Spatiotemporal Variation and Characteristics of Gravity Waves in China Revealed by High-Resolution Radiosonde Network

Gravity waves play significant roles in various atmospheric processes, including turbulence in the boundary layer, convective processes in the troposphere, and energy momentum fluxes in the stratosphere. These waves are generated by a variety of factors such as mountains, jets, convections, shear instability, and their interactions. In China, gravity waves are strongly influenced by the complex topography, East Asian Monsoon, and corresponding convective processes. However, the characteristics and behaviors of gravity waves have only been analyzed at a few stations in China. In the present study, we analyzed high-resolution L-band radiosonde data from 120 stations, collected twice a day over eight years (2010-2017), to investigate the spatial and temporal variations of gravity wave parameters. We also explore the potential roles of interactions between low-level jets and orography in generating gravity waves.

The eastern edge of the Tibetan Plateau experiences a high occurrence rate of both tropospheric and lower-stratospheric gravity wave events, coinciding with frequent low-level jet activity. In the troposphere, the gravity wave events near terrain occur more frequently in winter than summer. Dominant vertical wavelength distributions show a relation with latitude. Lower-stratospheric vertical wavelengths decrease with latitude, while in the troposphere, the longest vertical wavelengths are observed in the North China Plain and Yangtze River Basin, with short wavelengths in South China.

The intrinsic frequency displays a similar latitudinal variation of increasing with latitude in both the troposphere and lower stratosphere, with higher values in the troposphere. Moreover, the lower-stratospheric intrinsic frequency is slight larger in winter than in summer. In the troposphere and lower stratosphere, the intrinsic frequency divided by the Coriolis parameter is close to 3~4 and 2~3, respectively, indicating the presence of inertial-gravity waves.

The lower-stratospheric gravity waves exhibit upward energy propagation in more than 80% of the events, whereas the tropospheric gravity waves tend to propagate equally upward and downward. Notably, the gravity wave events in the troposphere at the eastern edge of the Tibetan Plateau propagate energy upwards, while those in the eastern coastal areas propagate downwards. The vertical energy propagation is likely connected to convections and the interactions between low-level jets and the terrain. The horizontal propagation direction may vary with the background wind and display distinct patterns between tropospheric and lower-stratospheric gravity waves.