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Title: Mechanistic links between underestimated CO 2 fluxes and non-closure of the surface energy balance in a semi-arid sagebrush ecosystem

Abstract

The surface energy balance non-closure problem in eddy covariance (EC) studies has been largely attributed to the influence of large-scale turbulent eddies (hereafter large eddies) on latent and sensible heat fluxes. However, how such large eddies concurrently affect CO 2 fluxes remains less studied and mechanistic links between the energy balance non-closure and CO 2 fluxes are not well understood. Here, using turbulence data collected from an EC tower over a sagebrush ecosystem during two growing seasons, we decomposed the turbulence data into small and large eddies at a cutoff frequency and analyzed their contributions to the fluxes. We found that the magnitude of CO 2 fluxes decreased concurrently with decreased sensible and latent heat fluxes (and thus increased energy balance non-closure), primarily caused by large turbulent eddies. The contributions of such large eddies to fluxes are dependent not only upon their magnitudes of vertical velocity (w) and scalars (i.e. temperature, water vapor density, and CO 2 concentration), but also upon the phase differences between the large eddies of w and scalars via their covariances. Enlarged phase differences between large eddies of w and these scalars simultaneously led to reductions in the magnitudes of both CO 2 and heat fluxes,more » linking the lower CO 2 fluxes to energy balance non-closure. Such increased phase differences of large eddies were caused by changes in the structures of large eddies from unstable to near neutral conditions. Given widespread observations in non-closure in the flux community, the processes identified here may bias CO 2 fluxes at many sites and cause upscaled regional and global budgets to be underestimated. More studies are needed to investigate how landscape heterogeneity influences CO 2 fluxes through the influence of associated large eddies on flux exchange.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [3]; ORCiD logo [3]; ORCiD logo [3]
  1. Washington State Univ., Pullman, WA (United States)
  2. Washington State Univ., Pullman, WA (United States); Lanzhou Univ., Lanzhou (People's Republic of China)
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1506141
Alternate Identifier(s):
OSTI ID: 1525293
Report Number(s):
PNNL-SA-142139
Journal ID: ISSN 1748-9326
Grant/Contract Number:  
AC05-76RL01830
Resource Type:
Published Article
Journal Name:
Environmental Research Letters
Additional Journal Information:
Journal Volume: 14; Journal Issue: 4; Journal ID: ISSN 1748-9326
Publisher:
IOP Publishing
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; CO2 flux; eddy covariance method; ensemble empirical mode decomposition; sensible and latent heat fluxes; surface energy balance closure

Citation Formats

Gao, Zhongming, Liu, Heping, Missik, Justine E. C., Yao, Jingyu, Huang, Maoyi, Chen, Xingyuan, Arntzen, Evan V., and Mcfarland, Douglas P. Mechanistic links between underestimated CO2 fluxes and non-closure of the surface energy balance in a semi-arid sagebrush ecosystem. United States: N. p., 2019. Web. doi:10.1088/1748-9326/ab082d.
Gao, Zhongming, Liu, Heping, Missik, Justine E. C., Yao, Jingyu, Huang, Maoyi, Chen, Xingyuan, Arntzen, Evan V., & Mcfarland, Douglas P. Mechanistic links between underestimated CO2 fluxes and non-closure of the surface energy balance in a semi-arid sagebrush ecosystem. United States. doi:10.1088/1748-9326/ab082d.
Gao, Zhongming, Liu, Heping, Missik, Justine E. C., Yao, Jingyu, Huang, Maoyi, Chen, Xingyuan, Arntzen, Evan V., and Mcfarland, Douglas P. Tue . "Mechanistic links between underestimated CO2 fluxes and non-closure of the surface energy balance in a semi-arid sagebrush ecosystem". United States. doi:10.1088/1748-9326/ab082d.
@article{osti_1506141,
title = {Mechanistic links between underestimated CO2 fluxes and non-closure of the surface energy balance in a semi-arid sagebrush ecosystem},
author = {Gao, Zhongming and Liu, Heping and Missik, Justine E. C. and Yao, Jingyu and Huang, Maoyi and Chen, Xingyuan and Arntzen, Evan V. and Mcfarland, Douglas P.},
abstractNote = {The surface energy balance non-closure problem in eddy covariance (EC) studies has been largely attributed to the influence of large-scale turbulent eddies (hereafter large eddies) on latent and sensible heat fluxes. However, how such large eddies concurrently affect CO2 fluxes remains less studied and mechanistic links between the energy balance non-closure and CO2 fluxes are not well understood. Here, using turbulence data collected from an EC tower over a sagebrush ecosystem during two growing seasons, we decomposed the turbulence data into small and large eddies at a cutoff frequency and analyzed their contributions to the fluxes. We found that the magnitude of CO2 fluxes decreased concurrently with decreased sensible and latent heat fluxes (and thus increased energy balance non-closure), primarily caused by large turbulent eddies. The contributions of such large eddies to fluxes are dependent not only upon their magnitudes of vertical velocity (w) and scalars (i.e. temperature, water vapor density, and CO2 concentration), but also upon the phase differences between the large eddies of w and scalars via their covariances. Enlarged phase differences between large eddies of w and these scalars simultaneously led to reductions in the magnitudes of both CO2 and heat fluxes, linking the lower CO2 fluxes to energy balance non-closure. Such increased phase differences of large eddies were caused by changes in the structures of large eddies from unstable to near neutral conditions. Given widespread observations in non-closure in the flux community, the processes identified here may bias CO2 fluxes at many sites and cause upscaled regional and global budgets to be underestimated. More studies are needed to investigate how landscape heterogeneity influences CO2 fluxes through the influence of associated large eddies on flux exchange.},
doi = {10.1088/1748-9326/ab082d},
journal = {Environmental Research Letters},
number = 4,
volume = 14,
place = {United States},
year = {2019},
month = {4}
}

Journal Article:
Free Publicly Available Full Text
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DOI: 10.1088/1748-9326/ab082d

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