High-resolution modeling of LIDAR data: Mechanisms governing surface water vapor variability during SALSA

An integrated tool that consists of a volume scanning high-resolution Raman water vapor LIDAR and a turbulence-resolving hydrodynamic model, called HIGRAD, is used to support the semi-arid land-surface–atmosphere (SALSA) program. The water vapor measurements collected during SALSA have been simulated by the HIGRAD code with a resolution comparable with that of the LIDAR data. The LIDAR provides the required “ground truth” of coherent water vapor eddies and the model allows for interpretation of the underlying physics of such measurements and characterizes the relationships between surface conditions, boundary layer dynamics, and measured quantities. The model results compare well with the measurements, including the overall structure and evolution of water vapor plumes, the contrast of plume variabilities over the cottonwoods and the grass land, and the mid-day suppression of turbulent activities over the canopy. The current study demonstrates an example that such an integration between modeling and LIDAR measurements can advance our understanding of the structure of fine-scale turbulent motions that govern evaporative exchange above a heterogeneous surface.