Exact mechanism of the Venusian topside ionospheric bulge

Identify the physical mechanism responsible for the formation of the topside bulge observed above the V2 layer in the dayside Venusian ionosphere at altitudes of approximately 160–200 km, determining what process(es) generate this persistent electron density enhancement.

Background

The paper analyzes 234 Venus Express VeRa dayside electron density profiles and systematically characterizes a recurrent topside bulge above the V2 peak, including its morphology (Types 1–3), altitude, and density. The bulge is detected in over 80% of profiles, with occurrence patterns suggesting external drivers such as solar wind interaction.

Despite multiple hypothesized origins—solar wind-induced magnetization and downward diffusion, photochemical variations (e.g., electron temperature increases), and energetic particle precipitation—the authors state that a definitive physical mechanism for the bulge remains unknown.