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 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 fluxesmore » 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.« less

Authors:

Gao, Zhongming ;

• Search DOE PAGES for author "Gao, Zhongming"
• Search DOE PAGES for ORCID "0000-0002-4390-753X"

Liu, Heping ;

• Search DOE PAGES for author "Liu, Heping"
• Search DOE PAGES for ORCID "0000-0002-2184-6924"

Missik, Justine E. C. ;

• Search DOE PAGES for author "Missik, Justine E. C."
• Search DOE PAGES for ORCID "0000-0002-6448-0694"

Yao, Jingyu ;

• Search DOE PAGES for author "Yao, Jingyu"
• Search DOE PAGES for ORCID "0000-0002-4675-9835"

Huang, Maoyi ;

• Search DOE PAGES for author "Huang, Maoyi"
• Search DOE PAGES for ORCID "0000-0001-9154-9485"

Chen, Xingyuan ;

• Search DOE PAGES for author "Chen, Xingyuan"
• Search DOE PAGES for ORCID "0000-0003-1928-5555"

Arntzen, Evan ;

• Search DOE PAGES for author "Arntzen, Evan"
• Search DOE PAGES for ORCID "0000-0002-9209-5670"

Mcfarland, Douglas P.

• Search DOE PAGES for author "Mcfarland, Douglas P."
• Search DOE PAGES for ORCID "0000-0001-5599-299X"

Publication Date:

Mon Apr 01 00:00:00 EDT 2019

Research Org.:

Pacific Northwest National Laboratory (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 Name: Environmental Research Letters Journal Volume: 14 Journal Issue: 4; Journal ID: ISSN 1748-9326

Publisher:

IOP Publishing

Country of Publication:

United Kingdom

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; CO2 flux; eddy covariance method; ensemble empirical mode decomposition; sensible and latent heat fluxes; surface energy balance closure