Global Aviation Turbulence Forecasting Techniques and Verification

A procedure is described by which operational NWP model output (either deterministic or ensembles) is used to diagnose turbulence likelihood, globally.  The strategy is to compute a set of diagnostics that identify regions of strong spatial gradients, and using an empirical mapping technique, convert these indicators into an equivalent energy dissipation rate to the 1/3 power.  This atmospheric turbulence metric is the ICAO standard for aircraft reporting and thus provides a convenient basis for verification.  Implicit in the process is the assumption of a downscale cascade of energy from the large scales resolved by operational NWP models to the smaller scales aircraft feels as turbulence (~hundreds of m).  Deterministic forecasts are provided using the ensemble mean of the many individual turbulence diagnostics.  This is the basis for the current CONUS Graphical Turbulence Guidance (GTG) algorithm.  Probabilities may be developed from the diagnostic ensemble or from the NWP ensemble or both.  In this way clear-air turbulence and mountain wave turbulence sources are captured, although convective sources are more problematic.  The G-GTG system is currently being evaluated for use by the World Area Forecast Centers in Washington, US and London, UK.  Initial verification results based on case studies and statistical evaluations will be presented for a Global GTG (G-GTG) based on the GFS and GEFS NWP models.

This research is in response to requirements and funding by the Federal Aviation Administration (FAA).  The views expressed are those of the authors and do not necessarily represent the official policy or position of the FAA