“…Figure 6a shows the contour plot of the normalised
‐velocity component field for this case, which exhibits continuous and straight longitudinal rolls that are parallel to the along‐slope direction. Such smooth rolls, which are initially stationary, start to meander when the
value is increased and without requiring any additional perturbation due to a secondary roll instability as described in Xiao and Senocak (
2022). Slightly increasing the stratification perturbation parameter to
, Figure 6b reveals how the instability rolls, while remaining aligned with the along‐slope direction, are now curved and create branches after colliding with each other as a result of secondary instabilities of vortical rolls.…”