scholarly journals Improving Boundary-layer Turbulence and Cloud Processes in CAM with a Higher-order Turbulence Closure Scheme and ASR Measurement

2015 ◽  
Author(s):  
Kuan-Man Xu ◽  
Anning Cheng
Keyword(s):  
Boundary Layer ◽  
Higher Order ◽  
Turbulence Closure ◽  
Boundary Layer Turbulence ◽  
Closure Scheme

scholarly journals On a solution of the closure problem for dry convective boundary layer turbulence and beyond

2021 ◽  
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Higher Order ◽  
Turbulence Closure ◽  
Analytical Models ◽  
Central Feature ◽  
Closure Problem ◽  
Convective Boundary ◽  
Higher Order Moments ◽  
Closure Models

Abstract We consider the closure problem of representing the higher order moments (HOMs) in terms of lower-order moments, a central feature in turbulence modelling based on the Reynolds-Averaged Navier-Stokes (RANS) approach. Our focus is on models suited for the description of asymmetric, non-local and semi-organized turbulence in the dry atmospheric convective boundary layer (CBL). We establish a multivariate probability density function (PDF) describing populations of plumes which are embedded in a sea of weaker randomly spaced eddies, and apply an assumed Delta-PDF approximation. The main content of this approach consists of capturing the bulk properties of the PDF. We solve the closure problem analytically for all relevant higher order moments (HOMs) involving velocity components and temperature and establish a hierarchy of new non-Gaussian turbulence closure models of different content and complexity ranging from analytical to semi-analytical. All HOMs in the hierarchy have a universal and simple functional form. They refine the widely used Millionshchikov closure hypothesis and generalize the famous quadratic skewness-kurtosis relationship to higher-order. We examine the performance of the new closures by comparison with measurement, LES and DNS data and derive empirical constants for semi-analytical models, which are best for practical applications. We show that the new models have a good skill in predicting the HOMs for atmospheric CBL. Our closures can be implemented in second-, third- and fourth-order RANS turbulence closure models of bi-, tri-and four-variate levels of complexity. Finally, several possible generalizations of our approach are discussed.

scholarly journals Higher-Order Turbulence Closure and Its Impact on Climate Simulations in the Community Atmosphere Model

2013 ◽  
Vol 26 (23) ◽  
pp. 9655-9676 ◽  
Author(s):  
Peter A. Bogenschutz ◽  
Andrew Gettelman ◽  
Hugh Morrison ◽  
Vincent E. Larson ◽  
Cheryl Craig ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Higher Order ◽  
Turbulence Closure ◽  
Trade Wind ◽  
Gradual Transition ◽  
Shallow Convection ◽  
Boundary Layer Clouds ◽  
Community Atmosphere Model ◽  
Climate Simulations ◽  
Atmosphere Model

This paper describes climate simulations of the Community Atmosphere Model, version 5 (CAM5), coupled with a higher-order turbulence closure known as Cloud Layers Unified by Binormals (CLUBB). CLUBB is a unified parameterization of the planetary boundary layer (PBL) and shallow convection that is centered around a trivariate probability density function (PDF) and replaces the conventional PBL, shallow convection, and cloud macrophysics schemes in CAM5. CAM–CLUBB improves many aspects of the base state climate compared to CAM5. Chief among them is the transition of stratocumulus to trade wind cumulus regions in the subtropical oceans. In these regions, CAM–CLUBB provides a much more gradual transition that is in better agreement with observational analysis compared to CAM5, which is too abrupt. The improvement seen in CAM–CLUBB can be largely attributed to the gradual evolution of the simulated turbulence, which is in part a result of the unified nature of the parameterization, and to the general improved representation of shallow cumulus clouds compared to CAM5. In addition, there are large differences in the representation and structure of marine boundary layer clouds between CAM–CLUBB and CAM5. CAM–CLUBB is also shown to be more robust, in terms of boundary layer clouds, to changes in vertical resolution for global simulations in a preliminary test.

scholarly journals Unified parameterization of the planetary boundary layer and shallow convection with a higher-order turbulence closure in the Community Atmosphere Model: single-column experiments

2012 ◽  
Vol 5 (6) ◽  
pp. 1407-1423 ◽  
Author(s):  
P. A. Bogenschutz ◽  
A. Gettelman ◽  
H. Morrison ◽  
V. E. Larson ◽  
D. P. Schanen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Higher Order ◽  
Turbulence Closure ◽  
Shallow Convection ◽  
Liquid Water Path ◽  
Community Atmosphere Model ◽  
Single Column ◽  
Atmosphere Model ◽  
Similar Accuracy

