Spatial Distribution of Return Flows Occurrence in the Venusian Magnetotail and Its Dependence on Upstream Conditions

Abstract

Venus‐ward return flow can significantly influence ion escape from Venus and may therefore play an important role in atmospheric evolution. However, the mechanism driving return flow remains under debate. Here, we investigate the occurrence rate and spatial distribution of ion return flows in the Venusian induced magnetotail, and their dependence on solar extreme ultraviolet (EUV) irradiance and solar wind dynamic pressure, using 8.5 years of Venus Express observations. We find that EUV irradiance is the primary controlling factor for return flows of both H ⁺ and O ⁺ . Under high EUV conditions, the occurrence of closed magnetic topologies and O ⁺ return flow both increase, particularly in the downtail region. In contrast, H ⁺ return flow occurrence decreases significantly compared with low EUV conditions, corresponding to a decrease in open magnetic field topologies. Our results provide observational evidence for understanding the driving mechanism of return flow at unmagnetized planets.