Comments on “Turbulent Exchange Coefficients for Sensible Heat and Water Vapor under Advective Conditions”

Abstract

The convincing evidence of Verma et al. that K/sub H/ does not equal K/sub W/ in conditions when H and LE are of opposite sign is not necessarily in conflict with the predictions of conventional flux-gradient relations, particularly when the gradient measurements are made very close to the canopy. Almost all the extensive flux-gradient investigations of the past 20 years have been conducted over relatively short, often sparse, vegetation. Before formulations derived from such circumstances can be extended to the case of deeper canopies, it must be assured that the zero-plane displacement heights are known to sufficient accuracy. Citing other studies the authors state that the suggestion that different zero planes might be appropriate to the cases of temperature and humidity profiles is fairly clear. The heights of observations listed in the data of Verma indicate that in their particular experiment zero-plane displacement inequalities might explain part of the observed differences between K/sub H/ and K/sub W/. On analysis of Verma's data for k/sub H//K/sub W/, the authors conclude that part of the observed difference between K/sub H/ and K/sub W/ might have been done to this effect. The authors also point out that attempts to relate K/sub H//K/sub W/more » to ..delta..T/..delta..e and LE/(R/sub n/ + S) are likely to be quite misleading. To illustrate this point, a surrogate data set was constructed from random numbers to provide values simulating ..delta..T/..delta..e ranging from -0.15 to -0.85 and uncorrelated values of LE/(R/sub n/ + S) ranging from -1.2 to -2.4. The data were treated in the same manner used by Verma. These values are then compared to those reported by Verman et al.« less