Oxygen Ion Escape From Venus Is Modulated by Ultra-Low Frequency Waves

Abstract

We study the solar wind-driven, nonthermal escape of O+ ions from Venus in a global hybrid simulation. In the model, a well-developed ion foreshock forms ahead of the Venusian quasi-parallel bow shock under nominal upstream conditions. Large-scale magnetosonic ultra-low frequency (ULF) waves at 20- to 30-s period are excited and convect downstream along the foreshock with the solar wind. We show that the foreshock ULF waves transmit through the bow shock in the downstream region and interact with the planetary ion acceleration, causing 25% peak-to-peak fluctuations in the O+ escape rate. These results demonstrate the importance of upstream plasma waves on the energization and escape of heavy ions from the planetary atmospheres.