Numerical Simulation of Orographic Gravity Waves Observed Over Syowa Station: Wave Propagation and Breaking in the Troposphere and Lower Stratosphere

• Published in: Journal of geophysical research. Atmospheres Vol. 129; no. 3
• Main Authors: Kohma, M., Sato, K., Fritts, D. C., Lund, T. S.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 16-02-2024
• Subjects: Adiabatic; Altitude; Atmospheric gravity waves; atmospheric radar; Coasts; critical level; Disturbances; Eddy kinetic energy; Energy dissipation; Energy exchange; Gravity waves; Hydraulic jump; Lower stratosphere; Mathematical models; Momentum; mountain waves; Numerical simulations; Orographic gravity waves; Radar; Simulation; Stratosphere; Temperature profile; Temperature profiles; Terrain; Troposphere; turbulence; Turbulent energy; Uplift; Vertical profiles; Vorticity; Wave fronts; Wave propagation; Wavelength; Wind; Antarctica
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2023JD039425

A high‐resolution model in conjunction with realistic background wind and temperature profiles has been used to simulate gravity waves (GWs) that were observed by an atmospheric radar at Syowa Station, Antarctica on 18 May 2021. The simulation successfully reproduces the observed features of the GWs, including the amplitude of vertical wind disturbances in the troposphere and vertical fluxes of northward momentum in the lower stratosphere. In the troposphere, ship‐wave responses are seen along the coastal topography, while in the stratosphere, critical‐level filtering due to the directional shear causes significant change of the wave pattern. The simulation shows the multi‐layer structure of small‐scale turbulent vorticity around the critical level, where turbulent energy dissipation rates estimated from the radar spectral widths were large, indicative of GW breaking. Another interesting feature of the simulation is a wave pattern with a horizontal wavelength of about 25 km, whose phase lines are aligned with the front of turbulent wake downwind of a hydraulic jump that occurs over steep terrain near the coastline. It is suggested that the GWs are likely radiated from the adiabatic lift of an airmass along an isentropic surface hump near the ground, which explains certain features of the observed GWs in the lower stratosphere.
Plain Language Summary
In this study, a high‐resolution computer model was used to simulate atmospheric gravity waves (GWs) that were observed by an atmospheric radar in Antarctica. The simulation successfully reproduced the characteristics of the observed GWs, such as the strength of vertical wind disturbances observed from the ground to 8 km altitude. The simulation showed ship‐wave‐like responses along the Antarctic coast, while, at higher altitudes, the wave pattern changed significantly due to the vertical structure of the background wind. Another interesting finding from the simulation is the presence of a wave pattern with a horizontal wavelength of approximately 25 km. The wavefronts of these waves align with the turbulent region formed downwind of a steep terrain along the coastline. The GWs are likely generated by the uplift of air along a particular type of atmospheric feature near the ground, which explain the upward transport of momentum observed by the radar.
Key Points
Numerical simulations of gravity waves (GWs) over Syowa Station, Antarctic, successfully reproduce their amplitudes and momentum fluxes
Ship‐wave responses along the coastal terrain and wave filtering in the vertical structure of background winds are observed
GWs are radiated from the lift of an airmass along an isentropic surface hump associated with a near‐surface a hydraulic jump