Evidence of mixed scaling for mean profile similarity in the stable atmospheric surface layer

TL;DR

This paper introduces a new mixed scaling parameter for the stable atmospheric surface layer that improves mean profile similarity modeling in simulations and field data, especially in strongly stable regimes.

Contribution

The study proposes a novel mixed scaling parameter $Z=z/\sqrt{Lh}$ that enhances similarity relations for wind speed and temperature in stable boundary layers, extending beyond traditional Monin-Obukhov theory.

Findings

Improved mean profile similarity using the new parameter $Z$ in simulations.

The new scaling aligns with field measurements in stable conditions.

Similarity for turbulent energy dissipation depends on both $Z$ and $

Abstract

A new mixed scaling parameter $Z=z/\sqrt{Lh}$ is proposed for similarity in the stable atmospheric surface layer, where $z$ is the height, $L$ is the Obukhov length, and $h$ is the boundary layer depth. Compared to the parameter $\zeta = z/L$ from Monin-Obukhov similarity theory (MOST), the new parameter $Z$ leads to improved mean profile similarity for wind speed and air temperature in large-eddy simulations. It also yields the same linear similarity relation for CASES-99 field measurements, including in the strongly stable (but still turbulent) regime where large deviations from MOST are observed. Results further suggest that similarity for turbulent energy dissipation rate depends on both $Z$ and $\zeta$. The proposed mixed scaling of $Z$ and relevance of $h$ can be explained by physical arguments related to the limit of z-less stratification that is reached asymptotically above the surface layer. While the presented evidence and fitted similarity relations are promising, the results and arguments are limited to a small sample of idealized stationary stable boundary layers. Corroboration is needed from independent datasets and analyses, including for complex and transient conditions not tested here.