Diabatic influence on turbulent wind fluctuations

Abstract

sUMMARYMean values of dimensionless characteristic quantities of turbulence near the ground in relation to stability are given, as derived from data published by Lettau and Davidson (1957).

On the Anisotropy of the Eddy Diffusivity

“…It has been suggested (Stewart, 1959) that, because in the turbulent energy equations only the one in w2 contains a buoyancy term, only w2 is affected by buoyancy and viscosity whereas u2 and v2 are only affected by viscosity. However, the available experimental results on the dependence of the variances on z/L, in which L is the Monin-Obukhov stability length, do not confirm Stewart's hypothesis (e. g. Takeuchi, 1961;Monin, 1962;Klug, 1965;Cramer, 1967). The data seem to show that under stable conditions the variances are practically independent of z/L but that they increase slightly with increasing instability.…”

“…Under unstable conditions the increase in B is more pronounced than that of the other two components. Klug's (1965) results show that C and B become approximately equal at z/L=0.40.…”

“…The reported ranges were 2.1*C*2.9, 1.3*B*2.6 and 0.7*A*1.33. More recently Klug (1965) from data by Lettau andDavidson (1957) calculated A=1.2, B=2.2, andC=3.1. Cramer's (1967) data display a wide range and suggest that A, B and C depend also on elevation and sampling time.…”