A contrary view of energy balance non-closure in eddy covariance: loss of sensible heat flux in the high frequency cospectrum

It is a commonly held view that the source of energy balance non closure in eddy covariance studies is attributable largely to inadequate measurement of the latent heat flux, or that latent heat flux and sensible heat are lost in equal proportion. The understanding of this source of loss is relevant to carbon cycle studies, because CO2 flux is presumed to be undermeasured by analagy to latent heat flux, because these two fluxes use the same instruments for their measurement. An analysis of cospectra of heat, water vapor and carbon dioxide is presented, which indicates that under the conditions of this experiment a significant amount of heat flux goes unmeasured beyond the Nyquist frequency, whereas latent heat and CO2 cospectra go approximately to zero at the Nyquist frequency. A model of the unmeasured heat flux is presented, which is linked to the dimensionless stability. These results should facilitate intercomparisons between sites in networks that use eddy covariance and those that use modified Bowen ratio techniques.