Gravity Wave Diagnostics and Characteristics in Mesoscale Fields

Abstract

Abstract As numerical models of complex atmospheric flows increase their quality and resolution, it becomes valuable to isolate and quantify the embedded resolved gravity waves. The authors propose a spatial filtering method combined with a selection of quadratic diagnostic quantities such as heat, momentum, and energy fluxes to do this. These covariant quantities were found to be insensitive to filter cutoff length scales between 300 and 700 km, suggesting the existence of a “cospectral gap.” The gravity waves identified with the proposed method display known properties from idealized studies, including vertical propagation, upwind propagation, the relationship between momentum and energy flux, and agreement with fluxes derived from an alternative method involving simulations with and without terrain. The proposed method is applied to 2- and 6-km-resolution realistic WRF simulations of orographic and nonorographic gravity waves over and around New Zealand within complex frontal cyclones. Deep mountain wave, shallow mountain wave, jet-generated gravity wave, and convection-generated gravity wave events were chosen for analysis. The four wave events shared the characteristics of positive vertical energy flux, negative zonal momentum flux, and upwind horizontal energy flux. Two of the gravity wave events were dissipated nonlinearly.