Post‐Midnight Enhancement in OI 630.0 nm Airglow Emission and Plausible Link to Wave Dynamics

Abstract We observed a significant enhancement in 630.0 nm airglow intensity near midnight on 15–17 April, 2023, with maximum on 17 April at Devasthal (29.4°N, 79.7°E; Mlat ∼20.7°N). Simultaneous airglow measurements from Silchar (24.68°N, 92.76°E; Mlat ∼15.5°N) corroborated these observations on 15 and 16 April, thereby confirming the latitudinal and longitudinal extent of the phenomenon and suggesting its association with a well‐known large‐scale geophysical process, the midnight temperature maximum (MTM). The moderate enhancements occurred on 15–16 April, but 17 April showed a much stronger peak. Higher GPS‐TEC levels contributed to increased post‐sunset airglow intensity on these days, but TEC alone could not explain the midnight peak variations in the OI 630.0 nm intensity. Ionosonde data from a longitude chain (from dip latitude to the airglow observation locations) showed a descending F‐layer (h′F and hmF2), with a stronger descent on 17 April, suggesting a role for ionospheric midnight descent in the airglow enhancement. The ionosonde‐derived F‐region winds showed a notable poleward flow on 17 April. Power spectral density (PSD) analysis revealed common wave periodicities (∼5–6 hr) in both the F‐region winds and the mesosphere–lower thermosphere (MLT) regions. Furthermore, the wind associated with MLT region waves was observed to be in phase with the F‐region wind during the strongest midnight peak on 17 April. Therefore, atmospheric waves are believed to have played a crucial role in the post‐midnight descent of the ionosphere through wind reversal, amplifying the airglow peak on 17 April.