A new eddy covariance theory for more accurate mass and energy flux measurements

The eddy covariance (EC) approach is our most advanced technique for measuring mass and energy exchanges on the Earth’s surface. Yet the EC approach cannot close the Earth surface’s energy budget. This problem has puzzled Earth system scientists for many decades. It casts doubt on the reliability of data used to validate Earth system models, and questions whether our current understanding of energy processes in our living environments is complete. We find that the current EC theory ignores the close coupling of mass and total (internal, kinetic, and potential) energy transfer on the Earth’s surface, which leads to simplistic equating of heat energy with enthalpy exchange, formation of misconceived concepts and theories, and misguided measurements of turbulent heat flux. Furthermore, the current EC theory assumes that the ideal gas law, which is valid only under the state equilibrium, is applicable in turbulent flows in open thermodynamic systems. This assumption leads to an inappropriate approach for constraining the mean vertical wind velocity which cannot be measured accurately enough by sonic anemometers, loss of covariance between wind and dry air density, and underestimation of diurnal variations in the mean vertical wind velocity and energy transfer due to mass motion. We propose a new EC theory based on the first principles of physical fluid mechanics and thermodynamics, and demonstrate that surface energy balance closure is much improved with measurements guided by our new EC theory.