Aviation turbulence forecasting at DWD with ICON: methodology, case studies and verification

Abstract

AbstractWe present a detailed evaluation of the turbulence forecast product EDP (Eddy Dissipation Parameter) used at the Deutscher Wetterdienst (DWD). It is based on the turbulence parameterization scheme TURBDIFF which is operational within the ICON (Icosahedral Nonhydrostatic) numerical weather prediction model used operationally by DWD. For aviation purposes, the procedure provides the cubic root of the eddy dissipation rate ε1/3 as an overall turbulence index. This quantity is a widely used measure for turbulence intensity as experienced by aircraft. The scheme includes additional sources of turbulent kinetic energy with particular relevance to aviation which are briefly introduced. These sources describe turbulence generation by the subgrid-scale action of wake eddies, mountain waves, convection as well as horizontal shear as found close to fronts or the jet stream. Furthermore, we introduce a post-processing, calibration to an empirical EDR distribution, and we demonstrate the potential as well as limitations of the final EDP-based turbulence forecast by considering several case studies of typical turbulence events. Finally, we reveal the forecasting capability of this product by verifying the model results against one year of aircraft in situ EDR measurements from commercial aircraft. We find that the forecasted EDP performs favorably when compared to the Ellrod index. In particular, the turbulence signal from deep convection, which is accounted for in the EDP product, is advantageous when spatial non-locality is allowed in the verification procedure.