Imprint of the Quasi‐Biennial Oscillation on the Ionosphere and Thermosphere

Abstract The Quasi‐Biennial Oscillation (QBO) is a dominant mode of stratospheric variability and is known to modulate the variability of the ionosphere‐thermosphere (IT) system. However, the extent of its influence on the ionosphere‐thermosphere system remains uncertain due to weak signals and confounding with similar periodicities in solar flux. In this study, we investigated QBO signatures in ionosonde derived peak electron density (NmF2), GNSS total electron content (TEC), and thermospheric composition ( O / N 2 ) from the Global Ultraviolet Imager on NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. Local empirical models are used to isolate the stratospheric QBO signature in NmF2 and TEC. Multi‐channel singular spectrum analysis is used to reveal seasonal modulation of the O/N 2 response to QBO. We found that the amplitude of non‐solar origin QBO in NmF2, TEC, and O/N 2 reaches up to 4% and exhibits an out‐of‐phase relation with stratospheric QBO phase at 30 hPa (QBO30). The TEC QBO signal shows strong regional variability, peaking over Europe. The O/N 2 QBO signal shows clear seasonality with maximum correlation with QBO30 around the equinoxes. The NmF2 response to stratospheric QBO is enhanced at most stations during the September equinox. The QBO signal in O / N 2 at different latitudes shows maximum correlation with the stratospheric QBO at different pressure levels. Overall, the global reduction in NmF2, TEC, and O / N 2 during the eastward QBO phase, along with their seasonal structure, is consistent with enhanced mixing driven by migrating diurnal tide. However, the regional structure in the TEC response implies additional mechanisms with varying spatial influence and vertical extent.