Storm‐Time Modulation of Ionospheric Midnight Collapses Over Arecibo: Role of Ion Drift Components and Thermospheric Tides

Using Arecibo incoherent scatter radar (ISR) observations from 1971 to 2019, we present a statistical analysis of 224 ionospheric midnight collapse events characterized by rapid decreases in the F‐region peak height near local midnight. Events are classified into geomagnetically disturbed and quiet periods. Both the first and second collapses occur more frequently during storms (97.2% and 22.2%) than during quiet conditions (92.2% and 15.5%). Although the overall distributions of onset time, duration, initial height, and magnitude are broadly similar, distinct storm‐time enhancements emerge. The first collapse initiates at higher altitudes and descends more rapidly during disturbed periods, while the second collapse exhibits stronger storm‐time amplification, with onset heights elevated by 15–50 km and magnitudes enhanced by up to ∼59 km. Decomposition of the ISR line‐of‐sight velocity shows that storm‐time modifications in both the field‐aligned () and perpendicular () ion drifts jointly regulate the vertical ion drift, producing the observed morphological differences between disturbed and quiet conditions. Specifically, storm‐time enhancements of the meridional wind () modulate , while electric‐field‐driven perturbations primarily affect . Tidal analysis further shows that geomagnetic activity amplifies major thermospheric tides, particularly the 12‐hr and 8‐hr components, and wind reconstructions highlight the central role of the 8‐hr tide in driving the storm‐time wind variability. Together, these results demonstrate that geomagnetic storms modify midnight collapse morphology through coupled electrodynamic forcing and tidal modulation of the neutral wind, which jointly control vertical ion transport over Arecibo.