Modeled mesoscale gravity waves: continuous spectrum and energy cascade

Numerous theoretical and observational studies have pointed to the linkage of gravity waves and turbulence in the atmosphere. Gravity waves interacting with turbulence are in scales right above turbulent inertial range, with wavelength typically on an order of few tens to a few kilometers. However, gravity waves (with pressure perturbation of a few millibars) have shown their strong presence in mesoscles, typically on the order of a few hundred kilometers. One obvious explanation for this scale separation of gravity waves is that different-scale waves are generated by different sources or a source with different intrinsic scales. Apart from this mechanism, there is also a possibility that these waves with different scales are genotypically related, i.e., smaller-scale gravity waves are generated from larger-scale gravity waves via wave-wave interactions.

Using spectral analysis and wavelet transformation technique, we analyzed modeled gravity waves from an idealized model simulation. The computed spectral power density from modeled vertical velocity field present a continuous expansion of wave scales from low wavenumbers to high wavenumbers with time. Wavelet analysis actually localized these waves in physical space. A time series of these wavelet-decomposed waves tends to indicate that smaller-scale waves are spawned by larger-scale waves.