The comparison of the calculations for motion, heat and moisture exchange of spray in the marine atmospheric boundary layer above surface waves within Lagrangian stochastic model and DNS
Authors: Ermakova Olga , Troitskaya Yuliya , Druzhinin Oleg , Gladskikh Daria 
Published: March 2022

&lt;p&gt;Within the framework of this study, the dynamics and thermodynamics of individual spherical droplets of various sizes injected into the air flow during their interaction with a marine atmospheric boundary layer were calculated within Lagrangian stochastic model (LSM). The fields of velocity, humidity, and temperature are presented as a superposition of the average component determined from the approximations of the Monin-Obukhov similarity theory and the fluctuation component. Turbulent fluctuations are calculated using a stochastic model based on the Langevin equation, containing the matrix of inverse relaxation times of turbulent fluctuations of the Lagrangian particles velocity. To define whether isotropic matrix or anisotropic one should be selected and also to determine the value of Kolmogorov constant the calculations within LSM were compared with the results of direct numerical simulation of the inertial particles in the atmospheric boundary layer above surface waves. It was shown that the isotropic diffusion matrix underestimates the turbulent diffusion of particles, so anisotropic one was selected.&lt;/p&gt;&lt;p&gt;It was assumed that the injection of droplets into the air flow was carried out through two main mechanisms - fragmentation according to the &quot;parachute&quot; type (Troitskaya et al., Scientific Reports, 2017) and the rupture of floating bubbles. In the calculations, new modifications of the spray generation functions were used, taking into account the dependence of the number of generation events on the number of spray, obtained within the laboratory experiments done by the authors in their previous studies.&lt;/p&gt;&lt;p&gt;The processes of heat-moisture exchange of droplets with a turbulent air flow, taking into account phase transitions, are described using the equations of droplet microphysics (Pruppatcher and Klett (1978)). Heat, moisture and momentum fluxes are calculated on the basis of averaging over the horizontal coordinate of the equations of thermoaerodynamics. These equations include volumetric sources of momentum, heat and moisture to take into account the effect of droplets on the temperature and humidity of atmospheric air, which are obtained by averaging the solution to the equations of microphysics of droplets. When calculating the profiles of average temperature and humidity, gradient hypotheses of closure with the coefficients of turbulent diffusion coefficients of heat and humidity were used.&lt;/p&gt;&lt;p&gt;The work is supported by the Russian Science Foundation (RSF) project &amp;#8470; 19-17-00209&lt;/p&gt;&lt;ul&gt;&lt;li&gt;Troitskaya, Y., Kandaurov, A., Ermakova, O., Kozlov D., Sergeev D., Zilitinkevich S. Bag-breakup fragmentation as the dominant mechanism of sea-spray production in high winds. Sci Rep 7, 1614 (2017). https://doi.org/10.1038/s41598-017-01673-9.&lt;/li&gt;
&lt;li&gt;Prupatcher H.R., Klett J.D. Microphysics of Clouds and Precipitation. Dordrecht: D. Riedel. 1978, 714 p. https://doi.org/10.1007/978-94-009-9905-3.&lt;/li&gt;
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