Generalized Non-dimensional Wind and Temperature Gradients in the Surface Layer

摘要

We propose a single generalized function for dimensionless wind and temperature gradients in stable and unstable conditions based on Monin-Obukhov similarity theory. The proposed function may be matched with the currently accepted universal functions for the dimensionless wind-speed and temperature gradients using the empirical coefficients a and b to yield differences within +/- 14% for both wind and temperature gradients in the interval of -2 < z/L < 0.5 (z is height and L is the Obukhov length). In neutral conditions, wind and temperature profiles are the same as the standard log-law profile. Under unstable conditions, the differences are smaller than 1.5%; conversely, under stable conditions, the differences reach up to- 5.2%. The coefficients a and b are analyzed here to evaluate the limits of this proposed semi-empirical function and possible physical characteristics are discussed. Although we use the same theoretical assumptions and limitations of Monin-Obukhov similarity theory in the surface layer, the proposed function has the flexibility of adjusting the wind and temperature gradients for specific sites using the empirical coefficients a and b within the range 0-1, with stable and unstable conditions able to be described by a single general function.