Nonlinear interactions between gravity waves with different wavelengths and diurnal tide

By using a compressible nonlinear two-dimensional gravity wave model, we simulate the nonlinear interactions between gravity waves (GWs) with three different vertical wavelengths and a meridional component of the diurnal tidal wind and temperature (30°N, September) calculated from GSWM-00. We also compare the results with the simulation of GWs propagation in a background with zero wind. Consistent with the dispersion relation, the numerical experiments show that tidal wind reduces the vertical wavelengths of the GWs when it is in the same direction as the wave propagation, and thus increases the perturbative shear and the likelihood of instability and wave breaking, especially for waves with shorter vertical wavelengths. The breaking of GWs below the critical level can increase the amplitude of diurnal tidal wind due to the momentum deposition. Because the GW penetration height increases with vertical wavelength, the amplitude of diurnal tidal wave at higher altitudes is more likely to be affected by GWs with large vertical wavelengths. Therefore gravity wave breaking not only accelerates the mean winds, but also increases the amplitudes of the diurnal tide at various altitudes.