Dust aerosol emissions under natural convection conditions

Under conditions of intensive surface warming over arid territories, in addition to wind effects, convective motions (up to 20-40%) influence the variations of dust aerosol concentration. They are manifested by the spontaneous formation of thermoclines [Ju et al., 2018] and the phenomenon of thermoconvective transport of dust microparticles from the upper sandy porous layer [Chkhetiani et al., 2012].
Data from multilevel daily measurements of dust aerosol concentration (0.2, 0.4, 0.8, 1.6, and 3.2 m) in arid conditions show a stepped dependence on height. In low winds, the degrees are close to -0.5, which is due to the collective effect of closely located bubbles of air heated around the air rising from the surface of dust particles [Malinovskaya E. A. et al., 2023].

Temperature profiles were obtained from multilevel high-frequency pulsation measurements up to a height of 1 m (0.1, 0.2, 0.4, 0.6, 0.8, 1.0 m; 1000 Hz), and the conditions and characteristic time of day for the occurrence of temperature inversions were identified. Convective structures of different scales were determined. The relationships between aerosol concentrations and temperature changes were analysed, with relatively intense changes causing distribution inversions in the lower air layer. 
A series of computational experiments using the open-source OpenFoam package has been realised to investigate the ascent of an ensemble of heated air bubbles from the surface. It is shown that the height, velocity, and character of the rise of warm air volumes depend on the number of heated air bubbles generated by the surface.

Under conditions of uneven surface warming due to the presence of natural aeolian relief, horizontal wind amplification occurs, contributing to the formation and detachment of thermoclines and the emergence of circulating movements near the surface. These effects are investigated and reproduced in a series of computational experiments. 
The detachment of turbulent structures of different scales moving near the surface is accompanied by the dust aerosol removal, manifested by burst changes in its concentration at different heights. High-frequency measurements of wind temperature and speed (1000 Hz) and dust aerosol concentration (10 Hz) allow us to identify such structures and estimate their scale [Malinovskaya E. A. et al., 2024]. The structures themselves, observed in all measured pulsation magnitudes, can be defined as synchronously appearing triangular Ramp structures with upward and downward vertices and exhibiting self-similarity properties.
For the spectra of temperature, velocity and concentration, in addition to the known slope of -5/3, other slopes -1, -3, -1/3 associated with convective processes are noted. The peculiarities of changes in the statistical characteristics depend on the time of day and height above the surface. For the joint probability density distributions of the pulsation components of temperature and velocity, there are two-peak distributions in the time interval from 13 to 15:00. 

Ju, T. et al. Atmospheric Environment, 2018, Vol. 187. P. 62-69.

Chkhetiani, O. G. et al. Atmospheric Chemistry and Physics, 2012, Vol. 12(11), P. 5147–5162.

Malinovskaya, E. A., et al. Doklady Earth Sciences, 2023. 509 (2).  222-229.

Malinovskaya E. A., Chkhetiani O. G., Azizyan G. V. Doklady Earth Sciences, 2024.  516(1). 888-895.