An analysis of the Hines and Warner-McIntyre-Scinocca non-orographic gravity wave drag parametrizations

A column model based on CIRA wind and temperature profiles is employed to assess the characteristics of the Hines Doppler-spread and Warner-McIntyre-Scinocca (WMS) non-orographic drag parametrizations for internal gravity waves. The Alexander-Dunkerton variant of the WMS scheme is also briefly considered. This study goes into more detail than previous comparisons by performing a spectral analysis of the momentum deposition and drag, and by examining the ability of each scheme to reproduce a high vertical wavenumber tail consistent with atmospheric measurements. We find several undesirable characteristics in the drag produced by the Hines scheme. For typical midlatitude wind profiles, it produces an abrupt onset of large accelerations that vary strongly from one layer to the next. It is also unable to reproduce spectra consistent with observed wave saturation at high vertical vertical wavenumbers, even for the windless case. The WMS scheme has the ability to reproduce the observed spectral tail for the case of no background wind. In the presence of typical CIRA midlatitude background winds, however, it is demonstrated that the WMS saturation threshold generally does not follow the observed spectral behaviour at high vertical wavenumbers, except for one specific frequency dependence not considered in previous work. Doppler shifting is also found to interfere with the production of high-wavenumber spectral tails consistent with observations.