The Departure from Mixed-Layer Similarity During the Afternoon Decay of Turbulence in the Free-Convective Boundary Layer: Results from Large-Eddy Simulations

Research output: Contribution to journalArticleResearchpeer review

Authors

  • Omar Elguernaoui
  • Joachim Reuder
  • Dan Li
  • Björn Maronga
  • Mostafa Bakhoday Paskyabi
  • Tobias Wolf
  • Igor Esau

External Research Organisations

  • University of Bergen (UiB)
  • Boston University (BU)
  • University of Tromso
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Details

Original languageEnglish
Pages (from-to)259-284
Number of pages26
JournalBoundary-Layer Meteorology
Volume188
Issue number2
Early online date21 Jun 2023
Publication statusPublished - Aug 2023

Abstract

This study analyses the departure of the velocity-variances profiles from their quasi-steady state described by the mixed-layer similarity, using large-eddy simulations with different prescribed shapes and time scales of the surface kinematic heat flux decay. Within the descriptive frames where the time is tracked solely by the forcing time scale (either constant or time-dependent) describing the surface heat flux decay, we find that the normalized velocity-variances profiles from different runs do not collapse while they depart from mixed-layer similarity. As the mixed-layer similarity relies on the assumption that the free-convective boundary layer is in a quasi-equilibrium, we consider the ratios of the forcing time scales to the convective eddy-turnover time scale. We find that the normalized velocity-variances profiles collapse in the only case where the ratio (r~) of the time-dependent forcing time scale to the convective eddy-turnover time scale is used for tracking the time, supporting the independence of the departure from the characteristics of the surface heat flux decay. As a consequence of this result, the knowledge of r~ is sufficient to predict the departure of the velocity variances from their quasi-steady state, irrespective of the shape of the surface heat flux decay. This study highlights the importance of considering both the time-dependent forcing time scale and the convective eddy-turnover time scale for evaluating the response of the free-convective boundary layer to the surface heat flux decay.

Keywords

    Afternoon transition, Free-convective boundary layer, Large-Eddy simulation, Mixed-layer similarity, Quasi-equilibrium assumption, Time scales

ASJC Scopus subject areas

Cite this

The Departure from Mixed-Layer Similarity During the Afternoon Decay of Turbulence in the Free-Convective Boundary Layer: Results from Large-Eddy Simulations. / Elguernaoui, Omar; Reuder, Joachim; Li, Dan et al.
In: Boundary-Layer Meteorology, Vol. 188, No. 2, 08.2023, p. 259-284.

Research output: Contribution to journalArticleResearchpeer review

Elguernaoui O, Reuder J, Li D, Maronga B, Paskyabi MB, Wolf T et al. The Departure from Mixed-Layer Similarity During the Afternoon Decay of Turbulence in the Free-Convective Boundary Layer: Results from Large-Eddy Simulations. Boundary-Layer Meteorology. 2023 Aug;188(2):259-284. Epub 2023 Jun 21. doi: 10.1007/s10546-023-00812-2
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title = "The Departure from Mixed-Layer Similarity During the Afternoon Decay of Turbulence in the Free-Convective Boundary Layer: Results from Large-Eddy Simulations",
abstract = "This study analyses the departure of the velocity-variances profiles from their quasi-steady state described by the mixed-layer similarity, using large-eddy simulations with different prescribed shapes and time scales of the surface kinematic heat flux decay. Within the descriptive frames where the time is tracked solely by the forcing time scale (either constant or time-dependent) describing the surface heat flux decay, we find that the normalized velocity-variances profiles from different runs do not collapse while they depart from mixed-layer similarity. As the mixed-layer similarity relies on the assumption that the free-convective boundary layer is in a quasi-equilibrium, we consider the ratios of the forcing time scales to the convective eddy-turnover time scale. We find that the normalized velocity-variances profiles collapse in the only case where the ratio (r~) of the time-dependent forcing time scale to the convective eddy-turnover time scale is used for tracking the time, supporting the independence of the departure from the characteristics of the surface heat flux decay. As a consequence of this result, the knowledge of r~ is sufficient to predict the departure of the velocity variances from their quasi-steady state, irrespective of the shape of the surface heat flux decay. This study highlights the importance of considering both the time-dependent forcing time scale and the convective eddy-turnover time scale for evaluating the response of the free-convective boundary layer to the surface heat flux decay.",
keywords = "Afternoon transition, Free-convective boundary layer, Large-Eddy simulation, Mixed-layer similarity, Quasi-equilibrium assumption, Time scales",
author = "Omar Elguernaoui and Joachim Reuder and Dan Li and Bj{\"o}rn Maronga and Paskyabi, {Mostafa Bakhoday} and Tobias Wolf and Igor Esau",
note = "Funding Information: The first author is grateful to Siegfried Raasch for inspiring discussions about the atmospheric boundary-layer, turbulence, and large-eddy simulation. The first author is grateful to Elie Bou-Zeid for invaluable input and insights about the concepts of equilibrium and quasi-equilibrium. We thank Bert Holtslag for his comments which helped improving the initial version of the manuscript. We thank Marie Lothon and Peter Sullivan for sharing with us their data. We thank Margaret LeMone and two anonymous reviewers for the constructive comments and insightful questions, which helped to improve the manuscript. The third author acknowledges support from U.S. National Science Foundation (NSF) under the Award number AGS-1853354 and also support from the Alexander von Humboldt Foundation. The computations were performed on resources provided by Sigma2—the National Infrastructure for High Performance Computing and Data Storage in Norway, Grant No NN9506k. Funding Information: The first author is grateful to Siegfried Raasch for inspiring discussions about the atmospheric boundary-layer, turbulence, and large-eddy simulation. The first author is grateful to Elie Bou-Zeid for invaluable input and insights about the concepts of equilibrium and quasi-equilibrium. We thank Bert Holtslag for his comments which helped improving the initial version of the manuscript. We thank Marie Lothon and Peter Sullivan for sharing with us their data. We thank Margaret LeMone and two anonymous reviewers for the constructive comments and insightful questions, which helped to improve the manuscript. The third author acknowledges support from U.S. National Science Foundation (NSF) under the Award number AGS-1853354 and also support from the Alexander von Humboldt Foundation. The computations were performed on resources provided by Sigma2—the National Infrastructure for High Performance Computing and Data Storage in Norway, Grant No NN9506k.",
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T1 - The Departure from Mixed-Layer Similarity During the Afternoon Decay of Turbulence in the Free-Convective Boundary Layer

