1. Hydrostatic and Non‐Hydrostatic Baroclinic Instability in the Dynamical Core of the DOE Global Climate Model.
- Author
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Sun, Xiaoming, Nadiga, Balasubramanya T., Taylor, Mark A., Puthan, Pranav S., and Urrego‐Blanco, Jorge R.
- Subjects
CLIMATE change models ,BAROCLINICITY ,ROSSBY number ,VERTICAL motion ,POTENTIAL flow ,TROPICAL cyclones ,ROSSBY waves - Abstract
The dynamical core of the Department of Energy global climate model is used to understand the role of non‐hydrostatic dynamics in the simulation of dry and moist baroclinic waves. To reduce computational cost, the Diabatic Acceleration and REscaling approach is adopted. Scale analysis and numerical simulations suggest that the model solution is not distorted by the change of spherical metric terms due to the change of Earth radius, neither are the inter‐scale interactions strongly altered as indicated by the analysis of spectral flux. Compared with hydrostatic simulations, the onset of baroclinic instability is delayed under non‐hydrostatic dynamics as the associated weaker vertical motions tend to increase the critical wavelength and narrow the range of waves that can be baroclinically unstable. During the development of baroclinic waves, non‐hydrostatic dynamics tends to induce vertical motions in the upper troposphere, accelerating the eastward propagation of upper‐level ridges through their impact on local vorticity tendency. These processes reduce the westward tilt of the vertical ridge axes and suppress the conversion of mean flow available potential energy to eddy kinetic energy, leading to weaker baroclinic eddies than in hydrostatic simulations. The contrasts between hydrostatic and non‐hydrostatic settings hold in supplemental experiments that vary the background flow Rossby number, the amount of water vapor content and vertical resolution. We also find that mesoscale and smaller‐scale activities can be considerably under‐represented when the vertical resolution is limited to that typically used in global climate models. Plain Language Summary: Limited by computational resources, comprehensive climate simulations are usually conducted with a horizontal grid spacing of 50–100 km. At such coarse resolutions, vertical motions can be approximated using hydrostatic balance in which the gravity force is balanced by the vertical component of the pressure gradient force. In high‐resolution simulations that aim at improving the representation of the Earth′s climate, this approximation breaks down, and one has to solve the complete vertical momentum equation to address non‐hydrostatic effects. Here, we examine the role of non‐hydrostatic dynamics in the simulation of baroclinic instability that is responsible for much of the weather in the midlatitudes. Our results show that non‐hydrostatic dynamics tends to delay the onset of baroclinic instability and reduce the amplitude of simulated baroclinic waves. We also find that mesoscale and smaller‐scale activities can be considerably under‐represented when the vertical resolution is limited to that typically used in global climate models. Besides illustrating the underlying physical mechanisms associated with non‐hydrostatic effects, this study implies the importance of including non‐hydrostatic dynamics in modeling midlatitude weather and climate in global high‐resolution simulations that are becoming affordable in the foreseeable future. Key Points: Non‐hydrostatic dynamics tends to delay the onset of baroclinic instability and reduce the amplitude of the simulated baroclinic wavesMesoscale and smaller‐scale processes are under‐represented with limited vertical resolution as typically used in global climate models [ABSTRACT FROM AUTHOR]
- Published
- 2023
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