Annual/Quasi‐Biennial Variability of Inertial Gravity Waves in the Tropical Western Pacific

Abstract Gravity wave activity is strongly influenced by the background flow. This study analyzes 12 years (2012–2023) of radiosonde data from five sites in the tropical western Pacific to examine the characteristics of inertial gravity wave (IGW) parameters and their interaction with the background flow. In the troposphere, IGWs exhibit larger vertical wavelengths and intrinsic frequencies compared to those in the stratosphere. Horizontal phase speeds in the troposphere are primarily between ±10 m/s with over half of IGWs propagating downward. In the stratosphere, horizontal phase speeds extend to ±20 m/s with most IGWs propagating upward. The troposphere shows a distinct annual cycle in mean meridional momentum flux and energy, peaking in winter and reaching a minimum in monsoon. Conversely, in the stratosphere, mean kinetic energy and zonal momentum flux of IGWs follow a quasi‐biennial cycle. This pattern is attributed to the distribution of IGW horizontal phase speeds and the Quasi‐Biennial Oscillation (QBO). Additionally, the slopes of temperature and horizontal wind spectra in the troposphere exhibit an annual cycle with minima (saturation) in winter and maxima (unsaturation) in the monsoon. In the stratosphere, temperature spectral slopes continue to show an annual cycle at altitudes between 18 and 24 km. However, at 24–30 km, horizontal wind spectral slopes fluctuate significantly, reflecting a quasi‐biennial cycle. By identifying these patterns, our study contributes to a better understanding of the interactions between gravity waves and the background wind field, which is essential for improving gravity wave parameterization in numerical models.