across various techniques. It compares zonal drift velocity dependencies based on the aspects considered, highlighting differences in techniques and approaches used in previous studies. Special emphasis is placed on the observation of zonal drift velocity using high-density Global Positioning System network, as this method has consistently demonstrated high performance compared to earlier techniques. Despite decades of investigation, reported EPB zonal drift velocity (V_E) values vary widely across studies which ranging from as low as 0 m/s to over 210 m/s — owing to differences in instrumentation, geographic coverage, and solar activity conditions. A critical gap remains in the systematic cross-comparison of these methods and their accuracy in capturing the full spatiotemporal variability of V_E, particularly in the Southeast Asia sector. This review addresses that gap by synthesising findings from over two decades of V_E studies, identifying consistent seasonal, local time, and solar activity trends, and evaluating the relative performance of each observational approach. The reviewed literature consistently shows that V_E peaks during equinox seasons and high solar activity and decreases from evening (~150–170 m/s) to post-midnight (~20–50 m/s). GPS-based methods using dense receiver networks emerge as the most comprehensive approach, enabling long-term and spatially resolved V_E monitoring.