Convective Gravity Waves in the Stratosphere and the Mesosphere: A Case Study of Airglow Over West Africa Using the Weather Research and Forecasting Model

• Published in: Journal of geophysical research. Atmospheres 2024-12, Vol.129 (23), p.n/a
• Main Authors: Chou, Yen‐Liang, Wang, Pao K.
• Format: Article
• Language: English
• Subjects: Airglow; Altitude; Altitude effects; deep convective storms; Dispersion; Filtration; Forecasting models; Gravity waves; Image acquisition; Lower mantle; Lower thermosphere; Mesopause; Mesosphere; Numerical weather forecasting; Pattern analysis; Phase velocity; Prediction models; Ring structures; Satellite imagery; Spectral analysis; Spectrum analysis; Standing waves; Storms; Stratopause; Stratosphere; Thermosphere; upper atmosphere; Vertical propagation; Wave propagation; Waves; Weather; Weather forecasting; Wind; Wind effects; Winds
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2024JD041725

The Weather Research and Forecasting (WRF) Model is employed to explore gravity waves excited by a storm complex over West Africa on 15 August 2020, propagating to the mesosphere and lower thermosphere. Although the simulation portrays gravity waves in the stratosphere in a complex structure, it reveals a concentric‐ring pattern of gravity waves in the mesosphere. The waves closely resemble the airglow image acquired by Suomi National Polar‐orbiting Partnership satellite near the mesopause. This intriguing phenomenon of the emergence of concentric rings after passing the stratopause is investigated by analyzing wave characteristics, including horizontal wavenumbers, frequency, and phase speed. The analysis reveals that the wind filtering effect directly influences the behavior of gravity waves, leading to variations in their appearance with altitude. The wind filtering effect, which typically breaks symmetric ring waves, could help reveal the ring pattern when the waves are subject to interference. Consequently, the concentric rings, propagating faster than the background winds, are shown to originate from the cloud tops of the storm complex. A wind duct at a specific location is identified through spectral analysis. This mechanism is further elucidated with the assistance of the dispersion relation of a classical linear theory. Plain Language Summary Storm‐generated gravity waves can propagate through the stratosphere into the mesosphere and lower thermosphere. They often appear in the form of concentric rings and observe as airglow. However, the presence of concentric rings is not consistently observed. The thermal and dynamic structures of the atmosphere can significantly influence the vertical propagation of gravity waves. We demonstrate that the wind filtering effect does not always lead to the disruption of the symmetric ring pattern. When the pattern is already affected by interference from other waves, the wind filtering effect can actually aid in revealing the ring structure by filtering out the complex interference pattern. We employ a numerical weather prediction model to simulate a real case observed in West Africa on 15 August 2020. The result shows that the simulated gravity waves closely align with observations at the airglow altitude. Subsequently, we differentiate the waves into slow and fast‐moving modes through spectral analysis, revealing that the fast‐moving mode, originating from the storm, propagates consistently up to the mesopause.