Dissertation
TURBULENCE STRUCTURES ACROSS LAYERS IN STABLE BOUNDARY LAYER
Washington State University
Doctor of Philosophy (PhD), Washington State University
01/2021
DOI:
https://doi.org/10.7273/000005506
Handle:
https://hdl.handle.net/2376/118995
Abstract
The stable atmospheric boundary layer (SBL), most often occurring at night and with the presence of a vertical temperature inversion, is characterized by very low levels of turbulence. Consequently, pollutants released from the surface are mainly trapped within the SBL, causing adverse effect on human health. Compared to the daytime convective boundary layer, the dynamics of the SBL remain poorly understood. This lack of understanding directly impacts our ability to model the SBL and the effects on pollutant transport and diffusion. Advancement in our understanding of the interaction of SBL state and turbulence can be fueled from a more in-depth study of SBL regime classification, variation of turbulence structures, and mechanisms regulating flux exchanges, which are the main subjects of this dissertation. This work can be divided into three parts. In the first part, eddy covariance data collected at four different heights are used to characterize the state of the SBL in terms of how upper and lower portions of the SBL may be coupled or not. The results indicate that the transport of momentum and heat across SBL layers is determined by large eddies. Therefore, distinct SBL coupling states are delineated by unique turbulence structures. Large gradients in momentum and heat fluxes are frequently observed, violating the ‘constant-flux’ assumption. In the second part, it is shown that increased vertical gradients of wind speed and potential temperature can cause flux gradients. This process is operated upon by downward penetrating large eddies with altered phase difference, contributing unevenly to fluxes and thus causing flux gradients. In the third part, the role of large eddies induced by wind profile distortion (WPD) in regulating flux exchanges and the transition of SBL states is examined. Results showed that the WPD-induced large eddies can penetrate downward to the surface, enhancing vertical mixing. As the WPD is intensified, both turbulent fluxes and flux transport efficiencies associated with large eddies are enhanced, causing a transition from strongly to weakly stable regimes. These results have important implications for how the SBL can be parameterized in numerical weather and pollutant transport models.
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Details
- Title
- TURBULENCE STRUCTURES ACROSS LAYERS IN STABLE BOUNDARY LAYER
- Creators
- Changxing Lan
- Contributors
- Heping HL Liu (Advisor)Brian Lamb (Committee Member)Candis Claiborn (Committee Member)Shelley Pressley (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Voiland College of Engineering and Architecture
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 181
- Identifiers
- 99900592056801842
- Language
- English
- Resource Type
- Dissertation