Exploring the influence of ionospheric O+ outflow on magnetospheric dynamics: The effect of outflow intensity

The ionospheric O+ outflow varies dramatically during geomagnetic activities, but the influence of its initial characteristics on the magnetospheric dynamics has not been well established. To expand a previous study on the impact of ionospheric heavy ions outflow originating from different source regions on the magnetotail dynamics and dayside reconnection rate, this study conducts two idealized numerical experiments with different O+ outflow densities to examine the consequent change in the magnetosphere system, especially on the solar wind‐magnetosphere coupling efficiency. Results indicate that a larger O+ outflow is capable of triggering the Kelvin‐Helmholtz instability (KHI) on the magnetopause flanks. The subsequent surface waves enhance the solar wind‐magnetosphere coupling efficiency by transmitting more solar wind energy into the magnetosphere‐ionosphere system, increasing the cross polar cap potential index. This index is initially reduced after the ionospheric mass loading owing to the direct depression in the dayside reconnection rate as commonly reported from earlier literature. The above KHI is generated under steady state solar wind conditions, suggesting that besides the commonly recognized cause, the elevated solar wind speed, ionospheric heavy ions outflow is another potential factor in disturbing the boundary by enhancing the mass density near the magnetopause and thus lowering the threshold for generating KHI. During storms, the increased ionospheric mass source causes an increased probability of KHI, which allows more solar wind plasma into the magnetosphere. This implies there is a possibility of even further nonlinear coupling between the magnetosphere and solar wind. Key Points The impact of different ionospheric O+ outflow density is investigated A large outflow could trigger Kelvin‐Helmholtz instability Increase SW‐M coupling efficiency despite reduced dayside reconnection rate