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Tracer dispersion in the turbulent convective layer

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.