A modified nonhydrostatic moist global spectral dynamical core using a dry‐mass vertical coordinate

Abstract

Most global models employ a vertical coordinate based on the moist hydrostatic pressure, and therefore do not conserve dry air mass. Such an issue should be taken seriously into account, especially in developing global high-resolution atmospheric models to address nonhydrostatic motions explicitly. In this article, we present a modified nonhydrostatic moist global spectral dynamical core using a dry-mass vertical coordinate, which conserves the mass of dry air naturally. In addition to the vertical coordinate, the modified dynamical core differs from the original Aladin-NH like dynamical kernel in the state variables employed. Specifically, a new temperature variable is introduced to formulate the governing equations and the mass continuity equation is expressed in terms of the dry air density. To assess its performance, an idealized splitting supercell test is conducted. Simulation results from both the modified and original dynamical cores are presented and compared. The results indicate that only the modified dynamic core is able to simulate the splitting supercell with good accuracy comparable to reference solutions from the Model for Prediction Across Scales (MPAS). K E Y W O R D SAladin-NH, dry-mass vertical coordinate, idealized supercell simulation, nonhydrostatic moist atmosphere, spectral dynamical core

An implementation of single‐precision fast spherical harmonic transform in Yin–He global spectral model

“…It is further seen that the introduction of a mass conservation fixer (Rasch and Williamson, 1990) does not significantly improve the anomaly correlation coefficients. This may be related to dry‐mass conserving the hydrostatic global spectral dynamical kernel (Peng et al ., 2019; 2020) used in YHGSM. The results shown in Figures 7 and 8 are consistent with the summary plots Figures 5 and 6 (i.e.…”

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

“…(2018), the formula used to compute the full pressure vertical velocity was derived more rigorously. We also reformulated the thermodynamic equation in terms of a modified temperature variable, which we originally introduced to develop a dry‐mass conserving non‐hydrostatic moist global spectral dynamical core (Peng et al ., 2019). Thus, the present dynamical core can also be regarded as an extension of our recent work to a hydrostatic moist atmosphere.…”

“…Following Peng et al . (2019), we introduce a hybrid terrain‐following coordinate η d based on the dry hydrostatic pressure, in which the pressure of the coordinate surface is defined by …”

“…Similarly to Peng et al . (2019), we also introduce a diagnosed variable, the moist pressure departure , defined by which ensures maximum consistency between the previous non‐hydrostatic dynamical core and the present hydrostatic core, and thus enables maximum reuse of code implemented for the non‐hydrostatic core.…”

“…At the start of this section, we make a few remarks on the validation of the new dynamical core. Firstly, this improved hydrostatic dynamical core is an extension of our newly developed non‐hydrostatic one (Peng et al ., 2019), which has passed a series of idealized tests including steady state, baroclinic waves with and without moisture, mountain waves in non‐sheared and sheared background flows, and supercell storms. Secondly, a three‐step strategy with the idealized baroclinic wave case from DCMIP2016 (Ullrich et al ., 2014) has been carried out at T L 159 resolution in order to further validate the improved and original IFS‐like dynamical cores: dry test, moist test without physics and moist test with physics.…”