Multiscale Equatorial Electrojet Turbulence: Energy Conservation, Coupling, and Cascades in a Baseline 2-D Fluid Model

TL;DR

This paper investigates the energy transfer mechanisms in equatorial electrojet turbulence using a 2-D fluid model, revealing how instabilities interact and cascade energy across scales, including the generation of large-scale structures.

Contribution

It provides a comprehensive analysis of energy conservation, coupling, and cascades in a unified fluid model of electrojet turbulence, including the verification of a two-step energy cascade theory.

Findings

Energy cascades from unstable wavenumbers to smaller scales.

Identification of reverse energy cascade leading to large-scale structures.

Validation of the two-step energy cascade theory.

Abstract

Progress in understanding the coupling between plasma instabilities in the equatorial electrojet based on a unified fluid model is reported. A deeper understanding of the linear and nonlinear evolution and the coupling of the gradient-drift and Farley-Buneman instabilities is achieved by studying the effect of different combinations of the density-gradient scale-lengths (Ln) and cross-field (E?B) drifts on the plasma turbulence. Mechanisms and channels of energy transfer are illucidated for these multiscale instabilities. Energy for the unified model is examined, including the injected, conservative redistribution (between fields and scales), and ultimate dissipation. Various physical mechanisms involved in the energetics are categorized as sources, sinks, nonlinear transfer, and coupling to show that the system satisfies the fundamental law of energy Oonservation. The physics of the nonlinear transfer terms is studied to identify their roles in producing energy cascades { the transference of energy from the dominant unstable wavenumbers and driving irregularities of different scale-lengths. The theory of two-step energy cascading to generate the 3-meter plasma irregularities in the equatorial electrojet is verified. In addition, the nonlinearity of the system allows the possibility for a reverse energy cascading, responsible for generating large-scale plasma structures at the top of the electrojet.