Navid C. Constantinou, Petros J. Ioannou, Brian F. Farrell
Coherent large scale jets, not forced directly at the jet scale, are a prominent feature of rotating turbulence. These jets arise and are supported by systematic organization of the turbulent Reynolds stresses. Understanding the mechanism producing the required eddy momentum flux convergence, and how the jets and associated eddy field mutually adjust to maintain a steady jet structure at finite amplitude, constitute fundamental theoretical problems. Stochastic Structural Stability Theory (SSST) provides a framework for understanding the emergence and equilibration of jets based on a statistical mean state dynamics of turbulence closed at second order. SSST reveals a new manifold of turbulent equilibria and linearization of the SSST dynamics about these equilibria allows formulation of a structural stability theory that predicts the emergence of jets from homogeneous turbulence. We compare results for both formation and equilibration of turbulent jets made using the SSST closure with results of simulations made using quasi-linear and nonlinear models of barotropic turbulence on a beta-plane. SSST accurately predicts both the qualitative nature and in large measure the quantitative bifurcation structure associated with both the emergence and the finite amplitude equilibration of jets. Quantitative differences in some parameter values are traced to modification of the perturbation spectrum by perturbation-perturbation nonlinearity in the form of modification of the continuum or formation of discrete non-zonal structures. The reality of the manifold of these SSST jet structure modes is revealed by stochastic excitation of the stable counterparts of these predicted SSST modes in quasi-linear and nonlinear simulations. The resulting intermittent jets provide an explanation for the observations of latent jets.
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http://arxiv.org/abs/1208.5665
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