This study investigates the concurrent evolution of subauroral storm-enhanced density (SED), the polar tongue of ionization (TOI), and the polar ionospheric hole (PIH) during the May 10, 2024 geomagnetic superstorm. Using global GNSS total electron content (TEC) and TIMED/GUVI thermospheric O/N2 ratio measurements, we focus on the interplay between ionized and neutral density structures at polar latitudes. Our observation exhibited the following scenario that highlights the new understanding of peculiar O/N2 influences on TOI and plasma patches during this storm. (1) With the arrival of the ICME shock and subsequent Interplanetary Magnetic Field (IMF) Bz southward turning, Prompt Penetration Electric Field (PPEF) drove Equatorial Ionization Anomaly (EIA) crests moving poleward, causing a midlatitude density enhancement. At midlatitude, the poleward Subauroral Polarization Stream (SAPS) provided significantly intensified sunward flow, while PPEF generated poleward flow, thus the two ion drift components led to the buildup of high electron density, forming the SED base and plume. (2) At noon, the SED plume was entrained into the anti-sunward flow channel toward the polar cap. (3) An unusual dayside PIH was formed as the neutral gas with a depleted O/N2 ratio began circulating in the morning sector toward afternoon. This presumed neutral circulation was primarily driven by the increased ion drag associated with significant storm-time auroral electric fields. (4) Fresh TOI plasma is moving into the polar cap and rotating eastward, with some portion continuing antisunward convecting. Successively following the TOI eastward convection, the PIH also rotates eastward. (5) PIH and TOI continued to be depleted, with TOI being segmented, as the entire polar cap was soaked by the substantially suppressed O/N2 air. The TOI and PIH remained eastward convicting for several hours, including a 2-hour interval of larger positive IMF By.
Tongue of ionization; storm-enhanced density; plasma patches; thermospheric composition (O/N$_2$); magnetosphere--ionosphere--thermosphere coupling; geomagnetic storms
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