Study of the atmospheric boundary layer processes over sloping terrain covered by sparse canopy

The aim of this thesis is the study of the exchange processes at atmosphere/biosphere interface, with a particular focus on momentum and heat transport over complex terrain morphology, varying surface roughness, and a wide range of atmospheric thermal conditions. The surface roughness object of the research is a sparse canopy layer evolving in time along the vegetative season, and characterized by a multiplicity of temporal and spatial scales influencing the properties of the turbulent fluxes. Both experimental and modelling approaches characterize the study methodology. Measurements are first performed in laboratory in order to calibrate flux sensors (i.e., ultrasonic anemometers), and subsequently into three N-W Italy vineyards fields, collecting long term turbulent flux observations over the canopy. Bulk and higher order statistics are explored from these dataset to investigate the turbulent properties of the momentum and heat transfer processes. The analysis is carried out using a conventional quadrant analysis technique and is tested against two models approximating the joint probability density function of the flow variables. Because of direct measurements at field scale are too costly and time consuming, the need to more easily measured parameters for applications in the meteorological and agricultural fields has motivated the examination of a land-surface model, by performing a validation against vineyard data and a sensitivity analysis on canopy parameters. The overall results suggest an improvement procedure for the estimation of turbulent heat flux using sonic anemometers, an insight on the perturbing effect of coherent structures on gradient-diffusion theory, and the key role of canopy parameterizations in the applicative models.