Effects of lateral wave propagation on the intermittency of nonorographic gravity waves

Abstract. The statistical distribution and intermittency of gravity-wave (GW) amplitudes are shaped by wave evolution during propagation as well as by source variability. While propagation effects have been studied mostly within a 1-dimensional framework, the role of lateral propagation remains poorly understood. Here, we investigate this role by comparing global model experiments using 3-dimensional (3D) and 1-dimensional (1D) variants of a transient GW parameterization. The statistical distributions of momentum flux in the 3D experiment are generally narrower than those in the 1D experiment, indicating lower GW intermittency. They also tend toward lognormal distributions for both convectively generated GWs and waves from a steady background source, suggesting that lateral propagation and the associated spatial redistribution of wave activity contribute to the approximately lognormal distributions widely found in observations. Lateral propagation also substantially modifies the spatiotemporal structure of GW intermittency: the excessive vertical increase in intermittency found in the extratropics in the 1D experiment largely disappears, while intermittency instead tends to vary with mean-wind magnitude. Similar latitude–season structures of intermittency and their association with the mean wind are found in HIRDLS and SABER observations. These results highlight lateral propagation as a fundamental dynamical process shaping GW amplitude distributions and intermittency and provide a basis for considering its effects in GW parameterizations.