Semi-empirical method for the prediction of mountain wave turbulence

Breaking topographically-induced gravity waves or mountain waves are a major source of turbulence encounters by commercial and general aviation aircraft world-wide. Although high-resolution 2D and 3D simulations of mountain waves have had success in modeling the relevant breakdown processes and consequent turbulence (usually as inferred through SGS TKE) these underlying numerical models are not generally available in an operational setting. Here, an empirical method for forecasting mountain wave-induced turbulence (MWT) is presented which uses a combination of terrain characteristics and turbulence diagnostics derived from operational numerical weather prediction (NWP) model output. These diagnostics attempt to quantify horizontal variability within the NWP model, and thus even if gravity waves are not fully resolved, these diagnostics provides hints as to their existence. Statistical accuracy assessments are provided through a unique verification technique where the model-derived MWT diagnostics are compared to thousands of pilot reports of turbulence in the troposphere to lower stratosphere over mountainous areas in the U.S. where the reports specifically indicated that the turbulence was mountain-wave related.