Profile relationships: The log‐linear range, and extension to strong stability

Abstract

Abstract The diabatic mean profile forms in the surface layer are studied, by applying analysis methods having high resolving power to data from O'Neill, U.S.A. (heights up to 6.4 m) and from Kerang and Hay, Australia (heights mostly up to 16 m). It is found, concordantly from the O'Neill and Australian data, that the log‐linear law is valid for z/L values between — 0.03 and + 1, which includes a small range of unstable and a surprisingly wide range of stable conditions. For all quantities studied (wind, potential temperature, and specific humidity), it is concluded that the Monin‐Obukhov coefficient α is near 4.5 in unstable and 5.2 in stable conditions, within a standard error of about 10 per cent. The ratios K H /K M and K W /K M evidently remain constant, equal to unity, over the whole of the log‐linear range (and somewhat beyond). In stable conditions, the log‐linear law implies that Ri approaches a critical value α −1 , approximately 0.2, as z/L → ∞. However, at z/L a second régime sets in, in which the profiles are only quasi‐determinate, approximating, on the average, a simple logarithmic form (gradients proportional to z −1 ); this régime covers the range approximately 1 < z/L < (α + 1), i.e. (α + 1) −1 < Ri < 1. A third range of extreme stability, Ri > 1, is practically unrepresented in the data examined. The major part of the unstable range, for z/L < − 0.03, will be discussed in a later paper.

Keywords

Affiliated Institutions

• Bureau of Meteorology AU

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