The modelling infrastructure of the Integrated Forecasting System: Recent advances and future challenges

With the objective to develop and maintain one of the most advanced and flexible modelling infrastructures in Europe for operational, global NWP applications, recent advances and future challenges are described. A particular challenge arises from the need to achieve computationally and energy efficient solutions for operating global, complex, high-resolution, ensemble based systems on high-performance computers so that they will remain affordable given tight operational schedules. In particular, the rising cost of quantifying uncertainty needs to be addressed. This paper presents the current status and steps taken towards increasing the model realism and complexity to improve forecasts with a sustainable modelling infrastructure. The progress to date includes the flexibility to explore unstructured horizontal discretizations, the addition of a new, powerful 3D solver for elliptic problems arising from the implicit discretization of the non-hydrostatic system, an option for inherently conserving, monotone, multi-tracer transport, and developments towards a flexible vertical coordinate formulation. Future scientific priorities are to combine the strengths of the newly developed, principally autonomous non-hydrostatic finite-volume module FVM with the hydrostatic semi-Lagrangian spectral transform options of the IFS, to review the vertical discretization, and to carefully address physics-dynamics as well as Earth-system component coupling.