A note on the flux-variance similarity relationships for heat and water vapour in the unstable atmospheric surface layer

Atmospheric surface layer (ASL) experiments over the past 10 years demonstr ate that the flux-variance similarity functions for water vapour are consis tently larger in magnitude than their temperature counterpart. In addition, latent heat flux calculations using the Bur-variance method do not compare as favorably to eddy-correlation measurements when compared to their sensi ble heat counterpart. These two findings, in concert with measured heat to water vapour transport efficiencies in excess of unity, are commonly used a s evidence of dissimilarity between heat and water vapour transport in the unstable atmospheric surface layer. In this note, it is demonstrated that e ven if near equality in flux-profile similarity functions for heat and wate r vapour is satisfied, the flux-variance similarity functions for water vap our are larger in magnitude than temperature for a planar, homogeneous, uns tably-stratified, turbulent boundary-layer flow.