Variability of eddy fluxes and turbulence structures due to local advection perturbations

The patch-by-patch, flood irrigation in a flat cotton field created the underlying surface with heterogeneous soil moisture during the Energy Balance Experiment (EBEX) which was conducted in the San Joaquin Valley, California in August of 2000. Moreover, the existence of an extremely dry, large bare soil field upstream beyond the cotton field created an even larger step transition from the bare soil field to the cotton field. In the morning, the ASL was unstable while in the afternoon a stably internal boundary layer (SIBL) was observed due to an “oasis effect” and horizontal advection effect. These advection perturbations were confirmed by the negative correlation coefficient of turbulent temperature and humidity. Under SIBL, negative buoyancy effects suppressed turbulent exchanges, leading to small or even negative sensible heat flux; while latent heat fluxes were maintained or promoted by mechanical mixing. Water vapor transport was more vulnerable than sensible heat transport to changes in advection perturbations. We found that the sensible heat and water vapor transfer showed a strong dissimilarity, highly depending upon intensity of advection perturbations generated by the patch irrigations. Intermittency was presented in the daytime SIBL and is analyzed in details to illustrate its flux contribution.