Naslov
Trapped lee wave interference in presence of surface friction

Autori
Stiperski, Ivana ; Grubišić, Vanda

Izvornik
Journal of the atmospheric sciences (0022-4928) 68 (2011), 4; 918-936

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Boundary layer; Double mountain; Linear model; Rotors; T-REX

Sažetak
Trapped lee wave interference over double bell-shaped obstacles in presence of surface friction is examined. Idealized high-resolution numerical experiments with the non- hydrostatic Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) model were performed to examine the influence of a frictional boundary layer and nonlinearity on wave interference and the impact of interference on wave-induced boundary-layer separation and the formation of rotors. The results show that the appearance of positive and negative interference is predicted well by linear interference theory, while the wave amplitude in the two interference patterns is not. The interference pattern is determined by the ratio of the intrinsic trapped lee wave wavelength to the ridge separation distance. This is found to be true with or without a frictional boundary layer. In presence of surface friction, boundary-layer separation develops and rotors form for mountain heights exceeding a certain critical value. For a double ridge this critical mountain height is strongly dependent on interference. Changes in wave amplitude due to interference affect the rotor strength most significantly in the lee of the downstream ridge, where destructive interference significantly delays the onset of boundary layer separation. Only in the strongest nonlinear regime examined is the rotor strength in the lee of the downstream ridge amplified by constructive interference beyond that obtained in the lee of a single ridge. On the other hand, destructive interference significantly diminishes the rotor strength. Over the valley the strength of rotors is found to saturate in the highly nonlinear regime and to be smaller compared to those in the lee of a single ridge. Destructive interference is shown to be a highly nonlinear process even for very low mountains and in absence of surface friction. “Complete” destructive interference, in which waves almost completely cancel out in the lee of the downstream ridge, develops for certain ridge separation distances but only for a downstream ridge smaller than the upstream one.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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