Branch Seminar Series: Hsin-Yuan Huang

UCLA Department of Civil & Environmental Engineering
Daytime land-atmosphere interactions are the result of two-way coupled processes where the land states strongly affect the overlying atmospheric properties, and vice versa. A numerical framework integrating a radiative parameterization, a large-eddy simulation and a force-restore land surface model to investigate the impact of surface heterogeneity scale on convective boundary layer structure (study 1) and local-scale atmospheric feedbacks on surface fluxes and states (study 2) is presented. Using field measurements collected during the NASA-sponsored Soil Moisture-Atmosphere Coupling Experiment 2002, a 12-hour daytime diurnal cycle simulation is performed to evaluate the coupled model performance and good agreement is obtained in comparisons between model outputs and observations at both footprint- and domain-averaged scales. Results from the first study show the surface heterogeneity scale has strong impact on the boundary layer structure as well as blending height. The second study shows the surface fluxes and near-surface states are dominated by the local-scale feedback of air temperature and wind speed, respectively. The total feedback of multiple air properties increases if all individual impacts are in the same phase; otherwise, the impacts partially cancel each other. Results indicate that the impact of ignoring local-scale atmospheric feedbacks results in a clear error in the estimation of sensible heat flux (up to 18 %) and near-surface soil moisture (up to 10 %).