Effects of Resolution on the Simulation of Boundary-layer Clouds and the Partition of Kinetic Energy to Subgrid Scales

Seven boundary-layer cloud cases are simulated with UCLA-LES (The University of California, Los Angeles – large eddy simulation) model with different horizontal and vertical gridspacing to investigate how the results depend on gridspacing. Some variables are more sensitive to horizontal gridspacing,...

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Main Authors: Anning Cheng, Kuan-Man Xu, Bjorn Stevens
Format: Article
Language:English
Published: American Geophysical Union (AGU) 2010-02-01
Series:Journal of Advances in Modeling Earth Systems
Subjects:
Online Access:http://james.agu.org/index.php/JAMES/article/view/v2n3
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spelling doaj-c746a69e95504a55a3d31d7f3121b6922020-11-25T00:53:22ZengAmerican Geophysical Union (AGU)Journal of Advances in Modeling Earth Systems1942-24662010-02-012Art. # 321 pp.10.3894/JAMES.2010.2.3Effects of Resolution on the Simulation of Boundary-layer Clouds and the Partition of Kinetic Energy to Subgrid ScalesAnning ChengKuan-Man XuBjorn StevensSeven boundary-layer cloud cases are simulated with UCLA-LES (The University of California, Los Angeles – large eddy simulation) model with different horizontal and vertical gridspacing to investigate how the results depend on gridspacing. Some variables are more sensitive to horizontal gridspacing, while others are more sensitive to vertical gridspacing, and still others are sensitive to both horizontal and vertical gridspacings with similar or opposite trends. For cloud-related variables having the opposite dependence on horizontal and vertical gridspacings, changing the gridspacing proportionally in both directions gives the appearance of convergence. In this study, we mainly discuss the impact of subgrid-scale (SGS) kinetic energy (KE) on the simulations with coarsening of horizontal and vertical gridspacings. A running-mean operator is used to separate the KE of the high-resolution benchmark simulations into that of resolved scales of coarse-resolution simulations and that of SGSs. The diagnosed SGS KE is compared with that parameterized by the Smagorinsky-Lilly SGS scheme at various gridspacings. It is found that the parameterized SGS KE for the coarse-resolution simulations is usually underestimated but the resolved KE is unrealistically large, compared to benchmark simulations. However, the sum of resolved and SGS KEs is about the same for simulations with various gridspacings. The partitioning of SGS and resolved heat and moisture transports is consistent with that of SGS and resolved KE, which means that the parameterized transports are underestimated but resolved-scale transports are overestimated. On the whole, energy shifts to large-scales as the horizontal gridspacing becomes coarse, hence the size of clouds and the resolved circulation increase, the clouds become more stratiform-like with an increase in cloud fraction, cloud liquid-water path and surface precipitation; when coarse vertical gridspacing is used, cloud sizes do not change, but clouds are produced less frequently. Cloud fraction and liquid water path decrease.http://james.agu.org/index.php/JAMES/article/view/v2n3Simulation of boundary-layer cloudsresolution dependenceturbulence kinetic energy
collection DOAJ
language English
format Article
sources DOAJ
author Anning Cheng
Kuan-Man Xu
Bjorn Stevens
spellingShingle Anning Cheng
Kuan-Man Xu
Bjorn Stevens
Effects of Resolution on the Simulation of Boundary-layer Clouds and the Partition of Kinetic Energy to Subgrid Scales
Journal of Advances in Modeling Earth Systems
Simulation of boundary-layer clouds
resolution dependence
turbulence kinetic energy
author_facet Anning Cheng
Kuan-Man Xu
Bjorn Stevens
author_sort Anning Cheng
title Effects of Resolution on the Simulation of Boundary-layer Clouds and the Partition of Kinetic Energy to Subgrid Scales
title_short Effects of Resolution on the Simulation of Boundary-layer Clouds and the Partition of Kinetic Energy to Subgrid Scales
title_full Effects of Resolution on the Simulation of Boundary-layer Clouds and the Partition of Kinetic Energy to Subgrid Scales
title_fullStr Effects of Resolution on the Simulation of Boundary-layer Clouds and the Partition of Kinetic Energy to Subgrid Scales
title_full_unstemmed Effects of Resolution on the Simulation of Boundary-layer Clouds and the Partition of Kinetic Energy to Subgrid Scales
title_sort effects of resolution on the simulation of boundary-layer clouds and the partition of kinetic energy to subgrid scales
publisher American Geophysical Union (AGU)
series Journal of Advances in Modeling Earth Systems
issn 1942-2466
publishDate 2010-02-01
description Seven boundary-layer cloud cases are simulated with UCLA-LES (The University of California, Los Angeles – large eddy simulation) model with different horizontal and vertical gridspacing to investigate how the results depend on gridspacing. Some variables are more sensitive to horizontal gridspacing, while others are more sensitive to vertical gridspacing, and still others are sensitive to both horizontal and vertical gridspacings with similar or opposite trends. For cloud-related variables having the opposite dependence on horizontal and vertical gridspacings, changing the gridspacing proportionally in both directions gives the appearance of convergence. In this study, we mainly discuss the impact of subgrid-scale (SGS) kinetic energy (KE) on the simulations with coarsening of horizontal and vertical gridspacings. A running-mean operator is used to separate the KE of the high-resolution benchmark simulations into that of resolved scales of coarse-resolution simulations and that of SGSs. The diagnosed SGS KE is compared with that parameterized by the Smagorinsky-Lilly SGS scheme at various gridspacings. It is found that the parameterized SGS KE for the coarse-resolution simulations is usually underestimated but the resolved KE is unrealistically large, compared to benchmark simulations. However, the sum of resolved and SGS KEs is about the same for simulations with various gridspacings. The partitioning of SGS and resolved heat and moisture transports is consistent with that of SGS and resolved KE, which means that the parameterized transports are underestimated but resolved-scale transports are overestimated. On the whole, energy shifts to large-scales as the horizontal gridspacing becomes coarse, hence the size of clouds and the resolved circulation increase, the clouds become more stratiform-like with an increase in cloud fraction, cloud liquid-water path and surface precipitation; when coarse vertical gridspacing is used, cloud sizes do not change, but clouds are produced less frequently. Cloud fraction and liquid water path decrease.
topic Simulation of boundary-layer clouds
resolution dependence
turbulence kinetic energy
url http://james.agu.org/index.php/JAMES/article/view/v2n3
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