Magnetosphere–Ionosphere Coupling Driven by Solar Wind Density Pulse Under Northward IMF B _<i>z</i> : Role of IMF B _<i>y</i>

Abstract Perturbations in the solar wind caused by space weather drivers can have a significant impact on the magnetosphere and subsequently on the ionosphere, producing global geomagnetic effects. Understanding and characterizing these responses requires a detailed study of magnetosphere–ionosphere (MI) coupling under varying space weather forcing conditions. In this study, we present global 3D magnetohydrodynamic (MHD) simulations with a two‐way coupled MI coupling module to study the impact of a solar wind density pulse on the spatial and temporal profiles of ionospheric field‐aligned currents (FACs) under northward interplanetary magnetic field (IMF) conditions. The pulse compresses and relaxes the magnetosphere, generating Alfvénic disturbances that manifest as alternating polarity FACs on the ionosphere. We find that the MI response is also significantly modulated by the IMF clock angle. For small, non‐zero IMF nT, FAC profiles show the largest enhancement and enable prompt penetration electric fields (PPEF). The IMF case shows weaker, symmetric enhancements, while a higher IMF nT creates a dominant convection cell that suppresses oscillatory currents, yielding diffuse and delayed responses. FACs intensify rapidly within min after impact, consistent with Alfvén wave travel time from magnetosphere to ionosphere. We compare our model results with relevant observations from AMPERE, which exhibit similar responses under comparable solar wind forcing. This demonstrates that, even under northward IMF conditions, compressive solar wind forcing can induce substantial ionospheric disturbances, with the IMF component modulating the nature of this response.