Regional Operational NWP with Sound-Proof Equations;
A COSMO Consortium Project

Contemporary dynamical cores for regional numerical weather prediction (NWP) typically originate from global circulation models, designed for relatively coarse horizontal resolutions and hydrostatic primitive equations. However, with horizontal grid intervals of regional NWP models already reaching O(1) km for O(1000x1000) km2 domains, such dynamical cores experience difficulties. The issues appear primarily related to feeble representation of the simulated orography (steepening with increasing resolution) and to inadequate coupling between dynamics and physics for moist convection. With anticipated refinements of the horizontal resolutions of future models to sub-kilometer scales, the difficulties will only amplify. Thus, there is a pressing need for dynamical cores that are robust at broad range of scales and resolutions.

It is generally believed that code robustness is closely related to the conservative properties of model numerics. Consequently, in parallel to fully compressible dynamical cores, the cores based on sound-proof fluid equations attract attention. This is because sound-proof equations naturally lend themselves to accurate large time step integrations in the fully conservative form. A notable example is EULAG, a computational research model with a proven record for a range of applications with scales from laboratory to stellar. Recently, the European Consortium for Small-Scale Modeling (COSMO) launched a development project called “Conservative Dynamical Core” (CDC) that aims for a robust dynamical core for future very-high resolution operational NWP. The anelastic branch of the project, led by the IMGW, investigates the suitability of EULAG for this aim. Current studies address idealized benchmarks for basic atmospheric dynamics and moist convection as well as Alpine orographic flows with different degrees of idealization. In this talk I shall summarize the group collaborative efforts, and substantiate the suitability of sound-proof equations for regional NWP with selected results.