Evaporation and turbulence structures over a cotton field with patchy irrigations

Quantifying evaporation over agricultural lands requires a better understanding of different processes that regulate turbulent exchange in the atmospheric surface layer (ASL). Here we analyze eddy-covariance data collected from the Energy Balance Experiment (EBEX) over a cotton field in the San Joaquin Valley, California in August 2000. During the experiment, patchy irrigations were performed, creating heterogeneous soil moisture conditions. Large run-to-run variations in latent heat fluxes (LE) are evident (e.g., up to 200 W m-2) despite fairly small changes in meteorological conditions. Our analysis illustrates that large coherent eddies and horizontal advection are largely responsible for run-to-run variations in LE. In this study, we use a combination of spectral analysis and wavelet tools to analyze turbulence structures that influence flux exchange. Our results indicate that asymmetric changes in dynamical features and temperature/humidity attributes of large eddies, created by patchy irrigations, are largely responsible for variations in LE. Horizontal advection plays an important role in the overall structures of the ASL, including stable internal boundary layer. Our analysis from the Hilbert-Huang transform (HHT) illustrates differences in turbulence structures leading to larger LE versus lower LE.