Characterization of wind-shear effects on entrainment in a convective boundary layer
Direct numerical simulations are used to characterize wind-shear effects on entrainment in a barotropic convective boundary layer (CBL) that grows into a linearly stratified atmosphere. We consider weakly to strongly unstable conditions �����zenc=LOb &4, where zenc is the encroachment CBL depth...
| Autores: | , |
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| Tipo de documento: | artigo |
| Data de publicação: | 2019 |
| País: | España |
| Recursos: | Universitat Politècnica de Catalunya (UPC) |
| Repositório: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglês |
| OAI Identifier: | oai:upcommons.upc.edu:2117/179796 |
| Acesso em linha: | https://hdl.handle.net/2117/179796 https://dx.doi.org/10.1017/jfm.2018.761 |
| Access Level: | Acceso aberto |
| Palavra-chave: | Turbulence Atmospheric turbulence Atmospheric flows Stratified turbulence Turbulent convection Turbulència atmosfèrica Àrees temàtiques de la UPC::Física |
| Resumo: | Direct numerical simulations are used to characterize wind-shear effects on entrainment in a barotropic convective boundary layer (CBL) that grows into a linearly stratified atmosphere. We consider weakly to strongly unstable conditions �����zenc=LOb &4, where zenc is the encroachment CBL depth and LOb is the Obukhov length. Dimensional analysis allows us to characterize such a sheared CBL by a normalized CBL depth, a Froude number and a Reynolds number. The first two non-dimensional quantities embed the dependence of the system on time, on the surface buoyancy flux, and on the buoyancy stratification and wind velocity in the free atmosphere. We show that the dependence of entrainment-zone properties on these two non-dimensional quantities can be expressed in terms of just one independent variable, the ratio between a shear scale .1zi/s p 1=31u=N0 and a convective scale .1zi/c 0:25zenc, where 1u is the velocity increment across the entrainment zone, and N0 is the buoyancy frequency of the free atmosphere. Here .1zi/s and .1zi/c represent the entrainment-zone thickness in the limits of weak convective instability (strong wind) and strong convective instability (weak wind), respectively. We derive scaling laws for the CBL depth, the entrainment-zone thickness, the mean entrainment velocity and the entrainment-flux ratio as functions of .1zi/s=.1zi/c. These scaling laws can also be expressed as functions of only a Richardson number .N0zenc=1u/2, but not in terms of only the stability parameter �����zenc=LOb. |
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