Wind and Turbulent Transport

Abstract

The flow of wind over crop canopies causes a transfer of momentum from the air to the canopy that generates turbulence which enhances the exchange of matter and energy between the atmosphere and crops. Turbulence increases with wind velocity and aerodynamic roughness which is proportional to crop height. Wind speed varies logarithmically with height. This profile can be described mathematically by two parameters that are related to crop height. Turbulence can also be expressed as an inverse function of aerodynamic resistance, which is indicative of the difficulty for 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 to the wind vector over it. Wind speed changes considerably over space and time, being generally low at night and maximum after noon; over the long term, higher average wind speeds are often registered at high latitudes.