Measurements of turbulent transfer in the near-surface layer over a rice paddy in China

Eddy covariance measurements were conducted on fluxes of moisture, heat, and CO2 in a near‐surface layer over a rice paddy in the central plain of China from 10 June to 20 July 2001. During this period, the canopy height increased from 0.16 to 0.65 m. The study site, typical of the agricultural region in China, was ∼600 m × 600 m, was surrounded by similar rice paddies and was flooded throughout the entire experiment. We estimated the zero plane displacement and the roughness length at the end of the experiment to be 0.43 m and 0.027 m, respectively. Aerodynamic roughness length increased with increasing wind speed when the rice height was >0.5 m. On the basis of footprint analysis, we expected >90% of the measured flux (at a height of 3 m above water) to occur within the nearest 600 m of upwind area. We examined daily and seasonal variations in the components of the surface energy balance and in CO2 flux. Results show that the pattern of energy partition had no obvious variation during the season. Daytime absorption and nighttime release of CO2 flux by the rice paddy gradually increased as the rice grew. We examined the energy budget closure and found it to be around 0.91. We tested the extended Louis scheme using eddy covariance techniques. It estimated surface stress in good agreement with direct measurements. However, on average, this scheme underestimated sensible heat flux by 10% and latent heat flux by 11%.