Turbulent Diffusion and Turbulent Thermal Diffusion of Aerosols in Stratified Atmospheric Flows

TL;DR

This paper investigates turbulent thermal diffusion in Earth's atmosphere, explaining aerosol layering near temperature inversions, validating the theory with observations, and assessing its impact on aerosol distribution through modeling.

Contribution

It provides a theoretical and observational analysis of turbulent thermal diffusion, linking it to aerosol layering and offering a new method to estimate turbulent diffusion coefficients.

Findings

Turbulent thermal diffusion causes aerosol accumulation near temperature inversions.

The theory explains observed aerosol profiles near the tropopause.

Numerical modeling shows upward aerosol forcing, especially for coarse particles.

Abstract

The paper analyzes the phenomenon of turbulent thermal diffusion in the Earth atmosphere, its relation to the turbulent diffusion and its potential impact on aerosol distribution. This phenomenon was predicted theoretically more than 10 years ago and detected recently in the laboratory experiments. This effect causes a non-diffusive flux of aerosols in the direction of the heat flux and results in formation of long-living aerosol layers in the vicinity of temperature inversions. We demonstrated that the theory of turbulent thermal diffusion explains the GOMOS aerosol observations near the tropopause (i.e., the observed shape of aerosol vertical profiles with elevated concentrations located almost symmetrically with respect to temperature profile). In combination with the derived expression for the dependence of the turbulent thermal diffusion ratio on the turbulent diffusion, these measurements yield an independent method for determining the coefficient of turbulent diffusion at the tropopause. We evaluated the impact of turbulent thermal diffusion to the lower-troposphere vertical profiles of aerosol concentration by means of numerical dispersion modelling, and found a regular upward forcing of aerosols with coarse particles affected stronger than fine aerosols.