Nonhydrostatic generalization of a pressure-coordinate-based hydrostatic model with implementation in HIRLAM: validation of adiabatic core

A nonhydrostatic pressure-coordinate model of atmospheric dynamics is developed. The model filters acoustic mode. Internal acoustic waves are filtered using the assumption of non-divergence of motion in pressure-space. External (Lamb mode) waves are filtered using the surface pressure adjustment. The model is implemented in the framework of the numerical weather prediction model HIRLAM (High Resolution Limited Area Model) as an extension to the hydrostatic kernel. The integration scheme is either the explicit or semi-implicit Eulerian leapfrog time stepping. Due to the acoustic filtration, the explicit scheme supports quite large time-steps. To check the validity of the model, several flow experiments with artificial orography are performed. The hydrostatic and nonhydrostatic flow regimes are investigated. The results of different models are compared mutually and with the analytic solutions. The real situation simulations are also presented to show the model’s forecasting capabilities.