Wind and Turbulent Transport

The wind flow over crop canopies causes a momentum transfer from the air to the canopy. That transfer generates turbulence, which enhances the exchange of matter and energy between the atmosphere and crops. Turbulence increases with wind velocity and aerodynamic roughness, proportional to crop height. Wind speed (U) varies logarithmically with height. This profile can be described mathematically by two parameters related to crop height. Turbulence can also be expressed as an inverse function of aerodynamic resistance, which reflects the difficulty of turbulent transport and is therefore very high when U is low and for smooth (short) crops. Inside the canopy layer, the wind speed acquires profiles more dependent on the architecture of the canopy than on the wind vector over it. Wind speed changes considerably over space and time, generally lower at night and attaining a maximum in the afternoon; over the long term, higher average wind speeds are often registered at higher latitudes.