Extended Abstract (264K)7.2
Measurements of the von Kármán constant in the atmospheric surface layer—further discussion
Edgar L. Andreas, U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, NH; and K. J. Claffey, C. W. Fairall, A. A. Grachev, P. S. Guest, R. E. Jordan, and P. O. G. Persson
We obtained estimates of the von Kármán constant, k, by analyzing wind speed profiles and eddy-correlation measurements of turbulent fluxes from two large data sets—one obtained over Arctic sea ice; the other, over Antarctic sea ice. A perfectly logarithmic wind speed profile is a robust feature of both sets although stratification is not necessarily neutral during these observations nor is the atmospheric surface layer necessarily a layer of constant momentum flux.
We suggest that, theoretically, k should depend on the roughness Reynolds number R*, as others have reported. And in fact, both data sets show that k depends dramatically on R*. That correlation seems to be totally fictitious, however. Evaluating both k and R* requires some of the same measured variables, the friction velocity u*, for example. Our mathematical analysis based on the assumption that none of these variables are correlated shows that, because k and R* share variables, the fictitious correlation between the two is essentially the same as what we see in the data.
On the other hand, when we evaluate R* from a bulk flux algorithm, k shows virtually no correlation with this bulk roughness Reynolds number. Consequently, we have over 600 individual measurements of k that scatter between 0.25 and 0.55—well beyond our experimental precision—and we have no obvious explanation why.
Session 7, Fundamental studies of turbulence: observations, theory, and models (Parallel with Session 8)
Thursday, 12 August 2004, 8:00 AM-12:15 PM, Vermont Room
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