Abstract
Abstract. A moist idealized test case (MITC) for atmospheric model dynamical cores is presented. The MITC is based on the Held–Suarez (HS) test that was developed for dry simulations on “a flat Earth” and replaces the full physical parameterization package with a Newtonian temperature relaxation and Rayleigh damping of the low-level winds. This new variant of the HS test includes moisture and thereby sheds light on the nonlinear dynamics–physics moisture feedbacks without the complexity of full-physics parameterization packages. In particular, it adds simplified moist processes to the HS forcing to model large-scale condensation, boundary-layer mixing, and the exchange of latent and sensible heat between the atmospheric surface and an ocean-covered planet. Using a variety of dynamical cores of the National Center for Atmospheric Research (NCAR)'s Community Atmosphere Model (CAM), this paper demonstrates that the inclusion of the moist idealized physics package leads to climatic states that closely resemble aquaplanet simulations with complex physical parameterizations. This establishes that the MITC approach generates reasonable atmospheric circulations and can be used for a broad range of scientific investigations. This paper provides examples of two application areas. First, the test case reveals the characteristics of the physics–dynamics coupling technique and reproduces coupling issues seen in full-physics simulations. In particular, it is shown that sudden adjustments of the prognostic fields due to moist physics tendencies can trigger undesirable large-scale gravity waves, which can be remedied by a more gradual application of the physical forcing. Second, the moist idealized test case can be used to intercompare dynamical cores. These examples demonstrate the versatility of the MITC approach and suggestions are made for further application areas. The new moist variant of the HS test can be considered a test case of intermediate complexity.
Highlights
Atmospheric general circulation models (GCMs) are important tools for understanding the climate system
We demonstrate that the moist idealized test case (MITC) approach exposes intricacies of the physics–dynamics coupling strategy that cannot be revealed in dry HS experiments
We demonstrate the strength of the MITC approach in revealing the intricacies of the physics–dynamics coupling strategy in CAM5-spectral element (SE)
Summary
Atmospheric general circulation models (GCMs) are important tools for understanding the climate system. Two moist extensions of the HS test were described by Grabowski and Smolarkiewicz (2002) and Kurowski et al (2015), who relaxed the water vapor mixing ratio towards specified relative humidity values Their method was not focused on mimicking the Earth’s atmospheric flow conditions, as we do in this paper, but instead only demonstrated the use of an idealized test in understanding the characteristics of new numerical methods with moisture feedbacks. We propose a slightly modified variant of the HS forcing and include moisture processes via very few simplified physical parameterizations on a water-covered planet similar to Reed and Jablonowski (2012) ( referred to as RJ12), such as some bulk aerodynamic latent and sensible heat fluxes at the surface, a simple boundary-layer mixing of temperature and moisture, and large-scale precipitation. 1 month always contains 30 days and is independent of the actual calendar months
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