Spurious Pressure Waves in Compressible Large-Eddy Simulations of Shallow Cumulus Clouds.
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| Title: | Spurious Pressure Waves in Compressible Large-Eddy Simulations of Shallow Cumulus Clouds. |
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| Authors: | Lin, Yi1 (AUTHOR), Zhou, Bowen1 (AUTHOR) zhoubowen@nju.edu.cn |
| Source: | Monthly Weather Review. Aug2025, Vol. 153 Issue 8, p1317-1333. 17p. |
| Subjects: | Cumulus clouds, Large eddy simulation models, Sound-wave attenuation, Sensitivity analysis, Sound waves |
| Abstract: | An investigation of the unclosed horizontal turbulent flux budget in compressible large-eddy simulations (LESs) of shallow cumulus (ShCu) clouds has inadvertently turned up omnipresent pressure waves. These waves originate from the simulated ShCu clouds and ripple radially outward in all directions at the speed of sound. They manifest as isolated spectral spikes in the pressure spectrum. Similar wave features are found with three compressible LES models and in two classic ShCu cases, suggesting their potential commonality. Spatial and temporal convergence tests show that the pressure wave is a spatially resolved yet spurious numerical artifact. Systematic sensitivity studies with respect to both numerical modeling and physical processes are conducted to ascertain the cause of the waves. Their effects on the simulated clouds and flow fields are found to be small, except for the pressure variance and the horizontal pressure-gradient interaction term. For wave removal, traditional numerical techniques designed for stabilizing gridscale acoustic noises are ineffective due to the resolved nature of the pressure waves. Two practical wave suppression approaches are to either limit the model time step or to switch to a soundproof pressure solver. Significance Statement: During the investigation of turbulent mixing associated with shallow cumulus clouds using high-resolution turbulence-resolving simulations (known as large-eddy simulations), we stumbled upon widespread pressure ripples that emanate from the simulated clouds at the speed of sound. These waves lead to increased pressure variance and unclosed horizontal turbulent flux budgets. Through sensitivity tests, the waves are determined to be a numerical artifact rather than a physical phenomenon. Similar wave presence is found with three different compressible models and in two test cases, suggesting that this is likely a common yet overlooked issue. Systematic investigations are conducted to analyze wave characteristics, to ascertain their cause, and to assess their effects on the simulations. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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