Statistical study of high-to-medium frequency and mesoscale gravity waves in the high-resolution Whole Atmosphere Community Climate Model (WACCM)

Abstract:

We present the statistical study of gravity waves with periods of 0.5-3 h and vertical wavelengths of 5-60 km that dominate vertical wind perturbations observed by lidar [Lu et al., 2017] and simulated by the high-resolution WACCM. 2-D wavelet transform is applied to identify wave packets first which determines the period and vertical wavelength simultaneously. 2D fitting is applied to the identified waves to compute horizontal wavelengths. The ratios of wave amplitudes in temperature vs vertical wind, probability density functions of these two amplitudes, and phase differences are examined. Similar to the lidar observations, the amplitude ratios are positively correlated with the ground-based periods in high-resolution WACCM but with slightly larger values than observations. The phase differences between vertical winds and temperatures (φ_W -φ_T ) follow a Gaussian distribution of 89.09±26.92°, compared with the observations of 84.2±26.7°. The mean vertical wavelength of this group of waves from model is around 20.3 km, which is consistent with the observation. The mean horizontal wavelength is about 239.7 km, which is larger than that derived from observation (~186 km). The intrinsic periods derived from the methods using 1) Doppler shift of mean wind (treated as ground-truth), 2) dispersion relation and 3) polarization relation with and without considering eddy viscosity diffusion are compared. From the cross-comparisons, the eddy viscosity diffusions are estimated for different scales of waves.