Tracer dispersion in the turbulent convective layer

TL;DR

This paper investigates how passive tracers disperse in the turbulent atmospheric surface layer under convective conditions, highlighting the roles of buoyancy and advection, and contrasting it with neutral stratification through experimental data.

Contribution

It provides experimental evidence on tracer dispersion mechanisms in convective turbulence and introduces new scaling laws differing from Richardson's law.

Findings

Buoyancy dominates tracer dispersion beyond the Monin-Obukhov length.

Tracer dispersion exhibits different scaling laws in convective vs. neutral layers.

Exit-time statistics reveal significant differences in dispersion behavior.

Abstract

Experimental results for passive tracer dispersion in the turbulent surface layer under convective conditions are presented. In this case, the dispersion of tracer particles is determined by the interplay of two mechanisms: buoyancy and advection. In the atmospheric surface layer under stable stratification the buoyancy mechanism dominates when the distance from the ground is greater than the Monin-Obukhov length, resulting in a different exponent in the scaling law of relative separation of lagrangian particles (deviation from the celebrated Richardson's law). This conclusion is supported by our extensive atmospheric observations. Exit-time statistics are derived from our experimental dataset, which demonstrates a significant difference between tracer dispersion in the convective and neutrally stratified surface layers.