Publication Date:
2022-11-01
Description:
An update of the two‐energy turbulence scheme is presented, the 2TE + APDF scheme. The original version of the two‐energy scheme is able to successfully model shallow convection without the need of an additional parameterization for non‐local fluxes. However, the performance of the two‐energy scheme is worse in stratocumulus cases, where it tends to overestimate the erosion of the stable layers. We have identified the causes: the non‐local stability parameter does not consider local stratification, the scheme lacks an internal parameter that could distinguish between a shallow convection regime and a stratocumulus regime, and it uses an inflexible turbulence length scale formulation. To alleviate this problem, we propose several modifications: an update of the stability parameter, a modified computation of the turbulence length scale, and the introduction of the entropy potential temperature to distinguish between a shallow convection and a stratocumulus regime. In addition, the two‐energy scheme is coupled to a simplified assumed probability density function method in order to achieve a more universal representation of the cloudy regimes. The updated turbulence scheme is evaluated for several idealized cases and one selected real case in the ICOsahedral Nonhydrostatic (ICON) modeling framework. The results show that the updated scheme corrects the overmixing problem in the stratocumulus cases. The performance of the updated scheme is comparable to the operational setup, and can be thus used instead of the operational turbulence and shallow convection scheme in ICON. Additionally, the updated scheme improves the coupling with dynamics, which is beneficial for the modeling of coherent flow structures in the atmospheric boundary layer.
Description:
Plain Language Summary:
The two‐energy turbulence scheme parametrizes turbulence and boundary layer clouds in a unified framework. This enables the scheme to be more consistent and more continuous in time and space than the classical combination of separate turbulence and convection schemes. The original version of the scheme tends to overestimate the erosion of the stable layers, particularly in stratocumulus cases. We have identified several reasons for this problem and updated the scheme accordingly. To achieve a more universal representation of the cloudy regimes, the two‐energy scheme has been also coupled to the assumed probability density function (PDF) method. This method is based on assuming the shape of the trivariate PDF of moisture, heat and vertical velocity. The new version of the scheme was implemented into the ICOsahedral Nonhydrostatic (ICON) modeling framework and was tested on several idealized cases and one realistic case. The results show that the updated scheme corrects the overmixing problem in the stratocumulus cases. The performance of the updated scheme is comparable to the operational setup, and can be thus used instead of the operational turbulence and shallow convection scheme in ICON. Additionally, the updated scheme improves the coupling with dynamics, which is beneficial for the modeling of coherent flow structures in the atmospheric boundary layer.
Description:
Key Points:
An update of the two‐energy scheme for the unified parameterization of the turbulence and clouds in the atmospheric boundary layer (ABL) is presented.
The performance of the updated scheme is comparable to the operational ICOsahedral Nonhydrostatic configuration.
The updated scheme shows the ability to model coherent flow structures in the ABL.
Description:
Hans Ertel Centre for Weather Research of DWD
Description:
Deutsche Forschungsgemeinschaft (DFG)
http://dx.doi.org/10.13039/501100001659
Description:
https://zenodo.org/record/822842
Description:
https://doi.org/10.5281/zenodo.6403030
Keywords:
ddc:550.724
;
ddc:551.5
Language:
English
Type:
doc-type:article
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