Transverse instability of dunes

TL;DR

This paper demonstrates that transverse dunes are inherently unstable to along-axis perturbations, leading to their decay into barchan dunes, with implications for understanding dune morphology evolution.

Contribution

It provides a numerical and linear stability analysis showing the instability mechanism of transverse dunes and estimates their decay distance into barchans.

Findings

Transverse dunes are unstable to along-axis perturbations.

Perturbations grow exponentially with a rate linked to dune turnover time.

Transverse dunes decay into barchan dunes over a quantifiable distance.

Abstract

The simplest type of dune is the transverse one, which propagates with invariant profile orthogonally to a fixed wind direction. Here we show numerically and with a linear stability analysis that transverse dunes are unstable with respect to along-axis perturbations in their profile and decay on the bedrock into barchan dunes. Any forcing modulation amplifies exponentially with growth rate determined by the dune turnover time. We estimate the distance covered by a transverse dune before fully decaying into barchans and identify the patterns produced by different types of perturbation.