Approaching coherent turbulence and the roll-cell transition with Lagrangian coherent structures and objective fluxes

Abstract

Abstract We present the first analysis of objective and material vortices in Large Eddy Simulations of atmospheric boundary layer turbulence. We extract rotating fluid features that maintain structural coherence over time for near-neutral, transitional, and convective boundary layers. In contrast to traditional analysis of coherent structures in turbulent boundary layers, we provide the first objective (frame-indifferent) identification of temporally coherent vortex boundaries that are responsible for organizing tracer distributions. We compare these rotating structures with qualitative descriptions of horizontal rolls and convective cells arising from decades of observational studies. We also quantify their contribution to turbulent fluxes of heat under varying atmospheric stability. Using recently developed tools from the theory of objective transport barriers, we derive connections between the relative orthogonality of objective momentum and heat transport with the presence of rolls and cells. This suggests the relationship between momentum and heat transport through vortex surfaces may help explain the physics behind roll-cell transitions.