| Autor: |
Zhongming Gao, Heping Liu, Justine E C Missik, Jingyu Yao, Maoyi Huang, Xingyuan Chen, Evan Arntzen, Douglas P Mcfarland |
| Jazyk: |
angličtina |
| Rok vydání: |
2019 |
| Předmět: |
|
| Zdroj: |
Environmental Research Letters, Vol 14, Iss 4, p 044016 (2019) |
| Druh dokumentu: |
article |
| ISSN: |
1748-9326 |
| DOI: |
10.1088/1748-9326/ab082d |
| Popis: |
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, 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. |
| Databáze: |
Directory of Open Access Journals |
| Externí odkaz: |
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