T2 - Results from Large-Eddy Simulations

AU - Elguernaoui, Omar

AU - Reuder, Joachim

AU - Li, Dan

AU - Maronga, Björn

AU - Paskyabi, Mostafa Bakhoday

AU - Wolf, Tobias

AU - Esau, Igor

N1 - Funding Information: The first author is grateful to Siegfried Raasch for inspiring discussions about the atmospheric boundary-layer, turbulence, and large-eddy simulation. The first author is grateful to Elie Bou-Zeid for invaluable input and insights about the concepts of equilibrium and quasi-equilibrium. We thank Bert Holtslag for his comments which helped improving the initial version of the manuscript. We thank Marie Lothon and Peter Sullivan for sharing with us their data. We thank Margaret LeMone and two anonymous reviewers for the constructive comments and insightful questions, which helped to improve the manuscript. The third author acknowledges support from U.S. National Science Foundation (NSF) under the Award number AGS-1853354 and also support from the Alexander von Humboldt Foundation. The computations were performed on resources provided by Sigma2—the National Infrastructure for High Performance Computing and Data Storage in Norway, Grant No NN9506k. Funding Information: The first author is grateful to Siegfried Raasch for inspiring discussions about the atmospheric boundary-layer, turbulence, and large-eddy simulation. The first author is grateful to Elie Bou-Zeid for invaluable input and insights about the concepts of equilibrium and quasi-equilibrium. We thank Bert Holtslag for his comments which helped improving the initial version of the manuscript. We thank Marie Lothon and Peter Sullivan for sharing with us their data. We thank Margaret LeMone and two anonymous reviewers for the constructive comments and insightful questions, which helped to improve the manuscript. The third author acknowledges support from U.S. National Science Foundation (NSF) under the Award number AGS-1853354 and also support from the Alexander von Humboldt Foundation. The computations were performed on resources provided by Sigma2—the National Infrastructure for High Performance Computing and Data Storage in Norway, Grant No NN9506k.

PY - 2023/8

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N2 - This study analyses the departure of the velocity-variances profiles from their quasi-steady state described by the mixed-layer similarity, using large-eddy simulations with different prescribed shapes and time scales of the surface kinematic heat flux decay. Within the descriptive frames where the time is tracked solely by the forcing time scale (either constant or time-dependent) describing the surface heat flux decay, we find that the normalized velocity-variances profiles from different runs do not collapse while they depart from mixed-layer similarity. As the mixed-layer similarity relies on the assumption that the free-convective boundary layer is in a quasi-equilibrium, we consider the ratios of the forcing time scales to the convective eddy-turnover time scale. We find that the normalized velocity-variances profiles collapse in the only case where the ratio (r~) of the time-dependent forcing time scale to the convective eddy-turnover time scale is used for tracking the time, supporting the independence of the departure from the characteristics of the surface heat flux decay. As a consequence of this result, the knowledge of r~ is sufficient to predict the departure of the velocity variances from their quasi-steady state, irrespective of the shape of the surface heat flux decay. This study highlights the importance of considering both the time-dependent forcing time scale and the convective eddy-turnover time scale for evaluating the response of the free-convective boundary layer to the surface heat flux decay.

AB - This study analyses the departure of the velocity-variances profiles from their quasi-steady state described by the mixed-layer similarity, using large-eddy simulations with different prescribed shapes and time scales of the surface kinematic heat flux decay. Within the descriptive frames where the time is tracked solely by the forcing time scale (either constant or time-dependent) describing the surface heat flux decay, we find that the normalized velocity-variances profiles from different runs do not collapse while they depart from mixed-layer similarity. As the mixed-layer similarity relies on the assumption that the free-convective boundary layer is in a quasi-equilibrium, we consider the ratios of the forcing time scales to the convective eddy-turnover time scale. We find that the normalized velocity-variances profiles collapse in the only case where the ratio (r~) of the time-dependent forcing time scale to the convective eddy-turnover time scale is used for tracking the time, supporting the independence of the departure from the characteristics of the surface heat flux decay. As a consequence of this result, the knowledge of r~ is sufficient to predict the departure of the velocity variances from their quasi-steady state, irrespective of the shape of the surface heat flux decay. This study highlights the importance of considering both the time-dependent forcing time scale and the convective eddy-turnover time scale for evaluating the response of the free-convective boundary layer to the surface heat flux decay.

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KW - Free-convective boundary layer

KW - Large-Eddy simulation

KW - Mixed-layer similarity

KW - Quasi-equilibrium assumption

KW - Time scales

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