An evaluation of different approaches for estimating shear velocity in aeolian research studies

Abstract

Sonic anemometry represents an important technological advance for aeolian studies, fostering better understanding of near-surface turbulence and improved methods for estimating shear velocity ($u_{\ast }$). Here, we compare $u_{\ast }$ estimated from the Law of the Wall approach and from four methods that use 3-D wind vector measurements from sonic anemometers: double rotation, triple rotation, planar fit, and a newly developed approach based on invariants of the Reynolds stress tensor. Data were collected over 7.5 months at the Jornada Experimental Range in the Chihuahuan Desert, southern New Mexico, USA. We used $u_{\ast }$ estimates from the double rotation method as a reference for comparing the other methods because of its prevalence in the aeolian literature. On average, $u_{\ast }$ estimates from the other three methods are within 5.0 % of estimates from the double rotation approach. Estimates from the triple rotation approach were 2.2 % lower on average. Estimates from the planar fit method were the most similar, within 1.3 % on average. Estimates from the stress tensor approach were 4.9 % larger on average. We found significant discrepancies, ranging from −14.7 % to 13.7 %, among $u_{\ast }$ estimated from the Law of the Wall and the other methods. This underscores the need for careful methodology selection to ensure accurate characterization of boundary layer turbulence.