Representing the Heat-to-Moisture Transport Efficiency in Stable Conditions: An Extension of Two Different Approaches

Using eddy-covariance turbulence measurements over a Tibetan glacier, we present a description of scalar turbulence characteristics in the stable boundary layer. Interesting behaviours are demonstrated in terms of temperature – humidity de-correlation and dissimilarity. That is, a lack of perfect correlation occurs between the two scalars (i.e., correlation coefficients <1 in magnitude); overall, sensible heat is more efficiently transported than water vapour over snow and ice surfaces. Such behaviours provide evidence of departures from the idealized expectation of Monin – Obukhov similarity theory — all scalars assume a perfect level of linear correlation and an equal efficiency level of vertical transport. Results presented herein are noteworthy in that observations over uniform glaciated surfaces involve negligible effects of either a canopy-induced roughness sublayer or heterogeneity in the temperature – humidity source / sink distributions. Moreover, we address two different approaches to representing the heat-to-moisture transport efficiency in stable conditions. A new approach is extended through application of the quadrant analysis technique, thereby representing it as a function of atmospheric stability. Caution is further advised in the use of this approach, when temperature – humidity turbulence becomes markedly de-correlated. A second approach, as previously applied for estimating forest evaporation fluxes in unstable conditions, is extended to a stable boundary layer over snow and ice surfaces.