Abstract. This paper describes the coupling of the Community Atmosphere Model (CAM) version 5 with a unified multi-variate probability density function (PDF) parameterization, Cloud Layers Unified by Binormals (CLUBB). CLUBB replaces the planetary boundary layer (PBL), shallow convection, and cloud macrophysics schemes in CAM5 with a higher-order turbulence closure based on an assumed PDF. Comparisons of single-column versions of CAM5 and CAM-CLUBB are provided in this paper for several boundary layer regimes. As compared to large eddy simulations (LESs), CAM-CLUBB and CAM5 simulate marine stratocumulus regimes with similar accuracy. For shallow convective regimes, CAM-CLUBB improves the representation of cloud cover and liquid water path (LWP). In addition, for shallow convection CAM-CLUBB offers better fidelity for subgrid-scale vertical velocity, which is an important input for aerosol activation. Finally, CAM-CLUBB results are more robust to changes in vertical and temporal resolution when compared to CAM5.

scholarly journals Unified parameterization of the planetary boundary layer and shallow convection with a higher-order turbulence closure in the community atmosphere model: single column experiments

2012 ◽  
Vol 5 (3) ◽  
pp. 1743-1780 ◽  
Author(s):  
P. A. Bogenschutz ◽  
A. Gettelman ◽  
H. Morrison ◽  
V. E. Larson ◽  
D. P. Schanen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Higher Order ◽  
Turbulence Closure ◽  
Shallow Convection ◽  
Liquid Water Path ◽  
Community Atmosphere Model ◽  
Single Column ◽  
Atmosphere Model ◽  
Similar Accuracy

Abstract. This paper describes the coupling of the Community Atmosphere Model (CAM) version 5 with a unified multi-variate probability density function (PDF) parameterization, Cloud Layers Unified by Binormals (CLUBB). CLUBB replaces the planetary boundary layer (PBL), shallow convection, and cloud macrophysics schemes in CAM5 with a higher-order turbulence closure based on an assumed PDF. Comparisons of single-column versions of CAM5 and CAM-CLUBB are provided in this paper for several boundary layer regimes. As compared to Large Eddy Simulations (LES), CAM-CLUBB and CAM5 simulate marine stratocumulus regimes with similar accuracy. For shallow convective regimes, CAM-CLUBB improves the representation of cloud cover and liquid water path (LWP). In addition, for shallow convection CAM-CLUBB offers better fidelity for sub-grid scale vertical velocity, which is an important input for aerosol activation. Finally, CAM-CLUBB results are more robust to changes in vertical and temporal resolution when compared to CAM5.

scholarly journals Atmospheric Boundary Layer Turbulence Closure Scheme for Wind-Following Swell Conditions

2017 ◽  
Vol 74 (7) ◽  
pp. 2363-2382 ◽  
Author(s):  
Lichuan Wu ◽  
Anna Rutgersson ◽  
Erik Nilsson
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Momentum Flux ◽  
Numerical Models ◽  
Atmospheric Model ◽  
Turbulence Closure ◽  
Atmospheric Convection ◽  
Boundary Layer Turbulence ◽  
The Impact ◽  
Surface Momentum Flux

Abstract Over the ocean, atmospheric boundary layer turbulence can be altered by underlying waves. Under swell conditions, the impact of waves on the atmosphere is more complicated compared to that under wind-wave conditions. Based on large-eddy simulation (LES), the wind-following swell impact on the atmospheric boundary layer is investigated through three terms: swell-induced surface momentum flux, the vertical profile of swell-induced momentum flux, and the swell impact on atmospheric mixing. The swell-induced surface momentum flux displays a decreasing trend with increasing atmospheric convection. The swell-induced momentum flux decays approximately exponentially with height. Compared with atmospheric convection, the decay coefficient is more sensitive to wave age. Atmospheric mixing is enhanced under swell conditions relative to a flat stationary surface. The swell impact on the atmospheric boundary layer is incorporated into a turbulence closure parameterization through the three terms. The modified turbulence closure parameterization is introduced into a single-column atmospheric model to simulate LES cases. Adding only the swell impact on the atmospheric mixing has a limited influence on wind profiles. Adding both the impact of swell on the atmospheric mixing and the profile of swell-induced momentum flux significantly improves the agreement between the 1D atmospheric simulation results and the LES results, to some extent simulating the wave-induced low-level wind jet. It is concluded that the swell impact should be included in atmospheric numerical models.

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