Turbulence integral length and footprint dimension with reference to experimental data measured over maize cultivation in Po Valley, Italy

Abstract

The atmospheric turbulence in the planetary boundary layer (PBL) governs the mass and energy exchange over the soil-vegetation-atmosphere system. Micrometeorological stations based on the eddy-covariance technique have been recently developed for the assessment of latent and sensible heat fluxes through high frequency measurements of the fluctuating component of wind velocity, temperature and air water content in the PBL. Correct interpretation of such measurements requires assessment of the actual source area (footprint) contributing to the eddy fluxes (latent and sensible heat). Many different approaches have been developed to estimate the source area function but there is no general consensus on the accuracy and applicability of these methods. The objective of this work is to demonstrate the existence of a relationship between the representative source area for eddy covariance measurements, and the large eddies responsible for the transport of turbulent kinetic energy (TKE). Moreover, the energy balance closure was used to analyze the possible effects of the different lengths of the source area on the heat fluxes. A series of measurements were carried out in a micrometeorological eddy covariance station located in a maize field in Landriano in Po Valley (PV), Italy. The results show that the dimension of the large eddies is tightly bound to the footprint size, leading to a new approach to study the eddy covariance measure based on the assessment of the turbulence scale.