Flux-profile relationships are usually obtained under the assumption that the mean field of interest is in equilibrium with the associated surface fluxes. In this study, the existence of an equilibrium state for dust concentration in the atmospheric surface layer above sources and sinks is evaluated using large-eddy simulation. Results show that for steady-state turbulence and negligible horizontal advection, an equilibrium mean vertical profile of dust concentration is reached after one boundary-layer eddy turnover time. This is true for cases over a source or sink, under different atmospheric stabilities, and for particles with negligible or significant settling velocity. A new model relating the net surface flux to the vertical concentration profile that accounts for both atmospheric stability and particle settling velocity is proposed. The model compares well with the simulation results for all particle sizes and atmospheric stability conditions evaluated, and it can be used to estimate the concentration profile based on the surface flux, and also to estimate the surface flux by fitting the vertical concentration profile. The resulting equation can be considered as an extension of Monin-Obukhov similarity theory to the concentration of settling particles, such as mineral dust, sea-salt, pollen and other suspended aerosols.
All Science Journal Classification (ASJC) codes
- Atmospheric Science