Variation of fluxes of water vapor, sensible heat and carbon dioxide above winter wheat and maize canopies |
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| Authors: | ZHANG Yongqiang SHEN Yanjun YU Qiang LIU Changming A Kondoh TANG Changyuan SUN Hongyong JIA Jinsheng |
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| Institution: | 1. Inst. of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China|
2. Shijiazhang Inst. of Agricultural Modernization, CAS, Shijiazhuang 050021, China|
3. Center for Environmental Remote Sensing, Chiba Univ., Chiba 265-8522, Japan|
4. Graduate School of Science and Technology, Chiba Univ., Chiba 263-8522, Japan |
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| Abstract: | Surface energy fluxes were measured using Bowen-Ratio Energy Balance technique (BREB) and eddy correlation system at Luancheng of Hebei Province, on the North China Plain from 1999 to 2001. Average diurnal variation of surface energy fluxes and CO2 flux for maize showed the inverse "U" type. The average peak fluxes did not appear at noon, but after noon. The average peak CO2 flux was about 1.65 mg m-2 s-1. Crop water use efficiency (WUE) increased quickly in the morning, stabilized after 10:00 and decreased quickly after 15:00 with no evident peak value. The ratio of latent heat flux (λE) to net solar radiation (Rn) was always higher than 70% during winter wheat and maize seasons. The seasonal average ratio of sensible heat flux (H) divided by Rn stayed at about 15% above the field surface; the seasonal average ratio of conductive heat flux (G) divided by Rn varied between 5% and 13%, and the average G/Rn from the wheat canopy was evidently higher than that from the maize canopy. The evaporative fraction (EF) is correlated to the Bowen ratio in a reverse function. EF for winter wheat increased quickly during that revival stage, after the stage, it gradually stabilized to 1.0, and fluctuated around 1.0. EF for maize also fluctuated around 1.0 before the later grain filling stage, and decreased after that stage. |
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| Keywords: | latent heat flux sensible heat flux carbon dioxide flux water use North China Plain |
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