Large-scale distortion of the dayside magnetopause under radial interplanetary magnetic field

The magnetopause is the key boundary that regulates solar-wind energy and plasma entry into Earth’s magnetosphere. While its responses under southward and northward interplanetary magnetic field (IMF) conditions have been extensively studied, whether a systematic, large-scale magnetopause reconfiguration can occur during radial IMF (IMF nearly aligned with the solar-wind flow) remains unclear. Here we investigate a prolonged (>30 min) radial-IMF interval using coordinated multi-point spacecraft measurements, Antarctic ground-based auroral observations, and a three-dimensional global hybrid simulation. We identify a previously unrecognized large-scale distortion of the dayside magnetopause, characterized by a sunward-protruding bulge coexisting with a cusp-to-cusp valley that extends from the Northern to Southern polar regions and reaches a depth of approximately one Earth radius. Observations indicate that magnetosheath high-speed jets can first produce localized magnetopause indentations and then trigger magnetic reconnection. The associated poleward moving auroral forms (PMAFs) provide independent ionospheric evidence for reconnection-driven flux transfer and dayside magnetosphere erosion. The global hybrid simulation further demonstrates that multiple jets can continuously impact the magnetopause and induce multi-site reconnection, allowing magnetosphere erosion to accumulate and thereby forming large-scale magnetopause valleys consistent with the observations. These results revise the conventional view that magnetosheath jets mainly cause short-lived, localized disturbances, and instead show that under sustained radial IMF they can drive large-scale magnetopause restructuring and enhance solar wind–magnetosphere–ionosphere coupling, with potential implications for space-weather processes