Scaling laws of passive tracer dispersion in the turbulent surface layer

TL;DR

This paper investigates how passive tracers disperse in the turbulent surface layer, identifying dominant mechanisms and validating findings through atmospheric observations and statistical analysis.

Contribution

It introduces a simplified Langevin model showing ballistic dispersion dominates at large times, supported by extensive atmospheric data.

Findings

Ballistic dispersion regime dominates at large times.

Exit-time statistics match theoretical asymptotes and multifractal predictions.

Experimental data supports the proposed dispersion mechanisms.

Abstract

Experimental results for passive tracer dispersion in the turbulent surface layer under stable conditions are presented. In this case, the dispersion of tracer particles is determined by the interplay of three mechanisms: relative dispersion (celebrated Richardson's mechanism), shear dispersion (particle separation due to variation of the mean velocity field) and specific surface-layer dispersion (induced by the gradient of the energy dissipation rate in the turbulent surface layer). The latter mechanism results in the rather slow (ballistic) law for the mean squared particle separation. Based on a simplified Langevin equation for particle separation we found that the ballistic regime always dominates at large times. This conclusion is supported by our extensive atmospheric observations. Exit-time statistics are derived from the experimental dataset and show a reasonable match with the simple dimensional asymptotes for different mechanisms of tracer dispersion, as well as predictions of the multifractal model and experimental data from other sources.