On the Relationship Between Critical Wind Velocity and Wind Direction and the Size Distribution of Dust Microparticles

Based on the data of field studies of dust aerosol concentration and meteorological parameters, the relationships between wind direction on the aeolian relief and the type of size distribution of transported dust microparticles have been revealed. Based on the field observations, two main cases can be distinguished related to the wind direction with respect to the line of dune ridges: tangential and frontal. At tangential wind direction slightly lower concentrations of fine dust particles are observed in comparison with the frontal wind direction case. This is attributed the electric field increases by increasing the dispersion of particle sizes and enhancing the tunnel effect of charge transfer from larger particles to smaller ones. Relative increase of coarse fraction at tangential wind direction is connected with involvement of larger particles from accumulation zone. The best conditions for generation of microparticles under the influence of electric field are relatively low wind velocities (close to critical). Therefore, during statistical evaluation of the indices in the power law of microparticle size distribution, a sample of data was taken at time moments with wind velocities from 3.5 to 5 m/s. This selection of data makes it possible to clearly highlight existing differences related to the physics of microprocesses in the near-surface soil–air layer for the two wind directions. A significant influence of mutual orientations of aeolian relief inhomogeneities and wind direction on the speed and size composition of dust aerosol emission was revealed. The development of accounting for such effects in the dust-emission blocks of atmospheric models seems relevant.