Submeso Motions and Intermittent Turbulence Across a Nocturnal Low-Level Jet: A Self-Organized Criticality Analogy
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One of the hallmarks of the stable boundary layer is the switching between turbulent (active) and non-turbulent (passive) states. In very stable conditions, the boundary layer becomes layered with fully-developed turbulence confined to a shallow region near the surface. In the quiescent region above this near-surface layer, the turbulence is weak, intermittent and detached from the ground. These conditions promote the development of a low-level jet that re-energizes the turbulence through an elevated shear layer. The Monin–Obukhov similarity theory fails in the layered stable boundary layer thereby making the quantification of mixing and transport properties challenging for numerical models. In the present study, multi-level time series from a tall (140 m) meteorological tower are analyzed using the telegraphic approximation to investigate analogies with a general class of intermittency models that include self-organized criticality. The analogy between turbulence and self-organized criticality is restricted to clustering properties of sign changes of flow variables for describing switching between turbulent and non-turbulent states. The telegraphic approximation provides a new perspective on clustering and on external and internal intermittency for periods dominated by turbulent motions, a low-level jet and submeso motions. Some of these periods are characterized by the absence of turbulence but occasionally punctuated by bursts of intermittent turbulent events. The switching probability of active–inactive states and the lifetimes of inactive states (related to intermittent turbulent bursts) show evidence of self-organized-criticality like behaviour in terms of scaling laws. The coexistence of self-organized criticality and intermittent turbulence may offer new perspectives on the genesis of scaling laws and similarity arguments, thereby improving the performance of numerical models in the stable boundary layer.
KeywordsIntermittent turbulence Low-level jet Self-organized criticality Stable boundary layer Submeso motions
The study has been developed within the context of a Research and Development project sponsored by companies Linhares Geração S.A. and Termeletrica Viana S.A., and named “Desenvolvimento de um modelo operacional para simulacão em tempo real da dispersão atmosferica de poluentes emitidos por termeletri ca a gas natural”. The Project is within the context of the investment program in Research and Development, regulated by Brazilian National Agency for Electric Energy. G.Katul acknowledges partial support from the U.S. National Science Foundation (NSF-EAR-1344703, NSF-AGS-1644382, and NSF-DGE-1068871). We would like to also acknowledge the collaboration with the Marche Region, and in particular the “Environmental assessments and authorizations, air quality and natural protection” section.
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