Instability cascade of strongly nonlinear gravity waves in a vertically sheared atmosphere

TL;DR

This paper investigates the complex cascade of instabilities in strongly nonlinear gravity waves within a vertically sheared atmosphere, revealing how different instability mechanisms interact and depend on shear sign.

Contribution

It identifies the interdependent instability cascade of nonlinear gravity waves modulated by vertical shear, highlighting the influence of shear sign on the dynamics.

Findings

Multiple instability mechanisms interact and compete.

The local cascade dynamics depend on the shear sign.

Different types of instabilities follow one another in the cascade.

Abstract

Although internal gravity waves are generally recognized as an important mechanism to distribute energy through the atmosphere, their dynamics near the instability is only partially understood to date. Many types of instabilities, notably the classical modulational instability, a novel point spectrum modulational instability, the triadic resonant instability, the shear instability and the static instability have been studied mostly in idealized settings and mostly isolated from one another. Here, we identify the instability cascade of a quasi one-dimensional and stationary internal gravity wave modulated by a vertically sheared mean flow. We find indicators of various interdependent instability mechanisms which partly compete for dominance and partly follow one another. A key finding is that the particular dynamics of the local cascade depends on the sign of the background shear.