Non-Oberbeck-Boussinesq zonal flow generation

TL;DR

This paper introduces new mechanisms for zonal flow generation in non-Oberbeck-Boussinesq regimes, emphasizing the roles of Favre stress and background density gradients, supported by gyro-fluid simulations.

Contribution

It presents the first detailed analysis of zonal flow generation mechanisms in NOB regimes, highlighting the importance of Favre stress and background density effects.

Findings

Favre stress drives zonal flows in NOB regimes.

Simulations confirm the predicted ZF propagation mechanisms.

NOB ZF terms are significant for large density fluctuations or steep gradients.

Abstract

Novel mechanisms for zonal flow (ZF) generation for both large relative density fluctuations and background density gradients are presented. In this non-Oberbeck-Boussinesq (NOB) regime ZFs are driven by the Favre stress, the large fluctuation extension of the Reynolds stress, and by background density gradient and radial particle flux dominated terms. Simulations of a nonlinear full-F gyro-fluid model confirm the predicted mechanism for radial ZF propagation and show the significance of the NOB ZF terms for either large relative density fluctuation levels or steep background density gradients.