Towards a dry-mass conserving hydrostatic global spectral dynamical core in a general moist atmosphere

The aim of this article is to develop a dry-mass conserving hydrostatic global spectral dynamical core in a general moist atmosphere, which can be regarded as an alternative, improved version of that used in the current Integrated Forecast System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). In contrast to the original IFS-like core, the dry-mass vertical coordinate is employed and the mass continuity equation is expressed in terms of the dry air density, which ensures the inherent conservation of dry air mass. Meanwhile, the thermodynamic equation is reformulated with a modified temperature variable and the formula used to compute the full pressure vertical velocity is derived rigorously. To assess the performance of this new core, an idealized tropical cyclone (TC) test is conducted. Simulation results from both the new core and the original IFS-like dynamical core are presented and compared. The results show that the TC-like storm produced by the new dynamical core is more intense, more compact and more concentric, and is thus much more in line with previous results from other global models. In this new dynamical core, the diagnosed full pressure vertical velocity is decomposed into four components, of which the first component, the dry hydrostatic pressure vertical velocity, dominates. Sensitivity experiments imply that despite their small numerical value the other three components should not be neglected, especially for medium-range forecasts.