Universität zu Köln

Yin, Xin (2023). A study on convective turbulent dust dry deposition: parameterization and application. PhD thesis, Universität zu Köln.

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Abstract

Current dust deposition schemes rarely consider the influence of atmospheric boundary layer (ABL) stability. However, it is increasingly recognized that ABL stability plays an important role in the dry deposition process of dust particles. Specifically, the deposition velocity is found to be greatly enhanced under convective conditions. The cause for this enhancement is not completely understood. This thesis aims to investigate why dust deposition velocity is affected by ABL stability and enhanced under convective conditions, and how these effects can be parameterized and incorporated into the dust deposition scheme. To achieve the goals, this thesis presents a WRF-LES/D that couples the Weather Research and Forecasting (WRF) Model in its large-eddy simulation (LES) mode with the dust deposition scheme of Zhang and Shao (2014) (ZS14). The ZS14 scheme is physics-based, developed and calibrated using wind-tunnel experimental data. WRF-LES/D is then applied to investigate the deposition process under different surface-heat-flux and friction-velocity conditions. The high-resolution atmospheric flow is simulated using WRF-LES, and the convective diffusion process of dust is represented using a coupled Chemistry (WRF-Chem) module, while the deposition velocity is calculated using the ZS14 scheme. The simulations indicate that deposition velocity depends on ABL stability as it is determined by the local vertical momentum flux (or shear stress), which is a stochastic quantity with statistical moments depending on ABL stability. The effects of ABL stability on particle deposition are most obvious for particles in the size range of 0.04 to 5 μm and can be estimated by considering instantaneous aerodynamic shear stress in the dust deposition scheme. Statistical analysis of the simulation results shows that the probability distribution of instantaneous aerodynamic shear stress can be well expressed as a Weibull distribution. The shape and scale parameters of this distribution can be described in terms of regional friction velocity and vertical scaling velocity. On this basis, a new dust deposition scheme is proposed. This scheme includes an ABL stability correction by introducing a shear stress distribution into the ZS14 scheme. The new dust deposition scheme is validated using measurements and WRF-LES/D predictions. The new scheme exhibits a relative difference of approximately 12% in settling velocities compared to the numerical experiments, whereas the original ZS14 scheme shows a relative difference of around 50% when compared to the numerical experiments. Finally, we apply both the ZS14 scheme and the newly developed scheme to regional-scale dust simulations. It is found that with the new deposition scheme, a greater amount of dust deposition is predicted in the near field, accompanied by lower dust concentration in the atmosphere in the far field. This work constitutes a further progression in the development of deposition schemes that account for the stochastic nature of the deposition process. The results hold notable implications for refining the accuracy of predictions pertaining to the dust cycle, spanning across both regional and global scales.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Yin, Xin xyin@smail.uni-koeln.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-708688
Date:	2023
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute for Geophysics and Meteorology
Subjects:	Natural sciences and mathematics
Uncontrolled Keywords:	Keywords Language Dust deposition English Atmospheic boundary layer stability English WRF in its Large-eddy-simulation mode English Dust deposition in regional scale English Instantaneous surface shear stress English
Date of oral exam:	14 April 2023
Referee:	Name Academic Title Yin, Xin Professor Neggers, Roel Professor
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/70868