科研之友
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摘要
Linear wave solutions in the spectral space are analyzed to help understand the structure of mountain waves. Nonrotating and hydrostatic waves generated in wind with directional shear past a circular bell-shaped mountain are studied. The power spectra of perturbed vertical velocity and pressure are symmetrically distributed about the orientation of dominant wave component, which bisects the angle between surface wind and local wind directions. The maximum power spectrum increases with the horizontal wind speed but decreases with the wind turning angle. The power spectra of potential temperature and horizontal velocity exhibit an asymmetric distribution except at the surface, which are infinite for the wave components normal to the mean wind. These large-amplitude perturbations of potential temperature and horizontal velocity are advected downstream and the waves finally break, giving rise to the occurrence of turbulent wakes at various heights. All the wavefields rotate with height in the same direction of the mean wind. However, the perturbed vertical velocity and pressure turn at a rate slower than that of horizontal velocity and potential temperature. The application of spectral analysis to the wave momentum flux is discussed, which helps explain the misalignment of wave momentum flux with the surface wind.
