TY - JOUR

T1 - Scale-Dependent Estimability of Turbulent Flux in the Unstable Surface Layer for Land Surface Modeling

AU - Liu, Shaofeng

AU - Zeng, Xubin

AU - Dai, Yongjiu

AU - Yuan, Hua

AU - Wei, Nan

AU - Wei, Zhongwang

AU - Lu, Xingjie

AU - Zhang, Shupeng

AU - Li, Xian Xiang

N1 - Publisher Copyright:
© 2023 The Authors. Journal of Advances in Modeling Earth Systems published by Wiley Periodicals LLC on behalf of American Geophysical Union.

PY - 2023/8

Y1 - 2023/8

N2 - Surface flux estimation is essential to land surface modeling in earth system models. In practice, parameterizations of surface turbulent fluxes are almost all based on the similarity theory. That is, the grid or subgrid mean surface-layer flow is assumed at equilibrium with the underlying earth surface, and therefore some empirical relations can be used to estimate surface fluxes. In this paper, scale-dependent estimability of turbulent flux in the unstable surface layer is systematically investigated based on high-resolution large-eddy simulation data over a flat and homogeneous domain, representing a typical land surface modeling grid. It is found that turbulent flow in the unstable surface layer inherently fluctuates over a wide range of scales. This kind of fluctuation affects the steady-state relations between mean atmospheric quantities and underlying earth surface, and hence affects the estimability of surface fluxes. Sensitivity tests show that the relative root mean square error of the estimated surface friction velocity for a subdomain generally increases as the subdomain becomes smaller. The error can be as high as 35% as the subdomain size decreases to the order of the surface layer height. To achieve an error of 10% for all cases, the subdomain size should be at least on the order of the boundary layer height. These findings imply that estimability-based strategies may be needed for representing subgrid heterogeneity for surface flux estimation in land surface modeling.

AB - Surface flux estimation is essential to land surface modeling in earth system models. In practice, parameterizations of surface turbulent fluxes are almost all based on the similarity theory. That is, the grid or subgrid mean surface-layer flow is assumed at equilibrium with the underlying earth surface, and therefore some empirical relations can be used to estimate surface fluxes. In this paper, scale-dependent estimability of turbulent flux in the unstable surface layer is systematically investigated based on high-resolution large-eddy simulation data over a flat and homogeneous domain, representing a typical land surface modeling grid. It is found that turbulent flow in the unstable surface layer inherently fluctuates over a wide range of scales. This kind of fluctuation affects the steady-state relations between mean atmospheric quantities and underlying earth surface, and hence affects the estimability of surface fluxes. Sensitivity tests show that the relative root mean square error of the estimated surface friction velocity for a subdomain generally increases as the subdomain becomes smaller. The error can be as high as 35% as the subdomain size decreases to the order of the surface layer height. To achieve an error of 10% for all cases, the subdomain size should be at least on the order of the boundary layer height. These findings imply that estimability-based strategies may be needed for representing subgrid heterogeneity for surface flux estimation in land surface modeling.

KW - land surface modeling

KW - large eddy simulation

KW - surface flux estimation

KW - turbulent fluctuation

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U2 - 10.1029/2022MS003567

DO - 10.1029/2022MS003567

M3 - Article

AN - SCOPUS:85166969647

SN - 1942-2466

VL - 15

JO - Journal of Advances in Modeling Earth Systems

JF - Journal of Advances in Modeling Earth Systems

IS - 8

M1 - e2022MS003567

ER -