Tidal Variability in the Lower Thermosphere: Relative Importance of ENSO, QBO, PJO, MJO, and Ly α

Atmospheric tides in the lower thermosphere play an important role in regulating upper‐atmospheric conditions relevant to space weather. However, their spatial and temporal variability remains poorly understood, apart from seasonal variations. Previous studies have shown that tides can be influenced by meteorological and solar conditions. This study clarifies the relative importance of the El Niño‐Southern Oscillation (ENSO), the Quasi‐Biennial Oscillation (QBO), the Northern and Southern Polar‐night Jet Oscillations (NPJO and SPJO), the Madden‐Julian Oscillation (MJO), and Lyman‐alpha (Ly) radiation to tidal variability in the lower thermosphere. Tides at 80–110 km are derived from hourly temperature and wind fields in the JAGUAR‐DAS Whole neutral Atmosphere Reanalysis (JAWARA) for the period September 2004–August 2025. Rotated empirical orthogonal function analysis is used to identify the dominant modes of de‐seasonalized tidal variability. The resulting principal component time series are used as daily indices of tidal activity and are compared with indices of ENSO, QBO, NPJO, SPJO, MJO, and Ly. Multiple linear regression analysis determines which tides exhibit statistically significant responses to these indices and quantifies their magnitudes. The most pronounced responses include those of the nonmigrating diurnal tide DE3 to ENSO (approximately 4 m in horizontal wind velocity), the migrating diurnal tide DW1 to QBO (∼10 m ), and the migrating semidiurnal tide SW2 to NPJO (∼12 m ) and SPJO (∼7 m ). Tidal responses to MJO and Ly are relatively weak and are therefore not identified with the same level of confidence.