Influence of the mean flow on zonal flow generation

TL;DR

This paper investigates how mean shear flow influences the generation of zonal flows through modulational instability, showing that small mean flows enhance instability while strong shear suppresses it.

Contribution

It reveals the dual role of mean shear flow in either promoting or inhibiting zonal flow generation via modulational instability.

Findings

Small mean flow increases the growth rate of instability.

Strong mean shear reduces the instability growth rate.

Mean shear flow has a significant impact on zonal flow dynamics.

Abstract

Excitation of zonal flow by the modulational instability in the presence of mean shear flow is considered. It is shown that the small amplitude mean flow favours the modulational instability, increasing the growth rate, whereas sufficiently strong mean shear significantly reduces the instability growth rate.