Is There a Scalar Atmospheric Surface Layer Within a Convective Boundary Layer? Implications for Flux Measurements
Year: 2025
Type: article
Abstract: Top‐down entrainment shapes the vertical gradients of sensible heat, latent heat, and CO2 fluxes, influencing the interpretation of eddy covariance (EC) measurements in the unstable atmospheric surface layer (ASL). Using large eddy simulations for convective boundary layer flows, we demonstrate that decreased temperature gradients across the entrainment zone increase entrainment fluxes by enhancing the entrainment velocity, amplifying the asymmetry between top‐down and bottom‐up flux contributions. These changes alter scalar flux profiles, causing flux divergence or convergence and leading to the breakdown of the constant flux layer assumption (CFLA) in the ASL. As a result, EC‐measured fluxes either underestimate or overestimate “true” surface fluxes during divergence or convergence phases, contributing to energy balance non‐closure. The varying degrees of the CFLA breakdown are a fundamental cause for the non‐closure issue. These findings highlight the underappreciated role of entrainment in interpreting EC fluxes, addressing non‐closure, and understanding site‐to‐site variability in flux measurements.
Source: Geophysical Research Letters
DOI: 10.1029/2024gl112619
Authors: Heping Liu, Cheng Liu, Yanzhao Zhou, Qianyu Zhang, Ankur R. Desai, Khaled Ghannam, Jianping Huang, Gabriel G. Katul
Institutions: Washington State University, East China University of Technology, Hebei Normal University, University of Wisconsin–Madison, Northeastern University, National Oceanic and Atmospheric Administration, NOAA National Centers for Environmental Prediction, NOAA Environmental Modeling Center, Duke University
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: gold
Estimated APC paid: $3,190
Awards: BOUNDARY LAYER THEORY FOR CANOPIES COVERING COMPLEX TERRAIN: GOING
FROM EDDIES IN MOTION TO BIOSPHERE-ATMOSPHERE EXCHANGES AND THEIR REPRESENTATION IN CLIMATE MODELS, Collaborative Research: CAS-MNP--Precursors of Long-Distance Aerial Transport of Microplastics from Urban Environments, G5240563719, Influences of Coherent Structures on Validity of the Constant Flux Layer Assumptions in the Unstable Atmospheric Surface Layer, Closing the energy balance gap at scale, Collaborative Research: The Role of Coherent Structures in Scalar Transport over Heterogeneous Landscapes
OpenAlex ID: W4408332478