Turbulence and Rossby Wave Dynamics with Realizable Eddy Damped Markovian Anisotropic Closure

TL;DR

This paper introduces the EDMAC, a computationally efficient and realizable closure model for two-dimensional anisotropic turbulence interacting with Rossby waves, extending existing turbulence modeling techniques.

Contribution

The paper develops the EDMAC, a new Markovian anisotropic closure that is realizable with Rossby waves and comparable in efficiency to EDQNM, based on systematic simplification of DIA.

Findings

EDMAC is as efficient as EDQNM.

Sufficient conditions for EDMAC realizability are identified.

Numerical comparisons show EDMAC's effectiveness in turbulence with Rossby waves.

Abstract

The theoretical basis for the Eddy Damped Markovian Anisotropic Closure (EDMAC) is formulated for two-dimensional anisotropic turbulence interacting with Rossby waves in the presence of advection by a large-scale mean flow. The EDMAC is as computationally efficient as the Eddy Damped Quasi Normal Markovian (EDQNM) closure but in contrast is realizable in the presence of transient waves. The EDMAC is arrived at through systematic simplification of a generalization of the non-Markovian Direct Interaction Approximation (DIA) closure that has its origin in renormalized perturbation theory. Markovian Anisotropic Closures (MACs) are obtained from the DIA by using three variants of the Fluctuation Dissipation Theorem (FDT) with the information in the time history integrals instead carried by Markovian differential equations for two relaxation functions. One of the MACs is simplified to the EDMAC with analytical relaxation functions and high numerical efficiency, like the EDQNM. Sufficient conditions for the EDMAC to be realizable in the presence of Rossby waves are determined. Examples of the numerical integration of the EDMAC compared with the EDQNM are presented for two-dimensional isotropic and anisotropic turbulence, at moderate Reynolds numbers, possibly interacting with Rossby waves and large-scale mean flow. The generalization of the EDMAC for the statistical dynamics of other physical systems, to higher dimension and higher order nonlinearity is considered.