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Preprints
https://doi.org/10.5194/acp-2019-1131
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-1131
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 03 Feb 2020

Submitted as: research article | 03 Feb 2020

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This preprint was under review for the journal ACP but the revision was not accepted.

Long-term energy and CO2 flux observations over an agricultural field in southeastern Tibetan Plateau

Anlun Xu1,2 and Jian Li3 Anlun Xu and Jian Li
  • 1Dali National Climate Observatory, Dali 671003, China
  • 2Dali Mountain Meteorological Field Experiment Base, China Meteorological Administration, Dali 671003, China
  • 3Chinese Academy of Meteorological Sciences, China Meteorological Administration, Beijing 100081, China

Abstract. Information on the exchange of energy, momentum and mass (H2O, CO2, CH4, etc.) over complex topography is critical for determining the development of the boundary layer, carbon and water cycles, weather and climate. This information can also improve the numerical modelling of physical atmosphere-land processes. Based on a 12-year (2007–2018) eddy covariance dataset over the Dali agricultural field in the southeastern Tibetan Plateau, we analysed the diurnal, seasonal and inter-annual changes in sensible heat flux (Hs), latent heat flux (LE) and CO2 flux (Fc) and their meteorological controls on multiple timescales (half-hourly, daily, monthly, and yearly). The results show that both Hs and LE have similar diurnal and seasonal variations, but the amplitude of LE is obviously larger than that of Hs throughout the year, which indicates that the LE plays a dominant role in surface heat exchange. The Fc has a noticeable diurnal cycle, reaching its minimum around noon, and clear seasonal variations, reaching its minimum in the summer. The annual average Hs increased from approximately 6 W m−2 during 2007–2012 to 19 W m−2 during 2013–2018, while the LE decreased from approximately 110 W m−2 during 2007–2013 to 79 W m−2 during 2014–2018. The Dali observational area is a carbon sink in all years, while the magnitude of net uptake decreases significantly from approximately 739 g C m−2 yr−1 during 2007–2013 to 218 g C m−2 yr−1 during 2014–2018. The results also show that wind speed (WS) is the major control of Hs, while the product of WS and vapour pressure deficit (VPD) is the main driver of LE on different timescales. The net radiation (Rn) and soil temperature (Ts) have the largest effects on Fc from the daily to monthly timescales, while the WS has the largest impact on annual total Fc.

Anlun Xu and Jian Li

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Anlun Xu and Jian Li

Anlun Xu and Jian Li

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Short summary
Based on 12-year eddy covariance measurement over an agricultural field, we investigated the diurnal, seasonal and inter-annual changes in sensible heat flux, latent heat flux and carbon dioxide flux and their meteorological controls on multiple timescales. We found that each control has distinct effect on turbulent heat and dioxide flux over different temporal scales. Our results are useful for improving the numerical modelling of physical atmosphere-land processes over the complex terrain.
Based on 12-year eddy covariance measurement over an agricultural field, we investigated the...
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