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An Improved Perturbation Pressure Closure for Eddy-Diffusivity Mass-Flux Schemes

He, Jia and Cohen, Yair and Lopez-Gomez, Ignacio and Jaruga, Anna and Schneider, Tapio (2020) An Improved Perturbation Pressure Closure for Eddy-Diffusivity Mass-Flux Schemes. . (Unpublished)

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Convection parameterizations such as eddy-diffusivity mass-flux (EDMF) schemes require a consistent closure formulation for the perturbation pressure, which arises in the equations for vertical momentum and turbulence kinetic energy (TKE). Here we derive an expression for the perturbation pressure from approximate analytical solutions for 2D and 3D rising thermal bubbles. The new closure combines a modified pressure drag and virtual mass effects with a new momentum advection term. This momentum advection is an important source in the lower half of the thermal bubble and at cloud base levels in convective systems. It represents the essential physics of the perturbation pressure, that is, to ensure the 3D non-divergent properties of the flow. Moreover, the new formulation modifies the pressure drag to be inversely proportional to updraft depth. This is found to significantly improve simulations of the diurnal cycle of deep convection, without compromising simulations of shallow convection. It is thus a key step toward a unified scheme for a range of convective motions. By assuming that the pressure only redistributes TKE between plumes and the environment, rather than vertically, a closure for the velocity pressure-gradient correlation is obtained from the perturbation pressure closure. This novel pressure closure is implemented in an extended EDMF scheme and is shown to successfully simulate a rising bubble test case as well as shallow and deep convection cases in a single column model.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper ItemPyCLES code ItemSCM code
He, Jia0000-0001-7096-7805
Cohen, Yair0000-0002-9615-2476
Lopez-Gomez, Ignacio0000-0002-7255-5895
Jaruga, Anna0000-0003-3194-6440
Schneider, Tapio0000-0001-5687-2287
Additional Information:© 2020. California Institute of Technology. Government sponsorship acknowledged. This research was made possible by the generosity of Eric and Wendy Schmidt by recommendation of the Schmidt Futures program, by Earthrise Alliance, Mountain Philanthropies, the Paul G. Allen Family Foundation, and the National Science Foundation (NSF, award AGS-1835860). We would like to thank the Resnick Sustainability Institute at Caltech for fellowship support. Parts of the research were carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration and funded through the internal Research and Technology Development program. The PyCLES code used to generate LES results is available at The SCM code is available at
Group:Resnick Sustainability Institute
Funding AgencyGrant Number
Eric and Wendy SchmidtUNSPECIFIED
Schmidt Futures ProgramUNSPECIFIED
Earthrise AllianceUNSPECIFIED
Mountain PhilanthropiesUNSPECIFIED
Paul G. Allen Family FoundationUNSPECIFIED
JPL Internal Research and Technology Development ProgramUNSPECIFIED
Record Number:CaltechAUTHORS:20201204-110354763
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106905
Deposited By: George Porter
Deposited On:05 Dec 2020 02:30
Last Modified:16 Nov 2021 18:57

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