Nocturnal tropospheric gravity waves in a double-jet duct over the southern Taklimakan Desert: lidar observations and WRF simulations

Abstract. Atmospheric gravity waves can transport momentum and energy and couple different atmospheric layers. Their propagation and dissipation have been widely studied in the stratosphere and mesosphere, whereas their excitation and trapping within tropospheric double-jet ducts remain less well constrained. Here we combine coherent Doppler wind lidar (CDWL) observations at Minfeng, ERA5 reanalysis, and WRF simulations to investigate how a nocturnal double-jet structure over the southern Taklimakan Desert excites and modulates tropospheric gravity waves. Three events in September 2021 occurred under a similar configuration, with a lower-level easterly jet below 4 km, an upper-level westerly jet at 6–7 km, and a weak-wind layer between them. Oscillations of 10–20 min occurred within the weak-wind layer, with maximum amplitudes near the strong shear zone at the base of the westerly jet, suggesting a role for shear-related dynamical instability in wave generation. ERA5 buoyancy-frequency profiles show a stable layer near 4–6 km that favored thermal ducting, and Scorer-parameter diagnostics further indicate concurrent Doppler ducting. As the easterly jet intensified, the waveguide compressed and wave frequencies increased, consistent with a shift of trapped modes toward higher frequencies. WRF reproduced the first two cases reasonably well, yielding dominant horizontal wavelengths of 7–14 km and eastward phase speeds near 6 m s⁻¹, but showed substantial discrepancies in the third. These results indicate that nocturnal double-jet structures can act as an effective tropospheric waveguide by trapping gravity waves through thermal and Doppler ducting and shifting trapped modes toward higher frequencies as the duct evolves.