engleski

Lee wave interference over double bell-shaped orography

The recent Terrain-induced Rotor Experiment (T-REX in 2006) and its pilot Sierra Rotors Project (SRP in 2004) have once again drawn attention to the problem of large-amplitude trapped lee waves and rotors. Taking place in the Owens Valley, surrounded by the Sierra Nevada and White-Inyo mountains, a nearly idealized 2D double mountain system, they have also raised questions about the possible resonant response of the flow to the surrounding terrain. Observational evidence from these experiments suggests that wavelengths that are close to the ridge separation distance are more likely to achieve large amplitudes. In addition a real-data simulation of the strongest lee wave event of SRP, the IOP8, shows that significant sensitivity of trapped lee-wave response to downstream orography exists during certain stages of the examined event. Here we report on the final results of our idealized high-resolution numerical simulations of the double-barrier problem, focusing on the most sensitive period of IOP8. Simulations, carried out using the NRL Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS), are otherwise free-slip, two-dimensional, irrotational and dry. The flow sensitivity to ridge separation distance, mountain height and mountain asymmetry as well as upstream profile is examined. The results confirm that both the amplitude and the horizontal wavelength are significantly affected by the introduction of a second mountain into the system, either when it is an upstream or a downstream one. The ridge separation distance in concert with the upstream profile (mainly the vertical wind shear) is shown to control the trapped lee wavelength, which exhibits oscillatory character as a function of the ridge separation distance. The same oscillatory behavior is also observed in the quasi-state-state value of gravity-wave drag, where the maxima and minima are signs of constructive and destructive non-linear interference. The interference pattern appears to be controlled by the inversion in the upstream profile since the separation distances for which these interferences occur are found to be very close to half the theoretical horizontal wavelength characteristic for the upstream profile when the inversion is present.

double bell-shaped mountain; inversion; trapped lee waves; T-REX

Rad je dobio nagradu "Best Student Poster Presentation Award" Američkog meteorološkog društva