Basic characteristics of canopy turbulence in a homogeneous rice paddy

To assess the interactions of key ecosystems with the overlying atmosphere, it is fundamental to understand the turbulence structure within and above their canopies. Rice is a staple crop particularly in Asia, and, yet, information on canopy turbulence of this vital food resource is limited by the scarcity of field measurement. The purpose of this study was to examine whether rice canopy shows an organized turbulence structure and, if so, whether such coherent structure scales to the patterns found in other canopies. Using the field data obtained during the 1996 International Rice Experiment (IREX96), we computed turbulence statistics such as mean, standard deviation, covariance, skewness, kurtosis, and turbulence length scales. When appropriately scaled with canopy height and friction velocity, these turbulence statistics showed coherent structures, which agreed well within the ranges of those reported for other canopies. Both quadrant and spectrum analyses confirmed that the intermittent and energetic eddies with length scale of the order of canopy height dominated the transfer processes within and above rice canopy. Such results were further substantiated by the countergradient fluxes observed during the IREX96. Furthermore, within-canopy turbulence became more intermittent under stable conditions.